Stable ratio of ipsilateral to contralateral sensory motor cortex activity despite varying effort and peripheral nerve block

Background: Ipsilateral sensory motor cortex (SMC) activation can occur during hand movements following cerebral injury. We studied the effect of increasing task difficulty and temporary peripheral paralysis on patterns of motor system activation. Methods: Six healthy subjects completed a functional MRI paradigm of right finger abduction with four stages; light resistance, strong resistance, imagined movement and attempted abduction after ulnar nerve blockade. Activation maps compared images acquired during rest and task, while region of interest analysis measured numbers of activated pixels. Results: All subjects showed some ipsilateral SMC activation. Across all subjects and all tasks involving hand movement, contralateral activation was proportional to ipsilateral activation (2.1:1; r=0.86). Conclusions: The relationship between ipsilateral and contralateral SMC activation remained stable despite differing effort or hand paralysis. The contralateral and ipsilateral SMC appear to act in a coordinated fashion during unilateral hand movements. (C) 2003 Published by Elsevier Ltd.