Manipulation (psychology)

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https://en.wikipedia.org/wiki/Manipulation_(psychology)

In psychology, manipulation is defined as an action designed to influence or control another person in an underhanded or subtle manner which facilitates one's personal aims. Methods someone may use to manipulate another person may include seduction, suggestion, coercion, and blackmail.Manipulation is generally considered a dishonest form of social influence as it is used at the expense of others. Humans are inherently capable of manipulative and deceptive behavior, with the main differences being that of specific personality characteristics or disorders.

Etymology

By 1730, the word manipulation was used to refer to a method of digging ore. The term derives from the French manipulation, which in turn comes from manipule, meaning "handful", a unit of measure used by pharmacists, later having a sense by 1828 of handling or managing people for one's own purposes. The word manipulate originated in 1827 as a back-formation from manipulation, initially meaning "to handle skillfully by hand." By 1864, its usage had expanded to include the figurative sense of "to manage or influence, especially for one's own advantage." The word is used in various different senses, but today it is most often used in psychological contexts.

Differentiation

Manipulation differs from general influence and persuasion. Manipulation, unlike persuasion, typically involves exploiting the vulnerabilities of an individual. Non-manipulative influence is generally perceived to be harmless and it is not seen as unduly coercive to the individual's right of acceptance or rejection of influence. Persuasion is the ability to move others to a desired action, usually within the context of a specific goal. Persuasion often attempts to influence a person's beliefs, religion, motivations, or behavior. Influence and persuasion are neither viewed as positive nor negative, unlike manipulation which is viewed as negative.

Elements of manipulation

While the motivations for manipulation are mostly self-serving, certain styles of social influence can be intended to be to the benefit of others. Manipulation can be defined as the use of strategies to further personal driven goals at the expense of others and is usually considered antisocial behavior. Pro-social behavior is a voluntary act intended to help or benefit another individual or group of individuals and is an important part of empathy.

Manipulative behavior is fundamentally deliberate and intentional, with the manipulator knowing full well the consequences of their actions, and what they want out of the person being manipulated.

Different measures of manipulativeness focus on different aspects or expressions of manipulation and tend to paint slightly different pictures of its predictors. Features such as low empathy, high narcissism, use of self-serving rationalizations, and an interpersonal style marked by high agency (dominance) and low communion (i.e. cold-heartedness) are consistent across measures.

A study by Buss, et al. explored how individuals use manipulation to shape their environments to fit their personal characteristics. Across two studies, researchers identified six main manipulation tactics: charm, silent treatment, coercion, reason, regression, and debasement. These tactics were consistent across different situations, with charm commonly used to initiate behavior and coercion or silent treatment used to stop it. The use of these tactics was linked to personality traits such as Neuroticism, Extraversion, and Agreeableness, and was consistent across self-reports and observer ratings. Another paper investigated the link between one's personality and social processes, and it concluded that "persons are not passive recipients of environmental presses" and that "persons actively avoid some social situations and selectively enter others", and that people "elicit and manipulate the social behavior of persons who reside in situations that have been selected."

Another study by Buss aimed to achieve three primary objectives, to identify the manipulation tactics commonly employed in close interpersonal relationships; to empirically examine the extent to which these tactics are general or specific across different relationship types, including romantic partners, friends, and parents; and to explore the associations between the use of manipulation tactics and the Big Five personality traits. Twelve distinct manipulation tactics were identified through separate factor analyses of two instruments derived from different data sources. These included six tactics Charm, Reason, Coercion, Silent Treatment, Debasement, Regression, and six additional tactics: Responsibility Invocation, Reciprocity, Monetary Reward, Pleasure Induction, Social Comparison, and Hardball (the latter encompassing threats, deception, and aggression). Personality traits were assessed using three sources of data: self-reports, spouse reports, and evaluations by independent interviewers. The findings revealed consistent associations between personality dimensions and manipulation strategies. Specifically, Surgency was linked to Coercion and Responsibility Invocation; Desurgency to Debasement; Agreeableness to Pleasure Induction; Disagreeableness to Coercion; Conscientiousness to Reason; Emotional Instability to Regression; and Intellect-Openness to Reason.

A family study of high-school students and their parents investigated the origin of individual differences in manipulation tactics. The results indicated significant familial aggregation of manipulation tactics, as shown by parent–offspring correlations and midparent–offspring regressions. While manipulation tactics were linked to low Agreeableness and high Neuroticism from the Five-Factor Model, personality traits played a minor role in explaining their selection and use.

Manipulative behavior occurs in a variety of outlets, such as on the internet. Researchers and pundits have expressed concern for the ability of technology to manipulate the opinions and actions of people. Scholars have discussed the potential modern technologies have to affect the autonomy of an individual. The concept has spawned an extensive literature within the field of psychology, and other disciplines interested in human behavior. Cambridge Analytica was under scrutiny for collecting personal data belonging to millions of Facebook users for political advertising without informed consent.

In popular psychology

Harriet B. Braiker identified the following ways that manipulators control their victims, with some of them including positive reinforcement, which includes praise, superficial charm, superficial sympathy (crocodile tears), excessive apologizing or forced laugh or smile. According to psychology author George K. Simon, successful psychological manipulation primarily involves the manipulator: Simon states that manipulative individuals may use a variety of deceptive techniques to exert control or avoid accountability. Methods include lying by commissioh, lying by omission, pretending to be in denial, rationalization, selective inattention/selective attention, and diversion. Martin Kantor advises in his 2006 book The Psychopathology of Everyday Life: How Antisocial Personality Disorder Affects All of Us that vulnerability to psychopathic manipulators can be due to being too dependent on others, having a lack of maturity, being naïve, impressionable, trusting, impulsive, altruistic, or greedy.

Assessment tools

MACH-IV

Manipulativeness is a primary feature found in the Machiavellianism construct. The MACH-IV, conceptualized by Richard Christie and Florence Geis, is a popular and widely used psychological measure of manipulative and deceptive behavior.

Emotional manipulation scale

The emotional manipulation scale is a ten-item questionnaire developed in 2006 through factor analysis, primarily to measure one's tendency to use emotions to their advantage in controlling others. At the time of publication, emotional intelligence assessments did not specifically examine manipulative behavior and were instead predominantly focused on Big Five personality trait assessment.

Managing the emotions of others scale

The "Managing the Emotions of Others Scale" (MEOS) was developed in 2013 through factor analysis to measure the ability to change emotions of others. The survey questions measure six categories: mood (or emotional state) enhancement, mood worsening, concealing emotions, capacity for inauthenticity, poor emotion skills, and using diversion to enhance mood. The enhancement, worsening and diversion categories have been used to identify the ability and willingness of manipulative behavior. The MEOS has also been used for assessing emotional intelligence, and has been compared to the HEXACO model of personality structure, for which the capacity for inauthenticity category in the MEOS was found to correspond to low honesty-humility scores on the HEXACO.

The SD3 and the Dirty Dozen

The dark triad Dirty Dozen and the Short Dark Triad (SD3 or simply D3) also measures a callous, manipulative, self oriented style.

Other measures

There are several measures that assess interpersonally manipulative characteristics. Measures of psychopathy and narcissism have their own subscales that address manipulation. Other examples include the Honesty-Humility subscale on the HEXACO model of personality, the Agreeableness factor in the Big Five personality test, and on certain factors of the MMPI.

In mental disorders

Personality disorders

Manipulative behavior is cited as one factor contributing to the reluctance of some psychiatric professionals to work with individuals diagnosed with personality disorders (PDs). Many times this behavior can elicit strong negative emotional reactions, potentially hindering effective care and treatment.

Manipulative tendencies may derive from cluster B personality disorders such as narcissistic personality disorder, antisocial personality disorder, and borderline personality disorder. Manipulative behavior has also been related with one's level of emotional intelligence. Discussion of manipulation may vary depending on which behavior is specifically included, and whether one is referring to the general population or in clinical contexts.

Under the ICD-11 classification of personality disorders, personality disorder is diagnosed dimensionally based on severity levels, with trait qualifiers providing additional specification in regards to how the pathology manifests itself. One of these is Dissociality, of which the aspect lack of empathy is characterized by deceitful, manipulative and exploitative behaviors.

Antisocial personality disorder

Antisocial personality disorder features deceit and manipulation of others as an explicit criterion. This includes behaviors like lying and superficial displays of charisma to frequent use of aliases and disguises, and criminal fraudulence. The related syndrome of psychopathy also features pathological lying and manipulation for personal gain, as well as superficial charm, as cardinal features.

The Alternative DSM-5 model for personality disorders (AMPD) in Section III of DSM-5 requires the presence of manipulative behavior for a diagnosis of ASPD, with two symptoms (deceitfulness and manipulativeness) reflecting such tendencies out of the seven listed, with six being required for diagnosis (the others are impulsivity, irresponsibility, risk-taking, callousness and hostility). The related syndrome of psychopathy also features pathological lying and manipulation for personal gain, as well as superficial charm, as cardinal features.

Paul Hofer interpreted manipulation to be a psychological defense in regards to those who are affected by their antisocial personality. Paul Babiak views manipulation to be a core feature in how those with high psychopathic traits behave in the workplace.

Borderline personality disorder

Borderline personality disorder is unique in the grouping as "borderline" manipulation is characterized as unintentional and dysfunctional manipulation. Marsha M. Linehan has stated that people with borderline personality disorder often exhibit behaviors which are not truly manipulative, but are erroneously interpreted as such. According to Linehan, these behaviors often appear as unthinking manifestations of intense pain, and are often not deliberate as to be considered truly manipulative. In the DSM-5, manipulation was removed as a defining characteristic of borderline personality disorder.

Narcissistic personality disorder

Narcissistic personality disorder is characterized by a belief of superiority, exhibitionism, self-centeredness and a lack of empathy. Individuals with NPD can be charming but also show exploitive behaviors in the interpersonal domain. They are motivated by success, beauty, and may have feelings of entitlement. Those with this disorder often engage in assertive self enhancement and antagonistic self-protection.

Other disorders

Conduct disorder is the appearance of antisocial behavior occurring in children and adolescents. Individuals with this disorder are characterized by a lack of empathy, a low sense of guilt, and shallow emotionality. Aggression and violence are two factors that characterize individuals with this disorder. In order for a child to be diagnosed with this disorder, the behavior must be consistent for at least 12 months.

Factitious disorder is a mental illness in which individuals purposely fake having symptoms of some condition, physically or psychologically. Fabricating illnesses allows individuals to feel a thrill and receive free aid in hospital admissions and treatment. Feelings of persistence, abuse in early childhood, and excessive thoughts were common for these individuals who connected to Borderline Personality Disorder.

Amygdala

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Amygdala
Location of amygdalae in the human brain (view from below, anterior is at top)
Subdivisions of the amygdala

Human brain in the coronal orientation. Amygdalae are shown in dark red.

The amygdala (/əˈmɪɡdələ/; pl.: amygdalae /əˈmɪɡdəli, -laɪ/ or amygdalas; also corpus amygdaloideum) is a paired nuclear complex present in the cerebral hemispheres of vertebrates. It is considered part of the limbic system. In primates, it is located medially within the temporal lobes. It consists of many nuclei, each made up of further subnuclei. The subdivision most commonly made is into the basolateral, central, cortical, and medial nuclei together with the intercalated cell clusters. The amygdala has a primary role in the processing of memory, decision-making, and emotional responses (including fear, anxiety, and aggression). The amygdala was first identified and named by Karl Friedrich Burdach in 1822.

Structure

Subdivisions of the mouse amygdala

T1 MRI images of amygdala in human (highlighted in green)

Coronal

Sagittal

Transversal

Thirteen nuclei have been identified, each with its own subdivisions and distinct connections to the rest of the brain. The chief nuclei are the basolateral complex, the central nucleus, the cortical nucleus, the medial nucleus, and the intercalated cell clusters. The cortical and medial nuclei connect with the olfactory system and hypothalamus. The central nucleus has extensive projections to the brainstem.

The basolateral complex can be further subdivided into the lateral, the basal, and the accessory basal nuclei. It has extensive connections with higher-order cortical areas in the prefrontal, temporal, insular cortices, and the hippocampus. The basolateral complex is surrounded by the intercalated cell net that is inhibitory and projects to a broad variety of areas in the basal forebrain, hypothalamus, and the amygdala.

The primate amygdala contains about 32 different types of neuron.

Hemispheric specializations

The right and left portions of the amygdala have independent memory systems, but work together to store, encode, and interpret emotion.

The right hemisphere of the amygdala is associated with negative emotion. It plays a role in the expression of fear and in the processing of fear-inducing stimuli. Fear conditioning, which occurs when a neutral stimulus acquires aversive properties, occurs within the right hemisphere. When an individual is presented with a conditioned, aversive stimulus, it is processed within the right amygdala, producing an unpleasant or fearful response. This emotional response conditions the individual to avoid fear-inducing stimuli and more importantly, to assess threats in the environment.

The right hemisphere is also linked to declarative memory, which consists of facts and information from previously experienced events and must be consciously recalled. It also plays a significant role in the retention of episodic memory. Episodic memory consists of the autobiographical aspects of memory, permitting recall of emotional and sensory experience of an event. This type of memory does not require conscious recall. The right amygdala plays a role in the association of time and places with emotional properties.

In one study, electrical stimulations of the right amygdala induced negative emotions, especially fear and sadness. In contrast, stimulation of the left amygdala was able to induce either pleasant (happiness) or unpleasant (fear, anxiety, sadness) emotions. Other evidence suggests that the left amygdala plays a role in the brain's reward system.

Development and sex distinction

See also: Neuroscience of sex differences

When controlling for total brain volume or intracranial volume, there is no significant difference in the average size of the amygdala between men and women. Raw amygdala volumes are, on average, 10.6% larger in men, but men also have larger bodies and brains on average.

There is considerable growth within the first few years of structural development in both male and female amygdalae. Within this early period, female limbic structures grow at a more rapid pace than the male ones. Amongst female subjects, the amygdala reaches its full growth potential approximately 1.5 years before the peak of male development. The structural development of the male amygdala occurs over a longer period than in women.

There are observable developmental differences between the right and left amygdala. The left amygdala reaches its developmental peak approximately 1.5–2 years prior to the right amygdala. Despite the early growth of the left amygdala, the right increases in volume for a longer period of time. The right amygdala is associated with response to fearful stimuli as well as face recognition. For the left amygdala, it is inferred that the early development of it functions to provide infants the ability to detect danger due to its reported responds predominantly to fearful events and faces.In childhood, the amygdala is found to react differently to same-sex versus opposite-sex individuals. This reactivity decreases until a person enters adolescence, where it increases dramatically at puberty.

Functional and structural differences have been discovered between male and female amygdalae. The results of PET scans showed a different lateralization of the amygdala in men and women after watching an emotional film. Enhanced memory for the film was related to enhanced activity of the left, but not the right, amygdala in women, whereas it was related to enhanced activity of the right, but not the left, amygdala in men. Studies involving patients with amygdala damage came to a similar conclusion. In patients with unilateral amygdala damage, men with right (but not left) amygdala damage were more likely to be impaired in decision-making ability, while women with left (but not right) amygdala damage were more likely to be impaired in decision-making ability. One study found evidence that, on average, women tend to retain stronger memories for emotional events than men.

Function

Connections

Variability in amygdala connectivity has been related to a variety of behaviors and outcomes such as fear recognition and social network size. A simple view of the information processing through the amygdala follows as: the amygdala sends projections to the hypothalamus, septal nuclei and BNST (via the amygdalofugal tract), the dorsomedial thalamus (via the amygdalothalamic tract), the nuclei of the trigeminal nerve and the facial nerve, the ventral tegmental area, the locus coeruleus, and the laterodorsal tegmental nucleus.

The basolateral amygdala projects to the nucleus accumbens, including the medial shell. Glutamatergic neurons in the basolateral amygdala send projections to the nucleus accumbens shell and core. Activation of these projections drive motivational salience. The ability of these projections to drive incentive salience is dependent upon dopamine receptor D1. The endocannabinoid system that produces lipoid neuromodulators has its specific receptors (CB1) found in amygdalae.

Coronal section of brain through intermediate mass of third ventricle. Amygdala is shown in purple.

The medial nucleus is involved in the sense of smell and pheromone-processing. It receives input from the olfactory bulb and olfactory cortex. The lateral amygdalae, which send impulses to the rest of the basolateral complexes and to the centromedial nuclei, receive input from the sensory systems. The centromedial nuclei are the main outputs for the basolateral complexes, and are involved in emotional arousal in rats and cats.

Emotional learning

Main article: Emotion and memory

In complex vertebrates, including humans, the amygdalae perform primary roles in the formation and storage of memories associated with emotional events. Research indicates that, during fear conditioning, sensory stimuli reach the basolateral complexes of the amygdalae, particularly the lateral nuclei, where they form associations with memories of the stimuli. The association between stimuli and the aversive events they predict may be mediated by long-term potentiation, a sustained enhancement of signaling between affected neurons. There have been studies that show that damage to the amygdala can interfere with memory that is strengthened by emotion. One study examined a patient with bilateral degeneration of the amygdala. He was told a violent story accompanied by matching pictures and was observed based on how much he could recall from the story. The patient had less recollection of the story than patients with functional amygdala, showing that the amygdala has a strong connection with emotional learning.

Emotional memories are thought to be stored in synapses throughout the brain. Fear memories, for example, are considered to be stored in the neuronal connections from the lateral nuclei to the central nucleus of the amygdalae and the bed nuclei of the stria terminalis (part of the extended amygdala). These connections are not the sole site of fear memories given that the nuclei of the amygdala receive and send information to other brain regions that are important for memory such as the hippocampus. Some sensory neurons project their axon terminals to the central nucleus. The central nuclei are involved in the genesis of many fear responses such as defensive behavior (freezing or escape responses), autonomic nervous system responses (changes in blood pressure and heart rate/tachycardia), neuroendocrine responses (stress-hormone release), etc. Damage to the amygdalae impairs both the acquisition and expression of Pavlovian fear conditioning, a form of classical conditioning of emotional responses. Accumulating evidence has suggested that multiple neuromodulators acting in the amygdala regulates the formation of emotional memories.

The amygdalae are also involved in appetitive (positive) conditioning. It seems that distinct neurons respond to positive and negative stimuli, but there is no clustering of these distinct neurons into clear anatomical nuclei. However, lesions of the central nucleus in the amygdala have been shown to reduce appetitive learning in rats. Lesions of the basolateral regions do not exhibit the same effect. Research like this indicates that different nuclei within the amygdala have different functions in appetitive conditioning. Nevertheless, researchers found an example of appetitive emotional learning showing an important role for the basolateral amygdala: The naïve female mice are innately attracted to non-volatile pheromones contained in male-soiled bedding, but not by the male-derived volatiles, become attractive if associated with non-volatile attractive pheromones, which act as unconditioned stimulus in a case of Pavlovian associative learning. In the vomeronasal, olfactory, and emotional systems, Fos (gene family) proteins show that non-volatile pheromones stimulate the vomeronasal system, whereas air-borne volatiles activate only the olfactory system. Thus, the acquired preference for male-derived volatiles reveals an olfactory-vomeronasal associative learning. Moreover, the reward system is differentially activated by the primary pheromones and secondarily attractive odorants. Exploring the primary attractive pheromone activates the basolateral amygdala and the shell of nucleus accumbens but neither the ventral tegmental area nor the orbitofrontal cortex. In contrast, exploring the secondarily attractive male-derived odorants involves activation of a circuit that includes the basolateral amygdala, prefrontal cortex, and ventral tegmental area. Therefore, the basolateral amygdala stands out as the key center for vomeronasal-olfactory associative learning.

Memory modulation

The amygdala is also involved in the modulation of memory consolidation. Following any learning event, the long-term memory for the event is not formed instantaneously. Rather, information regarding the event is slowly assimilated into long-term (potentially lifelong) storage over time, possibly via long-term potentiation. Recent studies suggest that the amygdala regulates memory consolidation in other brain regions. Also, fear conditioning, a type of memory that is impaired following amygdala damage, is mediated in part by long-term potentiation. During the consolidation period, the memory can be modulated. In particular, it appears that emotional arousal following the learning event influences the strength of the subsequent memory for that event. Greater emotional arousal following a learning event enhances a person's retention of that event. Experiments have shown that administration of stress hormones to mice immediately after they learn something enhances their retention when they are tested two days later.

The amygdala, especially the basolateral nuclei, are involved in mediating the effects of emotional arousal on the strength of the memory for the event, as shown by many laboratories including that of James McGaugh. These laboratories have trained animals on a variety of learning tasks and found that drugs injected into the amygdala after training affect the animals' subsequent retention of the task. These tasks include basic classical conditioning tasks such as inhibitory avoidance, where a rat learns to associate a mild footshock with a particular compartment of an apparatus, and more complex tasks such as spatial or cued water maze, where a rat learns to swim to a platform to escape the water. If a drug that activates the amygdalae is injected into the amygdalae, the animals had better memory for the training in the task.

Amygdala activity at the time of encoding information correlates with retention for that information. However, this correlation depends on the relative "emotionalness" of the information. More emotionally arousing information increases amygdalar activity, and that activity correlates with retention. Amygdala neurons show various types of oscillation during emotional arousal, such as theta activity and gamma activity. These synchronized neuronal events could promote synaptic plasticity (which is involved in memory retention) by increasing interactions between neocortical storage sites and temporal lobe structures involved in declarative memory.

In rats, DNA damage was found to increase in the amygdala immediately after exposure to stress. Stress was induced by 30 minutes of restraint or by forced swimming. By seven days after exposure to these stresses, increased DNA damage was no longer detectable in the amygdala, probably because of DNA repair.

Buddhist monks who do compassion meditation have been shown to modulate their amygdala, along with their temporoparietal junction and insula, during their practice. In an fMRI study, more intensive insula activity was found in expert meditators than in novices.

Rorschach test blot 03

Research using Rorschach test blot 03 finds that the number of unique responses to this random figure links to larger sized amygdalae. The researchers note, "Since previous reports have indicated that unique responses were observed at higher frequency in the artistic population than in the nonartistic normal population, this positive correlation suggests that amygdalar enlargement in the normal population might be related to creative mental activity."

Neuropsychological correlates of amygdala activity

Early research on primates provided explanations as to the functions of the amygdala, as well as a basis for further research. As early as 1888, rhesus monkeys with a lesioned temporal cortex (including the amygdala) were observed to have significant social and emotional deficits. Heinrich Klüver and Paul Bucy later expanded upon this same observation by showing that large lesions to the anterior temporal lobe produced noticeable changes, including overreaction to all objects, hypoemotionality, loss of fear, hypersexuality, and hyperorality, a condition in which inappropriate objects are placed in the mouth. Some monkeys also displayed an inability to recognize familiar objects and would approach animate and inanimate objects indiscriminately, exhibiting a loss of fear towards the experimenters. This behavioral disorder was later named Klüver–Bucy syndrome accordingly, and later research proved it was specifically due to amygdala lesions. Monkey mothers who had amygdala damage showed a reduction in maternal behaviors towards their infants, often physically abusing or neglecting them. In 1981, researchers found that selective radio frequency lesions of the whole amygdala caused Klüver–Bucy syndrome.

Social function

The amygdala has a role in social function. Amygdala volume is associated with the size and complexity of social networks. Amygdala volume correlates positively with both the size (the number of contacts) and the complexity (the number of different groups) of social networks.

The amygdala is involved in facial recognition and emotional expressions. Its role in analysis of social situations stems specifically from its ability to identify and process changes in facial features, although it does not process the direction of a gaze toward a person.

The amygdala processes reactions to violations concerning personal space.

Alcoholism

The amygdala appears to play a role in binge drinking, being damaged by repeated episodes of intoxication and withdrawal. Protein kinase C-epsilon in the amygdala is important for regulating behavioral responses to morphine and ethanol and controlling anxiety-like behavior. The protein is involved in controlling the function of other proteins and plays a role in the development of the ability to consume a large amount of ethanol. The duration of chronic alcohol consumption and abstinence may affect dynamic brain network adaptations. When excessive drinking occurs, the amygdala is affected through behavioral changes and reduces the brain's plasticity. Often, when binge drinking or alcoholism occurs, the amygdala is affected and leads to behavior damage. These behavioral damages can be lack of control, inability to conduct oneself in a mature manner, irritability and aggressive behavior, anxiety, depression, personality disorders, excessive drug intake, bipolar disorder, confusion, higher tolerance levels, and inappropriate sexual behaviors with others and self.

Anxiety

Feelings of anxiety start with an environmental stimulus that provokes stress. This can include various smells, sights, and internal sensations that result in anxiety. The amygdala reacts to this stimuli by preparing to either stand and fight or to turn and run. The amygdala sends signals to the paraventricular nucleus of the hypothalamus for the initiation of the HPA axis response. Consequently, blood sugar rises, becoming immediately available to the muscles for quick energy. Shaking may occur in an attempt to return blood to the rest of the body. Long-term changes in amygdala neurons may also increase anxiety after long-term or traumatic stress, led by the action of stress-related hormones within the amygdala. On the flip side, blocking the action of stress hormones in the amygdala reduces anxiety. There may also be a link between the amygdala and anxiety.

The central nucleus of the amygdala has direct correlations to the hypothalamus and brainstem—areas directly related to fear and anxiety. This connection is evident from studies of animals that have undergone amygdalae removal.

The clusters of the amygdala are activated when an individual expresses feelings of fear or aggression. This occurs because the amygdala is the primary structure of the brain responsible for fight-or-flight response. Anxiety and panic attacks can occur when the amygdala senses environmental stressors that stimulate fight-or-flight response. The amygdala is involved in the expression of conditioned fear. Conditioned fear is the framework used to explain the behavior produced when an originally neutral stimulus is consistently paired with a stimulus that evokes fear. Fear is measured by changes in autonomic activity including increased heart rate, increased blood pressure, as well as in simple reflexes such as flinching or blinking. Studies in 2004 and 2006 showed that normal subjects exposed to images of frightened faces or faces of people from another race will show increased activity of the amygdala, even if that exposure is subliminal. However, the amygdala is not necessary for the processing of fear-related stimuli, since persons in whom it is bilaterally damaged show rapid reactions to fearful faces, even in the absence of a functional amygdala.

Patient S.M., sometimes referred to as SM-046, is an American woman with exclusive and complete bilateral amygdala destruction since late childhood as a consequence of Urbach–Wiethe disease, and has a physiologically greatly reduced ability to feel fear as a result. First described by scientists in 1994, S.M. has been studied extensively in scientific research; she has helped researchers elucidate the function of the amygdala.

Psychological disorders

With advances in neuroimaging technology such as MRI, neuroscientists have made significant findings concerning the amygdala in the human brain. A variety of data shows the amygdala has a substantial role in mental states, and is related to many psychological disorders. Some studies have shown children with anxiety disorders tend to have a smaller left amygdala. In the majority of the cases, there was an association between an increase in the size of the left amygdala with the use of SSRIs (antidepressant medication) or psychotherapy. The left amygdala has been linked to social anxiety disorder, obsessive and compulsive disorders, and post-traumatic stress disorder (PTSD), as well as more broadly to separation and generalized anxiety disorder.^[89] Multiple studies have found that the amygdalae may be responsible for the emotional reactions of PTSD patients. One study in particular found that when PTSD patients are shown pictures of faces with fearful expressions, their amygdalae tended to have a higher activation than someone without PTSD.

In 2006, researchers observed hyperactivity in the amygdala when patients were shown threatening faces or confronted with frightening situations. Patients with severe social phobia showed a correlation with increased response in the amygdala. Individuals with psychopathy show reduced autonomic responses to instructed fear cues than otherwise healthy individuals. Similarly, depressed patients showed exaggerated left amygdala activity when interpreting emotions for all faces, and especially for fearful faces. This hyperactivity was normalized when patients were administered antidepressant medication.

In a 2003 study, subjects with borderline personality disorder showed significantly greater left amygdala activity than normal control subjects. Some borderline patients even had difficulties classifying neutral faces or saw them as threatening. The amygdala has been observed to respond differently in people with bipolar disorder. Amygdala dysfunction during face emotion processing is well-documented in bipolar disorder. Individuals with bipolar disorder showed greater amygdala activity (especially the amygdala/medial-prefrontal-cortex circuit). For people with manic bipolar I disorder, a decreased negative functional connectivity between the orbitofrontal cortex and the amygdala was also observed. A 2003 study found that adult and adolescent bipolar patients tended to have considerably smaller amygdala volumes and somewhat smaller hippocampal volumes. Many studies have also focused on the connections between the amygdala and autism.