Encoder-Controlled Functional Electrical Stimulator for Bilateral Wrist Activities-Design and Evaluation.

Upper limb impairment following stroke is often characterized by limited voluntary control in the affected arm. In addition, significant motor coordination problems occur on the unaffected arm due to avoidance of performing bilateral symmetrical activities. Rehabilitation strategies should, therefore, not only aim at improving voluntary control on the affected arm, but also contribute to synchronizing activity from both upper limbs. The encoder-controlled functional electrical stimulator, described in this paper, implements precise contralateral control of wrist flexion and extension with electrical stimulation. The stimulator is calibrated for each individual to obtain a table of stimulation parameters versus wrist angle. This table is used to set stimulation parameters dynamically, based on the difference in wrist angle between the set and stimulated side, which is continuously monitored. This allows the wrist on the stimulated side to follow flexion and extension patterns on the set side, thereby mirroring wrist movements of the normal side. This device also gives real-time graphical feedback on how the stimulated wrist is performing in comparison to the normal side. A study was performed on 25 normal volunteers to determine how closely wrist movements on the set side were being followed on the stimulated side. Graphical results show that there were minor differences, which were quantified by considering the peak angles of flexion and extension on the set and stimulated side for each participant. The mean difference in peak flexion and extension range of movement was 2.3 degrees and 1.9 degrees, respectively, with a mean time lag of 1 s between the set and the stimulated angle graphs.

Transcranial direct current stimulation: A review of electrode characteristics and materials.

Electrode characteristics are crucial in transcranial direct current stimulation (tDCS) since electrode design and placement determine the cortical area being modulated, current density and spatial resolution of stimulation. Early research on tDCS sought to determine optimal parameters for stimulation by specifying maximum current, duration and sizes of electrodes. Further research focused on determining efficient ways to deliver stimulation to targeted regions on the cortex with minimal discomfort to the user by altering electrode size, placement, shape and material. This review aims to give an insight on the main characteristics of electrodes used in tDCS and on the variability found in electrode parameters and placements from tDCS to high definition tDCS (HD-tDCS) applications and beyond.

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.

Reducing the sensation of electrical stimulation with dry electrodes by using an array of constant current sources.

Hydrogel electrodes are commonly used for functional and other electrical stimulation applications since the hydrogel layer has been shown to considerably reduce the perception of stimulation compared to dry electrodes. However, these hydrogel electrodes must be changed regularly as they dry out or become contaminated with skin cells and sweat products, thus losing their adhesiveness and resistive properties. Dry electrodes are longer lasting but are more uncomfortable due to unequal current distribution (current hogging). We hypothesise that if current through a dry electrode is equally shared amongst an array of small sub-electrodes, current hogging and thus the sensitivity perceived due to stimulation will be reduced. We constructed an 8 × 8 array of millimetre sized dry electrodes that could either be activated as individual current sources, or together as one large source. A study was performed with 13 participants to investigate the differences in sensation between the two modes of operation. The results showed that 12 out of 13 participants found the new (distributed-constant-current) approach allowed higher stimulation for the same sensation. The differences in sensation between single and multiple sources became larger with higher intensity levels.