New research has found that white matter affects how people respond to brain stimulation therapy aimed at depression and stroke.

The research, led by a team at Imperial College London, studied how tiny changes in the microscopic structure of the human brain may affect how patients respond to an emerging therapy for neurological problems.

The researchers reported that the technique, called non-invasive electrical brain stimulation, involves applying an electrical current to the surface of a patient’s head to stimulate brain cells, altering the patient’s brain activity. It is being trialled for a range of neurological problems including recovery from stroke, traumatic brain injury, dementia, and depression, but research to date has found the effects to be inconsistent.

The group has shed more light on why these inconsistencies occur and may provide physical evidence for why some patients respond better than others – because of the fine structure of their brain tissue. The new research suggests it may be possible to target the therapy to those patients most likely to benefit.

They found that differences in the makeup of the brain’s white matter – the tissue deep in the brain and rich in the branching ‘tails’ of nerve cells – were key, and revealed that those who had more connectivity in the regions being stimulated were more likely to respond better to the treatment.

The team ultimately found that “people with stronger white matter connections in their brain had better improvement with stimulation,” Dr Lucia Li, a clinical lecturer in neurology in the Department of Brain Sciences at Imperial College London, explained.

“This might be an important reason why previous studies have found that some people benefit from stimulation, whilst others don't and means we can start using brain stimulation in a more personalised way.”

In the study, researchers looked at 24 healthy patients and 35 patients recovering from a moderate or severe traumatic brain injury (TBI). Participants performed a task inside an MRI scanner while receiving small amounts of electrical current through electrodes on the surface of the scalp or a placebo, and they were unable to tell whether they were receiving brain stimulation or not.

The results showed that healthy participants who received brain stimulation performed better in the task than when they didn’t receive the treatment. For patients with TBI, task performance in response to stimulation varied widely.

The team cautioned in a release that while more work is needed to confirm the findings, it could mean that brain stimulation might prove a useful treatment approach for other neurological conditions with abnormal brain activity as a feature, such as dementia.