Brains affected by Alzheimer's disease and mild cognitive impairment look older than their owners' birthdays suggest - and more so than brains affected by any other condition examined in a large new imaging study. The work, published in the open access journal PLOS Medicine and led by Shile Qi of the Nanjing University of Aeronautics and Astronautics in China, compared structural MRI scans across a wide span of neurological and psychiatric conditions.
The measure at the centre of the analysis is called predictive age difference, or PAD. Software estimates a person's age from the structure of their brain, and that estimate is set against their actual age. When the brain-based estimate comes out higher, the PAD is positive, which is taken as a sign that the brain has aged faster than the calendar would predict.
Qi's team drew on scans from 45,900 control participants pooled from several brain imaging databases and compared them with 2,698 people living with conditions including ADHD, autism, alcohol or tobacco addiction, Alzheimer's, mild cognitive impairment, schizophrenia, bipolar disorder and major depressive disorder. Alcohol addiction and psychiatric conditions such as schizophrenia were also linked to signs of accelerated aging, but the two neurodegenerative conditions - Alzheimer's and MCI - topped the list.
The more interesting detail for future diagnostics is that the aging did not look the same everywhere. Different conditions were associated with distinct patterns across brain regions, which raises the possibility that the shape of accelerated aging, and not just its size, could eventually help distinguish one disorder from another on a scan.