In the hippocampus, the amplitude of gamma oscillations is modulated by theta phase [5]. This may imply that gamma-mediated cell assemblies are integrated across space and time by theta rhythms [29]. A recent study showed that mPFC gamma power is modulated by hippocampal theta phase (Figure 1b), with localized gamma bursts transiently occurring at different mPFC locations [22]. Thus, spatially distributed gamma-mediated mPFC cell assemblies could be linked within the same theta cycle, while sequences of gamma-mediated cell assemblies could be integrated across successive theta cycles. The correlation between hippocampal theta phase and mPFC gamma amplitude has been replicated in more recent studies [18,30].
