Scientists at the Mark and Mary Stevens Neuroimaging and Informatics Institute (Stevens INI) at the Keck School of Medicine of USC have uncovered evidence that two neighboring types of brain tissue may work together to support thinking abilities later in life. Their findings suggest that the condition of the brain's local communication pathways could influence how strongly gray matter loss affects cognition. The study, published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, included brain imaging and cognitive testing from 459 adults aged 60 and older living in communities across India.
The research is among the first to investigate superficial white matter in a community-based population from a low- and middle-income country. Superficial white matter forms a thin layer of nerve fibers directly beneath the gray matter covering the outside of the brain. These short, curved fibers connect nearby regions of the cerebral cortex, allowing them to exchange information.
They can be thought of as local roads linking neighboring areas of the brain. Gray matter serves a different role. It contains many of the nerve cells responsible for processing information.
Together, gray matter and the white matter directly beneath it form closely connected systems that may both contribute to cognitive health. "Gray matter and superficial white matter are physically close and may play different roles: gray matter processes information, while superficial white matter helps nearby brain regions communicate," said Yingxu Liu, PhD, a postdoctoral scholar at the Stevens INI and first author of the study. "Our findings suggest that cognitive health depends not only on how much gray matter is preserved, but also on the condition of the wiring that connects it." To investigate these local connections, the researchers used an advanced type of diffusion MRI.
This imaging technique tracks the movement of water through brain tissue, allowing scientists to examine microscopic features that conventional brain scans may not reveal. The researchers focused on measurements related to neurite density and the amount of freely moving water surrounding these structures. Neurites are the small projections through which nerve cells send and receive signals.
A lower density of neurites or an increase in free water can indicate damage or disruption in tissue associated with processes including loss of myelin, inflammation, or swelling. Participants also underwent assessments covering several areas of cognition, including language, memory, executive function, and visuospatial ability. The most consistent connection between superficial white matter health and cognitive performance involved language.
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