Topological organization of the information coding in hippocampus

Yuri Dabaghian

Frank Lab

Sloan Swartz Centers for Integrative Neuroscience   

UCSF 

Hippocampus and space coding

• Navigational difficulties in hippocampal (e.g. Alzheimer’s) patients

• Inability to imagine space for hippocampal patients (Hassabi, 2007)

• Lesion experiments in rats: bad performance in Morris maze test, sequential goal tasks

Hippocampal damage results in:

Electrophysiology: place fields

What is the nature of spatial coding in the hippocampus?

What information about space can be extracted from hippocampal spikes?

Adjacency maps? Spatial Scales? Distances? Directions?

Global topology of the space

…topology, compatible with many geometries.

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

Spikes code for local topological relationships:

and to build a space

Only a few (e.g. 5) fundamental relationships are needed to describe a space

What does it take to describe a space based on spikes?

What does it take to construct a space from spikes?

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))

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

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 spaceTopological representation of

spaceand of the memory maps can

be built constructively as a result

of the hippocampal network

computations

SB CA1

Testing topological hypothesis

Acknowledgements

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

Sloan Swartz Foundation

Frank Lab:

Mattias KarlssonCaleb Kemere Steve KimAna NatheAnnabelle Singer