title: EEG frequency tagging using ultra-slow periodic heat stimulation of the skin reveals cortical activity specifically related to C fiber thermonociceptors.
abstract: The recording of event-related brain potentials triggered by a transient heat stimulus is used extensively to study nociception and diagnose lesions or dysfunctions of the nociceptive system in humans. However, these responses are related exclusively to the activation of a specific subclass of nociceptive afferents: quickly-adapting thermonociceptors. In fact, except if the activation of Aδ fibers is avoided or if A fibers are blocked, these responses specifically reflect activity triggered by the activation of Type 2 quickly-adapting A fiber mechano-heat nociceptors (AMH-2). Here, we propose a novel method to isolate, in the human electroencephalogram (EEG), cortical activity related to the sustained periodic activation of heat-sensitive thermonociceptors, using very slow (0.2Hz) and long-lasting (75s) sinusoidal heat stimulation of the skin between baseline and 50°C. In a first experiment, we show that when such long-lasting thermal stimuli are applied to the hand dorsum of healthy volunteers, the slow rises and decreases of skin temperature elicit a consistent periodic EEG response at 0.2Hz and its harmonics, as well as a periodic modulation of the magnitude of theta, alpha and beta band EEG oscillations. In a second experiment, we demonstrate using an A fiber block that these EEG responses are predominantly conveyed by unmyelinated C fiber nociceptors. The proposed approach constitutes a novel mean to study C fiber function in humans, and to explore the cortical processing of tonic heat pain in physiological and pathological conditions.
authors.affiliation: Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium; Center for Pain and the Brain, Department of Anesthesiology, Perioperative and Pain Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA. Electronic address: elisabeth.colon@uclouvain.be.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Colon
authors.affiliation: Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Giulia
authors.initials: G
authors.lastname: Liberati
authors.affiliation: Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium.
authors.forename: André
authors.initials: A
authors.lastname: Mouraux
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology*; D004569:Electroencephalography; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology*; D059225:Nociception / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D012867:Skin / Q000294:innervation; D012879:Skin Physiological Phenomena; D013697:Thermosensing / Q000502:physiology*; D055815:Young Adult
keywords: C fiber; Electroencephalogram; Frequency-domain analysis; Heat; Laser stimulation; Thermoreceptors