Microelectrode techniques in localization of stereotactic targets.

Although physiological corroboration of the target is essential in functional stereotactic surgery, the collected data can also be used for the offline study of normal and abnormal brain function. Such studies have the advantage of being made in actual clinical states with the unique opportunity of communicating with the patient. Correlations were made between microelectrode recordings and microstimulation at the same thalamic site with the same microelectrode in 'normal' patients, in those with tremor and in those with central and deafferentation pain. Human somatosensory organization is similar to that of subhuman primates. Five types of tremor cells have been identified-unresponsive nonsynchronous, unresponsive synchronous, kinaesthetic, voluntary, and voluntary with receptive field. While the last two qualify in latency and connectivity as tremor pacemakers, system analysis suggests an important element of long loop feedback as well. In the pain patients, five features were identified-somatotopic reorganization, altered firing in reorganized cells, bursting cells induction of burning widespread in thalamus and reproduction of the patient's pain by microstimulation-possibly a 'central allodynia' found in deafferented somatosensory thalamus particularly in patients with allodynia or hyperpathia. All but the latter effects may be merely the consequence of deafferentation and were seen in a 'control' stroke patient with dystonia, sensory loss but no pain.