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

Gamma oscillations are critical for cortical cognitive processing. 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 and the developmental mechanisms underlying the generation of adult-like gamma oscillations are poorly understood. Here, we combine in vivo electrophysiology and selective optogenetic manipulations of parvalbumin- (PV+) and somatostatin-positive (SOM+) interneurons in the mouse medial prefrontal cortex of both hemispheres along 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. The inhibitory effect of PV+ interneurons follows a similar timeline, enabling them to functionally operate within the classical gamma frequency range from adolescence onwards. In contrast, SOM+ interneurons have an age-independent inhibitory function, modulating beta-band oscillatory activity along development. These data identify the SOM+ to PV+ interneuron shift as a mechanism of gamma ontogeny and emergence of crosshemispheric synchrony in the developing prefrontal cortex.