Psychophysiological aspects of voluntary skilled movement after stroke: a follow-up study

The aim of the study was to follow the psychophysiological evolution of a self-paced voluntary skilled movement in hemiparetic subjects after ischemic stroke by means of a skilled performance task (SPT). The task consisted in starting a sweep of an oscilloscope trace by pushing one button with the left index finger (trigger point), and in stopping it within a central area on the oscilloscope screen, between 40 and 60 ms (correct performance) after the start of the sweep, by pushing the other button with the right index finger. A SPT yields a considerable amount of information on the electrophysiological components, which reflect pre-programming activity (Bereitschaftspotential--BP), control strategies (Skilled Performance Positivity--SPP) and behavioural response (Correct Performances). The study was also aimed at detecting any longitudinal changes in the psychophysiological pattern, as evaluated by the clinical examination and specific motility scales, that parallel motor recovery.

Movement related potentials (MRPs) were recorded in 12 control subjects and 9 patients in the acute phase, before the start of neurorehabilitation (time 0), when the patients were able to execute an index finger press with the affected hand. The patients (mean age = 62.33 years, SD = 8.17) presented a mild to moderate central arm paresis caused by a first-ever unilateral supratentorial and subcortical ischemic lesion. The subsequent recordings were carried out respectively 3, 9 and 12 months later.

At the first recording, hemiparetic patients achieved a significantly lower percentage of correct performances and had a lower BP amplitude than controls (p < 0.001); SPP was absent. The number of correct performances did not improve significantly during the subsequent recordings. BP amplitude showed a mild increase in the second, third and fourth recordings (p < 0.05), while SPP amplitude revealed a slight improvement at the second and a marked improvement at the third and fourth recordings, when there was no longer a statistically significant difference from controls.

Our findings point to an early recovery of pre-programming activity and a delayed improvement in control activity. The delayed development of control activity in the absence of procedural learning, i.e. skill learning through practice, forces patients to exploit attentional strategies to compensate for their procedural learning impairment. SPT shows that the efficacy of physical therapy aimed at motor ability recovery in hemiparetic patients does not keep up with the slow recovery process of an automatic motor level.