Movement initiation and inhibition are impaired in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) features central and peripheral paresis owing to the degeneration of upper and lower motor neurons. Here, we asked whether motor preparation and inhibition are also affected. Thirteen ALS patients and thirteen matched controls participated in an event-related brain potentials (ERP) experiment in which a cue stimulus indicated whether the following target stimulus was to be responded to by the left or the right hand by a speeded button press. In 25% of the trials a stop-signal followed the target stimulus (onset asynchrony 150 ms) indicating that participants had to abort the already initiated motor response. ERPs indicated deficits of the ALS patients in the preparation and inhibition of motor responses: The lateralized readiness potential indicating motor preparation had a grossly reduced amplitude. A right frontal negative component following about 200 ms after the stop-signal and known to indicate inhibitory processes was diminished in amplitude and prolonged in latency in ALS. Finally, a later negative component associated with error processing was also reduced in amplitude in ALS. These electrophysiological changes were accompanied by behavioral deficits in the patient group (less efficient stopping of movements, no reaction time adaptation after stop trials). In conclusion, ALS patients showed deficits in both, movement initiation and inhibition, with the latter associated with prefrontal dysfunction.