System uses small electrical currents to aid stroke patients

A medical device that applies very small electric currents directly to the scalp could augment rehabilitation for stroke patients.

Researchers at Oxford University have shown that their technique — which applies milliamp current through simple pads — is safe and temporarily improves hand dexterity.

‘Electric currents have been used for the treatment of neurological diseases for thousands of years, from electric fish in ancient Egypt through to galvanic currents in depression,’ said Dr Charlotte Stagg of the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB).

‘We’re beginning to understand a bit more about how it works, and we think simply that it changes the membrane potential and that has an effect on the firing rate of the neuron, and then that changes the strength of the connection between the neurons.’

Stagg explained that neurons are held at a resting membrane potential of around -70mV and when that increases to -40mV, the cell fires. The researchers believe the technique, called anodal transcranial direct current stimulation (TDCS), increases that resting potential slightly, making it more likely neurons will fire, increasing the overall firing rate.

‘Rehabilitation works by trying to get the patient to move as much as they can to get those cells to fire, and what we’re trying to do is just make it a bit easier to get them to fire, with the idea that the more they fire together in a useful pattern, the easier that pattern becomes and therefore the better the function,’ Stagg said.

The device set-up comprises two carbon-fibre conductive pads with 5KΩ resistors — one over the targeted area of the brain around the motor cortex and another ‘reference electrode’ placed somewhere that does not affect performance.

Running the current from the active electrode to the reference electrode thereby, in theory, increases excitability. In a recent trial, stroke patients carried out a simple task involving a hand movement in response to images on a computer screen three times — before, during and after brain stimulation using the electric current for 20 minutes. This resulted in an approximate 5–10 per cent improvement in patients’ response times, which lasted for around one hour.

When the current was applied in the opposite direction, from the reference electrode to the active one, it tended to reduce brain activity in the stroke-affected region.

The research group is working with medical device manufacturer Magstim of South Wales in the hope of eventually having an easy-to-use package that physiotherapists can take into therapy sessions.