Impairment of motor function is one of the most severe deficit in ischemic stroke patients. Therefore, evaluations of brain function reorganization during spontaneous motor recovery are extremely valuable. To date, much attention has been paid to understand the effect of stroke using functional connectivity (FC) with resting-state functional magnetic resonance imaging (rs-fMRI). Many researchers held the idea that inter-hemispheric FC especially FC between homotopic brain areas could discriminate between varying levels of motor recovery while intra-hemispheric connectivity, even within the damaged hemisphere, showed much less relationship with behavioral performance. However, most of these previous studies adopted either a retrospective, cross-sectional or interventional design in stroke patients without specific subcortical infarction location^[1,2]. Thus, in the present study, we used a voxel-mirrored homotopic connectivity (VMHC) method to investigate the longitudinal functional homotopic changes in patients with unilateral pontine infarction during a 180-day-period follow-up and explored its relationship with the standard of patient’s clinical motor recovery. We were willing to evaluate whether homotopic FC is adequacy to be a biomarker of motor recovery following stroke.A total of 15 first-episode unilateral pontine infarction patients (43-68 years old; mean age, 58.1 years old) and 15 age-matched healthy volunteers (45-70 years old; mean age, 55.9 years old) were recruited for this study. All patients were examined with a 3T scanner (MAGNETOM Tim Trio, Siemens Healthcare, Erlangen, Germany) five times during a period of 6 months (7, 14, 30, 90, and 180 days after stroke onset). Structural images were acquired with a sagittal MP-RAGE three-dimensional T1-weighted sequence (TR, 1600 ms; TE, 2.15 ms; flip angle, 9°; 1.0 mm isotropic voxels; FOV, 256×256). Functional Images were acquired using the gradient-echo echo-planar pulse sequence (TR, 3000ms; TE, 30 ms; flip angle, 90°; 3 mm isotropic voxels). Clinical neurological assessment was performed with Fugl-Meyer scale (FM) which was generally used to evaluate upper-limb motor recovery after stroke. Whole-brain homotopic functional connectivity in each individual scan was measured by voxel-mirrored homotopic connectivity (VMHC) method. Voxel-wise one-way ANCOVA tests were performed to examine the differences in regional VMHC between stroke patients and healthy controls. Finally, we analyzed the relationships between the whole-brain VMHC value in acute stroke stage and FM scores during the recovery process.

1. In comparison with normal controls, patients with acute pontine infarction (within 7 days) showed significant decreased VMHC in two clusters overlapping post/pre central gyrus and precuneus/posterior cingulate cortex (PCC). Additionally, increased VMHC was demonstrated in two clusters overlapping hippocampus/amygdala and frontal pole (Fig.1). Afterwards, during the recovery period of stroke patients (14-180 days), these above mentioned four clusters presented dynamic alterations - VMHC in post/pre central gyrus and precuneus/PCC showed progressively increasing tendency but still continuously lower than that in normal controls on day 180, while VMHC in hippocampus/amygdala and frontal pole represented persistently higher level of intensity than that in normal controls during all time points without an obvious variation tendency (Fig.2).

2. When correlated with behavioral performance, VMHC between cognitive brain areas in acute infarction stage (within 7 days) showed significant association with clinical motor recovery in the chronic period. VMHC value of hippocampus/amygdala in acute phase was negatively correlated with FM scores on day 14 (r=-0.59, p=0.021), day 30 (r=-0.643, p=0.01), day 90 (r=-0.693, p=0.004) and day 180 (r=-0.668, p=0.007) (Fig.3). Furthermore, VMHC value of frontal pole was negatively correlated with FM scores on day 30 (r=-0.662, p=0.013), day 90 (r=-0.606, p=0.017) and day 180 (r=-0.552, p=0.033). Nevertheless, VMHC between motor brain regions such as post/pre central gyrus didn’t present significant correlation with behavioral scores (Fig.4).

1. Resting-state fMRI could demonstrate dynamic whole-brain homotopic functional connectivity changes in patients with pontine infarction which might be helpful to further discuss brain function reorganization after stroke.

2. VMHC between cognitive brain areas in acute stage had significant correlation with clinical behavioral performance in chronic period which might be meaningful in predicting motor outcome and discriminating between dynamic levels of motor recovery process in stroke patients.