Information in small neuronal ensemble activity in the hippocampal CA1 during delayed non-matching to sample performance in rats

Susumu Takahashi,Yoshio Sakurai

doi:10.1186/1471-2202-10-115

Abstract

BackgroundThe matrix-like organization of the hippocampus, with its several inputs and outputs, has given rise to several theories related to hippocampal information processing. Single-cell electrophysiological studies and studies of lesions or genetically altered animals using recognition memory tasks such as delayed non-matching-to-sample (DNMS) tasks support the theories. However, a complete understanding of hippocampal function necessitates knowledge of the encoding of information by multiple neurons in a single trial. The role of neuronal ensembles in the hippocampal CA1 for a DNMS task was assessed quantitatively in this study using multi-neuronal recordings and an artificial neural network classifier as a decoder.ResultsThe activity of small neuronal ensembles (6-18 cells) over brief time intervals (2-50 ms) contains accurate information specifically related to the matching/non-matching of continuously presented stimuli (stimulus comparison). The accuracy of the combination of neurons pooled over all the ensembles was markedly lower than those of the ensembles over all examined time intervals.ConclusionThe results show that the spatiotemporal patterns of spiking activity among cells in the small neuronal ensemble contain much information that is specifically useful for the stimulus comparison. Small neuronal networks in the hippocampal CA1 might therefore act as a comparator during recognition memory tasks.

Highlights

The matrix-like organization of the hippocampus, with its several inputs and outputs, has given rise to several theories related to hippocampal information processing
We examined the activities of the neuronal ensembles to provide quantitative constraints for hippocampal function
The decoding approach consists of training and regularizing a classifier to learn the map from neuronal ensemble activity to each behavioral label (Figures 2D-2I), as has been done in recent studies of the inferior temporal and motor cortices [18,19,20]

Summary

Introduction

The matrix-like organization of the hippocampus, with its several inputs and outputs, has given rise to several theories related to hippocampal information processing. Singlecell electrophysiological studies and studies of lesions or genetically altered animals using recognition memory tasks such as delayed non-matching-to-sample (DNMS) tasks support the theories. In rodent studies, two views respectively hold that the hippocampus is dedicated to spatial memory processing [3] and that it associates general memory items [4]. Results of several analyses of the stability of place cells have shown that pattern separation and pattern completion are apparent in neuronal ensembles of the hippocampus [5,6]. In support of the general view, several experiments directly showed activity related to match/ non-match conditions using recognition memory tasks, such as a delayed non-matching-to-sample (DNMS) task [7,8,9,10]. Place cells might code multiple events constructing a place experienced in the past [4]

Methods

Results

Discussion

Conclusion