Sleep Deprivation May Worsen Memory in Early MS
A link also was observed between a lack of sleep and worse cognitive efficiency in early MS, but that association was caused by the worse moods that occur in people with sleep disturbances, the researchers said.
“The initial observations of this study connect patient-reported sleep disturbance specifically to poor memory in early MS, even when controlling for key covariates [independent variables] including mood, fatigue, and disability,” the investigators wrote.
The study, “Sleep disturbance and memory dysfunction in early multiple sclerosis,” was published in Annals of Clinical and Translational Neurology.
Memory consolidation — the process of preserving vital memories or experiences and discarding unnecessary information — occurs during sleep. Sleep-deprived people may develop poor memory, researchers say, because the brain has insufficient time to consolidate memory and prepare to learn new information upon waking.
Impaired memory is common in MS, with some studies linking it to a deterioration in parts of the brain. Specifically, research has pointed to degradation in the hippocampus — essential for memory and learning — and the thalamus, which transmits messages to the cerebral cortex, a part of the brain that interprets and processes information from memories.
However, these studies only show a modest link between brain deterioration and impaired memory, so scientists believe other factors are involved.
People with MS are known to frequently experience poor sleep and show signs of sleep deprivation. Since past studies have established a link between sleep and memory, a team of researchers in New York now sought to determine whether poor sleep contributes to impaired memory in people with multiple sclerosis.
A total of 185 adults diagnosed with CIS or RRMS in the previous five years were included in the analysis, which was funded by the National Institutes for Health. These patients, who were part of the Reserve against Disability in Early MS (RADIEMS) study, underwent a number of assessments, including a patient-reported sleep disturbance questionnaire, and measures of memory and cognitive speed.
The memory and cognition tasks also were completed by 50 healthy individuals (controls) with matched characteristics to the MS patients in the study.
Overall, 40.2% of the MS patients reported sleep disturbances. Patients with sleep deprivation were similar to those without sleep problems in terms of age, sex, disease course, medications, caffeine consumption, and physical disability.
However, those with trouble sleeping reported worse mood and increased fatigue, and had a higher number of brain lesions than those without sleep disturbances.
Participants with sleep deprivation also had significantly worse memory than people without sleep disturbances — even after controlling for variables that may affect sleep, such as age, sex, mood, fatigue, body mass index (BMI), and medications. However, patients without sleep problems performed as well as the healthy controls on memory tests.
“Self-reported sleep disturbance was associated with memory dysfunction in our early MS cohort, even when controlling for important potential confounds,” or other potentially impacting factors, the researchers wrote.
An initial link also was observed for worse cognitive efficiency, or speed, and sleep disturbances. Importantly, however, this association was no longer present when mood was taken into account.
According to the researchers, this “suggests that the simple association between sleep disturbance and cognitive efficiency … was mediated through (explained by) worse mood.”
Based on animal and human studies, an explanation for the link between sleep and memory could be that inadequate rest impairs the hippocampus’ ability to process new information, leading to worse memory.
Other studies have not found a link between poor sleep and memory, but that may possibly be due to the fact that their samples were small and the researchers did not measure visual memory, the investigators in this study said.
However, this larger and more uniform group of patients “may have yielded more power to detect a relationship,” the researchers wrote.
Limitations of the study, as highlighted by the researchers, included measuring sleep deprivation only once with self-reported questionnaires and conducting memory assessments at just one time point.
However, the team concluded that their observations “connect patient-reported sleep disturbance specifically to poor memory in early MS.”
“Future research is needed to replicate our current findings with objective measures of sleep disturbance … which will help identify basic mechanisms of this relationship in MS,” the researchers added.
Additional data could point the way to potential therapeutic targets, the team said.
“Sleep treatments may represent biologically plausible interventions to improve memory, which would be valuable given the absence of validated memory treatments in MS,” the researchers wrote.