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Open Access Open Badges Research article

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

Susumu Takahashi12* and Yoshio Sakurai34

Author Affiliations

1 Khoyama Center for Neuroscience, Faculty of Computer Science and Engineering, Kyoto Sangyo University, Kyoto 603-8555, Japan

2 Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi 332-0012, Japan

3 Department of Psychology, Kyoto University, Kyoto 606-8501, Japan

4 Core Research for Evolution Science and Technology (CREST), Japan Science and Technology Agency, Kawaguchi 332-0012, Japan

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BMC Neuroscience 2009, 10:115  doi:10.1186/1471-2202-10-115

Published: 15 September 2009



The 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.


The 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.


The 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.