Biology subjects

Courtin, A. S.

Publications and source records attributed to Courtin, A. S..

3 recordsLinked to original sources

bioRxiv2024

Evidence of interplays between the vascular and nociceptive systems revealed by changes in capsaicin pain caused by limb position change

This experiment aimed at confirming our incidental observation that, when capsaicin is applied on the volar forearm, raising the arm to a vertical position leads to a dramatic increase in capsaicin-evoked pain and to explore possible underlying mechanisms. Twenty healthy volunteers received a 2% capsaicin patch on one forearm and a vehicle patch on the other. Patches were kept in place for 60 minutes. The sensation caused by the patch was assessed repeatedly -in resting position and when the arm was raised vertically-before, during and after patch application. In addition, capsaicin-induced secondary hyperalgesia was assessed using mechanical pinprick stimuli. Half of the participants were seated upright while the other half were lying supine, to assess whether the effect of limb position was due to gravity. After a few minutes of patch application, raising the capsaicin treated arm (but not the vehicle treated arm) led to a strong increase of the pain experienced at the patch. This effect of raising the arm did not differ between participants in the supine and seated groups and is therefore likely related to the position of the arm relative to the ground (gravity) rather than to the body. Mechanical secondary hyperalgesia and the arm raising effect were strongly decorrelated at the last time point after patch removal, indicating different underlying mechanisms. Our results indicate that capsaicin-evoked pain can be strongly modulated by limb posture and that this effect may be caused by an interplay between vascular and nociceptive systems.

neuroscience↗

bioRxiv2024

Exploration of the EEG response to periodic thermal and vibrotactile stimuli

Under certain conditions, a stimulus applied at a given frequency will lead to a periodic variation of neural activity at the same frequency. Taking advantage of this periodicity, it is possible to tag this response in the EEG frequency spectrum. Frequency tagging of sustained periodic noxious heat stimuli led to the recording of phase-locked and non-phase-locked responses whose functional significance remains unclear. This study aimed at assessing whether such responses can also be recorded during the repetitive presentation of brief innocuous cold, noxious heat and vibrotactile stimuli. Comparison between the responses obtained with different stimulation modalities should inform us on the nature of the neural processes underlying these responses (modality aspecific, somatosensory, thermosensory, nociceptive). Comparison between upper and lower limb stimulation should inform us on the somatotopic organization of these responses and, therefore, on their potential sources. Based on our results, on one hand, trains of brief innocuous cold, noxious heat and vibrations can elicit phase-locked and non-phase-locked responses which appear highly similar to those evoked by sustained periodic noxious heat stimuli when frequency tagged. On the other hand, when analysed in the time domain or using time-frequency decomposition, these responses appeared highly similar to those that can be recorded following isolated brief noxious heat or tactile stimuli. These responses consisted in phase-locked activity corresponding to the vertex potential, thought to reflect modality non-specific attentional processes, and in an alpha-to-beta ERD originating in the S1/M1 area contralateral to the stimulated hand, probably reflecting non-specific somatosensory activity.

neuroscience↗

bioRxiv2023

Temporal Contrast Enhancement in Thermosensation: A Framework for Understanding Paradoxical Heat Sensation

Paradoxical Heat Sensation (PHS) is the remarkable feeling of warmth or heat pain while the skin is cooling. Despite its initial documentation over 100 years ago, a unified explanation for this perplexing experience remains elusive. Here we apply contrast enhancement principles, known for their instrumental role in understanding visual illusions, to the domain of thermosensation. Contrast enhancement describes the amplification of two contrasting visual features, such as the enhanced perception of an edge between a light and dark bar. In thermosensation, this encompasses an enhancement of the difference between sequential warming and cooling of the skin, and is defined as the normalised difference between successive temporal warm and cold temperatures. Remarkably, thermal contrast predicts the occurrence of PHS. Our findings reveal compelling evidence supporting the role of thermal contrast in the generation of PHS, shedding light on its underlying mechanism and offering a framework for broader encoding principles in thermosensation and pain.

neuroscience↗