Diverse activity in prefrontal projections promotes temporal control of action

Prefrontal neurons can have diverse activity during cognitive functions like working memory, attention, and timing; however, the importance of this heterogeneity is unclear. Our goal was to better understand the diversity of prefrontal activity through connectivity. We harnessed circuit-specific tools to capture activity within prefrontal projections during interval timing, an elementary cognitive process that requires working memory for temporal rules and attention to the passage of time to estimate a temporal interval of several seconds. We used human electroencephalography and single neuronal recordings in mice to capture prefrontal activity during interval timing, with major patterns characterized by time-dependent ramping (monotonic changes) over a temporal interval. We then leveraged retrograde viruses to interrogate prefrontal cortex (PFC) projections to the mediodorsal thalamus (PFC-MD) and to the dorsomedial striatum (PFC-DMS). We report three novel results. First, circuit-specific calcium fiber photometry revealed that PFC-MD and PFC-DMS activity encoded distinct temporal signals, with PFC-MD projections ramping down and PFC-DMS ramping up to interval timing response times. Second, circuit-specific inactivation revealed that PFC-DMS inactivation disrupted animals' internal estimates of time. Third, circuit-specific single-nucleus RNA sequencing of prefrontal projections revealed distinct transcriptomic profiles between PFC-MD and PFC-DMS projections, with enriched genes for cortical layers and neuromodulators, and specific genes such as Cux2, Camk2n1, Htr4, and Foxp2 . These data suggest differences in gene expression and connectivity give rise to the diversity of prefrontal activity during interval timing. These findings advance our fundamental understanding of prefrontal function and dysfunction in human disease.