Hippocampal cell firing correlates of delayed-match-to-sample performance in the rat

Hippocampal CA1 and CA3 neurons were recorded in rats performing a delayed-match-to-sample (DMTS) task. Complex spike cells showed significant firing peaks following sample and match responses and during delivery of water reward. Individual cells were classified into 4 subtypes according to the presence or absence of firing in each of these 3 phases. There were significant differences in delay interval firing among the 4 subtypes, but firing during the delay did not predict the correct response: 34% of the cells showed a linear change in firing during the delay. Further analyses revealed significant lever position firing biases in approximately 70% of the cells tested irrespective of subtype. The complexity of firing correlates of the neurons recorded in this DMTS task suggests that the hippocampus divides specific aspects of the performance demands of the task across different cell subtypes, which together provide sufficient information to resolve the matching-to-sample problem on any given trial.