The Effects of Unpleasant Thermal and Auditory Stimulus on Forearm Muscle Activity During Discrete and Continuous Wrist Movements

Experimental models of pain have demonstrated alterations in motor control in healthy subjects. However, pain involves different dimensions (cognitive-evaluative and affective-motivational, and sensory-discriminative) that have not been studied separately. Indeed, an aversive auditory stimulus is known to produce an unpleasant experience similar to a conventional thermal pain stimulus and may mobilize the cognitive-evaluative and affective-motivational dimensions of pain. The aim of this study was to evaluate forearm muscle activity using surface electromyography (sEMG) during discrete and continuous wrist movements in the presence of thermal and auditory stimuli compared to a control condition. Sixteen healthy subjects were recruited. The conditions were administered to each participant in a randomized order. Participants were instructed to perform a full range of wrist movements in both a discrete (single movement) and continuous (repetitive movements) modality. The auditory and control conditions did not alter motor activity, whereas the thermal stimulus increased wrist extensor activity only during the continuous movement modality. Other types of sEMG analysis (timing and frequency) were not affected by stimulus type. These results suggest that the cognitive-evaluative and affective-motivational dimensions of pain may not affect muscle activity, whereas the sensory-discriminative dimensions may be more susceptible to altering motor function.