Relevance of negative BOLD signal changes in stroke patients upon motor recovery

Abstract

Objective Positive BOLD signals in functional MRI (fMRI) are widely reported in stroke patients upon recovery. With the increased observations of negative BOLD signals in normal subjects during motor activations, negative signals may be relevant in motor recovery of stroke patients. We aimed to report changes in both positive and negative signals over the motor-implicated cortex of stroke patients with motor deficits before and after a course of rehabilitation. Methods Acute stroke patients with moderate to severe arm weakness were recruited. The first fMRI was performed within 2 weeks after stroke onset. The second fMRI was performed 8 weeks later. Motor assessments were done on the same day. fMRI data were acquired with a 3T clinical MRI scanner. Voxel size was 3.6 X 3.6 X 3 mm. Forty-four contiguous slices, covering the whole brain, were acquired every 3 s. A block design with RARA sequence was used. Each study consisted of 60 images: 15 for each resting or activation block. Patient was asked to perform gripping with the weak hand during the activation block. Data analysis was performed using SPM2 implemented in MatLab. Images were realigned, normalized and smoothed. A high-pass filter was applied. T-test was used to show task-related significance (p<0.05). Positive and negative contrasts were applied to the parameter estimates to identify areas showing increased (positive) and decreased (negative) signals relative to resting state. Number of voxels in Brodmann area (BA) 3, 4, 6 and 40 with positive or negative signals was counted. Comparisons were made between the first and second fMRI. Results All results presented were classified into the hemisphere contralateral or ipsilateral to the side with motor deficits. Increased positive and decreased negative signals over the motor-implicated cortex of the hemisphere contralateral to motor deficits were seen in 6 stroke patients with improved upper limb motor functions. In addition, increased negative signals were observed in other areas (BA 20 and 21) in the hemisphere ipsilateral to side of motor deficits. Conclusions Negative BOLD signals during stroke recovery were presented. Positive and negative signals may be equally important in motor recovery after stroke. Negative BOLD signals may represent transcortical inhibition of motor functions from the unaffected motor cortex.