The Limbic System
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Introduction
The close connections among emotions, perception, thoughts, and memories lends for close connections among the limbic system and cortex. The hypothalamus is also closely involved with these connections due its autonomic response.
In this sesne, the limbic system can be thought of as the bridge between autonomic and voluntary responses.
Amygdala
The amygdala is a colleciton of nuclei lying under the uncus of the limbic lobe.
Functions
The amygdala has extensive interconnections, dominated by those of the hypothalamus and prefrontal cortex. This allows it to influence drive-related behaviours and the emotions behind them.
It can be thought of as a higher order modulating influence on the hypothalamus.
Stimulation of the amygdala can result in a variety of emotions, but the most common is fear, along with sympathetic manifestations.
The amygdala helps determine whether things are good or bad, based on the association of emotion with memory.
it also helps reinforce the strength of memories, such that emotionally laden memories tend to be longer lasting.
Connections
The amygdala receives different sensory modalities, including somatosensory, visual, auditory, and visceral, from:
- hypothalamus and septal nuclei, via stria terminalis
- thalamus, hypothalamus, and orbital and cingulate cortex, via ventral pathway
- olfactory bulb and cortex via lateral olfactory tract
- directly from temporal lobe structures such as hippocampus
- from brainstem
The amygdala sends information, via two major pathways, to:
- hypothalamus
- basal ganglia: ventral striatum -> ventral pallidum -> dorsomedial nucleus of thalamus
- influence on orbitofrontal prefrontal cortex
Cingulate gyrus
Parahippocampal Gyrus
Hippocampus
The hippocampus is important in explicit/declarative memory, but not so much at all for procedural memory.
The fornix is its primary output. One outp loop courses out to the mammilary body and then sequentially to the anterior thalamic nucelus, cingulate gyrus, parahippocampal gyrus, and finally back to the hippocampus.
Resources and References
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