Remember the picture of Muhammad Ali lighting the Olympic flame at the Atlanta Games? The famously swift hands that mesmerised the world and knocked out many a doughty boxer now jerking awkwardly upwards because of Parkinson's disease affecting his movements? The legendary motor-mouth struggling with every word?

At the time when Ali was diagnosed with the disease, the most potent treatment available was levodopa and a common side effect of the drug was dyskinesia, the involuntary, erratic movement of the face and limbs.