Behavioral neuroscience, also known as biological psychology, biopsychology, or psychobiology, is part of the broad, interdisciplinary field of neuroscience, with its primary focus being on the biological and neural substrates underlying human experiences and behaviors, as in our psychology. Derived from an earlier field known as physiological psychology, behavioral neuroscience applies the principles of biology to study the physiological, genetic, and developmental mechanisms of behavior in humans and other animals.
Behavioral neuroscientists examine the biological bases of behavior through research that involves neuroanatomical substrates, environmental and genetic factors, effects of lesions and electrical stimulation, developmental processes, recording electrical activity, neurotransmitters, hormonal influences, chemical components, and the effects of drugs. Important topics of consideration for neuroscientific research in behavior include learning and memory, sensory processes, motivation and emotion,
as well as genetic and molecular substrates concerning the biological
bases of behavior. Subdivisions of behavioral neuroscience include the
field of cognitive neuroscience,
which emphasizes the biological processes underlying human cognition.
Behavioral and cognitive neuroscience are both concerned with the neuronal and biological bases of psychology, with a particular emphasis on either cognition or behavior depending on the field.
History
Behavioral neuroscience as a scientific discipline emerged
from a variety of scientific and philosophical traditions in the 18th
and 19th centuries. René Descartes proposed physical models to explain animal as well as human behavior. Descartes suggested that the pineal gland,
a midline unpaired structure in the brain of many organisms, was the
point of contact between mind and body. Descartes also elaborated on a
theory in which the pneumatics of bodily fluids could explain reflexes and other motor behavior. This theory was inspired by moving statues in a garden in Paris.
Other philosophers also helped give birth to psychology. One of the earliest textbooks in the new field, The Principles of Psychology by William James, argues that the scientific study of psychology should be grounded in an understanding of biology.
1907 image of a brain
The emergence of psychology and behavioral neuroscience as
legitimate sciences can be traced from the emergence of physiology from anatomy, particularly neuroanatomy.
Physiologists conducted experiments on living organisms, a practice
that was distrusted by the dominant anatomists of the 18th and 19th
centuries. The influential work of Claude Bernard, Charles Bell, and William Harvey helped to convince the scientific community that reliable data could be obtained from living subjects.
Even before the 18th and 19th centuries, behavioral neuroscience was beginning to take form as far back as 1700 B.C. The question that seems to continually arise is: what is the connection
between the mind and body? The debate is formally referred to as the mind-body problem. There are two major schools of thought that attempt to resolve the mind–body problem; monism and dualism. Plato and Aristotle
are two of several philosophers who participated in this debate. Plato
believed that the brain was where all mental thought and processes
happened. In contrast, Aristotle believed the brain served the purpose of cooling down the emotions derived from the heart. The mind-body problem was a stepping stone toward attempting to understand the connection between the mind and body.
Another debate arose about localization of function or functional specialization versus equipotentiality
which played a significant role in the development in behavioral
neuroscience. As a result of localization of function research, many
famous people found within psychology have come to various different
conclusions. Wilder Penfield was able to develop a map of the cerebral cortex through studying epileptic patients along with Rassmussen. Research on localization of function has led behavioral neuroscientists
to a better understanding of which parts of the brain control behavior.
This is best exemplified through the case study of Phineas Gage.
The term "psychobiology" has been used in a variety of
contexts, emphasizing the importance of biology, which is the discipline
that studies organic, neural and cellular modifications in behavior,
plasticity in neuroscience, and biological diseases in all aspects, in
addition, biology focuses and analyzes behavior and all the subjects it
is concerned about, from a scientific point of view. In this context,
psychology helps as a complementary, but important discipline in the
neurobiological sciences. The role of psychology in this questions is
that of a social tool that backs up the main or strongest biological
science. The term "psychobiology" was first used in its modern sense by Knight Dunlap in his book An Outline of Psychobiology (1914). Dunlap also was the founder and editor-in-chief of the journal Psychobiology.
In the announcement of that journal, Dunlap writes that the journal
will publish research "...bearing on the interconnection of mental and
physiological functions", which describes the field of behavioral
neuroscience even in its modern sense.
In relation to the discipline, Solomon Carter Fuller
(1872 – 1953) also aided in the advancement of neurology and psychology
with his Alzheimer's research. Dr. Fuller was the first African
American psychiatrist and one of the pioneers of Alzheimer's disease. In 1904, Dr. Fuller began working as a research assistant under the
founder of Alzheimer's disease, Alois Alzheimer, studying presenile
dementia. Later in 1912, Dr. Fuller published the first review on
Alzheimer's disease that included information regarding his patient who
was the 9th person to ever be diagnosed with the disease. During his
time as a researcher and doctor, he worked with black veterans to
prevent them from getting misdiagnosed and deemed ineligible for
military benefits; he also trained staff to diagnose side effects from
sexually transmitted infections. In 1969, an award was established by
the American Psychiatric Association called the Solomon Carter Fuller
Award to honor black pioneers who worked to help other black people.
Neuroscience
is considered a relatively new discipline, with the first conference
for the Society of Neuroscience occurring in 1971. The meeting was held
to merge different fields focused on studying the nervous system (ex. neuroanatomy, neurochemistry, physiological psychology, neuroendocrinology, clinical neurology, neurophysiology, neuropharmacology, etc.) by creating one interdisciplinary field. In 1983, the Journal of Comparative and Physiological Psychology, published by the American Psychological Association, was split into two separate journals: Behavioral Neuroscience and the Journal of Comparative Psychology.
The author of the journal at the time gave reasoning for this
separation, with one being that behavioral neuroscience is the broader
contemporary advancement of physiological psychology. Furthermore, in
all animals, the nervous system is the organ of behavior. Therefore,
every biological and behavioral variable that influences behavior must
go through the nervous system to do so. Present-day research in
behavioral neuroscience studies all biological variables which act
through the nervous system and relate to behavior.
Relationship to other fields of psychology and biology
In many cases, humans may serve as experimental subjects in
behavioral neuroscience experiments; however, a great deal of the
experimental literature in behavioral neuroscience comes from the study
of non-human species, most frequently rats, mice, and monkeys. As a result, a critical assumption in behavioral neuroscience is that
organisms share biological and behavioral similarities, enough to permit
extrapolations across species. This allies behavioral neuroscience closely with comparative psychology, ethology, evolutionary biology, and neurobiology. Behavioral neuroscience also has paradigmatic and methodological similarities to neuropsychology,
which relies heavily on the study of the behavior of humans with
nervous system dysfunction (i.e., a non-experimentally based biological
manipulation).
Research methods
The distinguishing characteristic of a behavioral neuroscience experiment is that either the independent variable of the experiment is biological, or some dependent variable is biological. In other words, the nervous system
of the organism under study is permanently or temporarily altered, or
some aspect of the nervous system is measured (usually to be related to a
behavioral variable).
Disabling or decreasing neural function
Lesions
– A classic method in which a brain-region of interest is naturally or
intentionally destroyed to observe any resulting changes such as
degraded or enhanced performance on some behavioral measure. Lesions can
be placed with relatively high accuracy "Thanks to a variety of brain
'atlases' which provide a map of brain regions in 3-dimensional" stereotactic coordinates.[25]The part of the picture emphasized shows the lesion in the brain. This type of lesion can be removed through surgery.
Surgical lesions – Neural tissue is destroyed by removing it surgically.
Electrolytic lesions – Neural tissue is destroyed through the application of electrical shock trauma.
Chemical lesions – Neural tissue is destroyed by the infusion of a neurotoxin.
Temporary lesions – Neural tissue is temporarily disabled by cooling or by the use of anesthetics such as tetrodotoxin.
Transcranial magnetic stimulation
– A new technique usually used with human subjects in which a magnetic
coil applied to the scalp causes unsystematic electrical activity in
nearby cortical neurons which can be experimentally analyzed as a
functional lesion.
Synthetic ligand injection
– A receptor activated solely by a synthetic ligand (RASSL) or Designer
Receptor Exclusively Activated by Designer Drugs (DREADD), permits
spatial and temporal control of G protein signaling in vivo. These systems utilize G protein-coupled receptors (GPCR) engineered to respond exclusively to synthetic small molecules ligands, like clozapine N-oxide (CNO), and not to their natural ligand(s). RASSL's represent a GPCR-based chemogenetic
tool. These synthetic ligands upon activation can decrease neural
function by G-protein activation. This can with Potassium attenuating
neural activity.
Optogenetic
inhibition – A light activated inhibitory protein is expressed in cells
of interest. Powerful millisecond timescale neuronal inhibition is
instigated upon stimulation by the appropriate frequency of light
delivered via fiber optics or implanted LEDs in the case of vertebrates, or via external illumination for small, sufficiently translucent invertebrates. Bacterial Halorhodopsins or Proton pumps
are the two classes of proteins used for inhibitory optogenetics,
achieving inhibition by increasing cytoplasmic levels of halides (Cl− ) or decreasing the cytoplasmic concentration of protons, respectively.
Enhancing neural function
Electrical stimulation – A classic method
in which neural activity is enhanced by application of a small electric
current (too small to cause significant cell death).
Psychopharmacological manipulations – A chemical receptor antagonist induces neural activity by interfering with neurotransmission.
Antagonists can be delivered systemically (such as by intravenous
injection) or locally (intracerebrally) during a surgical procedure into
the ventricles or into specific brain structures. For example, NMDAantagonistAP5 has been shown to inhibit the initiation of long term potentiation
of excitatory synaptic transmission (in rodent fear conditioning) which
is believed to be a vital mechanism in learning and memory.
Synthetic Ligand Injection – Likewise, Gq-DREADDs
can be used to modulate cellular function by innervation of brain
regions such as Hippocampus. This innervation results in the
amplification of γ-rhythms, which increases motor activity.
Transcranial magnetic stimulation – In some cases (for example, studies of motor cortex), this technique can be analyzed as having a stimulatory effect (rather than as a functional lesion).
Optogenetic excitation – A light activated excitatory protein is expressed in select cells. Channelrhodopsin-2 (ChR2), a light activated cation channel, was the first bacterial opsin shown to excite neurons in response to light, though a number of new excitatory optogenetic tools have now been
generated by improving and imparting novel properties to ChR2.
Measuring neural activity
Optical techniques – Optical methods for
recording neuronal activity rely on methods that modify the optical
properties of neurons in response to the cellular events associated with
action potentials or neurotransmitter release.
Voltage sensitive dyes
(VSDs) were among the earliest method for optically detecting neuronal
activity. VSDs commonly changed their fluorescent properties in response
to a voltage change across the neuron's membrane, rendering membrane
sub-threshold and supra-threshold (action potentials) electrical
activity detectable. Genetically encoded voltage sensitive fluorescent proteins have also been developed.
Calcium imaging relies on dyes or genetically encoded proteins that fluoresce upon binding to the calcium that is transiently present during an action potential.
Synapto-pHluorin is a technique that relies on a fusion protein
that combines a synaptic vesicle membrane protein and a pH sensitive
fluorescent protein. Upon synaptic vesicle release, the chimeric protein
is exposed to the higher pH of the synaptic cleft, causing a measurable
change in fluorescence.
Single-unit recording
– A method whereby an electrode is introduced into the brain of a
living animal to detect electrical activity that is generated by the
neurons adjacent to the electrode tip. Normally this is performed with
sedated animals but sometimes it is performed on awake animals engaged
in a behavioral event, such as a thirsty rat whisking a particular
sandpaper grade previously paired with water in order to measure the
corresponding patterns of neuronal firing at the decision point.[45]
Multielectrode recording – The use of a bundle of fine
electrodes to record the simultaneous activity of up to hundreds of
neurons.
Functional magnetic resonance imaging – fMRI, a technique most frequently applied on human subjects, in which changes in cerebral blood flow can be detected in an MRI
apparatus and are taken to indicate relative activity of larger scale
brain regions (i.e., on the order of hundreds of thousands of neurons).
PET brain scans can show chemical differences in the brain
between addicts and non-addicts. The normal images in the bottom row
come from non-addicts while people with addictions have scans that look
more abnormal.Positron emission tomography
- PET detects particles called photons using a 3-D nuclear medicine
examination. These particles are emitted by injections of radioisotopes
such as fluorine. PET imaging reveal the pathological processes which
predict anatomic changes making it important for detecting, diagnosing
and characterising many pathologies.
Electroencephalography – EEG, and the derivative technique of event-related potentials,
in which scalp electrodes monitor the average activity of neurons in
the cortex (again, used most frequently with human subjects). This
technique uses different types of electrodes for recording systems such
as needle electrodes and saline-based electrodes. EEG allows for the
investigation of mental disorders, sleep disorders and physiology. It
can monitor brain development and cognitive engagement.
Electrocorticography
– ECoG, similar to an EGG, the ECoG records the brains electrical
activity and is commonly used on patients to monitor and evaluate
epilepsy or seizures. However, the ECoG is an invasive medical procedure
that measures signals directly from the brains surface. The ECoG
provides high spatial and temporal resolution as opposed to its
non-invasive counterpart, the EEG which has low temporal and spatial
resolution. Due to the invasiveness of the procedure, the data for human
patients is harder to collect than a standard EEG assessment.
Functional neuroanatomy – A more complex counterpart of phrenology. The expression of some anatomical marker is taken to reflect neural activity. For example, the expression of immediate early genes is thought to be caused by vigorous neural activity. Likewise, the injection of 2-deoxyglucose
prior to some behavioral task can be followed by anatomical
localization of that chemical; it is taken up by neurons that are
electrically active.
Magnetoencephalography
– MEG shows the functioning of the human brain through the measurement
of electromagnetic activity. Measuring the magnetic fields created by
the electric current flowing within the neurons identifies brain
activity associated with various human functions in real time, with
millimeter spatial accuracy. Clinicians can noninvasively obtain data to
help them assess neurological disorders and plan surgical treatments.
Genetic techniques
QTL mapping – The influence of a gene in some behavior can be statistically inferred by studying inbred strains of some species, most commonly mice. The recent sequencing of the genome of many species, most notably mice, has facilitated this technique.
Selective breeding – Organisms, often mice, may be bred selectively among inbred strains to create a recombinant congenic strain. This might be done to isolate an experimentally interesting stretch of DNA
derived from one strain on the background genome of another strain to
allow stronger inferences about the role of that stretch of DNA.
Genetic engineering – The genome may also be experimentally-manipulated; for example, knockout mice
can be engineered to lack a particular gene, or a gene may be expressed
in a strain which does not normally do so (the 'transgenic'). Advanced
techniques may also permit the expression or suppression of a gene to
occur by injection of some regulating chemical.
Quantifying behavior
Fruit fly (Drosophila melanogaster) leg joints being tracked in 3D with Anipose.Markerless pose estimation – The advancement of computer vision
techniques in recent years have allowed for precise quantifications of
animal movements without needing to fit physical markers onto the
subject. On high-speed video captured in a behavioral assay, keypoints
from the subject can be extracted frame-by-frame, which is often useful to analyze in tandem with neural
recordings/manipulations. Analyses can be conducted on how keypoints
(i.e. parts of the animal) move within different phases of a particular
behavior (on a short timescale), or throughout an animal's behavioral repertoire (longer timescale). These keypoint changes can be compared with corresponding changes in
neural activity. A machine learning approach can also be used to
identify specific behaviors (e.g. forward walking, turning, grooming,
courtship, etc.), and quantify the dynamics of transitions between
behaviors.
Other research methods
Computational models - Using a computer to formulate real-world problems to develop solutions. Although this method is often focused in computer science, it has begun
to move towards other areas of study. For example, psychology is one of
these areas. Computational models allow researchers in psychology to
enhance their understanding of the functions and developments in nervous
systems. Examples of methods include the modelling of neurons, networks
and brain systems and theoretical analysis. Computational methods have a wide variety of roles including clarifying
experiments, hypothesis testing and generating new insights. These
techniques play an increasing role in the advancement of biological
psychology.
Limitations and advantages
Different manipulations have advantages and limitations.
Neural tissue destroyed as a primary consequence of a surgery, electric
shock or neurotoxin can confound the results so that the physical trauma
masks changes in the fundamental neurophysiological processes of
interest.
For example, when using an electrolytic probe to create a purposeful
lesion in a distinct region of the rat brain, surrounding tissue can be
affected: so, a change in behavior exhibited by the experimental group
post-surgery is to some degree a result of damage to surrounding neural
tissue, rather than by a lesion of a distinct brain region. Most genetic manipulation techniques are also considered permanent. Temporary lesions can be achieved with advanced in genetic
manipulations, for example, certain genes can now be switched on and off
with diet. Pharmacological manipulations also allow blocking of certain
neurotransmitters temporarily as the function returns to its previous
state after the drug has been metabolized.
Topic areas
Experimental
setup for noninvasive theta-burst stimulation of the human striatum to
enhance striatal activity and motor skill learning.
In general, behavioral neuroscientists study various neuronal and biological processes underlying behavior, though limited by the need to use nonhuman animals. As a result, the
bulk of literature in behavioral neuroscience deals with experiences and
mental processes that are shared across different animal models such as:
However, with increasing technical sophistication and with
the development of more precise noninvasive methods that can be applied
to human subjects, behavioral neuroscientists are beginning to
contribute to other classical topic areas of psychology, philosophy, and
linguistics, such as:
Behavioral neuroscience has also had a strong history of
contributing to the understanding of medical disorders, including those
that fall under the purview of clinical psychology, clinical neuropsychology, and biological psychopathology (also known as abnormal psychology). Although animal models
do not exist for all mental illnesses, the field has contributed
important therapeutic data on a variety of conditions, including:
Parkinson's disease, a degenerative disorder of the central nervous system that often impairs motor skills and speech.
Huntington's disease,
a rare inherited neurological disorder whose most obvious symptoms are
abnormal body movements and a lack of coordination. It also affects a
number of mental abilities and some aspects of personality.
Alzheimer's disease,
a neurodegenerative disease that, in its most common form, is found in
people over the age of 65 and is characterized by progressive cognitive
deterioration, together with declining activities of daily living and by
neuropsychiatric symptoms or behavioral changes.
Clinical depression,
a common psychiatric disorder, characterized by a persistent lowering
of mood, loss of interest in usual activities and diminished ability to
experience pleasure.
Schizophrenia,
a psychiatric diagnosis that describes a mental illness characterized
by impairments in the perception or expression of reality, most commonly
manifesting as auditory hallucinations, paranoid or bizarre delusions
or disorganized speech and thinking in the context of significant social
or occupational dysfunction.
Autism,
a brain development disorder that impairs social interaction and
communication, and causes restricted and repetitive behavior, all
starting before a child is three years old. However, neuropsychologist,
which are individuals in a behavioral neuroscience subfield have used
mindfulness interventions to combat socially disruptive behaviors in
autistic children.
Anxiety,
a physiological state characterized by cognitive, somatic, emotional,
and behavioral components. These components combine to create the
feelings that are typically recognized as fear, apprehension, or worry.
Drug abuse, a chronic behavioral disorder in which individuals seek reward and pleasure reinforcement through uncontrollable drug use.
Alcoholism,
a behavioral disorder in which individuals compulsively consume
alcoholic substances. This disorder can result in several medical,
neurological, and psychiatric conditions.
Behavioral neuroscientists conduct research on various cognitive processes through the use of different neuroimaging
techniques. Examples of cognitive research might involve examination of
neural correlates during emotional information processing, such as one
study that analyzed the relationship between subjective affect and
neural reactivity during sustained processing of positive (savoring) and negative (rumination)
emotion. The aim of the study was to analyze whether repetitive
positive thinking (seen as being beneficial) and repetitive negative
thinking (significantly related to worse mental health) would have
similar underlying neural mechanisms. Researchers found that the
individuals who had a more intense positive affect during savoring, were
also the same individuals who had a more intense negative affect during
rumination. fMRI
data showed similar activations in brain regions during both rumination
and savoring, suggesting shared neural mechanisms between the two types
of repetitive thinking. The results of the study suggest there are
similarities, both subjectively and mechanistically, with repetitive
thinking about positive and negative emotions. This overall suggests
shared neural mechanisms by which sustained emotional processing of both
positive and negative information occurs.
Stress
Research within the field of behavioral neuroscience
involves looking at the complex neuroanatomy underlying different
emotional processes, such as stress.
Godoy et al. (2018) did so by providing an in-depth analyzation of the
neurobiological underpinnings of the stress response. The article
features on an overview on the historical development of stress research
and its importance leading up to research related to both physical and
psychological stressors today. The authors explored various
significators of stress and their corresponding neuroanatomical
processing, along with the temporal dynamics of both acute and chronic
stress and its effects on the brain. Overall, the article provides a
comprehensive scientific overview of stress through a neurobiological
lens, highlighting the importance of our current knowledge in
stress-related research areas today.
Sensation and Perception
Another common research topic within behavioral neuroscience is sensation and perception.
Wu et al. (2023) conducted a study that analyzed auditory and
somatosensory realms association with psychosocial factors (e.g.,
depression) and cognitive impairment among the geriatric population. The
article discussed how hearing loss is the most common form of sensory
dysfunction within the geriatric population as 2.5 billion people will
experience this type of sensory depletion. The researchers used the
Chinese version Mini-Mental State Examination (MMSE), Nottingham Sensory
Assessment scale (NSA), Albert's test, Geriatric Depression Scale-30,
and the Lubben Social network Scale-6 (LSNS-6) to assess cognitive
function, sensation, perception, and negative socio-psychological
factors (i.e., depression and social isolation), respectively. After
performing a statistical analysis based on the participants assessment
scores it was found that older people with auditorial sensory loss,
atypical perception, and depression are more at risk for cognitive
impairment. However, implications such as rehabilitation,
non-pharmacological interventions for sensory loss and depression may
reduce the amount of cognitive impairment older adults experience.
Evolutionary neuroscientists examine changes in genes,
anatomy, physiology, and behavior to study the evolution of changes in
the brain. They study a multitude of processes including the evolution of vocal, visual, auditory, taste, and learning systems as well as language evolution and development. In addition, evolutionary neuroscientists study the evolution of specific areas or structures in the brain such as the amygdala, forebrain and cerebellum as well as the motor or visual cortex.
History
Studies of the brain began during ancient Egyptian times
but studies in the field of evolutionary neuroscience began after the
publication of Darwin's On the Origin of Species in 1859. At that time, brain evolution was largely viewed at the time in relation to the incorrect scala naturae.
Phylogeny and the evolution of the brain were still viewed as linear.
During the early 20th century, there were several prevailing theories
about evolution. Darwinism was based on the principles of natural selection and variation, Lamarckism was based on the passing down of acquired traits, Orthogenesis was based on the assumption that tendency towards perfection steers evolution, and Saltationism
argued that discontinuous variation creates new species. Darwin's
became the most accepted and allowed for people to starting thinking
about the way animals and their brains evolve.
The 1936 book The Comparative Anatomy of the Nervous System of Vertebrates Including Man by the Dutch neurologist C.U. Ariëns Kappers (first published in German in 1921) was a landmark publication in the field. Following the Evolutionary Synthesis,
the study of comparative neuroanatomy was conducted with an
evolutionary view, and modern studies incorporate developmental
genetics. It is now accepted that phylogenetic changes occur independently
between species over time and can not be linear. It is also believed
that an increase with brain size correlates with an increase in neural
centers and behavior complexity.
Major arguments
Over time, there are several arguments that would come to
define the history of evolutionary neuroscience. The first is the
argument between E.G. St.Hilaire and G. Cuvier over the topic of "common plan versus diversity". St.Hilaire argued that all animals are built based on a single plan or archetype and he stressed the importance of homologies
between organisms, while Cuvier believed that the structure of organs
was determined by their function and that knowledge of the function of
one organ could help discover the functions of other organs. He argued that there were at least four different archetypes. After Darwin, the idea of evolution was more accepted and St.Hilaire's idea of homologous structures was more accepted. The second major argument is that of Aristotle's scala naturae (scale of nature) and the great chain of being versus the phylogenetic bush. The scala naturae,
later also called the phylogenetic scale, was based on the premise that
phylogenies are linear or like a scale while the phylogenetic bush
argument was based on the idea that phylogenies were not linear, and
more resembled a bush – the currently accepted view. A third major
argument dealt with the size of the brain and whether relative size or
absolute size was more relevant in determining function. In the late
18thcentury, it was
determined that brain to body ratio reduces as body size increases.
However more recently, there is more focus on absolute brain size as this scales with internal structures and functions, with the degree of structural complexity, and with the amount of white matter
in the brain, all suggesting that absolute size is much better
predictor of brain function. Finally, a fourth argument is that of
natural selection (Darwinism)
versus developmental constraints (concerted evolution). It is now
accepted that the evolution of development is what causes adult species
to show differences and evolutionary neuroscientists maintain that many
aspects of brain function and structure are conserved across species.
Techniques
Throughout history, we see how evolutionary neuroscience has been dependent on developments in biological theory and techniques. The field of evolutionary neuroscience has been shaped by the
development of new techniques that allow for the discovery and
examination of parts of the nervous system. In 1873, C. Golgi
devised the silver nitrate method which allowed for the description of
the brain at the cellular level as opposed to simply the gross level. Santiago
and Pedro Ramon used this method to analyze numerous parts of brains,
broadening the field of comparative neuroanatomy. In the second half of
the 19th century, new techniques allowed scientists to identify neuronal
cell groups and fiber bundles in brains. In 1885, Vittorio Marchi
discovered a staining technique that let scientists see induced axonal
degeneration in myelinated axons, in 1950, the "original nauta
procedure" allowed for more accurate identification of degenerating
fibers, and in the 1970s, there were several discoveries of multiple
molecular tracers which would be used for experiments even today. In the
last 20years, cladistics has also become a useful tool for looking at variation in the brain.
Many of Earth's early years were filled with brainless creatures, and among them was the amphioxus, which can be traced as far back as 550million
years ago. Amphioxi had a significantly simpler way of life, which made
it not necessary for them to have a brain. To replace its absence of a
brain, the prehistoric amphioxi had a limited nervous system,
which was composed of only a bunch of cells. These cells optimized
their uses because many of the cells for sensing intertwined with the
cells used for its very simple system for moving, which allowed it to
propel itself through bodies of water and react without much processing
while the cells remaining were used for the detection of light to
account to the fact that it had no eyes. It also did not need a sense of
hearing. Even though the amphioxi had limited senses, they did not need
them to survive efficiently, as their life was mainly dedicated to
sitting on the seafloor to eat.Although the amphioxus' "brain" might seem severely underdeveloped
compared to their human counterparts, it was set well for its respective
environment, which has allowed it to prosper for millions of years.
Although many scientists once assumed that the brain
evolved to achieve an ability to think, such a view is today considered a
great misconception. 500million years ago, the Earth entered into the Cambrian
period, where hunting became a new concern for survival in an animal's
environment. At this point, animals became sensitive to the presence of
another, which could serve as food. Although hunting did not inherently
require a brain, it was one of the main steps that pushed the
development of one, as organisms progressed to develop advanced sensory
systems.
In response to progressively complicated surroundings,
where competition between animals with brains started to arise for
survival, animals had to learn to manage their energy.As creatures acquired a variety of senses for perception, animals progressed to develop allostasis,
which played the role of an early brain by forcing the body to gather
past experiences to improve prediction. Since prediction beat reaction,
organisms who planned their manoeuvres were more likely to survive than
those who did not. This came with equally managing energy adequately,
which nature favoured. Animals that had not developed allostasis would
be at a disadvantage for their purpose of exploration, foraging and
reproduction, as death was a higher risk factor.
As allostasis continued to develop in animals, their bodies
equally continuously evolved in size and complexity. They progressively
started to develop cardiovascular systems, respiratory systems and immune systems
to survive in their environments, which required bodies to have
something more complex than the limited quality of cells to regulate
themselves. This encouraged the nervous systems of many creatures to
develop into a brain, which was sizeable and strikingly similar to how
most animal brains look today.
Evolution of the human brain
Darwin, in The Descent of Man,
stipulated that the mind evolved simultaneously with the body.
According to his theory, all humans have a barbaric core that they learn
to deal with. Darwin's theory allowed people to start thinking about the way animals and their brains evolve.
Reptile brain
Plato's insight on the evolution of the human brain
contemplated the idea that all humans were once lizards, with similar
survival needs such as feeding, fighting and mating. In the classical eraPlato first described this concept as the "lizard mind" – the deepest layer and one of three parts of his conception of a three-part human mind. In the 20thcentury P. MacLean developed a similar, modern triune brain theory.
Recent research in molecular genetics has demonstrated
evidence that there is no difference in the neurons that reptiles and
nonhuman mammals have when compared to humans. Instead, new research
speculates that all mammals, and potentially reptiles, birds and some
species of fish, evolve from a common order pattern. This research
reinforces the idea that human brains are structurally no t any
different from many other organisms.
The cerebral cortex of reptiles resembles that of mammals, although simplified. Although the evolution and function of the human cerebral cortex is
still shrouded in mystery, we know that it is the most dramatically
changed part of the brain during recent evolution. The reptilian brain,
300million years ago, was
made for all our basic urges and instincts like fighting, reproducing,
and mating. The reptile brain evolved 100million
years later and gave us the ability to feel emotion. Eventually, it was
able to develop a rational part that controls our inner animal.
Visual perception
Vision allows humans to process the world surrounding them
to a certain extent. Through the wavelengths of light, the human brain
can associate them to a specific event. Although the brain obviously
perceives its surroundings at a specific moment, the brain equally
predicts the upcoming changes in the environment. Once it has noticed them, the brain begins to prepare itself to
encounter the new scenario by attempting to develop an adequate
response. This is accomplished by using the data the brain has at its
access, which can be to use past experiences and memories to form a
proper response. However, sometimes the brain fails to predict accurately which means
that the mind perceives a false illustration. Such an incorrect image
occurs when the brain uses an inadequate memory to respond to what it is
facing, which means that the memory does not correlate with the real
scenario.(pp 75–76)
The rabbit–duck illusion
is a famous ambiguous image in which a rabbit or a duck can be seen.
The earliest known version is an unattributed drawing from the 23October 1892 issue of Blätter magazine.
Research about how visual perception has developed in
evolution is today best understood through studying present-day primates
since the organization of the brain cannot be ascertained only by
analyzing fossilized skulls.
The brain interprets visual information in the occipital
lobe, a region in the back of the brain. The occipital lobe contains the
visual cortex and the thalamus, which are the two main actors in
processing visual information. The process of interpreting information
has proven to be more complex than "what you see is what you get".
Misinterpreting visual information is more common than previously
believed.
As knowledge of the human brain has evolved, researchers
discover that our visual perception is much closer to a construction of
the brain than a direct "photograph" of what is in front of us. This can
lead to misperceiving certain situations or elements in the brain's
attempt to keep us safe. For example, an on-edge soldier believes a
young child with a stick is a grown man with a gun, as the brain's
sympathetic system, or fight-or-flight mode, is activated.
An example of this phenomenon can be observed in the rabbit–duck illusion.
Depending on how the image is looked at, the brain can interpret the
image of a rabbit, or a duck. There is no right or wrong answer, but it
is proof that what is seen may not be the reality of the situation.
Auditory perception
The organization of the human auditory cortex is divided
into core, belt, and parabelt. This closely resembles that of
present-day primates.
The concept of auditory perception resembles visual
perception very similarly. Our brain is wired to act on what it expects
to experience. The sense of hearing helps situate an individual, but it
also gives them hints about what else is around them. If something
moves, they know approximately where it is and by the tone of it, the
brain can predict what moved. If someone were to hear leaves rustling in
a forest, the brain might interpret that sound as being an animal which
could be a dangerous factor, but it would simply be another person
walking. The brain can predict many things based on what it is interpreting, however, those predictions may not all be true.
Language development
Evidence of a rich cognitive life in primate relatives of
humans is extensive, and a wide range of specific behaviours in line
with Darwinian theory is well documented. However, until recently, research has disregarded nonhuman primates in
the context of evolutionary linguistics, primarily because unlike vocal
learning birds, our closest relatives seem to lack imitative abilities.
Evolutionary speaking, there is great evidence suggesting a genetic
groundwork for the concept of languages has been in place for millions
of years, as with many other capabilities and behaviours observed today.
While evolutionary linguists agree on the fact that
volitional control over vocalizing and expressing language is a quite
recent leap in the history of the human race, that is not to say
auditory perception is a recent development as well. Research has shown
substantial evidence of well-defined neural pathways linking cortices to
organize auditory perception in the brain. Thus, the issue lies in our
abilities to imitate sounds.
Beyond the fact that primates may be poorly equipped to
learn sounds, studies have shown them to learn and use gestures far
better. Visual cues and motoric pathways developed millions of years
earlier in our evolution, which seems to be one reason for our earlier
ability to understand and use gestures.
Cognitive specializations
Evolution shows how certain environments and surroundings
will favor the development of specific cognitive functions of the brain
to aid an animal or in this case human to successfully live in that
environment.
Cognitive specialization in a theory in which cognitive
functions, such as the ability to communicate socially, can be passed
down genetically through offspring. This would benefit species in the
process of natural selection. As for studying this in relation to the
human brain, it has been theorized that very specific social skills
apart from language, such as trust, vulnerability, navigation, and
self-awareness can also be passed by offspring.
Transgenerational trauma, intergenerational trauma, or generational trauma
is the psychological and physiological effects that the trauma
experienced by people has on subsequent generations in that group. The
primary mode of transmission is the shared family environment of the infant, causing psychological, behavioral and social changes in the individual.
Transgenerational trauma can be a collective experience that affects groups of people who share a cultural identity (e.g., ethnicity, nationality, or religious identity). It can also be applied to single families or individual parent–child dyads. For example, survivors of individual child abuse and both direct survivors of the collective trauma and members of subsequent generations individually may develop complex post-traumatic stress disorder.
While transgenerational trauma gained attention in recent decades, the hypothesis of an epigenetic mechanism remains controversial due to a lack of rigorous experimental results on humans.
History
This field of research is relatively young, but was expanded in the mid-to-late-2000s. Intergenerational trauma was first recognized in the children of Holocaust survivors. In 1966, psychologists began to observe large numbers of children of
Holocaust survivors seeking mental help in clinics in Canada. The
grandchildren of Holocaust survivors were overrepresented by 300% among
the referrals to a psychiatry clinic in comparison with their
representation in the general population. Since then, transgenerational trauma has been noted amongst descendants of African-Americans forced into slavery, Native American genocide survivors, war survivors, refugees, survivors of domestic violence, and many other groups that have experienced collective distress.
Research on possible biological mechanisms for inheritance of trauma began in the late 1990s. It has been suggested that traumatic stress can be passed down to future generations via epigenetics. However, the effect is difficult to separate from environmental and
cultural transmission and conclusive evidence that it occurs in humans
has yet to be found.
Although methylation of stress-related genes in humans may affect development, there is no evidence that these changes in humans are passed on to subsequent generations. Methylation is normally erased when an egg cell is fertilized.
Definitions and description
Transgenerational trauma is a collective experience that affects groups of people because of their cultural identity (e.g., ethnicity, nationality, or religious identity). Because of its collective nature, the term is not usually applied to single families or individual parent–child dyads. However, like survivors of individual child abuse, individually, both direct survivors of the collective trauma and members of subsequent generations may develop complex post-traumatic stress disorder.
Trauma may be transmitted socially (e.g., through learned
behaviors) or through the effects of stress on development before birth
(inc. increased smoking/alcohol use).
Historical trauma
Historical trauma,
a sub-type of transgenerational trauma, is the collective devastation
of the past that continues to affect populations in the present through
inter-generational transmission. Historical trauma results in
vulnerability to mental and physical health problems due to ancestral
suffering which has been collected throughout generations into "legacies
of disability for contemporary descendants". Although the actual traumatic event and affect group(s) are
heterogeneous, all historical traumas consist of three elements: a
traumatic event, a resulting collective suffering, and a
multigenerational impact of that trauma. Over time the trauma and
relationship to the victims typically evolve in a similar but more
complicated way to genetic anticipation, resulting in a greater loss of
identity of the victims and further integration into society.
For individual victims, historical trauma often manifests in four ways: depression, hyper-vigilance, traumatic bond formation, and reenactment of the trauma. Building upon the clinical observations by Selma Fraiberg, child trauma researchers such as Byron Egeland, Inge Bretherton, and Daniel Schechter
have empirically identified psychological mechanisms that favor
intergenerational transmission, including dissociation in the context of
attachment, and "communication" of prior traumatic experience as an effect of parental efforts to maintain self-regulation in the context of post-traumatic stress disorder and related alterations in social cognitive processes.
Symptoms
Symptoms of intergenerational trauma always begins with the survivor of a trauma, which tend to manifest as symptoms of PTSD. Oftentimes trauma in the second generation is deemed as a traumatic response to parental trauma. Transmission between the parent and child can be broken down into five
measures: communication, conflict, family cohesion, parental warmth, and
parental involvement. High levels of maternal stress were directly correlated with weak
family functioning and indirectly correlated with deviant behavior among
children. Common symptoms in children consisted of depression,
antisocial behavior, delinquency, and disruptive behavior in school. Some children experienced direct transmission in which their trauma
stemmed from the interactions and relationships with their parents,
while others experienced indirect transmission in which their trauma was
mainly rooted in guilt. Those who were affected through direct
transmission were more likely to lash out through their actions, while
those who were affected through indirect transmission were more likely
to develop depression, anxiety, and guilt.
Symptoms also differed based on ethnicity and type of original trauma. Enslavement, genocide, domestic violence, sexual abuse, and extreme poverty
are all common sources of trauma that lead to intergenerational trauma.
A lack of therapy also worsens symptoms and can lead to transmission.
For instance, survivors of child sexual abuse
may negatively influence future generations due to their past
unresolved trauma. This can lead to increased feelings of mistrust,
isolation, and loneliness. Descendants of enslaved persons when faced with racism-motivated violence, microaggressions,
or outward racism, react as if they were faced with the original trauma
that was generationally transmitted to them. There are a variety of
stressors in one's life that led to this PTSD-like reaction such as
varying racist experiences, daily stressors, major race-related life
events, or collective racism or traumas. This also presents itself in parenting styles. Goodman and West-Olatunji proposed potential transgenerational trauma in the aftermath of natural disasters. In a post-Hurricane Katrina New Orleans, residents have seen a dramatic increase in interpersonal violence with higher mortality rates. This phenomenon has been also been reported in the descendants of Indigenous students at residential schools, who were removed from their parents and extended family and lacked models for parenting as a result. Being punished for speaking their native language
and forbidden from practicing traditional rituals had a traumatic
effect on many students, and child abuse was rampant in the schools as
well.
Symptoms of transgenerational trauma have in recent years
been identified among black Americans, in relation to the effects of
slavery and racial discrimination. This passing of trauma can be rooted
from the family unit itself, or found in society via current
discrimination and oppression. The traumatic event does not need to be individually experienced by all
members of a family; the lasting effects can still remain and impact
descendants from external factors. For example, black children's
internalization of others' reactions to their skin color manifests as a
form of lasting trauma originally experienced by their ancestors. This reaction to black skin stems from similar attitudes that led to
the traumatizing conditions and enslavement of slaves. Black children
and youth are more susceptible to racial trauma
because they have not yet acquired the knowledge to have a full
understanding of racism and its effects. However, these traumatizing
behaviors experienced at such a young age are a reflection of a child's
parenting. A White child may learn racist behaviors from their
environment, but by the same token a black child can learn to assert
their blackness and how to respond to racist remarks and actions from
their parents. Traces of trauma have an impact on black and other minority children's
success in an educational context. Transgenerational trauma has also
been heavily recorded in refugees and their children, which can last
through several generations. Such traumas can stem from violence,
political persecution, familial instability, as well as the hardships of
migration.
Affected groups
Descendants of enslaved people
In general, black Americans who have any mental illness
are resistant to receiving treatment due to stigma, negative
conceptions, and fear of discrimination. This reduces the number of
those affected to seek help. Lack of treatment causes the symptoms to compound leading to further
internalization of distress and a worsening of mental health in the
individual. Those affected by race-based trauma oftentimes do not seek treatment
not only because of stigma but because of fear that the medical
professional will not understand their perspective of a disenfranchised
minority. Furthermore, the existing stigma of mental health has led to a
lack of research and consequently treatment. However, lack of treatment
can also be attributed to the misdiagnosis of symptoms. Signs of trauma
exhibited in black children are often labeled as behavioral or
educational disabilities, allowing the trauma to go untreated. While
trauma symptoms often manifest as other mental illnesses such as
depression and anxiety, the larger diagnosis often goes untreated.
Han
is a concept of an emotion, variously described as some form of grief
or resentment, among others, that is said to be an essential element of
Korean identity by some, and a modern post-colonial identity by others.
Michael D. Shin argues that the central aspect of han is loss of identity, and defines han as "the complex of emotions that result from the traumatic loss of collective identity". Han is most commonly associated with divided families: families who were separated during the Korean War. According to Shin, all Koreans may experience han, or a "constant feeling of being less than whole", because of not having a collective identity as a result of the continued division of Korea. Furthermore, new generations of Koreans seemingly inherit it because of growing up in a divided country.
Refugees
Refugees are often at risk of experiencing transgenerational trauma. While many refugees experience some sort of loss and trauma,
war-related trauma has been documented to have longer-lasting effects on
mental health and span through more generations. Children are especially prone to the trauma of resettling, as their
childhood may have been disrupted by migration to a new country.
Additionally, they often face the difficulty of learning a new language,
adapting to a new environment, and navigating the school's social
system in their host country. Normal caregiving is disrupted by the
process of fleeing from their original home, and it may continue to be
disrupted by their parents' PTSD symptoms and challenges faced in their new home. Furthermore, many host countries do not provide adequate mental healthcare systems to refugees, which can worsen symptoms and lead to transmission of trauma. In general, children of refugees exhibited higher overall levels of depression, PTSD, anxiety, attention deficiency, stress, and other psychological issues. Most refugees who flee from their homes do so to escape war, conflict, or natural disasters. More often times than not the wellness of refugees' homeland does not
improve which causes continuous exposure to the originating trauma. This can be described as secondhand trauma and can be experienced by many. However, the offspring who have both transgenerational trauma and
intergenerational trauma may experience secondhand trauma and a greater
scale.
Vietnam war refugees
Since 1975, the US has accepted many refugees from Vietnam, Cambodia, Thailand, and Laos. As a result of the Vietnam War,
many of these Southeast Asian refugees are at high risk of experiencing
transgenerational trauma. Factors occurring both before and after immigration to America
could contribute to traumatization in these groups. Being forced to
witness and flee violence and war was a uniquely traumatic occurrence,
resulting in high levels of psychological distress. Upon arriving in the United States, Vietnamese Americans struggled to adapt to their new environment, resulting in limited social mobility,
high rates of poverty within the community, and exposure to community
violence. Exposure to these stressors is correlated with higher trauma
symptoms in first-generation Vietnamese-American refugees. In turn, these traumatic experiences impacted the ways that refugees
raised their children since they internalized notions of being outsiders
in a new country and emphasized success in the face of their many
sacrifices. This cultural and familial transmission of trauma has led
second-generation Vietnamese Americans to face their own forms of
intergenerational trauma. These unique forms of mental health and stress
are often not addressed due to socio-cultural standards of silence and
refusal to seek treatment.
While a majority of these groups were fleeing war and poverty, Cambodian refugees were also fleeing a genocide from the Khmer Rouge. The atrocities of violence, starvation, and torture were common themes experienced by these refugees. Many Cambodian refugee families refused to talk about their trauma
which created an isolating environment for the child. This led to a
transmission of trauma through the continuing pattern of silence and
refusal to acknowledge an issue or seek treatment. There has also been data showing that the children of survivors from
regions with higher rates of violence and mortality displayed stronger
overall symptoms. The parenting style of caregivers may also contribute to the rate of
impact among children of Khmer Rouge survivors. A 2013 study found that
among Khmer Rouge survivors with PTSD who engage in role-reversal
parenting, a form of parenting where the parent looks to the child for
emotional support, there may be higher rates of anxiety and depression
in the children.
Indigenous Australians
Many Aboriginal Australian and Torres Strait Islander children were forcibly removed from their parents and placed in Aboriginal reserves and missions
in the late 19th and first half of the 20th century. Some were
subsequently placed with white families, and this practice continued
after people were no longer forcibly removed to reserves. These people
became known as the Stolen Generations, and successive generations suffer from intergenerational trauma as a result of this as well as other issues related to the colonisation of Australia, such as dispossession of land, loss of language, etc. Many Aboriginal Australians often face discrimination and resistance
when trying to access many services including legal, health, housing,
and education. It was found that in 2019, 28% of the total prison population consisted of Aboriginal Australians and Torres Strait Islanders. As of 2022, this percentage has increased to 32% of all prisoners. A study consisting of 43 Aboriginal women found that Aboriginal women
often face more struggles when incarcerated compared to their peers. With these struggles Aboriginal Australians face, the trauma is often
passed down to their offspring as they are on the receiving end of the
discrimination, often are targeted themselves as children, or grow up to
face similar of not the same struggles as their family members.
Native/Indigenous Peoples of the Americas
Settler-colonization
encompasses a wide range of practices: war, displacement, forced labor,
removal of children, relocation, destruction, massacre, genocide,
slavery, unintentional and intentional spread of deadly diseases,
banning of indigenous language, regulation of marriage, assimilation,
eradication of culture, social and spiritual practices. European
colonization has, in some instances, involved subjugation of the indigenous peoples of the Americas through violence, ethnic cleansing, forced assimilation, and acculturation. Indian reservations, and harmful policies excluding and oppressing
Natives evoked similar responses to trauma as the descendants of
Holocaust survivors. In a similar way we find transgenerational trauma
in Holocaust survivors we find the same patterns and effects in
Indigenous populations and their children and grandchildren.
Due to the effects of settler colonialism, oppression,
racism, and other aversive events, Native Americans disproportionately
experience adverse childhood experiences
as well as health disparities, including high rates of posttraumatic
stress, depression, substance abuse, diabetes, and other psychiatric
disorders.
Military personnel and their families
Transgenerational trauma is also commonly known as
secondary trauma due to the transmission of symptoms that can take place
between individuals in close proximity (i.e., children,
spouses/partners, and other family members). Transgenerational trauma affects everyone, including those in the military and their families. Patterns of transgenerational trauma can be recognized through the use of a genogram,
a family tree that provides a visual representation of hereditary
patterns. Specifically, a trauma-focused genogram can be used with those
who suffer from acute stress disorder (ASD) and posttraumatic stress disorder (PTSD). Traumatic family patterns could include things such as sexual abuse,
domestic violence, and even things such as natural disasters. This type
of genogram is inclusive to military personnel in that it takes into
consideration the servicemembers' experiences. Some of these
considerations include taking into account how long the servicemember
served, what their role was, if they were a prisoner of war and if they
witnessed the death or injury of others. However, not all military personnel pass down intergenerational trauma.
Military personnel who have seen or participated in
abusive acts of violence have been found to transmit the trauma they
experienced to their children. Children of these veterans have been found to suffer from behavioral
disturbances such as aggression, hyperactivity, and delinquency. Children whose parent was diagnosed with PTSD had a higher rate of
anxiety as well as aggression when compared to children of civilians or
non-veterans. These children can also have increased depressive symptoms and other PTSD symptoms. However, it has been found that spouses and partners of military
veterans can help to buffer the effects of the transmission of trauma
symptomology.
This type of intergenerational trauma can be experienced
and transmitted not only to children of veterans but also to their
spouses/partners, ultimately affecting the whole family unit. Veterans
who experienced PTSD or wartime combat stress reaction (CSR) had spouses/partners who experienced increased psychiatric symptoms. These symptoms included feelings of loneliness and having impaired relationships within the family unit and marriage. Much like veterans who suffer from PTSD, their spouses or partners can
suffer from many of the same symptoms as well. Spouses or partners of
military veterans can experience the avoidance of thoughts, behaviors,
and emotions. Spouses or partners may also experience intrusions such as
unwanted cognitions and images that may remind them of the negative
experiences of their spouse or partner. Common symptoms of emotional
distress that spouses may experience are depression and anxiety. These symptoms are intergenerational trauma symptoms that are being passed down from the veteran to the spouse.
Intergenerational trauma can sometimes go unrecognized by
the spouse or partner suffering from the transmission of trauma. It
sometimes can be difficult for those suffering from intergenerational
trauma to recognize that they are emotionally affected, and thus
difficult for these individuals to find treatment. Resources such as a genogram can be an excellent way in which an
individual can recognize the trauma that has been passed down to them.
When it comes to transgenerational trauma, it can be
transmitted quite quickly and can affect many people in which the
servicemember has encountered. This also includes mental health workers and primary care physicians
with whom the servicemember may be working. Mental health workers and
primary care physicians asked to take a survey entitled "Secondary
Traumatic Stress Scale" reported that they had trouble sleeping, feeling
emotionally numb, and having intrusive thoughts about clients.
Treatment
Mental health workers who are considering working with
veterans who suffer from PTSD and other traumatic experiences should
have experience working with veterans and servicemembers. Cultural sensitivity
is another aspect to consider when working with this population.
Understanding the military culture and lifestyle is informative when
developing the therapeutic relationship
and treatment plans. Another cultural consideration is the family
component. This can include the servicemember's actual family or their
chosen family. The military can bring on a lot of stress when it comes to the
servicemember and his family. These include, moving to different places
on short notice, deployment plans constantly changing, difficulty
transitioning when coming back from deployment, and many other
stressors. Therefore, it is crucial that a mental health worker truly
understands military life.
In the case of PTSD, in order to prevent or minimize
intergenerational trauma, it is important that the family also seek
mental health services. A spouse/partner who is receiving mental health services and is at a
better place in their life because of these interventions can help the
family unit overall. In a military family, the roles are constantly changing due to the
servicemember being on deployment and other factors. The family, as a
unit, needs to adjust to the servicemember coming into and out of their
lives. With a healthy family unit, the spouse/partner becomes a
predicting factor of soldier retention and a functioning family unit. Resiliency can also play a role in this dynamic. A few things can
contribute to resiliency in a family unit. These include
flexibility/organizational style, the family's belief system, and the
communication process. These are important things to look for and identify as they can help in
the treatment of intergenerational trauma. Making the family unit
strong can help to empower each individual member of the family, and
together they can overcome intergenerational trauma within the family.
Understanding military culture can help aid families through the process
of overcoming intergenerational trauma.
In addition to the genograms, solution-focused brief therapy (SFBT) has been found to be successful with military families. It uses an emphasis on the client's successes and creating small steps
that are attainable for the client. This type of therapy uses the
client's language and experience to address things systematically within
the family. SFBT, together with the genograms, can be informative to both the
client and clinician and can help to inform the future of practice. As
the genograms can help to give a clear picture as to what the trauma
patterns are in the family, SFBT can help to change these patterns and
provide the family with a healthier way of living and functioning. This
specific type of therapy can help to educate the client and their family
as to what exactly has been passed down from previous generations. It
can also inform the family as to what is now beginning to be transmitted
and can help to change the trajectory in the future and change the
family dynamic principles.
Transmission
There are many current transgenerational studies that have
been done on adults that have experienced natural disasters or
adversities. One study found that the children of torture victims showed
more symptoms of anxiety, depression, post-traumatic stress, attention
deficits, and behavioral disorders than the comparison group of those
who had not experienced the specific trauma. A qualitative study was done on the Brazilian children of Holocaust
survivors and proposed a supported model of the transgenerational
transmission of traumatic experiences but also one of resilience
patterns, which can be transmitted in between generations and developed
within generations. According to Froma Walsh,
resilience theory suggests that individuals' and families' responses to
traumatic experiences is an ever-changing process that involves both
exposure to challenges and the development of coping mechanisms that
aide in one's ability to overcome such challenges. Regardless of risk, there are also opportunities for the development of
resilience via exposure to meaningful resources that support one's
ability to overcome adversity. The researchers Cowan, Callaghan, and Richardson studied the impact of
early-life adversities on individuals and their descendants. Their
research was also consistent with the transmission theory in which their
findings revealed that the stress phenotype that was expressed in
individuals who experienced the adversity was also observed in children
and even grandchildren.
The oppression that black people experienced through slavery and racism has a psychological impact on how they view achievement. In terms of the social aspects, that seems to make it difficult for black people to surpass a certain socioeconomic status threshold, escape a certain neighborhood, or move beyond a certain lifestyle or status.
For Native Americans, past government policy and internal displacements are theorized to have an effect even generations later. The social enforcement of their ostracization causes them to be
generally removed from society, to be powerless and uninvited in
government, and to be left to fend for themselves. The transgenerational transmission of colonial trauma is also
considered a contributing factor in the high rates of mental health
difficulties that Native Canadian
communities experience. Displacement and maltreatment during
colonization had led to negative effects in the children of those who
survived such experiences. This is passed down generationally via
ongoing social marginalization and lateral violence.
The loss of cultures and resulting lack of community cohesion poses a
further challenge for groups in resolving transgenerational trauma.
The fetal environment is influenced by the maternal diet.
This environmental history can cause the fetal developmental response to
change to produce a metabolic phenotype that suits the anticipated
environment.
It has been suggested that a mother's mood may influence the fetus, though studies on this have mixed results. It is unclear whether any of the effects persist after birth.
Treatment
Because transgenerational trauma is a form of indirect
traumatic exposure, it often goes unrecognized or is misdiagnosed by
clinicians. A lack of treatment accessibility can have several consequences such as
health, behavioral, and social issues that may persist across an
individual's lifespan.
The experience of traumatic stress can modify cognitive,
behavioral, and physiological functions, which can increase
susceptibility to both mental and physical health issues. Because transgenerational trauma is a form of traumatic stress, it can
increase risk for developing psychological disorders such as
post-traumatic stress disorder, major depressive disorder, generalized anxiety disorder, schizophrenia, autism, and substance use disorders.
Several therapy modalities have been found to be effective in treating various trauma and stress disorders, such as cognitive behavioral therapy, cognitive processing therapy, prolonged exposure, compassion focused therapy, dialectical behavior therapy, and narrative therapy. Each of these therapies share similar components that are useful in addressing trauma, such as psychoeducation,
emotion regulation and processing, cognitive processing and
reconstruction, and trauma processing. Given that transgenerational
trauma is a unique form of traumatic exposure, such therapy modalities
can be effective in reducing its negative long-term effects. However,
there are specific components of transgenerational trauma that must be
addressed directly despite the modality of therapy chosen. Because the
attachment relationship between parent or caregiver and child is a
dominant mechanism through which transgenerational trauma is
transmitted, treatment should focus on the importance familial and
interpersonal patterns relative to the client, and utilize
attachment-focused interventions.
Effective treatment for those experiencing
transgenerational trauma also focuses on exploring, developing, and
maintaining protective factors that can reduce the negative impact of
transgenerational trauma. Some protective factors include fostering secure attachment between
parent and child, as well as having access to several sources of support
(i.e., family, peers, community). One treatment model that places focus on the parent-child relationship is the Intergenerational Trauma Treatment Model (ITTM). The model incorporates several features from existing empirically
supported methods of treatment, such as trauma exposure, cognitive
processing and reframing, stress management, and parent education. ITTM gives specific attention to the intergenerational nature of
traumatic experiences and targets the parent's or caregiver's ability to
respond to a child's traumatic experiences. Fostering secure attachment and a supportive home environment can
mitigate the potential negative impact of transgenerational trauma.
Other less conventional modalities of therapy have also
been found useful in addressing the negative impact of transgenerational
trauma. Music therapy has been found to be an effective form of treatment for those who have witnessed or experienced a traumatic event. For example, music therapy has been successfully implemented with
military personnel, traumatized refugees, and Holocaust survivors. Specifically, analytic music therapy (AMT) was found to be effective in
facilitating a degree of healing through self-exploration that
mitigates the negative impact of transgenerational trauma. Trauma healing stories have been suggested as a form of therapy.
Outside the treatment modalities described, several tools
and techniques were also found to be helpful in bringing awareness to
the effects of transgenerational trauma, as well as decreasing its
psychological impact. For example, the Transgenerational Script
Questionnaire (TSQ) has been used to compliment psychotherapy sessions
as a means of helping to develop consciousness of both the internal and
external family system. The TSQ targets transgenerational scripts, which are unconscious
systemic patterns that persist in families and groups, and are
perpetuated through emotions, beliefs, and behaviors. These scripts are then used to explore a client's implicit and explicit perceptions about their family dynamic and system. In using the TSQ, the clinician can guide the client to separate their
ancestors' experiences from their own. In more complex cases of
intergenerational trauma, the Transgenerational Trauma and Resilience
Genogram (TTRG) can help guide clinicians to better understand and
assess the impact of such trauma. The TTRG targets the various components that contribute to the
maintenance of transgenerational trauma by implementing an ecosystemic
view of trauma, as well as attention to specific sociopolitical
concerns. The TTRG maps out the family unit, marking those who have
experienced trauma and their experience, as well as relationships
between individuals, and patterns of functioning. This process allows for clinicians to better assess the origins and
maintaining factors of an individual's experience of transgenerational
trauma, which ultimately contributes to a more comprehensive
conceptualization of treatment.
In conceptualizing treatment for individuals experiencing
transgenerational trauma, it is critical to take into account the ways
in which various cultural factors impact how different treatments may be
received or perceived. Although the mechanisms through which
transgenerational trauma are consistent across cultures, there are
variations in the degree of salience regarding sociocultural factors
that may exacerbate the effects of transgenerational trauma in different
marginalized communities. Additionally, therapists must incorporate a culturally responsive
perspective to whichever modality of therapy they chose to implement. It
is imperative for therapists to focus on establishing a concrete basis
of trust and safety within the therapeutic relationship, as several
minoritized groups who have transgenerational trauma may have developed
significant mistrust within interpersonal interactions, as well as
mistrust of larger organizations or institutions.
Criticism of inherited trauma via epigenetics
One discredited model suggests that a parent's trauma could be inherited through an epigenetic biological mechanism. Although the idea has been widely touted in the media, it is not supported by robust evidence.
Research in rodents suggests that epigenetic changes can be observed in genes associated with the hypothalamic-pituitary-adrenal (HPA) axis, which coordinates the body's stress response system. Non-heritable stress-related epigenetic changes have also been studied in monkeys. However, most epigenetic effects are not transmitted to the next
generation, and most transfer of information across generations does not
involve epigenetic inheritance.
According to geneticist Kevin Mitchell, "these are, in
fact, extraordinary claims, and they are being advanced on less than
ordinary evidence." He says "This is a malady in modern science: the
more extraordinary and sensational and apparently revolutionary the
claim, the lower the bar for the evidence on which it is based, when the
opposite should be true." Mitchell adds that many have looked at it as a "get out of genetics
free card" and adds, "I think people don't like the idea, some people
anyway, that we are born with certain predispositions that are hard to
change." He says that experiences are expressed through changes in human
neuroanatomy,
not patterns of gene expression and says that scientists in this area
have contributed to the misleading research in this area: "There is a
hype industry around science, which I think is corrosive. And I think
scientists are willing participants in it in a way that I find more and
more distasteful the older I get, because it does a massive disservice
cumulatively to how science is understood by the general public because
we have this constant hype."
The biologist Ewan Birney
specifically criticized a paper which used a sample size of 32 people
to back its claim that children of Holocaust survivors showed evidence
of inherited stress. He argues that a mechanism for epigenetic inheritance in humans remains
elusive due to the many other influencing factors including "complex
societal forces that persist over time", and the fact that human
developing females already have all their eggs as a foetus in the womb,
and lastly that throughout one individual's life epigenetic influences
remain so influential that "epigenetic cell memory" is what cause our
genetically identical cells to differentiate into their specific forms.
Furthermore, even in mice, where these confounding influences can be
controlled, "true trans-generational epigenetic inheritance is extremely
rare."
A 2026 review examining the transgenerational inheritance
of post-traumatic stress disorder (PTSD) and war-related trauma
confirmed these methodological limitations in the human literature. While some studies report DNA methylation variations in stress-related genes (such as FKBP5, NR3C1, NR3C2, and BDNF) among parents or offspring exposed to combat or genocide, the results across the field remain highly inconsistent. The reviewers concluded that genuine epigenetic inheritance and
causality cannot be definitively established, as the majority of
existing human studies are heavily limited by small sample sizes,
cross-sectional designs, and an inability to adequately control for
environmental and psychosocial confounding variables.
To address the ongoing controversy and methodological
bottlenecks in mammalian models, recent literature has proposed
stringent validation frameworks. A 2025 review examining the
transgenerational transmission of acquired nervous system phenotypes
emphasized that establishing true epigenetic inheritance of trauma
requires overcoming severe confounding factors, including postnatal
care, the maternal uterine environment, and the global epigenetic
reprogramming that naturally erases most DNA methylation during
embryonic development. The authors critique the frequent misapplication of the term
"transgenerational" in trauma literature, noting that many studies
erroneously conflate it with "intergenerational" inheritance—where the
F1 fetus or F2 germ cells are directly exposed to the maternal stressor in utero. To definitively prove that behavioral or stress-related traits are
inherited epigenetically rather than socially or genetically, it has
been proposed that researchers meet strict criteria: the phenotype and
corresponding molecular marks must persist into unexposed generations
(the F2 generation for paternal exposure, or F3 for maternal),
transmission must be isolated to the germ cells, and study designs must
utilize absolute controls like cross-fostering and in vitro fertilization to exclude environmental transmission.
Furthermore, human observational cohorts are inevitably
confounded by socioeconomic status, culture, and parenting practices,
which can easily mimic or obscure epigenetic inheritance. The review also cautions against the ethical and societal risks of
attributing psychiatric or cognitive vulnerabilities to ancestral
epigenetic trauma; doing so without solid mechanistic proof risks
stigmatizing families or inappropriately blaming prior generations.
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