Experience and behavior modulate piriform cortex odor representation in freely moving mice

Abstract

In rodents, activity in the piriform cortex (PC) has been shown to reliably encode the identity of olfactory information within single sessions of odor delivery. However, recent evidence from chronic PC recordings found significant unreliability in this ensemble code over longer periods. The causes of this phenomenon, termed representational drift, are still being investigated across multiple sensory systems, but prior work has suggested a role for animal behavior in this observed unreliability of coding. To explore this possibility in PC, we recorded from the same populations of neurons in freely-moving, awake mice using micro-endoscopic calcium imaging as they gained passive experience with a panel of odorants over 5 consecutive days. As in prior studies, PC odor responses within a single session could be used to accurately decode odor identity. However, responses became less consistent across days of experience as odor-evoked response properties of the neurons shifted with experience. During these recordings, within and across sessions, decreases in olfactory investigative behavior correlated with decreased odor-evoked response from PC neurons. Similarly, decreases in odor investigation correlated with a decrease in representational consistency, and trials with greater odor investigation could be used to decode odor identity from PC neurons more accurately over time. Overall, this data supports recent evidence of long-term shifts in the ensembles of PC neurons encoding odor-identity (drift) but supports a role for behavioral modulation of overall PC activity and ensemble response consistency.