DISCUSSION
excessive head motion, stroke, upper limb motor recovery, upper limb motor function, hand motor tasks
STROKE, CORTEX
Emerging neuroimaging studies have identified neuroimaging biomarkers of functional recovery in stroke patients.The activation of the passive movement of the affected hand showed an abnormal bilateral activation pattern compared with the contralateral‐lateralized activation of the passive movement of the unaffected hand. When stroke patients passively moved the unaffected hand, the activation focused on the contralateral sensorimotor cortex (contralesional M1, S1, SMA) and ipsilateral (ipsilesional) cerebellum, presenting a typical activation pattern that was similar to cortical representation for hand motor tasks in healthy individuals.After MIT, the compensatory activation of bilateral sensorimotor networks decreased. The decrease was associated with the adjunctive efficacy of MIT. The activation of the passive movement of the affected hand in the contralesional S1 and ipsilesional M1 decreased significantly after the intervention in the MIT group compared with the control group. Correlation analyses further demonstrated that decreased activation in these two areas was significantly negatively correlated with FM‐UL improvement. These findings suggest that the withdrawal of bilateral compensation was associated with better motor recovery in the MIT group. Previous studies have suggested that although the temporary compensatory activation could support the functional improvement in the acute and subacute phases after stroke, in the long run, overreliance on compensatory brain activation may hinder the recovery of motor ability.Moreover, it was observed that the effects of MIT were found only on the brain activation of the affected hand and had no effect on the unaffected hand. The findings indicate that the training‐induced brain plasticity was restricted to BOLD responses of the MIT‐targeted hand since patients were only instructed to imagine moving the hand and upper limb at the affected side during the training. Likewise, TMS studies have revealed that the increase in cortico‐spinal excitability is specific to the muscles involved in the imagined movement.MIT potential mechanisms for stroke treatment may also associate with the changes in FC with the ipsilesional M1. The FC of the ipsilesional M1 significantly decreased in the ipsilesional IPL and increased in the ipsilesional putamen after MIT but remained unchanged after sole CRT. The change in these FCs was significantly correlated with FM‐UL improvement. The change of FC patterns indicated that the remodeling of activation time course synchronization mainly occurred within the damaged hemisphere and reflected the possible neural substrate underlying the rehabilitation effects of MIT on the motor functions of the patient. Similarly, change in FC has been observed in a resting‐state fMRI study. Zhang et al.The IPL of the human brain is engaged in numerous mental processes such as visuospatial attention, memory, and mathematical cognition.The enhanced FC resulting from MIT therapy might improve upper limb fine movements, creating a positive correlation between FM‐UL improvement and change in FC relative to the ipsilesional putamen. The lentiform nucleus comprises putamen and globus pallidus which combine with the caudate nucleus to shape the striatum. The striatum receives afferent input from different parts of the cortex and sends efferent output to the cortex through the thalamus.The current study has several limitations that should be noted. Firstly, the FM‐UL was used as the only clinical assessment of upper limb motor function. Thus, additional comprehensive assessments, such as the Wolf Motor Function Test, Action Research Arm Test, and Box and Block Test, should be applied in future studies to improve the interpretation of results. Secondly, we calculated the sample size based on our preliminary data and related studies. However, only 29/39 patients with complete fMRI data were included in the analysis due to the dropout and excessive head motion during MRI scanning. Therefore, more participants should be recruited in the future to increase the validity of the results. Thirdly, our results indicated that the contralesional S1, the ipsilesional M1, IPL, and putamen were key sensorimotor nodes which correlated with upper limb motor recovery after MIT. Although these brain areas modulate motor planning, motor execution, and motor learning, it remains unclear whether these nodes participate in neuromodulation when combined with MIT. In the future, an intervention study combining MIT and noninvasive brain stimulation is advocated to promote the development of novel treatment paradigms to improve stroke recovery.