Aδ nociceptor response to laser stimuli: Selective effect of stimulus duration on skin temperature, brain potentials and pain perception

Objective: To disclose a possible effect of duration of pulsed laser heat stimuli on Aδ nociceptor responses, skin temperature profiles, brain evoked potentials and pain perception. Methods: We used a laser stimulator which works in the millisecond range and allows us to change the duration of the pulse while keeping the total energy of the stimulus constant. In 10 healthy volunteers, we measured the intensity of perceived pain with a 0-10 scale and the latency and amplitude of the early N1 and late N2 components of the scalp potentials evoked by laser pulses of equal energy and three different stimulus durations (2, 10, and 20 ms). Using a specifically developed pyrometer with a temporal resolution lower than 1 ms we also measured stimulus-induced changes of skin temperature. Results: Stimulus duration significantly influenced temperature rise times, pain perception, and brain potentials. Shorter stimulus durations yielded steeper slopes in the skin temperature profiles and higher pain ratings, shortened the latency of the N1 and N2 components, and increased the amplitude of N1. Conclusions and significance: The shorter stimulus duration shortens receptor activation times and yields a more synchronous afferent volley, thus providing a stronger spatial-temporal summation at central synapses that enhances intensity of first pain and brain potentials. This may prove useful in clinical applications. © 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.