Contact heat evoked potentials as a valid means to study nociceptive pathways in human subjects Andrew C.N. Chen * , David M. Niddam, Lars Arendt-Nielsen Human Brain Mappingand Cortical Imaging Laboratory, The International Doctoral School in Biomedical Sciences and Engineering, Centre for Sensory–Motor Interaction, Aalborg University, Fredrik Bajer Vej 7, D-3, Aalborg 9220, Denmark Received 9 August 2001; received in revised form 10 October 2001; accepted 10 October 2001 Abstract Contact heat evoked potentials (CHEPs) have been difficult to elicit due to slow temperature rise times. A recently developed heat-foil technology was used to elicit pain and CHEPs. Two groups of subjects were separately stimulated at the left arm with contact heat via one fast-acting (708C/s) heat-foil thermode. A set of CHEPs was recorded, each at three subjective intensities: warm; slight; and moderate pain. In CHEPs, the 3D topography exhibited four components: T3–T4/ N450; Cz/N550; Cz/P750; and Pz/P1000. A vertex topography map was observed in the late Cz/N550–Cz/P750 and parietal topography in the very-late Pz/P1000 components. Consistent statistical values in the peak latencies and amplitudes were noted between consecutive investigations. The correlation between the pain intensity ratings and the major Cz/ P750 amplitudes was highly significant in each study. Our validity tests suggested CHEPs to be useful for research and clinical applications in studying human pain activation related to thermal and nociceptive pathways. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Contact heat evoked potentials; Pain perception; Late/very-late components; Consistency; Thin-fibre afferent Although heat pain examined by laser evoked potentials (LEPs) has been studied for 25 years [2,6], the coherent beam and its small stimulation area (,5 mm diameter) may not constitute a natural activation as in contact heat. In addition, laser stimuli are too brief to simulate real life experience of thermal pain, especially the nagging quality of deep pain associated with natural thermal injury. LEPs often consist of late [3], and even ultra-late, vertex potentials [1]. Ultra-late LEPs, first found in a nerve block study [4], can be obtained by a specially designed apparatus of tiny beam [1], rectified cohesive beam [13] and a thin hole in metal film [16]. Nevertheless, it is quite difficult to directly record the brain potentials of C-fibre thin afferents by the available laser stimulation unless specific adjustment is implemented. One further drawback is that lasers often cause superficial burns lasting several days with hyper-pigmented spots. The laser apparatus is also expensive, and difficult to calibrate and operate. Contact heat can generally evoke both fast and slow pain. However, due to its slow rising and falling times, the aver- aged evoked potentials to contact heat have rarely been studied. Here, we report a newly developed heat-foil with a rapid rising time at 708C/s to elicit contact heat evoked potentials (CHEPs). The aims of this study were to: (a), examine the 3D spatio-temporal dynamic topography of CHEPs; (b), extract the major components in CHEPs; (c), relate these components to heat pain perception; and finally (d), investigate the consistency of CHEPs for potential use in clinical applications. CHEPs were recorded from two separate groups of 13 (Study-I: age, 25.5 ^ 4.1) and ten (Study-II: age, 26.8 ^ 5.2) males studied independently 2 months apart; informed consent was obtained from each subject. Contact heat was delivered via one 2 cm circular (3.14 cm 2 ), fast- acting (708C/s), heat-foil thermode (Minco Products, Inc., USA), which is a resistive heating element. Pulsed thermal stimuli were delivered by a computer-controlled stimulator via one thermode [12]. Heat pulses were sent from the base- line (adaptive temperature, 31.58C) using an adjustable power for 300 ms at three intensity levels (Fig. 1). The stimuli were applied within the volar surface of the forearm in the left hand. The subject could withdraw his hand if the stimulus was intolerable. The subject was instructed to move the arm and area of thermode contact Neuroscience Letters 316 (2001) 79–82 0304-3940/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S0304-3940(01)02374-6 www.elsevier.com/locate/neulet * Corresponding author. Tel.: 145-9635-9826; fax: 145-9815- 4008. E-mail address: ac@smi.auc.dk (A.C.N. Chen).