89. Limbic System

Question 1

What are the 5 big areas of the limbic system? What are the 4 overall functions of the limbic system?

Answer 1

1. Paralimbic Cortex (Limbic Lobe)
2. Amygdala
3. Hippocampal Formation
4. Olfactory Cortex
5. Hypothalamus (mammillary bodies)

Homeostasis (autonomic, neuroendocrine control - hypothalamus)
Olfaction (olfactory cortex)
Memory (Hippocampus)
Emotions/drive (Amygdala)

Question 2

What are the structures of the paralimbic cortex? What are their functions?

Answer 2

Surrounds limbic core; connects neocortex (6 layers) to limbic core (3 layers)

Cingulate Gyrus - Paraolfactory gyrus - orbitofrontal cortex - insula - uncus - parahippocampal gyrus - cingulate gyrus

(entorhinal cortex: anterior portion of parahippocampal cortex)

Question 3

What are the 3 parts of the hippocampal formation? What are their functions?
What are the 2 cortical areas and 2 pathways through the hippocampal formation?

Answer 3

1. Dentate Gyrus - input to archicortex
2. Hippocampus - continuous w/ fornix (CA1 + CA2 - most susceptible to ischemia; CA3, CA4)
3. Subiculum - mesocortex transition from 3-6 layers

Areas: Dentate and Hippocampus

Perforant Path: mossy fibers from CA3 to fornix (bend above thalamus to mammillary bodies of hypothalamus)
Alvear Path: fibers from CA1 to fornix

Question 4

Describe the path through the Papez circuit.

Answer 4

1. Parahippocampal Gyrus
2. Dentate Gyrus
   (alvear, perforant path)
3. Hippocampus
4. Subiculum
5. Fornix
6. Mammillary Bodies
   (mammillothalamic tract)
7. Anterior Thalamic Nuclei
8. Cingulate Gyrus
9. Parahippocampal Gyrus (Entorhinal Cortex)

Question 5

What is the function of the hippocampus?

Describe disease pathophys of anterograde amnesia, alzheimer’s disease, transient global amnesia

Answer 5

Hippocampus: convert short term memory to long term memory; encodes spatial memory

Anterograde Amnesia: bilateral hippocampal damage; cannot form new memories

Alzheimer’s Disease: dementia, neurodegeneration in Papez circuit causing impairment/inability to learn new info

Transient Global Amnesia: rare disorder of episodic memory problems due to damage in hippocampus or medial temporal lobe structures in Papez circuit

Question 6

Describe the disease states of:
Wernicke-Korsakoff (cause, sx triad, imaging)
HSV-1 Encephalitis (cause)
Autoimmune Limbic Encephalitis (cause, sX)

Answer 6

WK: vit B1 (thiamine) deficiency = bilateral necrosis of mammillothalamic tract and nearby nuclei; most often in alcoholics (malnutrition)
sx triad: ataxia, eye movement abnormalities, confusional states
causes anterograde/retrograde amnesia
imaging: high intensity in periaqueductal gray, mammillary bodies, dorsomedial thalami

HSV1E: tropism for limbic cortex - severe damage to limbic system preferentially (memory problems)

AILE: antigens to limbic system = limbic dysfx (misperceptions, mood changes, sleep problems, seizures); autoimmune or viral