Researchers at the Keck School of Medicine of USC have found that two distinct types of brain tissue work together to support cognition in older adults, and that the health of the brain’s short-range wiring, known as white matter, may help soften the cognitive effects of gray matter loss. The study, published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, analyzed brain scans and cognitive assessments from 459 community-dwelling adults age 60 and older across India. It is among the first studies to examine the brain’s superficial white matter in a community-based population from a low- and middle-income country. The researchers used an advanced form of diffusion MRI, which measures how water moves through brain tissue, to assess microscopic features of superficial white matter. They focused on measures that reflect neurite density, the small projections that allow nerve cells to send and receive signals, and the amount of freely moving water around them. Lower neurite density or more free water can indicate tissue disruption associated with processes such as loss of myelin, inflammation, or swelling. Participants also completed tests of language, memory, executive function, and visuospatial ability. The team found that healthier superficial white matter was most consistently associated with stronger language skills. The clearest links appeared in frontotemporal areas involved in recognizing words, speaking fluently, and holding language information in mind. Gray matter atrophy measures remained the strongest overall predictors of cognition. However, the relationship between gray matter and cognitive performance depended in part on superficial white matter: when this local wiring showed poorer integrity, gray matter loss was more strongly tied to worse language performance and cognitive impairment. When superficial white matter was healthier, those associations were weaker.
