AMYGDALA

Dona Das
Assistant Professor
PG Department of Psychology
Sahrdaya College of Advanced Studies
CONTENTS
❖Medial and lateral nuclei- Attention, Fear, Rage, Aggression
❖Emotional language and the Amygdala,
❖The limbic system and testosterone
❖Sexual orientation and heterosexual device
❖The homosexual limbic system
STRUCTURE AND LOCATION
The amygdala is a complex of multiple small nuclei located immediately
beneath the cerebral cortex of the medial anterior pole of each temporal
lobe.

The left and right amygdalae play a central role in our emotional responses,
including feelings like pleasure, fear, anxiety and anger.
The amygdala also attaches emotional content to our memories, and so plays
an important role in determining how robustly those memories are stored.
It is a almond shaped structure which is a part of the limbic system

Amygdala has an influence on cognitive processes such as memory-formation,

decision-making, attention, and social behavior.
The amygdaloid body, or just the amygdala, is a subcortical gray matter of
the limbic system which is supplied with blood by the anterior choroidal artery.
It contains 13 nuclei that are grouped into three functionally different divisions
of nuclei:
•the basolateral group
•the central group
•the cortico medial group
FUNCTIONS
❖Preeminent in the control and mediation of all higher order emotional and
motivational activities.
❖Serves as a seat of social and emotional intelligence.
❖Ability to find out and express even subtle social– emotional differences such
as friendliness, fear, love, affection , distrust, anger.
❖Ability to determine if something might be good or bad to eat.
❖Very sensitive to somesthetic input and physical contact , such that even a
slight touch in a very limited area of the body can produce amygdala
excitation.
❖Maintains a functionally interdependent relationship with the hypothalamus. It is
able to modulate and even control rudimentary emotional forces governed by the
hypothalamic nucleus.
❖Acts at the demands of hypothalamically induced drives.
❖If the amygdala via environmental surveillance discovers a potentially threatening
stimulus, it acts to excite and drive the hypothalamus so that the organism is mobilized
to take appropriate action.
❖The amygdala can tap into the reservoir of emotional energy mediated by the
hypothalamus so that certain ends may be attained.
MEDIAL AND LATERAL NUCLEI
Phylogenetically ancient anteromedial group
– MEDIAL AMYGDALA –involved in olfaction
and motor activity

Relatively newer basolateral division –

LATERAL AMYGDALA
MEDIAL AMYGDALA
❖The medial amygdala is the first portion of the basal ganglia striatal
complex to appear during development.
❖As it circles in an arc from the frontal to temporal lobe, the tail of the
caudate nucleus actually terminates and merges with the amygdala.
❖Hence this portion of the amygdala is in fact part of the basal ganglia and
is heavily involved in motivating and coordinating gross, or whole-body, motor
activity.
❖The medial amygdala receives fibers from the olfactory tract and through a
rope of fibers called the stria terminalis, projects directly to and receives
fibers from the medial hypothalamus (through which it exerts inhibitory
influences) as well as the septal nucleus.
❖Stria terminalis is larger and thicker in males ,hence the information and
impulse exchange between hypothalamus and amygdala is different in men and
women.
❖The medial (and lateral) regions are rich in cells containing enkephalins, and
opiate receptors can be found throughout the amygdala.
LATERAL AMYGDALA
The lateral amygdala contributes fibers to the stria terminalis and gives rise to the
amygdalo-fugal pathway, through which it projects to
 the lateral and medial hypothalamus (upon which it exerts inhibitory and excitatory
influences, respectively),
 the dorsal medial thalamus (which is involved in memory, attention, and arousal),
 olfactory tubercle,
 as well as other subcortical regions
It also receives fibers from the medial forebrain bundle, which in turn has its site of
origin in the lateral hypothalamus
The lateral amygdala maintains rich interconnections with :
❑the inferior, middle, and superior temporal lobes, as well as
❑the insular temporal region, which in tum allows it to sample and influence the
auditory, somesthetic, and visual information being received and processed in these
areas, as well as to scrutinize this information for motivational and emotional
significance.
❑Intimately involved in all aspects of higher order emotional activity, hence its rich
interconnections with the lateral and medial hypothalamus and the neocortex.
❖Gustatory and respiratory sense are also represented in this vicinity and the lateral
division maintains rich interconnections with cingulated gyrus, orbital frontal lobes and
the parietal cortex through which it receives complex somesthetic information.
❖The lateral amygdala is highly important in analyzing information received and
transferring information back to the neocortex so that further elaboration may be
carried out at the cortical level.
❖It is through the lateral division that emotional meaning and significance can be
assigned to as well as extracted from that which is experienced
ATTENTION
❖The amygdala acts to perform environmental surveillance and can trigger orienting
responses, as well as mediate the maintenance of attention, should something of
interest or importance appear.
❖Electrical stimulation of the lateral division can initiate quick and/or anxious
glancing and searching movements of the eyes and head such that the organism
appears aroused and highly alert as if in expectation of something that is going to
happen.
❖The EEG becomes desynchronized, heart rate becomes depressed, respiration
patterns change, and the galvanic skin response significantly alters.
❖Once a stimulus of potential interest is detected, the amygdala acts to analyze its
emotional-motivational importance and will act to alert other nuclei, such as the
hypothalamus and basal ganglia, so that appropriate action may take place.
❖Increased vigilance is seen in cases where emotional stimuli are used. The
amygdala plays a pivotal role in the recognition of emotional stimuli. Thus the
amygdala appears to be an important brain structure in the regulation of
vigilance.
❖Emotional arousal, a process mediated by the amygdala, can enhance
attention to stimuli in a non-spatial manner.
❖The dorsal side of the brain stem in the midbrain region appear to play a
key role in controlling a particular but vital type of eye movement in which
objects initially in the peripheral field of vision ‘draw’ attention.
❖The amygdala plays a role in both early and late emotion processing.
❖Attention has only an influence on late emotion processing and thus on
amygdala activation.
FEAR, RAGE AND AGGRESSION
❖Initially, electrical stimulation of the amygdala produces sustained attention and
orienting reactions.
❖If the stimulation continues , fear and/or rage reactions are elicited.
❖When fear follows the attention response, the pupils dilate and the subject will
cringe, withdraw and cower. This cowering reaction , in turn may give way to extreme
fear and/or panic such that the animal will attempt to take flight.
❖Among humans, the fear response is one of the most common manifestations of
amygdaloid electrical stimulation and abnormal activation.
❖Moreover, unlike hypothalamic on/off emotional reactions, attention and fear
reactions can last up to several minutes after the withdrawal of stimulation.
In addition to behavioral manifestations of heightened emotionality, amygdaloid
stimulation can result in intense changes in emotional facial expression.
This includes facial contortions, barring of the teeth, dilation of the pupils, widening or
narrowing of the eyelids, flaring of the nostrils, tearing, as well as sniffing, licking,
and chewing
Indeed, some of the behavioral manifestations of a seizure in this vicinity (i.e.,
temporal lobe epilepsy) typically include chewing, smacking of the lips, and licking.
❖In many instances, rather than fear, there instead results anger, irritation, and rage,
which seems to build up gradually, until finally the animal or human attacks.
❖Unlike hypothalamic sham rage, amygdaloid activation results in attacks directed at
something real or, in the absence of an actual stimulus, at something imaginary.
❖Moreover, rage and attack will persist well beyond the termination of the electrical
stimulation of the amygdala.
❖Amygdala remains electrophysiologically active for long periods even after a
stimulus has been removed .
❖ Hence the amygdala is also responsible for generating and maintaining mood.
❖Amygdala is involved in motivating the organism to engage in the seeking of hidden
objects or continuing a certain activity in anticipation of achieving some particular
long term goal.
❖Anticipation is very important in the prolongation of emotional and mood states
such as fear or anger as well as the generation of more complex emotions such as
anxiety.
❖Fear and rage reactions have also been triggered in humans following depth
electrode stimulation of the amygdala
❖Tumors invading the amygdala have been reported to trigger rage attacks.
❖The amygdala appears capable of not only triggering and steering hypothalamic
activity but acting on higher level neocortical processes so that individuals form
emotional ideas.
❖Indeed, the amygdala is able to overwhelm the neocortex and the rest of the brain
so that the person not only forms emotional ideas but responds to them.
❖Bilateral destruction of the amygdala usually results in increased tameness, docility,
and reduced aggressiveness in cats, monkeys and other animals
❖In humans, bilateral amygdala destruction (by neurosurgery) has been reported to
reduce and/or eliminate paroxysmal aggressive and violent behavior.
❖In some creatures, however, bilateral ablation of the amygdala has been reported
to at least initially result in increased aggressive responding and, if sufficiently
aroused or irritated, even the most placid of amygdalectomized (removal of
amygdala) animals can be induced to fight fiercely.
❖However, these aggressive responses are very short-lived and appear to be
reflexively mediated by the hypothalamus.
❖Thus, these findings suggest that true aggressive feelings are dependent on the
functional integrity of the amygdala (versus the hypothalamus) .
EMOTIONAL LANGUAGE AND THE AMYGDALA
There are 2 amygdala per person
It reviews sensory information from 2 separate pathways :
❖Short route : when the message is first sent to thalamus then directly to the
amygdala. (fast reaction)
❖Long route : when the message travels from the cortex where it is evaluated then
sent to the thalamus then the amygdala. (slow reaction)
❖Removal of amygdala causes fearlessness
❖Electrical stimulation of intact amygdala leads to increased vigilance or attention
❖lateral amygdala – fear and violent aggression.
In humans and animals, a wide range of emotional sounds have been evoked through
amygdala activation, such as sounds indicative of pleasure , sadness ,happiness and
anger.
In humans, destruction to the right amygdala abolishes the ability to sing, convey
melodic information or properly pronounce via vocal inflection.
Similar disturbances occur with right hemisphere damage.
When the right temporal region has been grossly damaged or surgically removed,
the ability to perceive, process or even vocally reproduce most aspects of musical
and emotional auditory input is significantly curtailed.
❖The amygdala receives inputs from all senses as well as visceral inputs.
❖Since the amygdala is very important in emotional learning it is not surprising that
visceral inputs are a major input source .
❖The central nucleus of amygdala produces autonomic components of emotions ( eg;
changes in heart rate, blood pressure, and respirations) primarily through output
pathways to the lateral hypothalamus and brain stem.
❖When the amygdala is stimulated forward, it’s sending signals to the frontal
lobe.This is where the brain handles cognitive functions such as long-term decision
making and appropriate social actions.
❖These functions can play a major role in determining levels of success and
happiness.
❖When amygdala signals backward it’s inducing a fear response.
❖Various nuclei of the amygdala become active when emotionally relevant stimuli
are presented.
❖The central nucleus of amygdala is the single most important part of brain for
expression of emotional responses provoked by aversive stimulus.
❖When threatening stimuli are presented , both the neural activity of central nucleus
and production of FOS protein increases.
❖Central nucleus is important for development of a conditioned emotional response.
Damage to the central nucleus:
❖Damage will reduce or abolishes a wide range of emotional behaviours and
physiological responses.
❖After damage, animals no longer show sign of fear when confronted with stimuli that
have been paired with aversive events.
Stimulation of the amygdala causes intense emotion, such as aggression or fear.
Irritative lesions of temporal lobe epilepsy have the effect of stimulating the
amygdala. In its extreme form irritative lesions of temporal lobe epilepsy can cause
a panic attack.
PET scans have shown an increase in blood flow to the parahippocampal gyri,
beginning with the right parahippocampal gyrus.
Similar but attenuated blood flow increases occurs during anxiety attacks.
Destructive lesions such as ablation of the amygdala cause an effect opposite to the
irritative lesions of temporal lobe epilepsy.
Destructive lesions of the amygdala cause tameness in animals, and a placid calmness
in humans characterized as a flatness of affect.
LIMBIC SYSTEM AND TESTOSTERONE
❖Testosterone is responsible for the development of primary sexual development,
which includes testicular descent, spermatogenesis, enlargement of the penis and
testes, and increasing libido.
❖The limbic system is a set of structures of the brain. These structures cover both
sides of the thalamus, right under the cerebrum. It is not a separate system, but a
collection of structures from the cerebrum, diencephalon, and midbrain.
❖It combines higher mental functions and primitive emotion into a single system often
referred to as the emotional nervous system.
❖Related sex differences in agressiveness are also a consequence of the relatively
higher concentrations of the activating hormone, testosterone , flowing through male
bodies and brains.
❖Studies show that females who have been prenatally exposed to high levels of
masculinizing hormones behave similarly to males, even in regard to enhanced spatial
abilities . they are also more aggressive and engage in more rough and tumble play
than normal females.
❖Female primates and other mammals who have been exposed to testosterone
during neonatal development display an altered sexual orientation as well as
significantly higher levels of activity, competitiveness, combativeness, and
aggressiveness.
❖The presence or absence of testosterone during the critical period of neuronal
differentiation that determines if one is in possession of a male versus a female limbic
system
❖Testosterone is also involved in regulating secondary male characteristics, which are
those responsible for masculinity.
MECHANISM OF LIMBIC SYSTEM AND
TESTOSTERONE
In puberty, the hypothalamic-pituitary-gonadal axis plays a major role in regulating
testosterone levels and gonadal function.
The hypothalamus secretes GnRH, which travels down the hypothalamo-
hypophyseal portal system to the anterior pituitary, which secretes luteinizing
hormone (LH) and follicle-stimulating hormone (FSH).
LH and FSH are two gonadotropic hormones that travel through the blood and act on
receptors in the gonads.
LH, in particular, acts on the Leydig cells to increase testosterone production.
Testosterone limits its own secretion via negative feedback.
High levels of testosterone in the blood sends feedback to the hypothalamus to
suppress the secretion of GnRH and also feedback to the anterior pituitary, making it
less responsive to GnRH stimuli.
SEXUAL ORIENTATION AND HETEROSEXUAL
DEVICE
The amygdalas, located in the left and right medial temporal lobes, play a
general role in the experience of emotions and social cognition.
With respect to sexual behavior, they seem to play a role in the identification
of potential mating partners based on sensory social signals, which are
primarily visual in humans
Amygdala contains facial recognition neurons which are sensitive to different facial
expressions and capable of determining the sex of the individual being viewed ,
which become excited when looking at a male versus a female face.
In this regard , the amygdala can act to find out and detect potential sexual partners
and then motivate sex appropriate behaviour , culminating in sexual intercourse and
orgasm.
An individual who possesses a “male” limbic system is likely to view the female face,
body and genitalia as sexually arousing because the amygdala and limbic system
respond with pleasure when stimulated by these particular features.
Likewise, male physical features are likely to excite and sexually stimulate the limbic
systems possessed by heterosexual females and homosexual males.
This happens because at a very basic level , emotional , sexual and motivational
perceptual / behavioural functioning becomes influenced and guided by the
anatomical sexual bias of the host.
In the study of bilateral amygdala lesions in male and female primates,
including humans, results showed that such lesions have a variety of effects on
primate behavior, which together have been termed the Kluver-Bucy
syndrome.
Humans display flat affect, hypersexuality, and a complete inability to limit
their sexual advances to appropriate partners or locations.
Males are more likely than females to be sexually aroused by erotic images
and this difference is reflected in differences in amygdalar activation.
In several studies, erotic images presented to male and female volunteers
undergoing functional brain scans produced greater amygdalar activation in
males.
HOMOSEXUAL LIMBIC SYSTEM
❖It has been reported that the hypothalamus in male homosexuals is organized in a
manner similar to the female pattern of development.
❖Moreover , the anterior commissure is not only larger in females but is 35% larger in
homosexual males versus male heterosexuals.
❖This raises the possibility that the sex differences in male versus female and
heterosexual male versus homosexual male sexual orientation , and thus the capacity
to experience sexual pleasure when with a heterosexual or homosexual partner
maybe determined by these nuclei.
❖It could be assumed that homosexual males respond to males with feelings of sexual
attraction and desires as do heterosexual females, i.e, because they are in possession
of a “female” limbic system which responds to male physical and facial features with
sexual arousal, i.e, the amygdala contains neurons that respond to face and facial
expressions and which can determine the sex of the individual viewed.
❖Conversely , heterosexual males, being in possession of a “male” hypothalamus and
amygdala not only respond to females with sexual arousal, but they behave and act
more aggressively than females and homosexual males.
❖Moreover , one might expect homosexuals with a female limbic system to be inclined
to behave in a manner similar to women. Indeed , homosexual males and females
tend to be more alike than different in regard to social-emotional reactions and
tendencies.
❖Homosexual males like heterosexual females demonstrate comparitively inferior
spatial perceptual capabilities as compared to heterosexual males.
❖It is tempting to speculate that because some homosexuals demonstrate an almost
hyper-developed pattern in the structure of the anterior commissure, this may account
for what some might consider excessive , if not dangerous and sometimes bizarre
sexual promiscuity.
❖Manifestation of Kluver-Bucy syndrome may also account for the high incidence of
emotional disorders, including suicide , in homosexuals : i.e, the consequence of a
dysfunctional and abnormal amygdala and limbic system.
❖This is not to deny the impact of social-environmental influences on the development
of these abnormalities as the environment can have a significant impact on the
amygdala as well as on one’s self concept.
❖Nor it is meant to imply that the majority of homosexuals engage in these excesses.
❖Even so, the possibility of a limbic system abnormality in regard to homosexual self-
destructiveness and indiscriminate and sometimes compulsive sexuality should not be
ruled out.