More cognitive fatigue reported by patients with MS, brain injury

Adults with multiple sclerosis (MS) or traumatic brain injury report more cognitive fatigue, or exhaustion resulting from mental work, than do healthy individuals — regardless of the nature of the tasks being performed — a study found.

However, cognitive fatigue built up at a similar rate among study participants while performing the tasks specified and was linked to longer response times in all three groups of adults. That suggests, according to the researchers, that such differences in cognitive fatigue, or mental exhaustion, were already present at the study’s start, or baseline.

“The similarities and differences of our findings across populations, regardless of the task used to induce fatigue, provides new insights into cognitive fatigue resulting from brain injury and disease,” Glenn R. Wylie, PhD, director of the Kessler Foundation’s Rocco Ortenzio Neuroimaging Center, said in a foundation press release.

“Demonstrating that cognitive fatigue is not task-dependent provides the direction needed to develop effective strategies for managing debilitating cognitive fatigue that severely impacts individuals’ daily functioning and quality of life,” Wylie said.

The study, “Evaluating the effects of brain injury, disease and tasks on cognitive fatigue,” was published in the journal Scientific Reports.

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In the general population, fatigue is often temporary and goes away on its own. In people with brain injury or disease, however, it can persist and contribute to a lower quality of life. In people with MS, for example, fatigue is common and one of the most debilitating symptoms of the disease, being also linked to cognitive impairment.

Still, whether people with neurological problems experience fatigue the same way as healthy people do, or have different levels of fatigue, remains unknown.

Wylie and other researchers at the Rocco Ortenzio Neuroimaging Center, in New Jersey, now focused on answering these questions, with a special focus on cognitive fatigue, noted as CF.

Their aim, they said, was “to develop a clear understanding of what fatigue is and to understand its role in cognition, both of which are necessary to develop effective treatments.”

Their study compared 31 adults with MS and 31 adults with traumatic brain injury with a control group of 30 healthy individuals. Those with MS were an average of 8.7 years older than were the healthy individuals; the MS group also had a higher proportion of women (90.3% vs. 56.7%).

A working memory task and a processing speed task were used to trigger cognitive fatigue among participants while MRI data were collected. State cognitive fatigue, which builds up over a short time window, was scored from zero (no fatigue) to 100 (maximally fatigued) on a visual analogue scale.

Working memory is the brain’s ability to temporarily hold and work with information while engaging on a task, like remembering a phone number while dialing. Processing speed is how quickly the brain can take in and respond to information.

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Findings suggest base levels of fatigue are higher with MS, brain injury

Adults with MS tended to report more cognitive fatigue than did healthy individuals, both before the tasks and while performing the tasks. This occurred regardless of whether working memory or processing speed were measured.

For adults with traumatic brain injury, fatigue was significantly higher when compared with healthy individuals. MS and traumatic brain injury groups “did not significantly differ from one another,” the researchers wrote.

“These differences provide support to the idea that CF experienced by clinical groups is similar and that this ‘pathological’ CF differs from the CF experienced by the control group,” they wrote.

However, cognitive fatigue built up at a similar rate in all three groups, as determined by scoring such mental exhaustion at several time points while performing the tasks. Moreover, cognitive fatigue scores remained stable across the tasks, meaning that all tasks led to similar increases in fatigue.

“This suggests that higher CF reported by clinical samples (‘pathological fatigue’) results from a baseline shift rather than from different accrual [buildup] rates of CF during task performance,” the researchers wrote.

MRI data revealed that brain activation in the caudate nucleus and thalamus was consistently linked to cognitive fatigue in all three groups, while differing in the dorsal (back part) of the caudate nucleus. The caudate nucleus and thalamus play roles in learning and memory.

“These results suggest the caudate and thalamus to be central to CF while more dorsal aspects of the caudate may be sensitive to damage associated with particular types of insult,” the researchers concluded.

The study was funded by the Kessler Foundation, the New Jersey Commission for Brain Injury Research, and the National MS Society.