Developmental embedding of parvalbumin interneurons drives local and crosshemispheric prefrontal gamma synchrony

Gamma oscillations are a pivotal trait of cortical cognitive processing. However, the ability to generate gamma oscillations evolves with age and requires cellular adjustments of the underlying neural networks. In the prefrontal cortex, gamma oscillations emerge relatively late compared to other cortical areas, yet the developmental mechanisms leading to the generation of adult-like gamma oscillations are poorly understood. Here, we combine bilateral in vivo electrophysiology and selective optogenetic manipulations of parvalbumin- (PV+) and somatostatin-positive (SOM+) interneurons in the mouse medial prefrontal cortex along late development to investigate their role for the age-dependent maturation of gamma oscillations. We show that crosshemispheric gamma synchrony strengthens with age, in line with the previously reported increase in local gamma power. Following a similar timeline, the inhibitory effect of PV+ interneurons emerges which start to functionally operate within the classical gamma frequency range from adolescence onwards. In contrast, SOM+ interneurons show no such age-dependent functional integration and display their beta oscillation modulating inhibitory effect across age. These data identify the SOM+ to PV+ interneuron switch as a mechanism of gamma ontogeny and emergence of crosshemispheric synchrony in the developing prefrontal cortex.