Effect of afferent input on motor cortex excitability during stroke recovery.

OBJECTIVE Afferent input is proposed to mediate its effect on motor functions by modulating the excitability of the motor cortex. We aimed to clarify - in a longitudinal study - how afferent input affects motor cortex excitability after stroke and how it is associated with recovery of hand function. METHODS The motor cortex excitability was studied by measuring the reactivity of the motor cortex beta rhythm to somatosensory stimulation. We recorded the amplitude of the suppression and subsequent rebound of the beta oscillations during tactile finger stimulation with MEG in 23 first-ever stroke patients within one week and at 1 and 3 months after stroke, with concomitant evaluation of hand function. RESULTS The strength of the beta rhythm rebound, suggested to reflect decreased motor cortex excitability, was weak in the affected hemisphere after stroke and it was subsequently increased during recovery. The rebound strength correlated with hand function tests in all recordings. CONCLUSION Motor cortex excitability is modulated by afferent input after stroke. The motor cortex excitability is increased in the AH acutely after stroke and decreases in parallel with recovery of hand function. SIGNIFICANCE The results implicate the importance of parallel recovery of both sensory and motor systems in functional recovery after stroke.