MIDDLE CEREBRAL ARTERY STROKE IMPAIRS TRANSFER OF LEARNING FOR COMPLEX BUT NOT SIMPLE MOTOR SEQUENCES

Abstract

Purpose/Hypothesis: The purpose of this series of experiments was to consider whether capability for transfer of sequence learning after stroke is influenced by motor task complexity. Number of Subjects: Two experiments tested the hypothesis that transfer of motor learning is deleteriously impacted by sequence complexity. In experiment 1, 10 individuals with middle cerebral artery (MCA) stroke (ST-C, 63 y/o) and 10 age-matched controls (AM-C, 64 y/o) practiced a complex motor sequence. In experiment 2, a different cohort of 10 people with MCA stroke (ST-S, 57 y/o) and 10 age-matched controls (AM-S, 58 y/o) learned a simple motor sequence. Materials/Methods: In experiment 1, all participants practiced a complex sequence (constructed to contain separate motor, spatial and temporal elements) for 2 days and returned on day 3 for retention and transfer tests. To test our hypothesis that sequence complexity explains transfer ability after stroke, experiment 2 followed the same procedures but employed a simple sequence of motor responses. Information theory indexed sequence complexity; the complex sequence (exp. 1) required 57 bits of information to be learned, while the simple sequence (exp. 2) contained 12 bits. Results: In experiment 1, both ST-C and AM-C groups significantly decreased their response times across acquisition practice (p=.00), and demonstrated learning of the complex motor sequence at retention (ST-C p=.03; AM-C p=.01). However, individuals with stroke did not demonstrate transfer of learning for any of the elements of the complex task; the AM-C group showed significant transfer of the motor element (p=.00). In contrast, in experiment 2 both individuals with stroke and age-matched controls demonstrated improved acquisition performance (p=.00), sequence learning at retention (ST-S p=.03; AM-S p=.00), and transfer (ST-S p=.01; AM-S p=00). Across experiments, there were no significant between group differences (e.g., age) that would explain our findings. Conclusions: Past experiments have demonstrated preserved capability for motor learning after stroke; however, little work has employed more robust assessments of motor learning such as transfer. This raises the possibility that motor learning after stroke might be skill-specific; indeed our findings suggest that as sequence complexity increases the ability to transfer learning to other related tasks is impaired. Because we quantified complexity using information theory we were able to control the amount of information that had to be learned in each experiment. Clinical Relevance: These data suggest that after stroke motor learning may be specific to the practiced sequence or task. The negative effect of complexity on transfer is particularly relevant for physical therapists who facilitate motor skill learning after stroke. If motor learning is sequence-specific after stroke, practice of complex motor skills (such as tasks of daily life) may be most effective when it occurs in an environment that closely resembles that in which the behavior will be performed.