Heterogeneity of network and coding states in CA1

Theta sequences and phase precession shape the activity time course of hippocampal place cells. Theta sequences are rapid sweeps of spikes from multiple cells, tracing trajectories from past to future. Phase precession is the correlation between a place cells theta firing phase and animal position. Here we present an analysis of the strongly variable character of these features in CA1. We identify a cell group that do not phase precess but reliably express theta sequences. The cells that do phase precess only do so when the medium gamma oscillations (60-90 Hz, linked to Entorhinal inputs) dominates but then they show less theta sequences. The same cells express more sequences but not precession when slow gamma (20-45 Hz, linked to CA3 inputs) dominates. Moreover, sequences occur independently in the two groups. Our results challenge a causal relationship between precession and sequences and highlights the highly heterogeneous character of the hippocampal output.