A new study establishes a correlation between brain damage to white matter and impaired cognitive functions. She thus challenges the idea that it is the gray matter that is most important in cognitive health.
- Contrary to what studies have suggested so far, it is damage to the white matter of the brain, and not damage to the gray matter, that is linked to impaired cognitive function after a cerebrovascular accident (CVA).
- This white matter, made up of millions of axons, connects the neurons of the different brain regions.
- Lesions appearing on the connection centers of this dense white matter are strongly linked to impaired cognitive functions, the study shows.
There is a generally accepted idea that the gray matter, made up of the neurons forming the cerebral cortex, is more important than the white matter. Filling almost half of our brain, this white substance is nevertheless essential for our cognitive functions: it is made up of millions of “cables” (axons) covered with myelin, which connect the neurons of different brain regions to each other.
A new study, conducted by researchers at the University of Iowa (USA) and published in the journal PNAS draws a different conclusion. Its authors, who studied brain scans and cognitive function tests of more than 500 people with localized areas of brain damage caused by strokes in particular, believe that the state of the white matter informs more than that of the gray matter. on cognitive health.
By examining the brain lesions of the patients, the researchers have indeed established a correlation between the level of connectivity of the damaged areas and the level of cognitive impairment of the patient. The results suggest that damage to highly connected regions of white matter is more predictive of cognitive impairment than damage to highly connected gray matter nuclei.
The key role of white matter in cognitive functions
To measure the connectedness of networks and identify nodes, i.e. highly connected brain regions, the researchers used mathematical models, which they then applied to analyze brain scans to find cases where areas damaged coincided with the knots. Using data from several cognitive tests for these patients, they were also able to measure the effect of hub lesions on cognitive outcomes. Surprisingly, damage to highly connected gray matter hubs was not strongly associated with poor cognitive outcomes. In contrast, damage to dense white matter centers was strongly linked to impaired cognitive function.
“The brain is not a blank canvas where all regions are equal; a small lesion in one region of the brain can have a minimal impact on cognition, while another can have a huge impact. These findings could help us to better predict, based on the location of the lesion, which patients are at risk of suffering from cognitive impairment after a stroke or other brain injury, explains Professor Boes, co-author of the work and member of the Iowa Neuroscience Institute. Knowing these things in advance is best because it gives patients and family members a more realistic prognosis and allows rehabilitation to be targeted more effectively.”
For Justin Reber, who also participated in the work, these new results show the value of working with clinical patients to better understand the relationships between structure and function of the brain.
“A lot of excellent research using functional brain imaging with healthy participants or computer simulations tells us that these gray matter nuclei are critical to brain function and can be used to predict performance in healthy people. health in cognitive tests. But when we look at how strokes and other brain damage actually affect people, it turns out that you can predict a lot more from white matter damage.”, he explains. According to him, “this study is a reminder that the connections between brain regions can be as important as those regions themselves, if not more”.
.
