Motor cortex abnormalities in amyotrophic lateral sclerosis with transcranial direct-current stimulation.

The aim of this study was to identify a neurophysiological marker of upper motoneuron involvement in patients with sporadic amyotrophic lateral sclerosis (ALS). For this purpose we evaluated the after-effects of transcranial direct-current stimulation (tDCS) on excitability of the motor cortex of eight ALS patients and eight healthy controls. Healthy controls showed a transient polarity-specific change in corticospinal excitability of about +/-45%, with anodal tDCS inducing facilitation and cathodal tDCS leading to inhibition, whereas no change could be induced in ALS patients after either type of tDCS. It is likely that the lack of tDCS after-effects in ALS is the result of alterations of the motoneuronal membrane or, alternatively, may represent an electrophysiological correlate of disordered glutamate neurotransmission. Further studies are warranted to confirm these results. The present findings may lead to a new, reliable electrophysiological marker of upper motoneuronal involvement in ALS.