Another of his departure from Galen and the medical theories of the time is his description of stroke as produced by the brain and caused by an obstruction of the arteries from the heart to the brain. This explanation is closer to the modern understanding of the disease compared to that of Galen, which attributes it to the obstruction between heart and the periphery. He was also the first to describe the signs and symptoms of Parkinson's disease in his Kulliyat, although he did not give the disease a name.