Arline Geronimus wrote about the weathering hypothesis
the early 1990s to account for health disparities of newborn babies and
birth mothers due to decades and generations of racism and social,
economic, and political oppression. It is well documented that people of color and other marginalized communities have worse health outcomes than white people. This is due to multiple stressors including prejudice, social alienation, institutional bias, political oppression, economic exclusion, and racial discrimination. The weathering hypothesis proposes that the cumulative burden of these
stressors as individuals age is "weathering", and the increased
weathering experienced by minority groups compared to others can account
for differences in health outcomes. In recent years, social scientists investigated the biological plausibility
of the weathering hypothesis in studies evaluating the physiological
effects of social, environmental and political stressors among
marginalized communities. The weathering hypothesis is more widely accepted as a framework for
explaining health disparities on the basis of differential exposure to racially based stressors. Researchers have also identified patterns connecting weathering to
biological phenomena associated with stress and aging, such as allostatic load, epigenetics, telomere shortening, and accelerated brain aging.
Origins
The weathering hypothesis was initially formulated by Arline Geronimus to explain the dire maternal health and birth outcomes of African American women that she observed in correspondence with increased age. While working part-time at a school for pregnant teenagers in Trenton, New Jersey, Geronimus first noticed that the teens who came to the school tended to have far more health problems than her classmates at Princeton University. She thus began to wonder whether the health conditions of the teens at that clinic may have been caused by their environment. Subsequent research on the disparity in maternal health
between African American and white women led Geronimus to propose the
weathering hypothesis. She proposed that the accumulation of cultural,
social and economic disadvantages may lead to earlier deterioration of
health among African American women compared to their non-Hispanic,
white counterparts. Geronimus specifically chose the term weathering as a metaphor for the effects she perceived that exposure to stress was having on the health of marginalized people. While the weathering hypothesis was initially proposed based on
observations of patterns in maternal health, academics have expanded its
application as a framework to examine other health disparities as well.
Geronimus' research
While conducting research in the Department of Public Health Policy and Administration as a graduate student at the University of Michigan in 1992, Geronimus noticed a trend in disparities between the fertility of African American women versus White women. She noted that, on average, White girls and women experience their
highest fertility rates and lowest risk of pregnancy complications or neonatal mortality
in their 20's and 30's, but African American women do not. Instead,
African American girls and women, teenagers have higher fertility rates
and healthy pregnancies. The data indicated a widening disparity in
black-white infant mortality
as maternal ages increase. Subsequently, Geronimus proposed the
"weathering hypothesis", which she initially conceived as a potential
explanation for the patterns of racial variation in infant mortality
with increasing maternal age.
Health disparities
In the context of the weathering hypothesis, individual
health is dynamic and shaped over time by social, economic, and
environmental influences. These social determinants dictate what different demographics are exposed to as they develop and age. Racism and discrimination
are two specific social determinants that lay the foundation for
systemic inequality in access and upward mobility. This entrenchment of
social inequities disproportionately impacts minorities and communities
of color, who remain in environments of poverty that have significantly
more stressors than those of wealthier, predominantly white communities. These stressors—and the associated burden of coping with them—manifest
as physiological responses that have detrimental effects on individual
health, often leading to a disproportionately high occurrence of chronic illness and shorter life expectancy in minority communities. Multiethnic studies have yielded significant data demonstrating that
weathering—accumulated health risk due to social, economic and
environmental stressors—is a manifestation of social stratification that systemically influences disparities in health and mortality between dominant and minority communities.
Maternal mortality is three to four times higher for Black mothers than white mothers in the United States. Infant mortality is also twice as high for infants born to non-Hispanic Black mothers compared to infants born to non-Hispanic white mothers. Additionally, there are racial disparities for negative birth outcomes like low birth weight, which has been found to influence risk of infant mortality and developmental outcomes after birth, and preterm birth. Across all women, older maternal age is associated with higher rates of these negative outcomes during pregnancy, but studies have consistently found that rates rise more rapidly for Black women than white women.The weathering hypothesis proposes that the accumulation of racial
stress over Black women's lives contributes to this observed pattern of
racial disparities in maternal health and birth outcomes that increase with maternal age. Research has consistently identified an association between preterm
birth and low birth weight in Black women and maternal stress caused by
experiences of racism, systemic bias, socioeconomic disadvantage, segregated neighborhoods, and high rates of violent crime. There is biological evidence of weathering, including the finding that Black women have shorter telomeres, a biological indicator of age, when compared with white women of the same chronological age. Though increased socioeconomic status serves as a protective factor
against negative birth outcomes for non-Hispanic white mothers,
disproportionate rates of preterm birth and low birth weight for
non-Hispanic Black mothers have been found at every education and income
level. The weathering hypothesis has also been used to explain this trend
because upward socioeconomic mobility is associated with increased
exposure to discrimination for women of color.
There is modest evidence supporting the effects of
weathering on mothers from other minority groups, including for high
birth weight outcomes among American Indian/Alaska Native women. Research has started to explore whether the weathering hypothesis could also explain racial disparities in the outcomes of assisted reproductive technologies, but so far the findings are inconsistent.
Mental health
Research shows that mental health disparities among
marginalized communities exist. Daily discrimination faced by
marginalized groups have been found to be associated with increased
depressive symptoms and feelings of loneliness. Low-income communities are more likely to have severe mental illnesses,
which is frequently heightened by the inaccessibility to quality
healthcare. Researchers found that persisting epigenetic changes lead to increased risk of postpartum depression as a result of adverse life events and cumulative life stress among Black, Latinx, and low-income women. In a study assessing African American men, experiences of racism were linked to a poorer mental health state.
Cognition
Black Americans often show mean level differences in
cognition across multiple cognitive domains compared to non-Hispanic
Whites.These cognitive disparities often are reduced or eliminated when factoring various social determinants of health such as stress, education quality, economic stability, or quality of healthcare. Black Americans also have higher rates of Alzheimer's disease and related dementias than non-Hispanic Whites. These higher rates of Alzheimer's disease might be due to the impact of more negative and pronounced social determinants of health, including racial discrimination, that might accelerate brain aging disproportionately in Black Americans.
Intersectionality of systems of oppression
Intersectionality is a term coined by Kimberlé Crenshaw
to describe the interconnected nature of different systems of
oppression, the layered effects of which can be seen in the healthcare
system. Research indicates that lower class status and increased
depressive symptoms are associated with higher levels of biological
weathering among Black individuals in comparison to white individuals. In a study exploring disparities in mental health, researchers found
that Black sexual minority women reported higher frequencies of
discrimination and decreased levels of social and psychological
well-being than their white sexual minority women counterparts. Black sexual minority women had decreased levels of social well-being and increased levels of depressive symptoms in comparison to Black sexual minority men. African American women are also more likely to contract COVID-19 than African American men and white women. The prevalence of medical racism
and sexism (lack of quality healthcare, harmful experimentation, etc.)
has led to negative relationships with healthcare systems and increased
risk of negative sexual and reproductive health outcomes among African American women. Existing research show how systems of oppression work together to
oppress marginalized groups within the healthcare system and, as a
result, these groups disproportionately experience negative health
effects. Aging adults experience further intersections with health, health care,
and structural inequalities that exacerbates health in marginalized
groups.
Criticism and related theories
Arline Geronimus faced significant pushback for the
weathering hypothesis from the medical community, economists, and
sociologists, whose research had attributed racial differences in health
outcomes to differing genetics, cultures, and life choices. Additionally, there was criticism regarding the quality of her data. Others pushed back against the weathering hypothesis because its
application to racial disparities in maternal health seemed to
contradict what advocacy groups had been saying about the negative
consequences of teen pregnancy on young mothers. A further criticism of this theory believes that Geronimus and others
have not sufficiently demonstrated a link between weathering and racial
and gender disparities in life expectancy.
The weathering hypothesis was initially proposed as a
sociological explanation for health disparities, but it is closely
related to biological theories like the allostatic load model, which proposes that an individual's exposure to repeated or chronic stress over their lifetime has physiological consequences which can be measured through various biomarkers. Research has tended to discuss allostasis
and allostatic load as the molecular mechanism behind the weathering
hypothesis, and Geronimus herself went on to study racial differences in
allostatic load. Another related theory is the life course approach,
which emphasizes focus on cumulative life experiences rather than
maternal risk factors as an explanation for birth outcome disparities. Researchers have also been interested in studying the possibility of
children inheriting the epigenetic changes which result from their
mother's cumulative life stress, which could relate the weathering
hypothesis with transgenerational trauma.
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.
.png)
