The effect of heterotopic noxious conditioning stimulation on Aδ-, C- and Aβ-fibre brain responses in humans

• Published in: The European journal of neuroscience 2015-11, Vol.42 (9), p.2707-2715
• Main Authors: Torta, Diana M., Churyukanov, Maxim V., Plaghki, Leon, Mouraux, André
• Format: Article
• Language: English
• Subjects: Adult; Cerebral Cortex - physiology; cold pressor test; Cold Temperature; diffuse noxious inhibitory control; Electric Stimulation; Electroencephalography; event-related potentials; Evoked Potentials; Female; heterotopic noxious conditioning stimuli; Humans; Lasers; Male; Middle Aged; Nerve Fibers, Myelinated - physiology; Nerve Fibers, Unmyelinated - physiology; Nociception - physiology; pain; Pain Measurement; Pain Threshold - physiology; Physical Stimulation; Young Adult
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.13071

Human studies have shown that heterotopic nociceptive conditioning stimulation (HNCS) applied to a given body location reduces the percept and brain responses elicited by noxious test stimuli delivered at a remote body location. It remains unclear to what extent this effect of HNCS relies on the spinal–bulbar–spinal loop mediating the effect of diffuse noxious inhibitory controls (DNICs) described in animals, and/or on top‐down cortical mechanisms modulating nociception. Importantly, some studies have examined the effects of HNCS on the brain responses to nociceptive input conveyed by Aδ‐fibres. In contrast, no studies have explored the effects of HNCS on the responses to selective nociceptive C‐fibre input and non‐nociceptive Aβ‐fibre input. In this study, we measured the intensity of perception and event‐related potentials (ERPs) to stimuli activating Aδ‐, C‐ and Aβ‐fibres, before, during and after HNCS, obtained by immersing one foot in painful cold water. We observed that (i) the perceived intensity of nociceptive Aδ‐ and C‐stimuli was reduced during HNCS, and (ii) the ERPs elicited by Aδ‐ and Aβ‐ and C‐stimuli were also reduced during HNCS. Importantly, because Aβ‐ERPs are related to primary afferents that ascend directly through the dorsal columns without being relayed at spinal level, the modulation of these responses may not be explained by an influence of descending projections modulating the transmission of nociceptive input at spinal level. Therefore, our results indicate that, in humans, HNCS should be used with caution as a direct measure of DNIC‐related mechanisms. In this study we have measured the intensity of perception and event related potentials (ERPs) to stimuli activating Aδ‐, C‐ and Aβ‐fibers, before, during and after HNCS, obtained by immersing one foot in painful cold water. We have observed that (i) the perceived intensity of nociceptive Aδ‐ and C‐ stimuli is reduced during HNCS, (ii) the ERPs elicited by Aδ‐ and Aβ‐, and C‐ stimuli are also reduced during HNCS. Importantly, because Aβ‐ERPs are related to primary afferents that ascend directly through the dorsal columns without being relayed at spinal level, the modulation of these responses may not be explained by an influence of descending projections modulating the transmission of nociceptive input at spinal level. Therefore, our results indicate that, in humans, HNCS should be used with caution as a direct measure of DNIC‐related mechanisms.