A review of transcranial electrical stimulation methods in stroke rehabilitation.

Transcranial electrical stimulation (TES) uses direct or alternating current to non-invasively stimulate the brain. Neuronal activity in the brain is modulated by the electrical field according to the polarity of the current being applied. TES includes transcranial direct current stimulation (tDCS), transcranial random noise stimulation, and transcranial alternating current stimulation (tACS). tDCS and tACS are the two non-invasive brain stimulation techniques that have been used alone or in combination with other rehabilitative therapies for the improvement of motor control in hemiparesis. Increasing research in these methods is being carried out to improvise on the existing technology because they have proven to exhibit a lasting effect, thereby contributing to brain plasticity and motor re-learning. Artificial stimulation of the lesioned or non-lesioned hemisphere induces participation of its cells when a movement is being performed. The devices are portable, stimulation is easy to deliver, and they are not known to cause any major side effects which are the foremost reasons for their trials in stroke rehabilitation. Recent research is focused on maximizing the outcome of stroke rehabilitation by combining them with other modalities. This review focuses on stimulation protocols, parameters, and the results obtained by these techniques and their combinations.