What is the earliest spark that ignites the memory-robbing march of Alzheimer’s disease? Why do some people with Alzheimer’s-like changes in the brain never go on to develop dementia? These questions have bedeviled neuroscientists for decades.

Now, a team of researchers at Harvard Medical School may have found an answer: lithium deficiency in the brain.

The work, published in Nature, shows for the first time that lithium occurs naturally in the brain, shields it from neurodegeneration, and maintains the normal function of all major brain cell types.