Cool evoked potentials: characterizing values for healthy subjects

Background: Laser evoked potentials are gold-standard for the assessment of spinothalamic tract integrity in neuropathic pain. However, they have several shortcomings. Cool evoked potentials might be an interesting technique to, at least, complement LEPs. Aims: The aim of this study was to characterise (latency, amplitude, topography) CEPs elicited by very fast cooling of the skin (up to 300°C/s) in healthy humans. Method : In a first experiment (21 participants aged 23.4 ± 4.8 years), cold stimuli (cooling the skin down to 10°C, slope: -300°C/s) were delivered using two surface areas: 38 and 115 mm². For each condition, 80 stimuli were applied to the volar forearm, with an inter-stimulus interval of, at least, 8s. Participants were asked to rate the intensity of the sensation elicited by every stimulus. In a second experiment (21 participants aged 24.8 ± 4.2 years), cold stimuli (surface area: 115 mm2) were delivered using four different temperature decreases (-5, -10, -15 and -20°C relative to baseline) and two different slopes (-133 and -200°C/s). For each condition, 20 stimuli were applied, with an inter-stimulus interval of approximatively 12 s. Intensity rating were asked after 5 stimulations of the same condition were delivered. Results : Clear CEPs were obtained in each participant and condition. The waveforms consisted of an early N1/P1 wave (≈172 ms) maximal over contralateral parietal electrodes, followed by an N2 wave (≈240 ms) also maximal over the contralateral hemisphere and a later P2 wave (≈420 ms) maximal over the vertex