Effects of tES Combined With CMDT Gait Training on Cognition, Cortical Activity, Spinal Motoneuron Excitability and Motor Performance in Stroke Individuals

The present study will use transcranial electrical stimulation (tES) which are transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) combined with conventional physical therapy and cognitive-motor dual task gait training in sub-acute (at least 2 weeks after stroke onset) to chronic (within 5 years post-stroke) to investigate the effect on cortical activity, spinal motoneuron excitability, cognition and motor performance. The findings may enhance the evidence to support usages of tES for improvimg cognition, motor performance as well as cortical activity and spinal motoneuron excitability in a clinical setting.

Stroke is a sudden neurological event which is leading cause of death and disability. An impaired blood flow and oxygen supply leading to neuronal cell death follwoing stroke. In addition, an electroencephalography demonstrated a decrease of high frequency power bands (alpha and beta) and increase of low frequency bands (theta and delta). An increase in delta frequency is negatively correlated with cognition, while an increase in high-frequency bands are correlatedw ith an improvement of motor recovery and cognition. Follwoing stroke, an alterations of cortical activity between ipsileasional hemisphere and contralesion hemisphere affect the spinal lelvel as it leads to increase spinal motoneuron excitability. An increase of spinal motoneuron excitability is likely due to abnormal control from cortex to spinal cord via descending pathway. Furthermore, hyperexcitability of spinal motoneuron is associated with post-stroke spasticity. However, the excat mechanisms of spasticity in post stroke remians unclear. Potential causes include imbalance in descending pathway regulation, abnormal intraspinal processing, and altered muscular viscoelasticity. Changes in spinal motoneuron excitability can be assessed using Hoffmann's reflex (H-reflex). Motor imapirments following stroke affects activities of daily living (ADLs), moreover cognitive impairements is commonly obsrved in post-stroke individuals that may limits motor and functional recovery and limits effectiveness of rehabilitation. These impairments affect both single- and duals-task activities, especially walking performance and increasing risk of falls in stroke individuals. In recent years, combining bottom-up and top-down approaches has been greater potential in promoting neural plasticity and enhancing motor recovery compared to single approach. Bottom-up approaches refers to rehabilitation that act on physical level and expected chnages in nervous system level, while top-down approach induce change in cortical level to induce change in motor function or physical level. The non-invasive brain stimulation (NIBS) is a top-down approach that enhance neural plasticity and mediated motor-relearning in neurological conditions. Transcranial electrical stimulation (tES) is one of NIBS which the most coom tES techniques are transcranial direct current stimulation (tDCS) and transcranial alternating currnt stimulation (tACS). Both tDCS and tACS are different in their wave forms. tDCS delivers a weak direct current with polartiy-specific effects, while tACS enhance neural plasticity and endogenous brain wave with frequency-specific. A recent review demonstrated the effectiveness of tDCS in improvement of motor function, functional abilities and cognitive function. Furthermore, a previous study demonstrated an improvement in cognitive function and ADLs following combining 2mA of tDCS with CMDT training. However, the amount of evidence on the effects of tACS is much less than that for tDCS, as it has only recently started to gain interest. The frequency used in tACS study mainly follows the association of brain wave and function. A previous review showed that gamma tACS enhance cognitive performance, working memory and logical thinking. In healthy population, a previous study demonstrated that applied gamma-tACS over M1 significantly improved velocity and acceleration of visuomotor task; nevertheless, this improvement did not found in beta-tACS. To provide evidence of the effects of tACS in the stroke population and to identify which type of transcranial electrical stimulation is most appropriate for stroke rehabilitation, a comparison between tDCS and tACS is necessary. Both tES technique will be combined with conventional physical therapy for 12 sessions (3 days/week for 4 weeks). tES will be provided for 20 minutes, then followed by convention physical therapy (1-hour) and cognitive-motor dual-task gait training (30-minute). Cortical activity will be assessed by EEG. Absoule spectral power of each frequency bands (alpha, beta, delta, and theta) will be analyze. The Hmax/Mmax ratio from flexor carpi radialis and soleus will be recorded to represent changes in spinal motoneuron excitability. The Fugl-Meyer assessment of upper and lower extremity and Timed up and go will be used to represent clinical outcomes of motor function and performance. The ERP recorded during Stroop color and word test and 2-Back test will be assessed together with the Montreal Cognitive Assessment (MoCA) in Thai version. Furthermore, behavoral data i.e. response time, accuracy will be collected to analyse to represent cogniton. For walking performance, dual-task interference or dual-task costs will be employed from dual-task walking. All outcomes will be assessed at baseline, post-intervention, 1-month follow-up, and 3-month follow-up.