Transient gamma events delineate somatosensory modality in S1

Gamma-band activity localized to the primary somatosensory cortex (S1) in humans and animals is implicated in the higher order processing of painful and tactile stimuli. However, it is unclear if gamma activity distinguishes these somatosensory modalities. Here, we coupled a reflex-based behavioral readout with chronic extracellular electrophysiology to investigate differences in S1 gamma-band activity elicited by noxious and innocuous stimuli in transgenic mice expressing channelrhodopsin2 (ChR2) in TRPV1-expressing sensory neurons. Like prior studies, trial-averaged gamma power increased following noxious and innocuous stimuli. However, stimulus-evoked gamma-band responses were not continuous oscillatory signals but were instead transient spectral events. We found that there was a higher incidence of gamma events following noxious stimulation, distinguishing them from innocuous stimulation. Our findings suggest that information about somatosensory stimuli may be embedded in features of gamma activity, which may provide insight into the mechanisms underlying processing of acute pain in the brain.