Early imaging correlates of subsequent motor recovery after stroke

There is unexplained variability in the extent to which patients recover after stroke, particularly from the reference point of the first few days after onset. Among studies tracking motor impairment and recovery, only 30–50% of the variance of recovery is explained by the most commonly reported predictors --lesion volume and initial stroke severity 1, 2. We hypothesized that functional imaging early after stroke could provide information over and above initial severity and lesion volume about the degree of subsequent recovery. Several prior functional imaging studies have reported altered brain activation patterns in patients at various stages of motor recovery after stroke3–6. These studies describe brain activation related to concurrent recovered performance at the time of scanning that differs to varying degrees from what is seen in age-matched controls. In this study we used functional imaging to ask a specific and unique question about motor recovery after stroke: can functional imaging in the early period after stroke detect brain activation related to subsequent recovered performance? Should such activation be identified then it could serve as a physiological target for intervention (e.g. non-invasive brain stimulation) in this early time period. To investigate whether brain activation early after stroke can be correlated with subsequent recovery, we scanned patients approximately 48 hours after stroke using fMRI, and defined recovery as the change in motor impairment from the time of scanning to a follow up point 3 months later. We used 3 different statistical tests: 1) a multivariate test, which is most sensitive to spatially diffuse activation, 2) voxel-wise statistical parametric mapping (SPM), which is most sensitive to focal activation, and 3) primary motor cortex (M1) region of interest (ROI) analysis, which is most sensitive to average activation within this region. The ROI analysis was chosen to test existing hypotheses implicating M1 and the corticospinal tract in recovery.7–9 All tests controlled for lesion volume and initial stroke severity, as well as other established clinical variables.