Despite approximately 2.3 million individuals worldwide currently living with multiple sclerosis (MS), the underlying mechanism behind the changes in cognition experienced, such as impaired concentration, attention, memory and judgment, have remained largely unknown. A new study, published recently in Neuropsychology, has revealed that the reduction in cognitive speed associated with all the common cognitive changes in MS may be due to a decrease in connectivity between network-specific brain regions.
During the study, which was carried out by researchers at the Center for BrainHealth at The University of Texas at Dallas and The University of Texas Southwestern Medical Center (both TX, USA), 29 patients with relapsing-remitting MS and 23 age- and sex- matched healthy controls were recruited. While completing an assessment of cognitive processing speed, all participants underwent functional magnetic resonance imaging (fMRI). Each participant was given 4 seconds to view a nine item key of number and symbol pairs and one number-symbol pair probe. They were then requested to indicate with a left or right thumb button press whether or not the probe was present within the key.
Results indicated that while accuracy was generally similar between the control and MS groups, response times were notably slower for individuals with MS. This was reinforced by evidence from the fMRI that revealed that MS patients also possessed weaker functional connections between the dorsolateral prefrontal cortex and posterior brain regions, equating to a breakdown in communication between the area of the brain responsible for goal-directed thought and action and those responsible for carrying out tasks related to cognitive speed e.g. object recognition, motor execution or visual processing.
In conclusion the team believe that this reduction in brain connections is most likely due to a decline in the white matter surrounding the neurons in the brain.
“Our study is the first to really zero in on the physiology of cognitive speed, the central cognitive deficit in MS,” explained Bart Rypma (Center for BrainHealth), prinicipal investigator for the study. “While white matter is essential to efficient network communication, white matter degradation is symptomatic of MS. This study really highlights how tightly coupled connectivity is to performance and illuminates the larger, emerging picture of white matter’s importance in human cognitive performance.”
Lead author, Nicholas Hubbard (Center for BrainHealth) also added: “Importantly, these decreases in connectivity predicted MS-related cognitive slowing both in and out of the fMRI environment suggesting that these results were not specific to our task, but rather were able to generalize to other situations where cognitive speed is required.”
The team are now looking to conduct further research into the physiology of white matter in order to increase understanding of cognitive speed declines in both MS and healthy aging individuals.