SEARCH FOR THE ENGRAM

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SEARCH FOR THE ENGRAM

• NEUROANATOMY.
• STORAGE SITES MUST BE DISTINGUISHED FROM
  PERFORMANCE SITES.

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SEARCH FOR THE ENGRAM

• NECESSARY VERSUS COINCIDENTAL NEURAL CHANGES.
• OTHER CONVERGING EVIDENCE.

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THEORY

• ?MULTIPLE LEARNING AND MEMORY SYSTEMS IN THE
  MAMMALIAN BRAIN THAT ARE FUNCTIONALLY
  DISSOCIABLE.

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THEORY

• ?THEY DIFFER IN THE CONTENT OF THE INFORMATION
  THAT THEY ACQUIRE AND STORE.
• ?ACQUIRE AND STORE INFORMATION SIMULTANEOUSLY AND
  IN PARALLEL.

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THEORY

• ?INTERACT SYNERGISTICALLY OR ANTAGONISTICALLY TO
  PRODUCE LEARNED BEHAVIORS.

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SPECIFIC SYSTEMS

• AMYGDALA?EMOTIONAL MEMORY.
• PERIRHINAL CORTEX?OBJECT MEMORY.

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SPECIFIC SYSTEMS

• HIPPOCAMPUS?RELATIONAL.
• DORSAL STRIATUM?HABIT.
• CEREBELLUM?CLASSICAL CONDITIONING.

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MEDIAL TEMPORAL LOBE
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NON-SPECIFIC SYSTEMS

• MEDIODORSAL THALAMUS?ENCODING.
• PREFRONTAL CORTEX?EXECUTIVE FUNCTION.

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HIPPOCAMPUS

• ANATOMY.
• ELECTROPHYSIOLOGY.
• LESIONS.

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HIPPOCAMPAL ANATOMY

• RECEIVES EXTENSIVE POLYMODAL SENSORY INFORMATION
  REPRESENTING THE EXTERNAL WORLD.

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HIPPOCAMPAL ANATOMY

• HORIZONTAL AND VERTICAL ORGANIZATION THAT ALLOWS
  SENSORY INPUT FROM NEOCORTEX TO BE DISTRIBUTED
  THROUGHOUT THE STRUCTURE.

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AMARAL WITTER
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AMARAL WITTER
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ELECTROPHYSIOLOGY

• DISCOVERY BY OKEEFE AND DOSTROVSKY (1971) OF
  PLACE UNITS IN HIPPOCAMPUS.
• PLASTICITY IS A DEFINING CHARACTERISTIC OF
  HIPPOCAMPAL NEURONS.

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PLACE UNITS

• A PLACE UNIT GENERALLY FIRES AT A RELATIVELY LOW
  RATE (ONE OR TWO SPIKES PER SECOND) EXCEPT WHEN
  THE RAT IS IN A PARTICULAR REGION OF THE
  RECORDING ENVIRONMENT.
• BURSTS OF 10 SPIKES PER SECOND OR HIGHER ARE
  COMMON.

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CHARACTERISTICS

• BECOME WELL ESTABLISHED WITHIN 10 MINUTES OF THE
  RATS INITIAL EXPOSURE TO A NEW ENVIRONMENT.

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CHARACTERISTICS

• LESIONS OF THE FORNIX OR ENTORHINAL CORTEX
  DISRUPT PLACE UNIT ACTIVITY IN THE HIPPOCAMPUS.

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CHARACTERISTICS

• FIRE AT SPECIFIC LOCATIONS IN RELATION TO A SET
  OF CONTROLLED SPATIAL CUES AND THEY CONTINUE TO
  FIRE IN THE APPROPRIATE PLACES WHEN THE CUES ARE
  REMOVED.

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CHARACTERISTICS

• PLACE FIELDS ARE NOT BASED ON GOALS OR INTENDED
  MOVEMENTS.

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OKEEFE AND SPEAKMAN
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Place Cells in Rats
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Place Cell Recording
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Place Cell Firing Characteristics

• Fire in Bursts, interrupted by (long) periods of
  silence
• Fire Complex spikes 2-10 spikes in 20ms

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Place cell Properties

• location specific firing
• head direction independent
• not topographic
• independent fields in different environments

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Tetrode Recording
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Place Cell Firing Fields
Day 1
Day 2

• Firing fields are independent of each other
• Independent in different environments
• Stable over time (memory)
• Anchored to dominant visual cues (rotate in B)

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Place Cell Firing Fields
Day 1
Day 2

• Independent in different environments (no field
  in grey, good field in black)

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BEHAVIOR

• SPATIAL.
• CONTEXT.
• NON-SPATIAL RELATIONAL.

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SPATIAL

• RADIAL MAZE.
• WATER MAZE.
• PLUS MAZE.

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CONTEXT

• RECOGNITION VERSUS DISCRIMINATION.

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CONTEXT DISCRIMINATION
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NON-SPATIAL RELATIONAL

• CONFIGURAL ASSOCIATION TASKS.
• NEGATIVE PATTERNING.

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NEGATIVE PATTERNING
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