Human Physiology/The Nervous System

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the center for identification of danger and is fundamental for self preservation. The amygdala is the nucleus

responsible for fear.

Thalamus

Lesions or stimulation of the medial, dorsal, and anterior nuclei of the thalamus are associated with changes in

emotional reactivity. However, the importance of these nuclei on the regulation of emotional behavior is not

due to the thalamus itself, but to the connections of these nuclei with other limbic system structures. The

medial dorsal nucleus makes connections with cortical zones of the prefrontal area and with the hypothalamus.

The anterior nuclei connect with the mamillary bodies and through them, via fornix, with the hippocampus and

the cingulated gyrus, thus taking part in what is known as the Papez's circuit.

Image of the brain showing the location of the

hypothalamus.

Hypothalamus

The Hypothalamus is a small part of the brain located just below

the thalamus on both sides of the third ventricle. Lesions of the

hypothalamus interfere with several vegetative functions and

some so called motivated behaviors like sexuality,

combativeness, and hunger. The hypothalamus also plays a role

in emotion. Specifically, the lateral parts seem to be involved

with pleasure and rage, while the medial part is linked to

aversion, displeasure, and a tendency to uncontrollable and loud

laughing. However, in general the hypothalamus has more to do

with the expression of emotions. When the physical symptoms

of emotion appear, the threat they pose returns, via the

hypothalamus, to the limbic centers and then the prefrontal

nuclei, increasing anxiety.

The Fornix and Parahippocampal

These small structures are important connecting pathways for the limbic system.

The Cingulate Gyrus

The Cingulate Gyrus is located in the medial side of the brain between the cingulated sulcus and the corpus

callosum. There is still much to be learned about this gyrus, but it is already known that its frontal part

coordinates smells and sights, with pleasant memories of previous emotions. The region participates in the

emotional reaction to pain and in the regulation of aggressive behavior.

Memory and Learning

Memory is defined as : The mental faculty of retaining and recalling past experiences, the act or instance of

remembering recollection. Learning takes place when we retain and utilize past memories.

Overall, the mechanisms of memory are not completely understood. Brain areas such as the hippocampus, the

amygdala, the striatum, or the mammillary bodies are thought to be involved in specific types of memory. For

example, the hippocampus is believed to be involved in spatial learning and declarative learning (learning

information such as what you're reading now), while the amygdala is thought to be involved in emotional memory.

Damage to certain areas in patients and animal models and subsequent memory deficits is a primary source of

information. However, rather than implicating a specific area, it could be that damage to adjacent areas, or to a

pathway traveling through the area is actually responsible for the observed deficit. Further, it is not sufficient to

describe memory, and its counterpart, learning, as solely dependent on specific brain regions. Learning and memory