Transcript Slide 1
Topological organization of the information coding in hippocampus Yuri Dabaghian Frank Lab Sloan Swartz Centers for Integrative Neuroscience UCSF Hippocampus and space coding Hippocampal damage results in: • 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 Electrophysiology: place fields 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? 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 Relational learning Episodic memory Space coding 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 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 space Topological representation of space and 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 Karlsson Caleb Kemere Steve Kim Ana Nathe Annabelle Singer