Learning and modality independent time cells tile stimulus and post-stimulus period.

Abstract

Hippocampal neurons represent multiple dimensions of stimulus and behavioural context, including time. It is unclear how soon time-encoding cells emerge during learning, and if they additionally encode context in a manner specific to behavioural paradigm. We investigated simultaneous time and context encoding using 2-photon calcium imaging of mouse hippocampus during a trace eyeblink conditioning (TEC) task with sound and light stimuli. We find that the fraction of time cells is independent of learning and of stimulus modality. Only 13% of cells retain time-encoding on successive days, but persisters remain active within their original stimulus and post-stimulus epochs. Finally, we show that 60% of modality-specific time-encoding cells are active after the stimulus period, but modality-agnostic time cells are rare post-stimulus. Thus, compared to other paradigms, time cells in TEC have distinct learning and turnover properties, and exhibit sustained coding of stimulus modality and time which may subserve associations with subsequent events.