What links Alzheimer’s disease, the bridges of Königsberg and Twitter?

A mathematical puzzle originating in 18th century Prussia has led to insights in fields as diverse as banking, social networking, epidemiology – and now Alzheimer’s disease

The progression of Alzheimer’s is accompanied by a buildup in the brain of amyloid plaque and the breakdown of communication between nerve cells. Recent research suggests that graph theory can provide fascinating insights into the faulty wiring behind the progressive memory loss of Alzheimer’s. But what exactly is graph theory?

To discover the origins of the theory we have to go back to the 18th century and the ancient Prussian city of Königsberg, now Kaliningrad – that tiny city state wedged between Poland and Lithuania. It was here that Leonard Euler solved the long-standing Bridges of Königsberg Problem, which has had a profound effect on the development of network theory.