Altered cortical activation with finger movement after peripheral denervation: comparison of active and passive tasks |
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Authors: | Reddy H Floyer A Donaghy M Matthews P M |
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Institution: | (1) Centre for Functional Magnetic Resonance Imaging of the Brain, Department of Clinical Neurology, University of Oxford, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU, UK, |
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Abstract: | We wished to contrast cortical activation during hand movements in profoundly weak patients with motor neuropathy and in
normal controls using a paradigm that is behaviourally matched between the two groups. Previous work has suggested that a
passive movement task could be appropriate. Using functional magnetic resonance imaging (fMRI), we first characterised patterns
of brain activation during active and passive index finger movements in healthy controls (n=10). Although the relative activation differences were highly variable, there was a trend for the mean number of significantly
activated voxels in the primary motor cortex contralateral to the hand moved (CMC) to be lower for the passive than for the
active task (40% relative decrease, P=0.09). There was a small posterior shift in the centre of mass of the CMC (mean, 8 mm, P<0.02) and of the ipsilateral sensorimotor cortex (IMC) (mean, 11 mm, P<0.05). No activation with passive movement was found in the patients with severe distal sensory neuropathy (n=2), suggesting that activation with passive movements is dependent on sensory feedback and unlikely to be due to mental imagery
alone. In contrast, patients with severe pure motor neuropathies (MN, n=2) showed substantial increases in the volumes of activation compared to controls. The relative increases in numbers of voxels
activated above threshold in different regions of interest for both the active (MN/controls: CMC, 2.1; IMC, 8.1; supplementary
motor area SMA], 5.2) and passive (CMC, 2.6; IMC, 8.0; SMA, 5.1) tasks were similar. These results confirm expansion of cortical
representation for finger movement in patients with motor neuropathy and demonstrate central reorganisation as a consequence
of the motor nerve loss. An expanded representation for finger movement in the primary motor cortex with peripheral weakness
suggests the possibility that the primary motor cortex may encode motor unit activation rather directly.
Electronic Publication |
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Keywords: | fMRI Motor cortex Motor control Neuropathy Denervation |
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