Intelligence Is a Whole-Brain Phenomenon
General cognitive ability and white matter connectivity may go hand in hand.
Intelligence involves gray matter and white matter connectivity throughout the entire brain, according to a new meta-analysis. The findings (Holleran et al., 2020) of this international collaboration, which involved over three-dozen scientists from around the globe, were published on March 26 in The American Journal of Psychiatry.
This meta-analysis project was led by Laurena Holleran of the NUI Galway in Ireland. Holleran is a professor in the School of Psychology and Centre for Neuroimaging Cognition and Genomics as well as a lecturer in clinical neuroscience.
In total, the international collaborative analyzed brain scans and cognitive function measurements from 1,717 participants. Some study participants were patients with schizophrenia (n = 760); others were part of a control group (n = 957) of healthy participants.
What Is the Relationship Between White Matter Microstructure and General Cognitive Ability in Patients With Schizophrenia and Healthy Participants?
"Schizophrenia has recently been associated with widespread white matter microstructural abnormalities, but the functional effects of these abnormalities remain unclear," the authors write.
A relatively new, state-of-the-art brain imaging technique called diffusion tensor imaging (DTI) provides fresh insights into the relationship between white matter microstructures that connect different brain regions and general cognitive ability.
"Previous literature suggested that general intelligence relies on specific gray matter areas of the brain, including temporal, parietal and frontal regions. However, the results from this study indicate that efficient connection pathways across the entire brain provide a neural network that supports general cognitive function," Holleran said in a news release.
In the NUI news release, Professor Gary Donohoe, who is the senior author of this paper, highlights three ways that this meta-analysis advances our knowledge:
[This research] demonstrates that the relationship between brain structure and intelligence involves not only gray matter but also white matter—the brain's wiring system.
It's not just one part of this [white matter] wiring system that is important for intelligence, but rather the wiring system as a whole.
The relationship between intelligence and the brain's [white matter microstructure] wiring system is basically the same in patients with schizophrenia and healthy people; the lack of pattern explains their cognitive abilities. This suggests that cognitive function in patients is the same as the general population, at least as far as white matter is concerned.
"To date, this is the largest meta-analysis study of brain structure and cognitive function in schizophrenia," Holleran noted.
Until now, there hasn't been a clear consensus on the link between white matter functional connectivity and general cognitive ability. The authors conclude that their meta-analysis "provides robust evidence that cognitive ability is associated with global structural connectivity, with higher fractional anisotropy associated with higher IQ."
Notably, the relationship between white matter microstructure and general cognitive ability appears to be independent of a schizophrenia diagnosis. According to the authors, "the comparable size of effect in each group suggested a more general, rather than disease-specific, pattern of association."
"Understanding the neural basis of cognitive function is essential so that effective therapies [can be developed] that address difficulties associated with disorders like schizophrenia," Holleran said. "This is important because cognitive deficits associated with the disorder strongly predict social and functional outcomes, such as employment or social relationships."
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