Topological organization of the information coding in hippocampus

1
Topological organization of the information
coding in hippocampus

• Yuri Dabaghian
• Frank Lab
• Sloan Swartz Centers for Integrative
  Neuroscience   
• UCSF 

2
Hippocampus and space coding
Hippocampal damage results in

• Navigational difficulties in hippocampal (e.g.
  Alzheimers) patients
• Inability to imagine space for hippocampal
  patients (Hassabi, 2007)
• Lesion experiments in rats bad performance
  in Morris maze test, sequential goal tasks

Electrophysiology place fields
3
What is the nature of spatial coding in the
hippocampus?
Adjacency maps? Spatial Scales? Distances?
Directions?
What information about space can be extracted
from hippocampal spikes?
4
Global topology of the space
topology, compatible with many geometries.
5
Topological coding hypothesis

• The existing experimental evidence is consistent
  with the hypothesis that the hippocampus codes
  for the topological arrangement of memory
  elements, which are invariant with respect to
  slow, topologically consistent variations of the
  environment

Spatial memory Episodic memory
Relational learning Space coding
6

Spikes code for local topological relationships
Only a few (e.g. 5) fundamental relationships are
needed to describe a space
and to build a space
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What does it take to describe a space based on
spikes?
What does it take to construct a space from
spikes?
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Spikes ? Regions ? Topological Space
Constructive pointfree topology

• To build a space
• Define the regions
• Show how to compute
• intersections,
• unions,
• etc.
• Define continuity
• etc.

Computationally, topological space is a logical
structure over a set of regions (RCC theory, A.
Cohn (1992))
9
Computing topological relationships

• Computations that are necessary to construct a
  topological space from a set of available
  regions
• can be realized in neural networks
• The relationships between regions
• and continuous transitions between them

10
Hippocampal loop may compute the topological
relationships between regions
The information contained in the patterns of
activity in the network is the same as in the
topological relationships between regions in the
pointfree topological space
Topological representation of space and of the
memory maps can be built constructively as a
result of the hippocampal network computations
SB
CA1
11
Testing topological hypothesis
12
Acknowledgements
Sloan Swartz Foundation Frank Lab Mattias
Karlsson Caleb Kemere Steve Kim Ana
Nathe Annabelle Singer

• Loren Frank
• Sen Cheng
• Anthony Cohn (Leeds Univ., UK)