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 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 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

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