Need Discovered for Multiple Sclerosis Treatments That Target White Matter

Decreased connectivity in network specific regions of brain at the core of cognitive changes.

The underlying cause of diminishing cognitive function in multiple sclerosis (MS) patients raises the need for treatments that target white matter, according to a recent study.

Among the 2.3 million people afflicted with MS, approximately half experience diminished concentration, attention, memory, and judgment. The study, published in Neuropsychology, found decreased connectivity between network-specific brain regions are the culprit for the central deficit common to cognitive changes linked to MS.

MS patients show weaker brain connections between the dorsolateral prefrontal cortex and posterior brain regions compared with healthy individuals. The lessened cognitive function indicates a communication breakdown between the brain portion responsible for carrying out goal-directed thought and action and the regions responsible for carrying out tasks related to cognitive speed, the study found.

The researchers believe this effect is likely due to decreased white matter surrounding 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," said principal investigator Bart Rypma, PhD, in a press release. "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."

The study included 29 relapsing-remitting MS patients age and sex matched with 23 healthy controls. Participants underwent functional magnetic resonance (fMRI) imaging as they completed a cognitive processing speed evaluation.

Accuracy was similar across both cohorts, however, response times among MS patients were significantly slower. Data from fMRI indicates that during testing, the MS patients exhibited weaker functional connections with dorsolateral prefrontal cortex.

As a result of the study, researchers concluded there is a need for therapies that target white matter structures and white matter proliferation. Research is ongoing to further explore the physiology of white matter to better understand decreasing cognitive speed in both MS patients and among the healthy aging population.

"These findings reveal a diffuse pattern of disconnectivity with executive areas of the brain," lead author Nicholas Hubbard said. "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."