MICROELECTRODE-GUIDED PALLIDOTOMY - TECHNICAL APPROACH AND ITS APPLICATION IN MEDICALLY INTRACTABLE PARKINSONS-DISEASE

Object. The authors describe the microelectrode recording and stimulat ion techniques used for localizing the caudal sensorimotor portion of the globus pallidus internus (GPI) and nearby structures (internal cap sule and optic tract) in patients undergoing GPI pallidotomy. Methods. Localization is achieved by developing a topographic map of the above mentioned structures based on the physiological characteristics of neu rons in the basal ganglia and the microexcitable properties of the int ernal capsule and optic tract. The location of the caudal GPi can be d etermined by ''form fitting'' the physiological map on relevant planes of a stereotactic atlas. A sensorimotor map can be developed by asses sing neuronal responses to passive manipulation or active movement of the limbs and orofacial structures. The internal capsule and optic tra ct, respectively, can be identified by the presence of stimulation-evo ked movement or the patient's report of flashes or speckles of light t hat occur coincident with stimulation. The optic tract may also be loc ated by identifying the neural response to flashes of light. The anato mical/physiological map is used to guide lesion placement within the s ensorimotor portion of the pallidum while sparing nearby structures, f or example, the external globus pallidus, nucleus basalis, optic tract , and internal capsule. The lesion location and size predicted by usin g physiological recording together with thin-slice high-resolution mag netic resonance imaging reconstructions of the lesion were confirmed i n one patient on histological studies. Conclusions. These data provide important information concerning target identification for ablative o r deep brain stimulation procedures in idiopathic Parkinson's disease and other movement disorders.