PNAS: The right hemisphere of the brain ages faster than the left

The right hemisphere of the brain ages faster than the left, with its “biological age” consistently higher. This imbalance becomes particularly pronounced in Alzheimer’s disease. The study was published in the journal Proceedings of the National Academy of Sciences.

Scientists at the University of Southern California’s Leonard Davis School of Gerontology trained a model to estimate the “age” of individual brain regions from MRI scans. The model was trained using data from nearly 15,000 healthy people aged 19 to 100 and tested on scans from about 2,000 participants in an Alzheimer’s disease study.

The model detected a consistently higher local “brain age” in the right hemisphere compared with the left. In addition, cortical sulci — the grooves or indentations — aged slightly faster than gyri, the raised folds. In patients with Alzheimer’s disease, subcortical structures were “older” by about 3.5 years compared with those of healthy people, while the hippocampus — a region crucial for memory — appeared more than three years older.

Why the right hemisphere is more vulnerable remains unclear, but this asymmetry could help detect diseases earlier and improve understanding of how the brain ages. Detailed “maps” of aging in individual brain regions could eventually allow for more precise risk assessment and monitoring of neurodegenerative diseases. For now, this is a research tool rather than an established diagnostic method, but it shows that brain aging is uneven — and that this unevenness can be measured.

The concept of the brain’s “biological age,” which may differ from a person’s chronological age, has been developing rapidly in recent years. MRI scans can be used to estimate how “worn” individual brain regions are. Detailed maps of this aging process can help researchers understand which areas are most vulnerable and how diseases such as Alzheimer’s alter this pattern, potentially making it possible to identify warning signs earlier.