Spasticity may obscure motor learning ability after stroke

Previous motor learning studies based on adapting movements of the hemiparetic arm in stroke subjects have not accounted for spasticity occurring in specific joint ranges (spasticity zones), resulting in equivocal conclusions about learning capacity. We compared the ability of participants with stroke to rapidly adapt elbow extension movements to changing external load conditions outside and inside spasticity zones. Participants with stroke (n=12, aged: 57.8±9.6 years) and healthy age-matched controls (n=8, 63.5±9.1 years) made rapid 40-50° horizontal elbow extension movements from an initial (3°) to a final (6°) target. Sixteen blocks (6-10 trials/block) consisting of alternating loaded (30% MVC) and non-loaded trials were made in one (controls) or two sessions (stroke; 1 wk apart). For the stroke group, the tonic stretch reflex threshold angle at which elbow flexors began to be activated during passive elbow extension was used to identify the beginning of the spasticity zone. The task was repeated in joint ranges that did or did not include the spasticity zone. Error correction strategies were identified by the angular positions before correction and compared between groups and sessions. Changes in load condition from no-load to load and vice-versa resulted in undershoot and overshoot errors respectively. Stroke subjects corrected errors in 1-4 trials compared to 1-2 trials in controls. When movements did not include the spasticity zone, there was an immediate decrease in the number of trials needed to restore accuracy, suggesting that the capacity to learn may be preserved after stroke but masked by the presence of spasticity.

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