Exploring the role of context-dependent hippocampal activity in spatial alternation behavior

In a continuous T-maze spatial alternation task, CA1 place cells fire differentially on the stem of the maze as rats are performing left- and right-turn trials (Wood et al. (2000) Neuron 27:623-633). This context-dependent hippocampal activity provides a potential mechanism by which animals could solve the alternation task, as it provides a cue that could prime the appropriate goal choice. The aim of this study was to examine the relationship between context-dependent hippocampal activity and spatial alternation behavior. We report that rats with complete lesions of the hippocampus learn and perform the spatial alternation task as well as controls if there is no delay between trials, suggesting that the observed context-dependent hippocampal activity does not mediate alternation behavior in this task. However lesioned rats are significantly impaired when delays of 2 or 10 s are interposed. Recording experiments reveal that context-dependent hippocampal activity occurs in both the delay and no-delay versions of the task, but that in the delay version it occurs during the delay period, and not on the stem of the maze. These data are consistent with a role for context-dependent hippocampal activity in delayed spatial alternation, but suggest that, according to specific task demands and memory load, the activity may be generated by different mechanisms and/or in different brain structures.