title: Dominance of the Unaffected Hemisphere Motor Network and Its Role in the Behavior of Chronic Stroke Survivors.
abstract: Balance of motor network activity between the two brain hemispheres after stroke is crucial for functional recovery. Several studies have extensively studied the role of the affected brain hemisphere to better understand changes in motor network activity following stroke. Very few studies have examined the role of the unaffected brain hemisphere and confirmed the test-retest reliability of connectivity measures on unaffected hemisphere. We recorded blood oxygenation level dependent functional magnetic resonance imaging (fMRI) signals from nine stroke survivors with hemiparesis of the left or right hand. Participants performed a motor execution task with affected hand, unaffected hand, and both hands simultaneously. Participants returned for a repeat fMRI scan 1 week later. Using dynamic causal modeling (DCM), we evaluated effective connectivity among three motor areas: the primary motor area (M1), the premotor cortex (PMC) and the supplementary motor area for the affected and unaffected hemispheres separately. Five participants' manual motor ability was assessed by Fugl-Meyer Motor Assessment scores and root-mean square error of participants' tracking ability during a robot-assisted game. We found (i) that the task performance with the affected hand resulted in strengthening of the connectivity pattern for unaffected hemisphere, (ii) an identical network of the unaffected hemisphere when participants performed the task with their unaffected hand, and (iii) the pattern of directional connectivity observed in the affected hemisphere was identical for tasks using the affected hand only or both hands. Furthermore, pairedt-test comparison found no significant differences in connectivity strength for any path when compared with one-week follow-up. Brain-behavior linear correlation analysis showed that the connectivity patterns in the unaffected hemisphere more accurately reflected the behavioral conditions than the connectivity patterns in the affected hemisphere. Above findings enrich our knowledge of unaffected brain hemisphere following stroke, which further strengthens our neurobiological understanding of stroke-affected brain and can help to effectively identify and apply stroke-treatments.
authors.affiliation: Department of Physics and Astronomy, Georgia State University, AtlantaGA, USA; Department of Psychiatry, College of Medicine, University of Arizona, TucsonAZ, USA.
authors.forename: Sahil
authors.initials: S
authors.lastname: Bajaj
authors.affiliation: Byrdine F. Lewis School of Nursing and Health Professions, Georgia State University, Atlanta GA, USA.
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Housley
authors.affiliation: Byrdine F. Lewis School of Nursing and Health Professions, Georgia State University, Atlanta GA, USA.
authors.forename: David
authors.initials: D
authors.lastname: Wu
authors.affiliation: Department of Physics and Astronomy, Georgia State University, AtlantaGA, USA; Joint Center for Advanced Brain Imaging, Center for Behavioral Neuroscience, Center for Nano-Optics, Center for Diagnostics and Therapeutics, Georgia State University, AtlantaGA, USA; Neuroscience Institute, Georgia State University, AtlantaGA, USA.
authors.forename: Mukesh
authors.initials: M
authors.lastname: Dhamala
authors.affiliation: Psychiatric Research Institute, University of Arkansas for Medical Sciences, Little Rock AR, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: James
authors.affiliation: Byrdine F. Lewis School of Nursing and Health Professions, Georgia State University, AtlantaGA, USA; Neuroscience Institute, Georgia State University, AtlantaGA, USA; Department of Veterans Affairs, Atlanta Rehabilitation Research and Development Center of Excellence, DecaturGA, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Butler
keywords: affected hemisphere; dynamic causal modeling (DCM); effective connectivity; functional magnetic resonance imaging (fMRI); motor task; stroke; unaffected hemisphere