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2/28/17 1 Whoever wants to reach a distant goal must take small - - PDF document

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2/28/17 1 Whoever wants to reach a distant goal must take small steps --Saul Bellow 1 2/28/17 Neural Navigation I: constructing a cognitive map of space 1. Intelligent navigation: getting from here to there 2. A place hierarchy in

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“Whoever wants to reach a distant goal must take small steps”

  • -Saul Bellow
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Neural Navigation I:

constructing a cognitive map of space

  • 1. Intelligent navigation: getting from here to

there

  • 2. A place hierarchy in the brain
  • 3. Functions of the hippocampus
  • A. Representing space and spatial memory
  • B. Memory consolidation

Where things are: coordinate frames

  • Egocentric frame of reference: represents

where things are relative to a specific part of my body (e.g. retina, trunk of body, hand)

  • Allocentric frame of reference: represents

where things are relative to fixed landmarks or boundaries.

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Conclusions from Grandmother Cells

  • Some medial temporal lobe neurons exhibit

responses to individuals, places, or objects that are

– Sparse: few cells respond to any given image – Selective: each cell seems to respond to a specific concept or category – Invariant: these cells respond regardless of the current appearance of the individual

  • Sparse conceptual (abstract) representations may

facilitate encoding specific memories and associations

How to get where you want to be

  • 1. identify landmarks: what is this?
  • 2. use landmarks to determine position and

heading: where am I and which way am I pointing?

  • 3. access memory of spatial relationships

between landmarks and goal: where are

  • ther relevant places?
  • 4. plan route…and go!
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Three strategies to get from here to there

  • Path integration: count steps in correct

direction, e.g. in the dark.

  • Perform memorized series of steps/decisions:

turn left at landmark X then right at Y.

  • Represent position on a cognitive map of

remembered places to guide your movement.

Neural Navigation I:

constructing a cognitive map of space

  • 1. Intelligent navigation: getting from here to

there

  • 2. A place hierarchy in the brain
  • 3. Functions of the hippocampus
  • A. Representing space and spatial memory
  • B. Memory consolidation
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Translating between two egocentric coordinate frames Parietal cortex represents where things in my visual field are, relative to me

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How to get where you want to be

  • 1. identify landmarks: what is this?
  • 2. use landmarks to determine position and

heading: where am I and which way am I pointing?

  • 3. access memory of spatial relationships

between landmarks and goal: where are

  • ther relevant places?
  • 4. plan route…and go!

Identifies landmarks Uses landmarks to determine the current location and direction Encodes a cognitive map that represents landmarks and goals in terms of their coordinates in allocentric space Para-hippocampal place area Retrosplenial complex Medial temporal lobe Hippocampus

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scenes > objects

These areas encode scene category and landmark identity

Multi-Voxel Pattern Analysis: A classification algorithm

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Parahippocampal Place Area identifies the current scene/place RetroSplenial Complex locates and orients the current scene in the larger space around it

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t n

Scanned while viewing images taken at different locations on a familiar college campus fMRI evidence that RSC codes location in a manner that abstracts away from perceptual features

Pattern similarity

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Hippocampus (MTL) represents locations on an allocentric cognitive map

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2/28/17 11 fMRI evidence that the human hippocampus encodes distances: a key feature of a cognitive map

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PPA: what is this? RSC: Where am I and which direction am I facing? Hippocampus: (allo) Where are other places? Parietal: Where are things relative to me? (ego)

Division of labor

Three strategies to get from here to there

  • Path integration: count steps in correct

direction, e.g. in the dark.

  • Perform memorized series of steps/decisions:

turn left at landmark X then right at Y.

  • Represent position on a cognitive map of

remembered places to guide your movement.

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Spatial navigation vs. sequence of stimulus-response steps/decisions

Spatial strategy: hippocampus Non-spatial strategy: striatum

Iaria et al 2003

Striatum = two elements of basal ganglia: – Caudate nucleus – Putamen

Striatum: Motor skills and habits, Procedural Memory

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Neural Navigation I:

constructing a cognitive map of space

  • 1. Intelligent navigation: getting from here to

there

  • 2. A place hierarchy in the brain
  • 3. Functions of the hippocampus
  • A. Representing space and spatial memory
  • B. Memory consolidation
  • Fig. 24.9

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Hippocampus!

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From JH Martin, Neuroanatomy

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HP lesion à can’t remember where the platform is à spatial memory

Morris Water Maze

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Hippocampal place cell Hippocampal place cells

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Grid cell

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Grid cell in entorhinal cortex

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Head Direction (HD) cell

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Place cells recorded in human hippocampus!

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Boundary cell

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