Compromised motor imagery ability in individuals with multiple sclerosis and mild physical disability: an ERP study.

Background: Motor imagery (MI) impairment has been reported in individuals with multiple sclerosis (MS). The present study was designed to investigate neural evidence for MI impairment and its relationship to working memory in MS patients.

Methods: The study participants included 24 early stage MS patients (age: 22-40/mean=32.7 years; M/F=4/20; years since duration: 1-10/mean=5.8) and 24 age-, gender-, and education-matched controls (age: 21-40/mean=31.8 years; M/F=5/19). Event-related potentials were recorded during a mental hand rotation task, in which participants were instructed to judge the laterality of hands displayed in different orientations. Furthermore, the Paced Auditory Serial Addition Test (PASAT) was used for assessment of working memory.

Results: At the behavioral level, MS patients were significantly less accurate and much slower (accuracy: 83.80 ± 7.72%; reaction time: 1665.95 ± 269.82 ms) than controls (accuracy: 88.35 ± 7.68%; reaction time: 1505.16 ± 225.11 ms). At the neural level, MS patients showed a significantly reduced amplitude (MS: 0.99 ± 0.89 μv, controls: 1.46 ± 1.00 μv) and delayed peak latency (MS: 458.45 ± 67.60 ms, controls: 417.91 ± 62.47 ms) at P3 for mental rotation effect. Moreover, there were significant correlations between individuals' PASAT scores and performance of the hand rotation task.

Conclusion: The results of the present study demonstrate MI impairment in patients with MS at both the behavioral and neural level. Neuronal activity dysfunction (decreased and delayed activity) in patients with MS provides new insights into MI impairment. Furthermore, our findings suggest the contribution of working memory dysfunction to compromised MI ability in patients with MS.