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.