Crossed cortico-spinal motor control after capsular stroke

While it is widely accepted that multiple nonprimary motor areas such as the dorsal premotor cortex contribute to recovery from stroke, the contribution of the ipsilesional and contralesional primary motor cortex (M1) is controversial. It has been suggested that re-instating 'near normal' activation patterns is a good strategy for recovery of function [Baron et at., (2004) Cerebrovasc. Dis., 18, 260-267; Ward & Cohen, (2004) Arch. Neurol., 61, 1844-1848]. The present study addressed this aspect of stroke recovery by combining transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG) in a cross-sectional design on nine patients with well-recovered motor function 17.6 +/- 5.5 months (mean +/- SD) after subcortical stroke. While TMS was applied to probe the integrity of the cortico-spinal tract (CST) at rest, MEG was used to test for recruitment of CST pathways during a motor challenge [cortico-muscular coherence (CMC) in a precision grip task]. With both techniques, crossed cortico-spinal connectivity could be demonstrated. A significant correlation (r= 0.85) of CMC magnitude and recovered muscle strength underlined the functional relevance of crossed CST integrity for successful recovery. In conclusion, at the descriptive level, crossed CST connectivity is a common finding in well-recovered patients with capsular stroke. This renders it likely that maintaining or regaining use of crossed CST fibers is one way to achieve effective recovery.