Targeted brain stimulation 'could aid stroke recovery'

"Stimulating the part of the brain which controls movement may improve recovery after a stroke," BBC News reports after researchers used lasers to stimulate a particular region of the brain with promising results in mice.

The researchers were looking at a sub-type of stroke known as ischaemic stroke, where a blood clot blocks the supply of blood to part of the brain.

With prompt treatment an ischaemic stroke is survivable, but even a temporary block to the blood supply can cause brain damage, which can impact on multiple functions such as movement, cognition and speech. Attempting to recover these functions is now an important aspect of post-stroke treatment.

The researchers used a technique called optogenetics in this study. Optogenetics uses a combination of genetics and light, where genetic techniques are used to "make" (code) certain brain cells sensitive to the effects of light. Light is produced by a laser and delivered through an optical fibre.

The researchers used light to stimulate an area of the brain (the primary motor cortex) in mice which had stroke-related brain damage. After stimulation, the mice's performance improved in behaviour tests assessing sensation and movement.

But to use this technique in humans, brain cells would have to be made sensitive to light, possibly by introducing a gene coding for a light-sensitive channel into nerve cells using gene therapy techniques. It is unclear whether this would be feasible based on current technology and techniques.

Where did the story come from?

The study was carried out by researchers from Stanford University School of Medicine in the US.

It was funded by the US National Institutes of Health, the National Institute of Neurological Disorders, a Stroke Grant, Russell and Elizabeth Siegelman, and Bernard and Ronni Lacroute.

The study was published in the peer-reviewed journal PNAS.

The research was well reported by BBC News.

What kind of research was this?

This animal study aimed to determine whether stimulating nerve cells in certain undamaged parts of the brain could help recovery in a mouse model of stroke.

Animal research such as this is a useful first step in investigating whether treatments could potentially be developed for testing in humans.

What did the research involve?

The researchers used a mouse that had been genetically engineered so the nerve cells in the part of the brain responsible for movement (the primary motor cortex) produced an ion channel sensitive to light. When light is shone on the nerve cells expressing this ion channel, the ion channel opens and the nerve cell is activated.

The researchers used healthy mice, as well as mice with brain damage caused by stopping blood flow in one of the arteries that supplies blood to the brain. This mimics the damage that occurs during an ischaemic stroke. The damage occurred in a different part of the brain from the primary motor cortex (the area that was stimulated). 

The researchers looked at whether stimulating the nerve cells in the primary motor cortex using light from a laser could promote recovery in a mouse model of stroke. This combination of light and genetics is called optogenetics.

What were the basic results?

Light stimulation of the nerve cells in the undamaged primary motor cortex significantly improved brain blood flow, as well as blood flow in response to brain activity in "stroke mice". It also increased the expression of neurotrophins, a family of proteins that promotes the survival, development and function of nerve cells, and other growth factors.

Stimulation of the nerve cells in the primary motor cortex also promoted functional recovery in the "stroke mice". "Stroke mice" who received stimulation showed faster weight gain and performed significantly better in a sensory-motor behaviour test (the rotating beam test).

Interestingly, stimulations in normal "non-stroke mice" did not alter motor behaviour or expression of neurotrophins.

How did the researchers interpret the results?

The researchers concluded that, "These results demonstrate that selective stimulation of neurons can enhance multiple plasticity-associated [the brain's ability to change] mechanisms and promote recovery."

Conclusion

This mouse model of stroke has found that stimulating nerve cells in the part of the brain responsible for movement (the primary motor cortex) can lead to better blood flow and the expression of proteins that could promote recovery, as well as leading to functional recovery after stroke.

But it remains to be determined whether a similar technique could be used in people who have had a stroke.

The mice were genetically modified so nerve cells in the primary motor cortex produced an ion channel that could be activated by light. The nerve cells were then activated using a laser.

To use this technique in humans, a gene coding for a light-sensitive channel would have to be introduced into nerve cells, possibly using gene therapy techniques.

Gene therapy in people is very much in its infancy, so it is unclear whether this would be achievable, let alone safe. The last thing you would want to do with a brain recovering from stroke-related damage is to make that damage worse.

Overall, this interesting technique shows promise, but much more research needs to be done before there will be any practical applications in the treatment of stroke patients.