The idea that one’s disposition can be analyzed by looking at their handwriting is considered spurious, yet medical graphology—the use of handwriting to detect disease—has diagnostic validity. “Writing is an exquisite fine motor skill—unlike brushing your hair, for instance,” explains neuroscientist José Contreras-Vidal. “People spend years practicing it, consolidating a very robust motor-control program in the brain.” As a result, the deterioration of that finely honed skill can be a neurological red flag.