Addiction and psychiatric disorders were also linked to increased PAD. By contrast, the researchers found no overall difference in PAD between controls and people with ADHD or autism spectrum disorder.

Different conditions, different regions

The study went beyond a single whole-brain number. The team also calculated PAD for individual brain regions and examined patterns of gene expression associated with each condition.

One area stood out across the board: the prefrontal cortex, the brain region behind the forehead that governs planning, decision-making, and self-control. It showed higher PAD across multiple brain disorders.

Psychiatric disorders were associated with elevated PAD in the frontal and temporal lobes — the latter sitting roughly at ear level and involved in memory and language. Dementia, meanwhile, was linked to higher PAD in the frontal and occipital cortex, the region at the back of the head that processes vision.

Addiction showed a different pattern altogether. Higher PAD appeared in the default mode network, a system active during daydreaming and self-referential thought, as well as in the salience network, the putamen, and the thalamus — structures involved in detecting important stimuli, habit formation, and relaying sensory signals.

The researchers also identified differences in gene transcription — the process by which genes are read and converted into working instructions — associated with particular conditions. This suggests that the observed patterns of brain aging may reflect distinct underlying biological processes, not a single shared mechanism.

Important caveats

The findings do not prove that these conditions directly cause accelerated brain aging. The study is correlational, meaning it identifies associations rather than cause and effect. The authors also note a practical complication: some conditions, particularly psychiatric disorders and addiction, frequently occur together, which makes their individual effects difficult to separate.

Even with those limitations, the researchers see real promise in the approach. Studying PAD more closely, they suggest, could eventually help identify biomarkers — measurable biological indicators — associated with common brain disorders, and provide new clues about the biological pathways involved.

"Different neurological disorders appear to leave different signatures on the brain aging clock, which may help researchers better understand the neural and biological pathways involved in these conditions," the authors write.

The study drew on a large author team spanning institutions in China and the United States, including co-authors such as Godfrey Pearlson, Vince D. Calhoun, and Kent E. Hutchison. Funding came from the Key Research and Development Plan of Jiangsu Province, China (BE2023668) and the National Natural Science Foundation of China (62376124), both awarded to Shile Qi. The funders had no role in study design, data collection and analysis, the decision to publish, or preparation of the manuscript.

For now, the brain aging clock remains a research tool rather than a clinical test. But if future work confirms these disorder-specific signatures, PAD could become a valuable window into how common brain conditions unfold — and where clinicians might one day intervene.