Limbic System

Introduction

• Function
  • the limbic system is involved in
    • Homeostasis
    • Olfaction
    • Memory
    • Emotions and drives
    • mnemonic “HOME”
• Anatomy
  • the main components of the limbic system includes
    • limbic cortex
    • hippocampal formation
      • involved in learning and memory
    • amygdala
      • involved in emotions and drives
    • olfactory cortex
    • hypothalamus
    • thalamus
  • Papez circuit
    • although it overly simplifies the circuitry of the limbic system, it is a useful way to expose yourself to this circuitry
      • fibers from the hippocampal formation enter the fornix to reach
        • the lateral and medial mammillary nuclei
      • fibers from the medial mammillary nuclei project to the
        • anterior nucleus of the thalamus (via the mammillothalamic tract), which subsequently project fibers to the
          • cingulate gyrus after passing through the internal capsule
      • fibers from the cingulate gyrus then project to the
        • parahippocampul gyrus and then to the
          • enterrhinal cortex and finally to the
            • hippocampal formation
• Clinical correlate
  • anterograde amnesia
    • this describes a deficit in forming new memories and can be seen in
      • bilateral medial temporal lobe damage
  • Wernicke-Korsakoff syndrome
    • this is caused by thiamine deficiency and results in
      • bilateral necrosis of the mamillary bodies (in most cases)
    • these patients typically present with the triad of
      • ataxia
      • eye movement abnormalities (e.g., ophthalmoplegia)
      • confusion
    • after the patient survives the acute stages of this disease, they can develop
      • anterograde and retrograde amnesia
  • Kluver-Bucy syndrome
    • this results from bilateral lesions of the amygdala and adjacent temporal lobe structures, which results in
      • placidity
        • decreased aggressive behavior and having little emotional reaction
      • psychic blindness
      • hyperorality
      • hypersexuality
  • Schizophenia
    • defective dopaminergic signaling in the mesolimbic pathway (ventral tegmental area of the midbrain to the ventral striatum)
      • responsible for positive psychotic symptoms (e.g., delusions, hallucinations)