Limbic System

The limbic system participates in complex and interrelated behaviors

-learning
-memory
-social interactions

The limbic system has 2 levels of structural and functional organization; the 1st level involves cortical structures on the medial edge of the hemisphere (limbus); these structures include

-Subcallosal area
-Cingulate gyrus
-Parahippocampal gyrus (from the temporal lobe )
-Uncus (from the temporal lobe)
-Hippocampus (structure deep within the parahippocampal gyrus)

The limbic system has 2 levels of structural and functional organization; the 2nd level includes all of the structures of the first plus some subcortical nuclei. These 2nd level structures include:

-septal nuclei
-Nucleus accumbens
-some hypothalamic nucleis-ESPECIALLY the mammillary bodies
-amygdala
-nucleus basalis of Meynert (substantia innominata)
-anterior and dorsomedial nuclei of the thalamus
-Habenular nuclei
-Ventral tegmental area (from the midbrain)
-Periaquaductal gray (from the midbrain)

Some of the main efferents from the limbic system include (4):

-fornix
-mammillothalamic tract
-stria terminalis
-ventral amygdalofugal pathway

the function of the Hippocampal formation

consolidate long term memories from immediate and short term memories

Main structures of the hippocampal formation include:

-Hippocampus
-dentate gyrus of the hippocampus

afferents to the hippocampal formatio

fibers from the entorhinal cortex ("parahippocampal cortex") synapse on the dentate and hippocampus

The major efferents leaving the hippocampus

the fornix

Papez circuit: the circuit itself

-hippocampal fornix fibers synapse on the mammillary bodies of the hypothalamus
-The mammillothalamic tract are the axons of the cell bodies of the mammillary bodies and
this pathway will synapse on the anterior nucleus of the thalamus
-the cell bodies of the anterior nucleus of the thalamus send their axons via the anterior limb of the internal capsule to the cingulate gyrus
-the axons of the cingulate gyrus projects to the entorhinal cortex, which projects its axons to the hippocampal formation

Papex circuit's function

plays a role in learning and memory

A lesion to the hippocampal formation

-inability to form long-term memories
-less severe lesions: more difficulty learning new things, and they may have trouble remembering to return to a previously started task if interrupted

Alzeheimer's disease

-excessive neuronal cell death not attributed to normal aging and thus causing severe cognitive dysfunction and death
-patients have neurofibrillary tangles and neuritic plaques which destroy the functionality of the neuron

First area to show evidence of Alzheimer's disease is

-the entorhinal cortex &
-the NUCELUS BASALIS OF MEYNERT

Korsakoff syndrome

-degenration seen in mamillary bodies, fornix, hippocampus and dorsomedial thalamic nucleus
-signs/symptoms include: dementia, confabulation, memory loss, confusion, cerebellar damage (ataxia)
-caused by a thiamine deficiency and seen in chronic alchoholics

Wernicke-Korsakoff syndrome

Korsakoff syndrome+ learning difficulties (thus involving Wenicke's area as well)
-dementia
-confabulation
-memory loss
-confustion
-cerebellar damage (ataxia)

Bilateral lesions to the anterior part of the cingulate gyrus can cause

-akinetic mutism (is immobile, mute, and unresponsive, but not in a
coma) OR
-patient may be alert, but have no idea who they are, or unable to recall the order of past events (VERY RARE; Sam Anderson)

akinetic mutism

patient is immobile, mute, and unresponsive, but not in a coma