In 2005, Stanford scientist Karl Deisseroth discovered how to switch individual brain cells on and off by using light in a technique he dubbed 'optogenetics'.
Research teams around the world have since used this technique to study brain cells, heart cells, stem cells and others regulated by electrical signals.
However, light-sensitive proteins were efficient at switching cells on but proved less effective at turning them off.
Now, after almost a decade of research, scientists have been able to shut down the neurons as well as activate them.
German neuropathologist Alois Alzheimer, born in 1864, first encountered the progressively degenerative disease, which would later be named Alzheimer's, in 1901 when examining a fifty-one year old woman named Auguste Deter.