Pain related gamma band activity is dependent on the features of nociceptive stimuli: A comparison of laser and contact-heat

Painful contact heat and laser stimulation offer an avenue to characterize nociceptive pathways involved in acute pain processing, by way of evoked potentials. Direct comparisons of radiant laser and contact heat are limited, particularly in context of examining time-frequency responses to stimulation. This is important in light of recent evidence to suggest that gamma band oscillations (GBOs) represent a functionally heterogeneous measure of pain. The purpose of the current study was to investigate differences in GBOs generated in response to laser and contact heat stimulation of the non-dominant forearm. Following intensity matching to pain ratings, evoked electroencephalography (EEG) responses to laser and contact heat stimulation were examined in the time-frequency domain in the same participants (19 healthy adults) across two sessions. At approximately 200ms, both contact heat and laser stimulation resulted in significant, group-level event related synchronization (ERS) in the low gamma band (i.e., 30 to 60Hz) in central electrode locations (Cc, Cz, Ci). Laser stimulation also generated ERS in the 60 to 100Hz range (i.e., high gamma), at approximately 200ms, while contact heat led to a significant period of desynchronization in the high gamma range between 400 and 600ms. Both contact heat and laser GBOs were stronger on the central electrodes contralateral to the stimulated forearm, indicative of primary somatosensory cortex involvement. Based on our findings, and taken in conjunction with previous studies, laser and contact heat stimulation generate characteristically different responses in the brain, with only the former leading to high frequency GBOs characteristic of painful stimuli.