Nociceptive contribution to the evoked potentials after painful intramuscular electrical stimulation.

Our study aimed at investigating the nociceptive contribution to the somatosensory evoked potentials after electrical intramuscular stimulation (mSEPs) at painful intensity. Scalp mSEPs were recorded in 10 healthy subjects after electrical stimulation of the left brachioradialis muscle at three intensities: non-painful (I2), slightly painful (I4) and moderately painful (I6). For each intensity, mSEPs were recorded in a neutral condition (NC) in which subjects did not have any task, and in an attention condition (AC) in which subjects were asked to count the number of stimuli. In both NC and AC, the N120 and P220 amplitudes were significantly higher at I6 than at I2. While the N120 amplitude did not vary between NC and AC, the P220 amplitude was significantly higher in AC than in NC at all stimulus intensities. Our results suggest that nociceptive inputs contribute to the N120 amplitude increase at painful stimulus intensity, while the P220 amplitude is more sensitive to changes of subjects' attention level. Therefore, the N120 amplitude increase to moderately painful stimuli, as compared to non-painful stimuli, may represent a marker of the activation of the muscular thin myelinated afferents.