Electrical stimulation of motor cortex for pain control: a combined PET-scan and electrophysiological study

Although electrical stimulation of the precentral gyrus (MCS) is emerging a s a promising technique for pain control, its mechanisms of action remain o bscure, and its application largely empirical. Using positron emission tomo graphy (PET) we studied regional changes in cerebral flood flow (rCBF) in 1 0 patients undergoing motor cortex stimulation for pain control, seven of w hom also underwent somatosensory evoked potentials and nociceptive spinal r eflex recordings. The most significant MCS-related increase in rCBF concern ed the ventral-lateral thalamus, probably reflecting cortico-thalamic conne ctions from motor areas. CBF increases were also observed in medial thalamu s, anterior cingulate/orbitofrontal cortex, anterior insula and upper brain stem; conversely, no significant CBF changes appeared in motor areas beneat h the stimulating electrode. Somatosensory evoked potentials from SI remain ed stable during MCS, and no rCBF changes were observed in somatosensory co rtex during the procedure. Our results suggest that descending axons, rathe r than apical dendrites, are primarily activated by MCS, and highlight the thalamus as the key structure mediating functional MCS effects. A model of MCS action is proposed, whereby activation of thalamic nuclei directly conn ected with motor and premotor cortices would entail a cascade of synaptic e vents in pain-related structures receiving afferents from these nuclei, inc luding the medial thalamus, anterior cingulate and upper brainstem. MCS cou ld influence the affective-emotional component of chronic pain by way of ci ngulate/orbitofrontal activation, and lead to descending inhibition of pain impulses by activation of the brainstem, also suggested by attenuation of spinal flexion reflexes. In contrast, the hypothesis of somatosensory corte x activation by MICS could not be confirmed by our results. (C) 1999 Intern ational Association for the Study of Pain. Published by Elsevier Science B. V.