Operational dynamics in the hippocampal-entorhinal axis.

How do ensembles of neurons distributed across the hippocampal and entorhinal cortices effectively interact? In the awake-behaving rat, specific subpopulations of hippocampal and entorhinal neurons become entrained into two prominent fast-frequency rhythms (gamma [40-100 Hz], and 200 Hz). These fast rhythms are coupled to slower synchronizing potentials (theta and sharp wave, respectively), are correlated to macroscopic behavioral states, and to some extent are anatomically distinct. These population dynamics allow distributed populations of neurons across the hippocampal and entorhinal cortices to discharge together in time on the order of tens of milliseconds, and thus allow interconnected domains of a distributed neural network to become transiently entraining into synchronized, fast-frequency, population ensembles. We believe that these transient population dynamics allow interconnected domains to "effectively communicate" and modify their synaptic connectivity.