Investigating the Effects of Transcranial Stimulation to Advance Stroke Rehabilitation

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Stroke is a leading cause of death and long-term disability worldwide. More than 70% of stroke survivors experience motor impairments, often resulting in difficulties in daily activities, such as walking, reaching and grasping objects. Regaining upper-limb motor function is key to quality of life and for reducing the high annual costs due to stroke. Research indicates that upper-limb motor function recovery depends on the plasticity of neural circuits controlling movement. Beta activity (β, \~13-30 Hz) in the sensorimotor cortex has been associated with brain plasticity and has been proposed to play a pivotal role in human movement and movement disorders. This activity attenuates during movement execution, known as event-related desynchronization (β-ERD), and temporarily increases after the end of movement, known as event-related synchronization (β-ERS). β-ERD and β-ERS are reliably observed during active and passive movement, movement imagination and movement observation. Changes in movement-related β-ERD and β-ERS have been linked to motor learning, and motor dysfunction in neurological conditions, such as stroke. Studies have shown that stroke survivors with upper limb impairments exhibit significantly lower beta activity compared to healthy individuals, and recovery-related improvements in motor function are accompanied by increases in both sensorimotor β-ERD and β-ERS. Therefore, modulation of movement-related beta activity (i.e., β-ERD and β-ERS) holds great promise for promoting motor function after stroke. Non-invasive brain stimulation (NIBS) can be applied during movements to increase plasticity and enhance motor learning and function. However, prior studies have delivered NIBS using a relatively broad approach; modulating general cortical excitability rather than enhancing specific endogenous oscillations in the brain. Transcranial alternating current stimulation (tACS) is a safe and well-tolerated type of NIBS which provides an option for modulating specific frequencies of brain oscillations by delivering a low-intensity sinusoidal electrical current to the brain at a specific frequency. Therefore, this study will deliver beta-tACS to the ipsilesional motor cortex (M1) aiming to modulate sensorimotor beta activity during upper limb movement in stroke survivors. This study will investigate whether functionally timed beta-tACS has the potential to enhance motor recovery, by assessing whether stimulation delivered at the end of the movement improves upper limb movement (accuracy, smoothness and hand function) and increases the modulation of beta activity. Additionally, the investigators will evaluate whether the effectiveness of the stimulation relates to baseline neuroimaging and neurophysiological measures. Identifying correlates of intervention responsiveness will help future studies to target patients who are most likely to benefit.