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Its primary role is in the processing of memory, decision-making and emotional responses: including fear, anxiety, and aggression.
The amygdalae are considered part of the ((limbic system)).
The regions of amygdala nuclei encompass several structures of the cerebrum with distinct connectional and functional characteristics: basolateral complex, the cortical nucleus, the medial nucleus, the central nucleus, and the intercalated cell clusters.
The basolateral complex can be further subdivided into the lateral, the basal, and the accessory basal nuclei.
Anatomically, the amygdala, has sometimes been classified as a part of the basal ganglia.
Electrical stimulation of the right amygdala induces negative emotions, especially fear and sadness.
Stimulation of the left amygdala induces either pleasant or unpleasant emotions.
Theleft amygdala is suspected to play a role in the brain’s reward system.
Each side of the amygdala holds specific functions on how we perceive and process emotions.
The amygdala and hippocampus create and encode the memory and emotion due to pain stimuli.
The amygdala is critical to affective fear, and painful sensation.
The amygdala has a key role in the descending modulation of pain.
The right and left portions of the amygdala have independent memory systems.
The right and left portions of the amygdala store, encode, and interpret emotion.
The right hemisphere of the amygdala is associated with negative emotion,expressing fear and in the processing of fear-inducing stimuli.
When presented withan aversive stimulus, it is processed within the right amygdala, producing an unpleasant or fearful response.
The right amygdala conditions the individual to avoid fear-inducing stimuli and to assess threats in the environment.
The amygdala is responsible for threat detection and the conditioned and unconditioned fear responses that are carried out as a response to a threat.
The right hemisphere is also linked to declarative memory, which consists of facts and information from previously experienced events and must be consciously recalled.
The right hemisphere 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.
Episodic memory does not require conscious recall.
The right amygdala plays a role in the association of time and places with emotional properties.
The amygdala is larger in males than females in children aged 7 to 11, and adult humans.
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, and the larger relative size of the male amygdala may be attributed to this extended developmental period.
The amygdala is rich in androgen receptors.
The grey matter volume on the amygdala is predicted by testosterone levels, which may also contribute to the increased mass of the male amygdala.
The left amygdala reaches its developmental peak approximately 1.5–2 years prior to the right amygdala.
Whileearly growth of the left amygdala occurs, 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.
The early development of the left amygdala functions to provide infants the ability to detect danger.
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 between male and female amygdalae have been observed.
There are different lateralization of the amygdala in men and women.
Enhanced memory is related to enhanced activity of the left, but not the right, amygdala in women, whereas it isrelated to enhanced activity of the right, but not the left, amygdala in men.
Men with right amygdala damage were more likely to be impaired in decision-making ability, while women with left amygdala damage were more likely to be impaired in decision-making ability.
Women tend to retain stronger memories for emotional events than men.
The amygdala is implicated in the processing of emotional content and behaviors related and to anxiety and panic.
The amygdala plays a roll in cataplexy, with episodes of muscle paralysis during wakefulness that can be triggered by strong, positive emotions in persons with narcolepsy.
Dopamine signaling in the amygdala regulates REM sleep and possibly cataplexy as well.
The amygdala is important in emotional processing both in normal REM sleep and in disorders of REM sleep.
In healthy persons both negative and positive emotions (anxiety, fear, and joy) are common during dreams.
REM sleep is believed to play a crucial role in the processing of emotional memories, strengthening some, weakening others, and activation of the amygdala occurs during REM sleep.
Information pathwaythrough the amygdala: to the hypothalamus, the dorsomedial thalamus, the thalamic reticular nucleus, 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.
The medial nucleus of the amygdala is involved in the sense of smell and pheromone-processing, receivinginput from the olfactory bulb and olfactory cortex.
The lateral amygdalae, receive input from the sensory systems.
The amygdalae perform primary roles in the formation and storage of memories associated with emotional events.
The amygdalahas a strong connection with emotional learning.
Emotional memories are stored in synapses throughout the brain.
Fear memories, are stored in the neuronal connections from the lateral nuclei to the central nucleus of the amygdalae and the nuclei of the stria terminalis,a part of the extended amygdala.
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 of the amygdala are involved in the genesis of many fear responses such as defensive behavior, autonomic nervous system responses , and neuroendocrine responses.
Damage to the amygdalae impairs both Pavlovian fear conditioning, a form of classical conditioning of emotional responses.
Multiple neuromodulators acting in the amygdala regulate the formation of emotional memories.
The amygdalae are also involved in positive conditioning.
The basolateral amygdala is a key center for vomeronasal-olfactory associative learning.
Glutamatergic neurons in the basolateral amygdala send projections to the nucleus accumbens shell and core, which activateand drive motivational salience, is dependent upon dopamine receptor D1.
The amygdala is involved in memory consolidation.
An 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.
The amygdala, especially the basolateral nuclei, are involved in mediating the effects of emotional arousal on the strength of the memory for the event.
Increased activity in the amygdala following compassion-oriented meditation may contribute to social connectedness.
More emotionally arousing information increases amygdalar activity.
Emotionally arousing activity correlates with retention.
Amygdala neurons show oscillation during emotional arousal, such as theta activity.
These neuronal events could promote synaptic plasticity.
Amygdalar enlargement might be related to creative mental activity.
The amygdala has a substantial role in mental states, and is related to many psychological disorders.
Studies have shown children with anxiety disorders tend to have a smaller left amygdala.
There is 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, obsessive and compulsive disorders, post traumatic stress syndrome, as well as more broadly to separation and general anxiety.
Patients with borderline personality disorder havegreater left amygdala activity than normal control subjects.
Some borderline patients even had difficulties classifying neutral faces or see them as threatening.
Pychopathy is associated with reduced autonomic responses to instructed fear cues than otherwise healthy individuals.
Hyperactivity in the amygdala occurs when patients are shown threatening faces or confronted with frightening situations.
Patients with severe social phobia show an increased response in the amygdala.[
Depressed patients showed exaggerated left amygdala activity when interpreting emotions for all faces, and especially for fearful faces.
Amygdala hyperactivity is normalized when patients were administered antidepressant medication.
The amygdala has been observed to respond differently in people with bipolar disorder.
Adult and adolescent bipolar patients have considerably smaller amygdala volumes and somewhat smaller hippocampal volumes.
There may be a connection between the amygdala and autism.
Homosexual men tend to exhibit more feminine patterns in the amygdala than heterosexual males.
Homosexual females tend to show more masculine patterns in the amygdala than heterosexual women do.
Amygdala connections were more widespread from the left amygdala in homosexual males, as is also found in heterosexual females.
Amygdala connections were more widespread from the right amygdala in homosexual females, as in heterosexual males.
Amygdala volume correlates positively with the number of contacts a person has, and the complexity and number of different social network groups to which a person belongs.
Individuals with larger amygdalae have larger and more complex social networks.
The amygdala is responsible for facial recognition and allows others to respond appropriately to different emotional expressions, enabling accurate social judgments about other persons’ faces.
The amygdala’s role in social situations relates its ability to identify and process changes in facial features.
The amygdala does not process the direction of the gaze of the person being perceived.
The amygdala is also thought to be a determinant of the level of a person’s emotional intelligence, allowingfor greater societal integration and cooperation with others.
The amygdala processes reactions to violations in personal space, andabsent in persons in whom the amygdala is damaged bilaterally.
Theamygdala is found to be activated in fMRI when people observe that others are physically close to them.
The amygdala may play a role in the display and modulation of aggression, and in triggering a state of fear.
The amygdala appears to play a role in binge drinking.
The amygdala can be damaged by repeated episodes of intoxication and withdrawal.
Alcoholism is associated with dampened activation in brain networks responsible for emotional processing, including the amygdala.
Protein kinase C-epsilon in the amygdala is important for regulating behavioral responses to morphine, ethanol, and controlling anxiety-like behavior.
Protein kinase C-epsilon in the amygdalaprotein plays a role in development of the ability to consume a large amount of ethanol.
A link between the amygdala and anxiety may be present.
The amygdala is the primary structure of the brain responsible for fight or flight response, as it senses environmental stressors that stimulate fight or flight responses of anxiety and panic attacks.
It is associated with conditioned fear, behavior produced when an originally neutral stimulus is consistently paired with a stimulus that evokes fear.
Fear is measured by changes in autonomic activity: increased heart rate, increased blood pressure, as well as in simple reflexes such as flinching or blinking.
The central nucleus of the amygdala has direct correlations to the hypothalamus and brainstem, which are areas directly related to fear and anxiety.
Many areas of the amygdala are critically involved in specific signs that are used to measure fear and anxiety.
Theamygdala plays a crucial role in theassessment of danger.
With an environmental stimulus that provokes stress, the amygdala reacts by preparing to either stand and fight or to turn and run.
Such a response triggers the release of adrenaline into the bloodstream, and elevates blood sugar.
Long-term changes in amygdala neurons may also increase anxiety after long-term or traumatic stress
Blocking the action of stress hormones in the amygdala reduces anxiety.
Studies have found that the amygdalae may be responsible for the emotional reactions of PTSD patients.
Amygdala dysfunction during face emotion processing is seen with bipolar disorder.
Individuals with bipolar disorder show greater amygdala activity.
Amygdala size has been correlated with political thinking: greater liberalism is associated with increased gray matter volume in the anterior cingulate cortex, whereas greater conservatism is associated with increased volume of the right amygdala.
The volume of the amygdala and anterior cingulate gyrus may be associated with an individual’s ability to tolerate uncertainty and conflict.