Amygdala
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What is the amygdala?
The amygdalae (singular: amygdala) is an almond shaped cluster of neurons located deep in the medial temporal lobes of the
brain of humans and other vertibrates. The amygdalae are considered part of the Lymbic System and play an important role in the
processing of memory in terms of emotional reactions.
Connections
The amygdala sends signals to the hypothalamus for activation of the sympathetic nervous system. There are also connections to
the reticular nucleus for increased reflexes and to the trigeminal nerve and facial nerve for facial expressions of fear.
Additionally, the amygdala has connections to the ventral tegmental area, locus coeruleus and latrodorsal tegmental nucleus for
the activation of the neurotransmitters of dopamine, norepinephrine, and epinephrine.
The amygdala has connections with all of the sensory systems of the body, creating emotional connections with each sensory
stimulus. The cortical nucleus is part of the amygdala and receives signals from the olfactory bulb and the olfactory cortex
involving the since of smell, more specifically the processing of pheromones. Perhaps it is through these connections that
people remember a particular person or place from a familiar smell or taste.
Role of Amygdala
The amygdala has been found to perform primary roles in the memory of emotional events involving fear or aversive stimuli. This
connection to memory could be through long-term potentiation, when affected synapses from an aversive event are primed to act
more rapidly and readily. For example, when participants are exposed to the pairing of a loud noise and a blue circle,
participants have a fight/flight reaction. Additionally, when they are exposed to the blue circle afterwards, they still
experience the sympathetic nervous system spike. This could serve as an evolutional benefit in order to escape and avoid
situations that pose as a danger. The amygdala is also believed to play a role in the processing of rewards and the emotional
states involved in aggressive behaviors, sexual behaviors, maternal behaviors and eating/drinking behaviors.
The amygdalae are also believed to play a role in the storage of memory during the consolidation period. Emotionally aroused
events activate the amygdalae to a higher level. When the amygdalae help consolidate memory, there tends to be a stronger
retention of the event in one’s memory.
The Amygdala's Involvement in Disorders
Patients with borderline personality disorder tend to have significantly greater left amygdala activity than normal
controls. Additionally, patients with a bipolar and unipolar disorders and states of depression tend to have a significantly
smaller amygdala volume, perhaps shedding light onto the erratic shifts of emotion related to the disorder. There are also
neuropsychology imaging studies that have tried to tie a role in the size of the amygdala to autism.
Damage to the amygdala could pose as a danger to the individual, and anyone the person comes into contact with. While a person
with amygdala damage may have normal cognitive functions, they may completely loose their sense of fear. It could be very
possible for someone with amygdala damage to walk out into the middle of a busy road without the fear of getting hit by a car.
Since patients with amygdala damage tend to make or decisions that are risky to their lives, they typically have to be
hospitalized and watched continuously.
References
http://www.biopsychiatry.com/amygdala.htm
http://www.benbest.com/science/anatmind/anatmd9.html
http://serendip.brynmawr.edu/exchange/node/1749
Bechara et al (1994). Different contributions of the human amygdala and ventromedial prefrontal cortex to decision-making. The Journal of Neuroscience. 19(13), 5473–5481
