Gradual Translocation of Spatial Correlates of Neuronal Firing in the Hippocampus towards Prospective Reward Locations

In a continuous T-maze alternation task, CA1 complexspike neurons in the hippocampus differentially fire as the rat traverses overlapping segments of the maze (i.e., stem) repeatedly via alternate routes. Temporal dynamics of this phenomenon were further investigated in the current study. Rats learned the alternation task from the first day of acquisition and the differential firing pattern in the stem was observed accordingly. More importantly, we report a phenomenon in which spatial correlates of CA1 neuronal ensembles gradually changed from their original firing locations, shifting toward prospective goal locations in the continuous T-maze alternation task. The relative locations of simultaneously recorded firing fields, however, were preserved within the ensemble spatial representation during this shifting. The within-session shifts in preferred firing locations in the absence of any changes in the environment suggest that certain cognitive factors can significantly alter the locationbound coding scheme of hippocampal neurons.