Abnormal blood flow to the brain (due to clots or bleeds), or “stroke”, kills about 4.5 million people every year and there are over 9 million survivors left afflicted worldwide. In the UK and USA, stroke is the third greatest killer and the leading cause of disability. In the UK, stroke services are estimated to account for up to 6% of the NHS budget, not including costs to social services and carers.

Stroke causes death of neurons and loss of their projections ("axons") to various target regions including the opposite side of the spinal cord. This often causes hemiplegia on the side of the body opposite the injury.

Treatment for stroke is currently limited to "clot busting" drugs and to rehabilitation.