IMPAIRED MOTOR CORTEX INHIBITION IN PATIENTS WITH AMYOTROPHIC-LATERAL-SCLEROSIS - EVIDENCE FROM PAIRED TRANSCRANIAL MAGNETIC STIMULATION

We investigated 14 patients with amyotrophic lateral sclerosis (ALS) b y paired conditioning-test transcranial magnetic stimulation to test t he hypothesis that the motor cortex is hyperexcitable in ALS. Intracor tical (corticocortical) inhibition was significantly less in ALS group than in an age-matched healthy control group (85.3 +/- 27.0% versus 4 5.2 +/- 15.5%, respectively; p < 0.0001). In contrast, intracortical f acilitation, motor threshold, and cortical silent period duration in t he ALS patients were not different from the control group. We suggest that the selective abnormality of intracortical inhibition is best com patible with an impaired function of inhibitory interneuronal circuits in the motor cortex than in turn renders the corticomotoneuron hypere xcitable.