INFORMATION ABOUT SPATIAL VIEW IN AN ENSEMBLE OF PRIMATE HIPPOCAMPAL CELLS

Citation
Et. Rolls et al., INFORMATION ABOUT SPATIAL VIEW IN AN ENSEMBLE OF PRIMATE HIPPOCAMPAL CELLS, Journal of neurophysiology, 79(4), 1998, pp. 1797-1813
Citations number
46
Categorie Soggetti
Neurosciences,Physiology
Journal title
ISSN journal
00223077
Volume
79
Issue
4
Year of publication
1998
Pages
1797 - 1813
Database
ISI
SICI code
0022-3077(1998)79:4<1797:IASVIA>2.0.ZU;2-3
Abstract
Hippocampal function was analyzed by making recordings from hippocampa l neurons in monkeys actively walking in the laboratory. ''Spatial vie w'' cells, which respond when the monkey looks at a part of the enviro nment, were analyzed. To assess quantitatively the information about t he spatial environment represented by these cells, we applied informat ion theoretic techniques to their responses. The average information p rovided by these cells about which location the monkey was looking at was 0.32 bits, and the mean across cells of the maximum information co nveyed about which location was being looked at was 1.19 bits, measure d in a period of 0.5 s. There were 16 locations for this analysis, eac h being one-quarter of one of the walls of the room. It also was shown that the mean spontaneous rate of firing of the neurons was 0.1 spike s/s, that the mean firing rate in the center of the spatial held of th e neurons was 13.2 spikes/s, and that the mean sparseness of the repre sentation measured in a 25-ms period was 0.04 and in a 500-ms time per iod was 0.19; (The sparseness is approximately equivalent to the propo rtion of the 25- or 500-ms periods in which the neurons showed one or more spikes.) Next it was shown that the mean size of the view fields of the neurons was 0.9 of a wall. In an approach to the issue of how a n ensemble of neurons might together provide more precise information about spatial location than a single neuron, it was shown that in gene ral the neurons had different centers for their view fields. It then w as shown that the information from an ensemble of these cells about wh ere in space is being looked at increases approximately linearly with the number of cells in the ensemble. This indicates that the number of places that can be represented increases approximately exponentially with the number of cells in the population. It is concluded that there is an accurate representation of space ''out there'' in the primate h ippocampus. This representation of space out there would be an appropr iate part of a primate memory system involved in memories of where in an environment an object was seen, and more generally in the memory of particular events or episodes, for which a spatial component normally provides part of the context.