Representation of interval timing by temporally scalable firing patterns in rat prefrontal cortex

Significance The ability to estimate time interval in the order of seconds is important for animal behaviors. However, how the brain estimates the passage of time remains mysterious. In the current study, we trained rats to estimate two different time intervals and recorded activities of single neurons from the medial prefrontal cortex (mPFC). We found that some PFC neurons showed activity changes during time estimation by the rat, with the same profile that was temporally scaled by a factor proportional to the estimated time intervals. Local cooling of mPFC slowed the time estimated by the rat. Thus, PFC neuronal activity contributes to time estimation, and temporal scaling of neuronal activity may be a circuit mechanism for estimating different time intervals. Perception of time interval on the order of seconds is an essential component of cognition, but the underlying neural mechanism remains largely unknown. In rats trained to estimate time intervals, we found that many neurons in the medial prefrontal cortex (PFC) exhibited sustained spiking activity with diverse temporal profiles of firing-rate modulation during the time-estimation period. Interestingly, in tasks involving different intervals, each neuron exhibited firing-rate modulation with the same profile that was temporally scaled by a factor linearly proportional to the instructed intervals. The behavioral variability across trials within each task also correlated with the intertrial variability of the temporal scaling factor. Local cooling of the medial PFC, which affects neural circuit dynamics, significantly delayed behavioral responses. Thus, PFC neuronal activity contributes to time perception, and temporally scalable firing-rate modulation may reflect a general mechanism for neural representation of interval timing.

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