Dual-hemisphere Transcranial Direct Current Stimulation on Lower Limb Motor Functions After Stroke

The aim of the present study is to evaluate the possible effect of using dual-tDCS combined with conventional physical therapy on lower limb function in stroke patients.

Stroke is a leading cause of adult motor disability. The recovery of motor function after stroke is often incomplete, despite classical rehabilitation techniques. In the beginning of the 21th century, transcranial direct current stimulation (tDCS) was introduced as a non-invasive tool to reversibly modulate brain excitability in humans in which a device sends constant low direct current (DC) delivered to the area of interest through the electrodes. These findings have opened the way to the therapeutic use of the brain stimulation for stroke. Based on the polarity-specific effects, anodal tDCS increases cortical excitability and cathodal tDCS decreases cortical excitability. To change the cortical excitability, tDCS differs from other brain stimulation techniques such as transcranial magnetic stimulation (TMS) in that it does not cause action potentials in cortical neurons, but rather induces shifts in neuronal resting membrane potential . This is considered to induce a lesser or no risk of a seizure. Given its advantages such as non-invasiveness, painlessness, safety, and possible after-effects, tDCS rapidly become a therapeutic adjuvant in neurorehabilitation especially in stroke patients with motor deficits . A number of studies in healthy subjects and stroke patients have reported that tDCS-induced excitability changes are related to increase in the performance of motor tasks and motor skills learning, mainly upper limb functions Recenty, dual-hemisphere tDCS in which, excites one hemisphere using anodal stimulation and inhibits the other by cathodal stimulation has been described in healthy subjects to greater enhance hand motor learning compared to uni-hemisphere tDCS. The corresponding tDCS-induced changes were reported in imaging study to involve interhemispheric interactions . An increase in the excitability of unaffected hemisphere and an abnormally high interhemispheric inhibition (IHI) drive from intact to lesioned hemisphere have been widely reported after unilateral stroke. Dual-tDCS has been more recent used in rehabilitation aiming to reduce the inhibition exerted by the unaffected hemisphere on the affected hemisphere and restore the normal balance of the IHI. Dual-tDCS combined with training or simultaneous occupational/physical therapy has been reported to improve motor skill learning and functions of the paretic upper limb in chronic stroke patients . Lower-limb functions are commonly disordered after stoke, however, less study has focused the effect of tDCS on lower limb functions. A single session of anodal tDCS over the lower limb M1 has reported to acutely enhance the effect of motor practice of the paretic ankle, force production of the paretic knee extensors, and postural stability in chronic stroke patients. However, little is known about effects of dual-tDCS on lower limb in stroke patients. Only one recent study showed an improvement of walking speed immediately after a single session of dual-tDCS alone in sub-acute stroke patients .

Dual transcranial direct current stimulation (tDCS) will be applied over the leg motor area (M1) priori to conventional physical therapy (1 hours). Anodal on affected hemisphere, Cathodal on unaffected hemisphere. Current intensity is fixed at 2 mA and current will flow continuously during 20 minutes for the active conditions. Physical therapist will give an intervention program exactly the same in all cases. The scope of intervention is administered to improve strength of weakened and postural lower limbs muscles such as trunk muscles, hip flexors/extensors/abductors, knee flexors/extensors.

Dual transcranial direct current stimulation (tDCS) will be applied over the leg motor area (M1) priori to conventional physical therapy (1 hours). Anodal on affected hemisphere, Cathodal on unaffected hemisphere. Current intensity is fixed at 2 mA and current will flow only 2 minutes for the sham conditions. Physical therapist will give an intervention program exactly the same in all cases. The scope of intervention is administered to improve strength of weakened and postural lower limbs muscles such as trunk muscles, hip flexors/extensors/abductors, knee flexors/extensors.

Dual Active/sham tDCS will be applied over the leg motor area (M1) priori to conventional physical therapy (1 hours). Anodal on affected hemisphere, Cathodal on unaffected hemisphere. Each participant will complete two experiments (active/sham tDCS). The interval between two experiments is at least 48 hours. The two experiments will be performed in random order for each subject.

Knee extensors strength is required to perform lower functions including sit-to-stand and gait. Knee extensor strength will measure using Biodex system, performing while the subjects comfortably seat in the position of knee flexed at 120° and ankle at 110° of plantar flexion on the attached footplate. Subjects will perform 3 isometric maximum voluntary contraction (MVC) of the knee extensor during a duration of 5 sec, separated by 2 min rest. The highest MVC in each session will be used as MVC level.

Subject will sits with arms folded across chest or the paretic arm at the side or in a sling. Subjects will be instructed as the following "I want you to stand up and sit down 5 times as quickly as you can when I say 'Go'." Subjects must be fully standing between repetitions. Timing will begin at "GO" and ends when the patient's buttocks touch the seat after the fifth sit-to-stand.

Subjects will sits on the chair and place their back against the chair. Timing will begin at "GO", the subjects will be asked to walk 3m, turn, walk back, and sit down. The stopwatch stops when the patient's buttocks touch the seat.

Inclusion Criteria: Age range 18-75 years. First ever-ischemic lesion in the territory of middle cerebral artery or anterior cerebral artery. CT scan/MRI result is thus required. Sub acute phase of stroke (less than 6 months) Able to sit-to-stand and stand-to-sit independently Able to walk without physical assistance at least 6 m Free of any neurological antecedent, unstable medical conditions or condition that may increase the risk of stimulation such as epilepsy; although tDCS is believed to induce less or no risk of seizure and epileptic seizure have never been reported in tDCS study even in a study with active epilepsy (Fregni et al., 2006). Exclusion Criteria: Pre-stroke disability Pregnant Be unable to understand the instruction No clear neurological antecedent history or psychiatric disorder Excessive pain in any joint of the paretic limb (numerical pain rating score > 7) Presence of intracranial metal implantation, cochlea implant, or cardiac pacemaker Subjects are participating in the other protocol or receiving alternative treatment such as acupuncture

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