Abstract Background and aims Unilateral stroke often causes bimanual impairments, which are critical to address since most daily activities require bimanual coordination. We aimed to elucidate the mechanisms underlying these early poststroke deficits. Methods In 95 patients with a single acute stroke (5.8 ± 4.2 days poststroke) and 60 age-matched healthy individuals (HI), we quantified bimanual motor control and coordination in the proximal upper limb (UL) using the REA2plan robot, and in the distal UL using the Dextrain Manipulandum. Multimodal MRI was employed to identify neural substrates of these impairments. Results Compared to HI, proximal bimanual motor control was significantly impaired in patients (Est = –0.38 a.u. –0.55, –0.21, p 0.001), as was bimanual coordination (–0.144 a.u. –0.18, –0.10, p 0.001). Distally (thumb–index pinches), both motor control and coordination were impaired (–0.32 a.u. –0.44, –0.21, p 0.001; –0.29 a.u. –0.49, –0.08, p = 0.005). Voxel-based lesion symptom mapping analysis showed that lesion along the corticospinal tract (CST) correlated with impaired distal bimanual control (Z=4.05562687, uncorrected p=0.05, 21mm3, peak MNI=-24,-6,28). Region-of-Interest-based tractography demonstrated that the microstructural integrity of the CST of acute patients correlated with proximal bimanual coordination (r=-0.49; p0.001) and with distal bimanual control (r=0.3, p=0.004). Microstructural integrity of the superior longitudinal fasciculus (r=-0.42; p=0.005) and the corpus callosum was related to proximal bimanual coordination (r=-0.4; p=0.004) and proximal bimanual motor control (r=-0.38; p=0.005). Conclusions Dissecting proximal and distal bimanual impairments and their neural substrates in the acute phase provides key insights for targeted neurorehabilitation. Conflict of interest N/A
Vandermeeren et al. (2026) studied this question.