Abstract
The interaction between pain and the motor system is well-known, with past studies showing that pain can alter corticomotor excitability and have deleterious effects on motor learning. The aim of this study was to better understand the cortical mechanisms underlying the interaction between pain and the motor system. Experimental pain was induced on 19 young and healthy participants using capsaicin cream, applied on the middle volar part of the left forearm. The effect of pain on brain activity and on the corticomotor system was assessed with electroencephalography (EEG) and transcranial magnetic stimulation (TMS), respectively. Compared to baseline, resting state brain activity significantly increased after capsaicin application in the central cuneus (theta frequency), left dorsolateral prefrontal cortex (alpha frequency), and left cuneus and right insula (beta frequency). A pain-evoked increase in the right primary motor cortex (M1) activity was also observed (beta frequency), but only among participants who showed a reduction in corticospinal output (as depicted by TMS recruitment curves). These participants further showed greater beta M1-cuneus connectivity than the other participants. These findings indicate that pain-evoked increases in M1 beta power are intimately tied to changes in the corticospinal system, and provide evidence that beta M1-cuneus connectivity is related to the corticomotor alterations induced by pain. The differential pattern of response observed in our participants suggest that the effect of pain on the motor system is variable from on individual to another; an observation that could have important clinical implications for rehabilitation professionals working with pain patients.
Highlights
Pain is a rapidly growing area of research, and the last years have shown huge advancement in our understanding of its neurophysiological process
The differential pattern of response observed in our participants suggest that the effect of pain on the motor system is variable from on individual to another; an observation that could have important clinical implications for rehabilitation professionals working with pain patients
The absence of difference between the two conditions was confirmed by the statistical analysis, with the paired-sample t test showing no difference in hierarchical linear modeling (HLM) slope values between the baseline and pain condition (p = 0.26)
Summary
Pain is a rapidly growing area of research, and the last years have shown huge advancement in our understanding of its neurophysiological process. A few neuroimagery studies have reported an increase in the activity of the primary motor cortex (M1) in the presence of experimental pain (Apkarian et al 2000; Tracey et al 2000; Burns et al 2016). Stancák et al demonstrated, using electroencephalography (EEG), that the application of a short-lasting painful heat stimuli on the hand decreased the β activity of the sensorimotor cortex (Stancák et al 2007). Exp Brain Res (2017) 235:1223–1231 decrease in M1 β activity noted by Stancák and colleagues suggests that the presence of a brief nociceptive stimulus could prime the motor brain regions (reduced inhibition), possibly to facilitate motor withdrawal responses. The results obtained by Stancák and colleagues were obtained following the application of brief/escapable, nociceptive stimuli and it remains uncertain whether the same pattern of results would be obtained with longer/unavoidable nociceptive stimulations
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