Stimulation of human thalamus for pain relief: Possible modulatory circuits revealed by positron emission tomography

Stimulation of the somatosensory thalamus was used for more than 2 decades to treat chronic pain in the human. However, despite clinical reports of su ccessful results, little is known about the actual mechanisms mediating thi s form of stimulation-produced analgesia. To reveal possible neuronal pathw ays evoked by thalamic stimulation, we measured regional changes in cerebra l blood flow (rCBF) in five patients who received successful long-term reli ef of chronic pain with somatosensory thalamic stimulation. Positron emissi on tomography during thalamic stimulation revealed significant activation o f the thalamus in the region of the stimulating electrodes as well as activ ation of the insular cortex ipsilateral to the thalamic electrodes (contral ateral to the patients' clinical pain). For these patients, thalamic stimul ation also evoked paresthesiae that included thermal sensations in addition to tingling sensations. Results of this study indicate that in some cases somatosensory thalamic stimulation may activate a thalamocortical pain modu lation circuit that involves thermal pathways. These results are consistent with other recent reports suggesting that activation of thermal pathways m ay contribute to modulation of nociceptive information.