CA1 20-40 Hz oscillatory dynamics reflect trial-specific information processing supporting nonspatial sequence memory

Abstract

The hippocampus is known to play a critical role in processing information about temporal context. However, it remains unclear how hippocampal oscillations are involved, and how their functional organization is influenced by connectivity gradients. We examined local field potential activity in CA1 as rats performed a complex odor sequence memory task. We find that odor sequence processing epochs were characterized by increased power in the 4-8 Hz and 20-40 Hz range, with 20-40 Hz oscillations showing a power gradient increasing toward proximal CA1. Running epochs were characterized by increased power in the 8-12 Hz range and across higher frequency ranges (>24 Hz), with power gradients increasing toward proximal and distal CA1, respectively. Importantly, 20-40 Hz power increased with knowledge of the sequence and carried trial-type-specific information. These results suggest that 20-40 Hz oscillations are associated with trial-specific processing of nonspatial information critical for order memory judgments.