Figure 3. Exhaustion of ipsilesional motor circuits precipitates recruitment of contralesional cortex and flexion synergy expression.

A, group‐average mean global field power over 100 ms immediately prior to movement onset (gray patch). Cortical activity is presented in reference to the Bereitschaftpotential (BP), including the early BP, late BP, and motor potential (MP). B, C, group‐average cortical current density reconstructions are shown for control (B) and stroke (C) over 100 ms immediately prior to movement onset. All brains are oriented such that the left side is contralateral to the tested arm. Thus, the left side corresponds to the lesioned hemisphere in stroke, and the right side is contralesional (ipsilateral to the paretic upper limb). Cortical activity was primarily localized in the contralateral hemisphere across all tasks for control participants. Stroke participants exhibited increased activity in the contralesional (R) hemisphere as SABD loading increased. D, cortical activation laterality. In control participants (blue), mean laterality index (LI) was indistinguishable across shoulder abduction (SABD) load levels. In stroke (green), mean LI decreased from 0.27 to −0.12 to −0.21 from Table to Floating to 25% shoulder abduction loading, with significant decreases from Table to Floating and from Table to 25% shoulder abduction. Stroke participants had significantly lower LI values than the control participants for Floating and 25% shoulder abduction (P = 0.01, 0.02, respectively), but only a strong trend towards lower mean LI for Table (P = 0.08). Mean global field power, MGFP. [Color figure can be viewed at http://wileyonlinelibrary.com]