Identified Cellular Correlates of Neocortical Ripple and High-Gamma Oscillations during Spindles of Natural Sleep

Ultra-high-frequency network events in the hippocampus are instrumental in a dialogue with the neocortex during memory formation, but the existence of transient ∼200 Hz network events in the neocortex is not clear. Our recordings from neocortical layer II/III of freely behaving rats revealed field potential events at ripple and high-gamma frequencies repeatedly occurring at troughs of spindle oscillations during sleep. Juxtacellular recordings identified subpopulations of fast-spiking, parvalbumin-containing basket cells with epochs of firing at ripple (∼200 Hz) and high-gamma (∼120 Hz) frequencies detected during spindles and centered with millisecond precision at the trough of spindle waves in phase with field potential events but phase shifted relative to pyramidal cell firing. The results suggest that basket cell subpopulations are involved in spindle-nested, high-frequency network events that hypothetically provide repeatedly occurring neocortical temporal reference states potentially involved in mnemonic processes. •Field potential events at ripple and high-gamma frequencies occur at spindle troughs•Interneurons fire in phase with spindle ripple and spindle high-gamma oscillations•Pyramidal cells fire sporadically and phase shifted relative to interneurons•Spindle ripple events might provide neocortical reference states in mnemonic processes Averkin et al. find local oscillatory events in neocortical field potentials in time windows at troughs of spindle oscillations during sleep. Subgroups of fast-spiking interneurons fire at ripple and high-gamma frequencies in phase with the local field oscillations.