Neocortical rhythm entrainment by parvalbumin-positive interneurons across cortical layers
Neocortical interneurons provide inhibition responsible for organizing neuronal activity into brain oscillations that subserve cognitive functions such as memory, attention or prediction. However, little is known about the interneuronal contribution to the entrainment of neocortical oscillations within and across different cortical layers. Here, using layer-specific optogenetic stimulations with micro-Light-Emitting Diode ({micro}LED) arrays, directed toward parvalbumin-expressing (PV) interneurons in non-anesthetized awake mice, we found that supragranular layer stimulations of PV neurons were most efficient at entraining supragranular local field potential (LFP) oscillations at gamma frequencies ({gamma}: 25 - 80 Hz), whereas infragranular layer stimulation of PV neurons better entrained the LFP at delta ({delta}: 2 - 5 Hz) and theta ({theta}: 6 - 10 Hz) frequencies. At the level of neuronal action potential activity, we observed that supragranular neurons better followed the imposed PV stimulation rhythm than their infragranular counterparts at most frequencies when the stimulation was delivered in their respective layer. Moreover, the neuronal entrainment evoked by local stimulation could propagate across layers, though with a lesser impact when the stimulation occurs in deep layers, suggesting an orientation-selective propagation. These results establish a layer-based framework for oscillation to entrain the primary somatosensory cortex in awake conditions.