Investigating the potential role of arousal in multisensory hypersensitivity

Filbrich, Lieve [UCL] Torta, Diana [UCL]

Recent studies have shown that experimentally induced long-lasting sensitization of nociceptive pathways in healthy human volunteers not only leads to the typically-observed hypersensitivity to mechanical pinprick stimuli, but also to an enhanced processing of non-nociceptive stimuli, as shown by amplitude increases in the cortical responses to visual and vibrotactile stimuli presented on a sensitized as compared to a non-sensitized body part. These latter effects have been hypothesized to share similarities with the hypersensitivity to a plethora of sensory stimuli that has been reported for some chronic pain conditions, such as fibromyalgia. However, to date, the mechanisms leading to such multisensory hypersensitivity remain unexplained, since they cannot be accounted for by the spinal mechanisms that increase pain perception after sensitization. We will present a study protocol that investigates whether increased arousal, triggered by the intense stimulation of the nociceptors, may be a potential underlying mechanism of both nociceptive and non-nociceptive hypersensitivity. In a between-subject design, we will use two different sensitization procedures (burst vs. continuous electrical stimulation applied on the arm during two minutes) in healthy participants and investigate 1) whether burst stimulation, which typically leads to higher nociceptive hypersensitivity, is also associated with higher arousal than continuous stimulation, by testing differences in mechanical pinprick sensitivity and arousal, measured as skin conductance level (SCL) before, during and after the sensitization, between the two procedures; 2) differences in somatosensory evoked potentials (SEPs) to vibrotactile stimuli on the sensitized vs. control arm; 3) the relationship between SCL and SEPs/mechanical pinprick sensitivity.