An old psychiatric mineral is drawing new scientific attention as researchers discover that Alzheimer's patients carry measurably less lithium in their brains than healthy individuals — a deficit that, when corrected in animal models, reversed cognitive decline and reduced the hallmarks of neurodegeneration. The inquiry is not about high therapeutic doses but about restoring what the brain may naturally require, targeting the earliest, most reversible stages of a disease that begins dismantling neural architecture long before memory falters. It is a reminder that medicine sometimes finds its m