Date Published: 7 December 2011

Tiny electric currents across regions of the brain to help stroke recovery

Tiny electric currents applied across regions of the brain can improve hand movements in recovering stroke patients for a short time, according to a recent study at Oxford University, England.

Strokes are thought to cause a loss of connectivity in the region of the brain involved in movement of the affected side of the body. The brain appears to respond by recruiting many other areas of the brain to try and do the same job. Recovery appears to be associated with the amount of activity that can be restored in the original brain region governing movement, the primary motor cortex.

The Oxford University researchers together with colleagues at the Oxford Centre for Enablement at the Nuffield Orthopaedic Centre, set out to investigate if a brain stimulation technique designed to increase the activity in the motor cortex would improve hand movements in people who had had a stroke. The brain stimulation technique, called transcranial direct current stimulation or TDCS, involves passing a small electrical current of about 1 milliamp across part of the brain using simple pads placed on the outside of the head. It is a relatively new technique known to increase the 'excitability' of neurons in the targeted region of the brain. It has been shown to be safe in many studies: if anything, people might feel a slightly tingly or itchy sensation on their scalp. The study included a wide range of patients who'd had a stroke at least six months previously – aged from 30 to 80, both sexes, and different types of stroke. The 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.

The study involved 13 patients and recorded a significant 5–10% improvement in patients' response times in making hand movements. The effect following a single treatment of application of tiny electric currents applied across regions of the brain lasted only an hour or so. However, neuroscience studies in other research areas have demonstrated effects that lasted months after daily application of this form of brain stimulation. The 5–10% improvement in reaction times was observed during and after the short time of applying the current. The improvement was not seen in dummy treatments when no current was applied. Nor was it seen when the current was applied in the opposite direction, which would tend to reduce brain activity in the stroke-affected region.

" The improvements in movement and reaction times were significant", said lead researcher Dr Charlotte Stagg of the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) at Oxford University. "Patients certainly noticed them, but they were short-lived. However, we are very hopeful that daily brain stimulation would lead to longer-lasting improvements."

Much larger clinical studies would be needed to show that brain stimulation had a lasting effect in producing clinical benefits for stroke patients, for example in greater recovery of movement and ability to carry out all the activities of daily life. For the next stage of this research the research scientists at Oxford University are recruiting approx. 30 stroke patients to participate in a trial that will consider if daily brain stimulation in addition to physiotherapy exercises can lead to tangible benefits after three months.

"This was a study in a small group. Large-scale trials would be needed before concluding that the approach benefits those recovering from strokes," said Dr Stagg.

She added that:

" The brain stimulation technique is relatively cheap, easy to use and it's portable. You could imagine physiotherapists using it in their practice in the future.
_ The damage caused by a stroke can be widespread and long-lasting, often involving weakness or loss of movement in one side of the body. Many people will need a significant period of rehabilitation and physiotherapy to recover. The amount of movement and independence people are able to regain is very variable, so developing extra therapies to aid recovery would be of great importance."

The study participants also completed similar tasks in an MRI scanner to detect whether there were any changes in brain activity. After the brain stimulation with the electric current, there was increased activity in brain regions associated with movement in the stroke-affected side of the body.

" The amount that brain activity increased, as seen in the fMRI scans, appeared to be linked to the level of improvement seen in people's reaction times," explained Dr Stagg.

The researchers hope that developing this brain stimulation technique further may lead to a valuable addition to standard physiotherapy to recover from a stroke.

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