title: Human brain responses to concomitant stimulation of Aδ and C nociceptors.
abstract: Intense radiant heat pulses concomitantly activate Aδ- and C-fiber skin nociceptors, and elicit a typical double sensation: an initial Aδ-related pricking pain is followed by a C-related prolonged burning sensation. It has been repeatedly reported that C-fiber laser-evoked potentials (C-LEPs) become detectable only when the concomitant activation of Aδ-fibers is avoided or reduced. Given that the saliency of the eliciting stimulus is a major determinant of LEPs, one explanation for these observations is that the saliency of the C-input is smaller than that of the preceding Aδ-input. However, even if the saliency of the C-input is reduced because of the preceding Aδ-input, a C-LEP should still be visible even when preceded by an Aδ-LEP response. Here we tested this hypothesis by applying advanced signal processing techniques (peak alignment and time-frequency decomposition) to electroencephalographic data collected in two experiments conducted in 34 and 96 healthy participants. We show that, when using optimal stimulus parameters (delivering >80 stimuli within a small skin territory), C-LEPs can be reliably detected in most participants. Importantly, C-LEPs are observed even when preceded by Aδ-LEPs, both in average waveforms and single trials. By providing quantitative information about several response properties of C-LEPs (latency jitter, stimulus-response and perception-response functions, dependency on stimulus repetitions and stimulated area), these results define optimal parameters to record C-LEPs simply and reliably. These findings have important clinical implications for assessing small-fiber function in neuropathies and neuropathic pain.
authors.affiliation: Key Laboratory of Cognition and Personality (Ministry of Education) and School of Psychology, Southwest University, 400715 Chongqing, China, Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, 100101 Beijing, China, and huli@swu.edu.cn g.iannetti@ucl.ac.uk.
authors.forename: L
authors.initials: L
authors.lastname: Hu
authors.affiliation: Key Laboratory of Cognition and Personality (Ministry of Education) and School of Psychology, Southwest University, 400715 Chongqing, China.
authors.forename: M M
authors.initials: MM
authors.lastname: Cai
authors.affiliation: Key Laboratory of Cognition and Personality (Ministry of Education) and School of Psychology, Southwest University, 400715 Chongqing, China.
authors.forename: P
authors.initials: P
authors.lastname: Xiao
authors.affiliation: Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, 100101 Beijing, China, and.
authors.forename: F
authors.initials: F
authors.lastname: Luo
authors.affiliation: Department of Neuroscience, Physiology and Pharmacology, University College London, WC1E 6BT London, United Kingdom huli@swu.edu.cn g.iannetti@ucl.ac.uk.
authors.forename: G D
authors.initials: GD
authors.lastname: Iannetti
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000503:physiopathology*; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D007834:Lasers / Q000009:adverse effects; D008297:Male; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D011601:Psychophysics; D011930:Reaction Time / Q000502:physiology; D055815:Young Adult
keywords: Aδ-fibers; C-fibers; evoked potentials; first pain; nociception; second pain