Functional imaging and neurophysiological assessment of spinal and brain therapeutic modulation in humans

Fire summarize here our experience in the neurophysiological and neuroimagi ng assessment of spinal and brain neuromodulation for pain relief. Techniqu es reviewed include somatosensory evoked potentials (SEPs), nociceptive spi nal (Rm) reflexes, and positron emission tomography (PET), which have been applied both to investigate the mechanisms and to optimize the application of neurostimulation procedures. SEPs are especially useful in the preoperat ive assessment of patients with neuropathic pain, as they allow the establi shment of the functional state of the dorsal column system. Patients with s trongly abnormal SEPs due to ganglionic or preganglionic pathology are not likely to benefit from spinal (SCS) or peripheral (TENS) neurostimulation, because ascending fibers disconnected from their soma will undergo rapid de generation and not be excitable. In the postoperative period, nociceptive s pinal reflexes yield objective data concerning the effects of neurostimulat ion on spinal circuitry. In our experience, the best clinical results are a chieved in patients with preserved preoperative SEPs, in whom neurostimulat ion entails profound attenuation of nociceptive reflexes. PET-scan imaging techniques have recently been used to demonstrate changes in cerebral blood flow during new neuromodulation schemes such as motor cor tex stimulation for pain control (MCS). PET studies highlight the thalamus as the key structure mediating functional MCS effects. Thalamic activation would trigger a cascade of synaptic events influencing activity in other pa in-related structures including the anterior cingulate gyrus, insula, and u pper brainstem. The combination of clinical electrophysiology and functiona l neuroimaging provides insight into the mechanisms of action of neuromodul ation procedures, guides clinical decision, and contributes to optimize pat ient selection. (C) 2000 IMSS, Published by Elsevier Science Inc.