Brief Communications Theta-Mediated Dynamics of Spatial Information in

In rodent hippocampus, neuronal activity is organized by a 6–10 Hz theta oscillation. The spike timing of hippocampal pyramidal cells with respect to the theta rhythm correlates with an animal’s position in space. This correlation has been suggested to indicate an explicit temporal code for position. Alternatively, it may be interpreted as a byproduct of theta-dependent dynamics of spatial information flow inhippocampus.Herewe show thatplace cell activity ondifferentphasesof theta reflects positions shifted into the futureorpast along the animal’s trajectory in a two-dimensional environment. Thephases encoding future andpast positions are consistent across recordedCA1 place cells, indicating a coherent representation at the network level. Consistent theta-dependent time offsets are not simply a conse-quence of phase-position correlation (phase precession), because they are no longer seen after data randomization that preserves the phase-position relationship. The scale of these time offsets, 100–300ms, is similar to the latencies of hippocampal activity after sensory input and beforemotor output, suggesting that offset activitymaymaintain coherent brain activity in the face of information processing delays. Key words: hippocampus; place cells; theta oscillation; phase precession; temporal coding; response latenc