IPSILATERAL MOTOR ACTIVATION IN PATIENTS WITH CEREBRAL GLIOMAS

Objective: The aim of this study is to provide neurophysiologic eviden ce of ipsilateral hemispheric activation in patients affected by intra cerebral gliomas via the use of transcranial magnetic stimulation. Bac kground: The mechanisms involved in such ipsilateral activation have y et to be established, but they may involve preexisting routes that eit her are suppressed or undetected in the normal brain. Ipsilateral path ways may act in reserve, activated by the impairment of contralateral control. This hypothesis is suggested by the fact that the considerabl e size of the tumors in our patients is not matched by a proportionate loss of motor performance in the limbs contralateral to the affected hemisphere. However, it remains possible that ipsilateral motor-evoked potentials (iMEPs) may reflect reorganizational changes without signi ficant functional effects. Methods: The effects of such activation wer e investigated using both focal and nonfocal coils stimulating cortica l motor areas, with MEPs recorded from both left and right thenar musc les. Fifteen healthy control subjects and seven patients were examined . Results: iMEPs were generally absent in normal subjects, but in cont rast they were obtained in the patients by stimulating the healthy hem isphere using both round and figure-of-eight coils. Distinct from cont ralateral MEPs, iMEPs are obtained with higher thresholds (range, 60 t o 80% of stimulator output) and display longer latencies (20.9 msec ve rsus 19.4 msec). Conclusions: Taken in conjunction with recent researc h using functional imaging brain exploration and a variety of clinical , anatomic, and neurophysiologic studies, our results reflect a growin g awareness of ipsilateral motor control and its potential compensator y role when contralateral routes are damaged.