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April 2003

Improving Hand Function in Chronic Stroke: Topography of the Lesion and Role of the Corpus Callosum

Arch Neurol. 2003;60(4):640. doi:10.1001/archneur.60.4.640-a

Concerning the "Original Contribution" by Muellbacher et al1 on improving hand function in chronic stroke, the following clinical and physiological considerations seem warranted assuming that the reported motor evoked potentials were from the weak (right) flexor pollicis brevis muscle (as the thrust of the article implies) and not from the left side, as reported in their "Patients and Methods" section. Clinically, the authors' understanding of an existing competition between proximal and distal musculature in affording the recovery of distal function in stroke victims does not jibe well with the available data in the literature. Specifically, in a prospective study on the same subject, Katrak et al2 found a positive relationship between the early presence of proximal function and its eventual recovery in the distal musculature of the same limb. Physiologically, all 7 of their patients (6 of them were apparently right-handed) had capsular or subcapsular strokes (some pontine), with left-sided lesions in 5. Given the chronicity of their condition, it seems reasonable that any possible improvement must necessarily have involved improved activation of the neuronal pool in the appropriate spinal cord level by the newly cultivated cortical connections. The authors, however, provide no data concerning this matter (eg, H and F responses or mirror activity on the opposite side), which is the only theoretical possibility for mediating the reported improvement. The reported absence of a significant change of pinch force on the intact (contralateral) side was expected given the selection of the patients regarding the lesion sites (see previously mentioned data). Such improvements only occur in dominant cortical lesions when the healing of a lesion is translated, via the corpus callosum, to improved functioning of the minor hemisphere (devoted to events occurring on the nondominant side).3,4 This outcome is always controlled by the major hemisphere (in which all voluntary movements are planned and executed). Regarding this matter, I have recently written about a modification of the doctrine of contralaterality of movement control in humans, in which more information relevant to the subject may be found.5

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