While the corpus callosum (CC) is important to normal sensorimotor function, its role in motor function after stroke is less well understood. This study examined the relationship between structural integrity of the motor and sensory sections of the CC, as reflected by fractional anisotropy (FA), and motor function in individuals with a range of motor impairment level due to stroke. Fifty-five individuals with chronic stroke (Fugl-Meyer motor score range 14 to 61) and 18 healthy controls underwent diffusion tensor imaging and a set of motor behavior tests. Mean FA from the motor and sensory regions of the CC and from corticospinal tract (CST) were extracted and relationships with behavioral measures evaluated. Across all participants, FA in both CC regions was significantly decreased after stroke (p < 0.001) and showed a significant, positive correlation with level of motor function. However, these relationships varied based on degree of motor impairment: in individuals with relatively less motor impairment (Fugl-Meyer motor score > 39), motor status correlated with FA in the CC but not the CST, while in individuals with relatively greater motor impairment (Fugl-Meyer motor score ≤ 39), motor status correlated with FA in the CST but not the CC. The role interhemispheric motor connections play in motor function after stroke may differ based on level of motor impairment. These findings emphasize the heterogeneity of stroke, and suggest that biomarkers and treatment approaches targeting separate subgroups may be warranted.
Compensatory activation in dorsal premotor cortex (PMd) during movement execution has often been reported after stroke. However, the role of PMd in the planning of skilled movement after stroke has not been well studied. The current study investigated the behavioral and neural response to the addition of action selection (AS) demands, a motor planning process that engages PMd in controls, to movement after stroke. Ten individuals with chronic, left hemisphere stroke and 16 age-matched controls made a joystick movement with the right hand under two conditions. In the AS condition, participants moved right or left based on an abstract, visual rule; in the execution only condition, participants moved in the same direction on every trial. Despite a similar behavioral response to the AS condition (increase in reaction time), brain activation differed between the two groups: the control group showed increased activation in left inferior parietal lobule (IPL) while the stroke group showed increased activation in several right/contralesional regions including right IPL. Variability in behavioral performance between participants was significantly related to variability in brain activation. Individuals post-stroke with relatively poorer AS task performance showed greater magnitude of activation in left PMd and dorsolateral prefrontal cortex (DLPFC), increased left primary motor cortex-PMd connectivity, and decreased left PMd-DLPFC connectivity. Changes in the premotor-prefrontal component of the motor network during complex movement conditions may negatively impact the performance and learning of skilled movement and may be a prime target for rehabilitation protocols aimed at improving the function of residual brain circuits after stroke.
Introduction: Responsiveness to motor rehabilitation varies greatly after stroke. Improved knowledge of the brain correlates of motor function are needed to assist in the development of more effective and personalized rehabilitation protocols. Changes in the integrity of the ipsilesional corticospinal tract after stroke have been well documented, but less is known about changes in the corpus callosum (CC). The purpose of this study was to determine if structural integrity of the motor and sensory portions of the CC change after stroke and whether any such changes are related to clinical measures of sensorimotor impairment and function. Methods: Fifty-five individuals with chronic stroke (age 60.5±13.2; days post-stroke 351.9±560; UE Fugl-Meyer (FM) motor score 38.5±14.6, no lesion in the CC) and 16 age-matched controls underwent diffusion tensor imaging (DTI) and behavioral assessments. Mean fractional anisotropy (FA) values for the motor and sensory regions of the CC were extracted and examined in relation to motor system behavioral measures including the UEFM, Box & Blocks (BB), Nottingham sensory score, and Stroke Impact Scale (SIS) hand subsection. Results: Participants with stroke had significantly lower FA values compared to controls in both the motor and sensory CC regions ( p <0.02) despite their strokes sparing the CC. In the CC motor region, FA was related to UEFM, BB, and SIS scores, such that higher structural integrity correlated with better motor status ( ρ >0.30, p <0.03 across comparisons). In the CC sensory region, FA was related to UEFM and SIS scores ( ρ >0.31, p <0.02) as well as Nottingham sensory scores (ρ=0.33, p<0.05). CC motor and sensory FA did not correlate with FA in the ipsilesional peduncle ( ρ <0.12, p >0.40), suggesting that the magnitude of change in each region of the motor system was distinct. Conclusions: Decreased structural connectivity between the sensorimotor regions of the two hemispheres is related to motor impairment in chronic stroke in a manner that is distinct from corticospinal tract injury. Interventions that target the communication between hemispheres during motor rehabilitation may be warranted.
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