Transcranial direct current stimulation (tDCS) has been applied to facilitate cortical excitability in stroke populations, as increasing evidence suggests that clinical recovery from stroke is attributed to neuroplastic reorganization. However, recovery from stroke following this kind of non-invasive neuromodulation remains divergent across stroke patients due to variations in their etiologies, lesion profiles and post-stroke duration.

A novel multisite high definition tDCS (HD-tDCS) in healthy people showed that such network-targeted stimulation could enhance motor excitability beyond conventional stimulation which targeting only one region. The electrode placements could be determined by the montage optimization, which targets individual motor network activation navigated by task-based fMRI using computation algorithms.

By targeting motor network, the new multisite electrode montage may provide a potential to facilitate better cortical activation than conventional tDCS montage.

Transcranial direct current stimulation (tDCS) has been applied to facilitate cortical excitability in stroke populations, as increasing evidence suggests that clinical recovery from stroke is attributed to neuroplastic reorganization. However, recovery from stroke following this kind of non-invasive neuromodulation remains divergent across stroke patients due to variations in their etiologies, lesion profiles and post-stroke durations. In the stroke application of tDCS, most non-invasive brain stimulation studies have mainly focused on the modulation of the primary motor cortex (M1) in motor skill relearning. Previous studies have shown that not only the M1, which is the most important area associated with the motor system, but also other secondary motor areas (e.g., premotor cortex (PM) and supplementary motor area (SMA)) can be influenced by the onset of stroke. In fact, SMA activations and shifts in the M1 are commonly observed in stroke patients. However, brain regions do not operate in isolation, but communicate and interact with other discrete regions through networks. Conventional stimulations of one region (normally the M1 in stroke) have neglected the network impact and the changed motor network composition after stroke, which is often limited in stroke rehabilitation. A novel multisite high definition tDCS (HD-tDCS) in healthy people showed that such network-targeted stimulation could enhance motor excitability beyond conventional stimulation which targeting only one region. It showed that the excitability following multisite HD-tDCS was more than double the increase following conventional tDCS.

To consider the various lesion site and the different activation patterns of individual stroke survivors, personalized lesion profiles and anatomical features can be determined using finite element modelling, with lesion profiles generated from MRI and advanced algorithms calculating the current density to maximize the modulation effect. The electrode placements could be determined by the montage optimization, which targets individual motor network activation navigated by task-based fMRI using computation algorithms. By targeting motor network, the new multisite electrode montage may provide a potential to facilitate better cortical activation than conventional tDCS montage.

In this study, A randomized cross-over designed trial will be conducted to explore motor activation and reorganization changes before and after multisite HD-tDCS, conventional tDCS, and sham tDCS in stroke survivors. The stimulation effect will be evaluated by fMRI.

Inclusion Criteria:

1. first-ever stroke, the duration after stroke exceeds 12 months;
2. mild to moderate upper extremity motor function deficit, determined by the Fugl-meyer assessment of upper extremity (FMAUE) scores between 15 and 53;
3. could voluntarily perform grasping hand movement.
4. sufficient cognitive function to follow the assessment and experiment instructions.

Exclusion Criteria:

1. history of epilepsy, or any other contradictions of brain stimulation and MRI scanning;
2. severe joint contracture of elbow or shoulder, or pain induced by any other neurological, neuromuscular, and orthopedic diseases.