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Limbic System
Limbic system
• Participate visceral and motor responses
involved in defense and reproduction and
processes involved in memories
• It includes parahipocampal, cingulate, the
septal area, hippocampus, dentate gyrus,
amygdaloid body, hypothalamus and
anterior nuclei of thalamus.
Connections
• Afferent fibers:
• Four sources
– Cerebral neocortex, the septal area, the
contralateral hippocampus, and the nuclei in
the reticular formation of brain stem
• Efferent fibers:
– Originate from hippocampal formation to
entorhinal area and neocortex, also include
descending fibers to diencephalon and brain
stem.
Function of Hippocampal
• Function of Hippocampal: Memory
• Declarative (explicit) memory: facts, and knowledge that
can be recalled into consciousness
• Short term memory: may be forgotten or push into long
term memory
• Procedural memory (implicit) memory: learned skills
• The hippocampus and its connections are necessary for
new and short form memories. Any long term memories.
May involve synthesis a new protein or synapse.
Amygdaloid body (amygdala)
• Located between the anterior end of the temporal horn of
the lateral ventricle and the ventral surface of the
lentiform nucleus
• Dorsaomedial poriton of the amygdaloid body (also
called corticomedial group), receives fibers from
olfactory bulb and is part of the lateral olfactory area.
• Ventrolateral portion can be subdivided into central and
basolateral groups
• Afferent fibers originate from frontal and temporal lobes
and from thalamus, substantia nigra, raphe nuclei and
parabrachial nuclei of the reticular formation.
• Efferent fibers from amygdala is the stria terminalis,
terminates in the septal area of the hypothalamus
Connections
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Connections of the amygdala
Major efferent fibers are stria terminalis
Functional considerations
Emotional and behavioral changes are associated with
amygdala (MRI shows different activity level when
different emotions are elicited by pictures); memories
change are associated with hippocampal formation and
the circuit of Papez.
• Animal studies indicated that bilateral removal of
hippocampal formation and amygdaloid could cause
increased male sexual acts, maybe towards either sex,
other species, or even nonalive objects.
Function of the amygdala
• In humans:
• Increased sexual acts (perverted possible),
flattened affect, visual agnosia with bilateral
removal of temporal lobes
• Emotional response
• Limbic system, especially amygdala is
responsible for affective reactions.
• Memory:
• Both short and long term memories could be
affected.
Circuit of the limbic system
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Hippocampoal connections:
Circuit of Papez:
A ring of interconnected neurons
Sequence of the ring:
Entorhinal cortex, hippocampus, mamillary
body, anterior thalamic nuclei, cingulate
gyrus back to entorhinal area and fibers
interconnected theses neurons
Phineas Gage
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