ABNORMAL EPSPS EVOKED BY MAGNETIC BRAIN-STIMULATION IN HAND MUSCLE MOTONEURONS OF PATIENTS WITH AMYOTROPHIC-LATERAL-SCLEROSIS

Using cross-correlation between magnetic brain stimulation and discharges of a motoneuron made active by a slight voluntary contraction, an indirect estimate of the EPSP evoked by magnetic brain stimulation in single hand muscle motoneurons was obtained in patients with amyotrophic lateral sclerosis (ALS) and normal controls. In total, 60 motoneurons of 3 normal subjects and 70 motoneurons of 7 patients with ALS were investigated. All motoneurons of normal subjects responded to the magnetic brain stimulus with a short-latency EPSP with a rise time between 1 and 5 msec. In contrast, only 67% of the motoneurons from ALS patients responded with an EPSP while the remaining 33% exhibited a clear short-latency inhibition in response to the brain stimulus. For those units of ALS patients showing an EPSP, both latency and EPSP amplitude were indistinguishable from those of normal subjects. The EPSP rise time, however, was massively prolonged in some units (up to 18 msec). These results provide a physiological basis for the interpretation of surface EMG responses in patients with ALS.