Gamma-Band Shift in the Activity of Rat Hippocampal CA1: A Comparison of Memory-Guided and Visually-Cued Spatial Choice

Recent studies have highlighted the contribution of theta-gamma oscillations in hippocampus in memory and cognition. Here we adapted a nose-poke paradigm in order to investigate the role of hippocampal theta-gamma oscillations in a memory-guided behavior. We compared the local field potentials (LFPs) from the hippocampal CA1 cell layer of the same rats in two tasks: a memory-guided spatial alternation task and a visual-spatial discrimination task with random cues. We noted theta-gamma band coupling during a critical fixation period, while the rat was immobile but alert; high and low gamma components were highly phase-locked to the ongoing theta oscillation in CA1 during the fixation period. These modulations from high gamma (55–90) at the onset of the fixation to low gamma (22–45) at the offset of the fixation occurred in both tasks, but were stronger in the memory-guided alternation task. Thus, these data provide further evidence for the role of hippocampus CA1 in mnemonic coding relating to spatial alternation.