Gamma-band oscillations (GBOs) elicited by transient nociceptive stimuli are one of the most promising biomarkers of pain across species. Still, whether these GBOs reflect stimulus encoding in the primary somatosensory cortex (Si) or nocifensive behavior in the primary motor cortex (Ml) is debated. Here we recorded neural activity simultaneously from the brain surface as well as at different depths of the bilateral Sl/MI in freely-moving male rats receiving nociceptive stimulation. GBOs measured from superficial layers of Si contralateral to the stimulated paw not only had the largest magnitude, but also showed the strongest temporal and phase coupling with epidural GBOs. Also, spiking of superficial SI interneurons had the strongest phase coherence with epidural GBOs. These results provide the first direct demonstration that scalp GBOs, one of the most promising pain biomarkers, reflect neural activity strongly coupled with the fast spiking of interneurons in the superficial layers of the Si contralateral to the stimulated side.