Cognitive Defects in Multiple Sclerosis Caused in Part By Brain Processing Speed

Trying to nail down the reason for executive deficits in multiple sclerosis can be difficult, considering the number of factors related to the condition. A team of researchers from the Kessler Foundation — led by Victoria Leavitt, PhD, who is now a part of the Manhattan Memory Center, and James Sumowski, PhD — discovered a link between executive deficits and slowed processing speed. They reported their results ahead of print in the journal Rehabilitation Psychology under the title, “Does Slowed Processing Speed Account for Executive Deficits in Multiple Sclerosis? Evidence From Neuropsychological Performance and Structural Neuroimaging.”

Executive deficits (also referred to as cognitive deficits) describe disabling symptoms that affect approximately half of multiple sclerosis patients’ quality of life. Processing speed, which is a measure of how fast the brain can intake information and decide how to respond to the information, is found to be slowed in multiple sclerosis patients. The team at Kessler Foundation was interested in a possible link between the two symptoms and compared 50 multiple sclerosis patients to 28 healthy participants with the intention of determining an effect of processing speed on executive function.

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When conducting the analysis, the team used degree of cerebral atrophy to define disease progression. Patients with greater brain atrophy had poorer executive function when tested with the Trail Making Test and Wisconsin Card Sorting Test. Interestingly, when results were adjusted based on processing speed, the difference was no longer evident. Moreover, patients performed equivalently on executive tasks that did not incorporate a speed element.

“Our results point to slowed processing speed as the mechanism underlying deficits in executive function,” said Nancy Chiaravalloti, PhD, a co-author on the study, in a news release from Kessler Foundation. “Understanding this association is an important step toward the development of effective cognitive rehabilitation strategies for individuals with multiple sclerosis. We should focus our efforts on two key domains–processing speed and memory.”

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The researchers came to the conclusion that processing speed contributes to executive function. Brain atrophy did not predict performance on nonspeeded executive tasks, but Dr. Chiaravalloti identified that “Additional neuropsychological measures should be included in future studies. We also need to focus on the contribution of specific brain pathology, such as frontal atrophy and lesion load, to executive deficits.”

Overall, the results of this study provide more information to researchers and clinicians interested in enhancing rehabilitation therapy for patients with multiple sclerosis.