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Chapter 4

The Limbic System and Higher Mental Functions

The Limbic System

The Limbic System is a complex set of structures found just
beneath the cerebrum and on both sides of the thalamus. It combines
higher mental functions, and primitive emotion, into one system. It is
often referred to as the emotional nervous system. It is not only
responsible for our emotional lives, but also our higher mental
functions, such as learning and formation of memories. The Limbic
system explains why some things seem so pleasurable to us, such as
eating and why some medical conditions are caused by mental stress,
such as high blood pressure. There are two significant structures
within the limbic system and several smaller structures that are
important as well. They are: Image of the brain, showing the
Limbic system.

1. The Hippocampus
2. The Amygdala
3. The Thalamus
4. The Hypothalamus
5. The Fornix and Parahippocampus
6. The Cingulate Gyrus

Structures of the Limbic System

Hippocampus
The Hippocampus is found deep in the temporal lobe, shaped like a seahorse. It consists of two
horns that curve back from the amygdala. It is situated in the brain so as to make the prefrontal
area aware of our past experiences stored in that area. The prefrontal area of the brain consults
this structure to use memories to modify our behavior. The hippocampus is responsible for
memory.

Amygdala
The Amygdala is a little almond shaped structure, deep inside the anteroinferior region of the
temporal lobe, connects with the hippocampus, the septi nuclei, the prefrontal area and the medial
dorsal nucleus of the thalamus. These connections make it possible for the amigdala to play its
important role on the mediation and control of such activities and feelings as love, friendship,
affection, and expression of mood. The amygdala is 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

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