correct response associated with a particular environment. More recently, Igarashi and colleagues showed that ~20–40 Hz oscillations in hippocampal subfield CA1 became more tightly locked to theta phase as animals learned odor-place associations [12]. This cross-frequency coupling was observed during the odor-sampling period of the task when animals presumably remembered which reward site was associated with a given odor. In another recent study, ~30–45 Hz gamma power in CA1 increased at the point in a delayed spatial alternation task when animals needed to remember which side to choose [13]. Taken together, these results support the hypothesis that coupling between theta phase and ~30–45 Hz gamma facilitates retrieval of previously learned memories.
