Better awareness of symptoms and improved treatments have helped reduce the number of people dying from stroke, leading to an increase in the number of stroke survivors. Unfortunately, many of these survivors are left with disabilities that limit their ability to live productive, independent lives.
Electrical brain stimulation is becoming widely used as a tool to help the brain recover following injury, but the absence of a clear mechanistic rationale for this tool has meant that it is being inconsistently applied, leading to mixed results. In this project Professor Bestmann has used cutting edge mathematical and brain imaging techniques to introduce a consistent approach will help to unlock the full potential of brain stimulation to promote recovery after stroke.
A stroke occurs when the blood supply to part of the brain is cut off. This can cause catastrophic damage.
Whilst the number of UK deaths from strokes is going down, the lower mortality rates mean that more people are surviving stroke than ever before. There are an estimated 1.3 million stroke survivors in the UK today, more than half of whom are left with a life-limiting disability. Stroke-related disabilities include limb weakness, impaired mobility, and problems with speech, balance and co-ordination.
In addition to the huge personal impact, the impact on society is enormous. The economic burden of stroke in the UK is estimated at £9 billion a year – including health and social care costs, informal care, productivity losses and benefit payments. Two-thirds of working age survivors are unable to return to work.
Improving stroke recovery to enable survivors to live independent, productive lives is therefore a key goal.
Improving stroke recovery is a crucial clinical and scientific goal but our healthcare systems struggle to deliver enough rehabilitation in the timeframe required.
Electrical brain stimulation is becoming widely used as a tool to help the brain recover following injury. It appears that it can increase the capacity of the brain to recover from the type of injury caused by stroke, and boost the effects of rehabilitation.
A lack of understanding about exactly how electrical stimulation drives changes in the brain, however, means that it is being inconsistently applied and results are mixed. This is because trials have lacked mechanistic rationale - or, in short, an understanding of when and how brain stimulation should be applied in order to achieve the best results.
In this project Professor Bestmann and team set out to address these key mechanistic questions and thereby improve consistency in the application of brain stimulation - to achieve the best results for patients.
In the first part of their study, they used electrical field modelling to demonstrate the great variability in how much current is actually delivered to the target area of the brain in individuals given the standard application of transcranial direct current stimulation (tDCS). They went on to show that this variability can be eliminated by using individual brain scans to personalise the application of tDCS. This has important implications for its future use, strongly suggesting that effective clinical use must account for individual brain anatomy.
In the second stage of their project, unable to work directly with stroke patients due to Covid restrictions, the team instead worked with a dataset provided by an Australian team. This dataset tracked brain changes following stimulation at different time points from one week to 12 months post-stroke, enabling them to study differences in response to stimulation in early versus late stages of stroke.
In essence, their work demonstrated that there is no 'one size fits all' approach for tDCS and similar brain stimulation techniques and that, in order to maximise their potential, these interventions must take into account individual brain anatomy, physiology, and lesion characteristics. The team demonstrated that the strength of response is more variable in stroke survivors than in neuro-typical participants, and that the timing of brain changes was not correlated with recovery of motor function in stroke survivors with mild stroke symptoms.
If non-invasive brain stimulation does not appear to work, one explanation is that the current simply missed the target, but there has previously been no way of knowing whether this is the case. This has prevented attempts to test whether non-invasive brain stimulation could help stroke survivors by increasing the effectiveness of physiotherapy, for example.
This project has provided, for the first time, a basic understanding and insight for designing clinical trials to determine whether brain stimulation can enhance rehabilitation after stroke, both in the first few weeks as well as years after. In other words, it will help us to determine the ‘who, how and when’ of non-invasive brain stimulation after stroke.
The team has shared their findings widely, running a number of workshops on the use of transcranial electric stimulation as well as publishing a number of journal articles. This will help ensure consistency in the way that electrical brain stimulation is used in future research as well as in the clinic, to unlock the full potential of brain stimulation to promote recovery after stroke.
Acquired brain and spinal cord injury (including stroke) is one of our current research priorities, reflecting the large unmet need in this area. Our aim is to fund research to advance understanding of how to promote repair of the brain and spinal cord following injury.
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