Systems Physiology II 6010

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Systems Physiology II 6010
Lecture 13 The Limbic System
Bradley Greger, PhD
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The Limbic System

• Parahippocampal gyrus
• Hippocampus
• Fornix
• Mamillary bodies
• Head of the Fornix
• Amygdala
• Cingulate gyrus

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Limbic System Cortical Input

• Primary cortical input to the limbic system is
  from the Inferior Temporal (IT) cortex
• Ventral Stream
• Object identification
• Hippocampal afferent

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Visual input to Hippocampus

• Hippocampus receives highly processed visual
  information

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Subdivisions of Hippocampus

• Entorhinal cortex
• Subiculum
• Dentate gyrus
• Cornu Amonnis (Ammon's horn)
• CA1
• CA2
• CA3
• Fimbria of the Fornix

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Subdivisions of Hippocampus

• Entorhinal cortex project to dentate gyrus via
  the perforant path
• Granule cells of the dentate gyrus project to the
  pyramidal cells of Cornu Amonnis subfield 3 (CA3)
  via mossy fibers
• CA3 pyramidal cells project to the pyramidal
  cells of the CA1 subfield via Schaffer
  collaterals
• Outputs via CA1 to Subiculum and the Fornix

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Long-term Potentiation (LTP)

• Record from CA1 cells, establish baseline
  responses
• High frequency stimulation (tetanus)
• Record from CA1 cells, responses are potentiated
• Potentiation persists for hours

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Mechanism of LTP

• Two receptors
• alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropioni
  c acid (AMPA)
• Primary post-synaptic currents
• N-methyl D-aspartate (NMDA)
• Typically blocked by magnesium ion

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Mechanism of LTP

• Large depolarization forces Mg ion out of NMDA
  channel
• NMDA channel passes Na and Ca ions
• Ca ions activate intracellular enzymes
• Increase receptor sensitivity
• Increase number of receptors
• Retrograde transmitter Nitric Oxide, increased NT
  release
• Eventually formation of new synapses

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Hippocampal Place Cells

• CA1 cells encode location of animal in space
• Response fields of hippocampus cells

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Recapitulation of place cells

• Place cells fire as a rat runs down a linear
  tract when it is at certain positions in the
  track
• This sequence of cell firing is repeated prior
  to, and after, the rat runs the track
• Time compressed playback
• Same time compressed playback has been observed
  during sleep

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Hippocampal RFs in Humans

• Jennifer Aniston response field

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Hippocampal RFs in Humans

• Cell responded to all pictures and even written
  name
• Very high level of abstraction
• Receives very highly processed visual information

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Lesions of Hippocampus

• Memories
• Episodic
• Facts, names, places
• hippocampus
• Procedural
• How to do things
• cerebellum
• Amnesia
• Retrograde
• Anterograde
• HM
• Conductor
• Memento movie

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Hippocampal Pathology

• Alzheimer's disease
• Short-term memory loss
• Names of people and object
• Function of objects
• Korsakoffs Syndrome
• disease of chronic alcoholics
• Mamilary body cortical damage
• severe retrograde and anterograde amnesia

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The Amygdala

• Receives afferent connection from hippocampus
• Emotional tagging of sensory input and memories

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The Papez Circuit

• The emotional encoding and learning circuit
• Highly processed information enters through
  hippocampus
• Repeated cycles through hippocampus, fornix,
  mamillary bodies, anterior thalamus, cingulate
  gyrus process emotions

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The expanded Papez Circuit

• Mamillary bodies and amygdala project to anterior
  thalamus
• Anterior thalamus projects to medial and orbital
  pre-frontal cortex
• Pre-frontal cortex projects to pre-motor areas
• Output of limbic system for the control of
  behavior

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Lesions of the Amygdala

• Animals have trouble indentify survival value of
  objects
• Danger
• Reproduction
• Food
• Patients dont experience anger or fear
• Unable to recognize expressions
• Diminished emotional response

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The Limbic Loops
Pre-Motor Cortex
Pre-Frontal Cortex
Cingulate Cortex
Inferior Temporal Cortex
Ant. Thalamus
Mamillary Body
Amygdala
Hippocampus