High-speed heating of the skin using a contact thermode elicits brain responses comparable to CO2 laser-evoked potentials

OBJECTIVE: To compare nociceptive event-related brain potentials elicited by a high-speed contact-thermode vs an infrared CO2 laser stimulator.

METHODS: Contact heat-evoked potentials (CHEPs) and CO2 laser-evoked potentials (LEPs) were recorded in healthy volunteers using a high-speed contact-thermode (>200 °C/s) and a temperature-controlled CO2 laser. In separate experiments, stimuli were matched in terms of target surface temperature (55 °C) and intensity of perception. A finite-element model of skin heat transfer was used to explain observed differences.

RESULTS: For 55 °C stimuli, CHEPs were reduced in amplitude and delayed in latency as compared to LEPs. For perceptually matched stimuli (CHEPs: 62 °C; LEPs: 55 °C), amplitudes were similar, but CHEPs latencies remained delayed. These differences could be explained by skin thermal inertia producing differences in the heating profile of contact vs radiant heat at the dermo-epidermal junction.

CONCLUSIONS: Provided that steep heating ramps are used, and that target temperature is matched at the dermo-epidermal junction, contact and radiant laser heat stimulation elicit responses of similar magnitude. CHEPs are delayed compared to LEPs.

SIGNIFICANCE: CHEPs could be used as an alternative to LEPs for the diagnosis of neuropathic pain. Dedicated normative values must be used to account for differences in skin thermal transfer.