Slow-wave sleep linked to Parkinson’s disease cognition

SAN DIEGO – Slow-wave sleep improves cognition in Parkinson’s disease, according to University of Alabama at Birmingham investigators.

After sleep studies, they compared the cognitive performance of 16 patients who spent more than 14% of their sleep time in slow-wave (SW) sleep with the cognitive performance of 16 who spent less than 14% in SW sleep; 13 of the patients in the low SW group (81%) met the criteria for mild Parkinson’s disease (PD) cognitive impairment versus 7 of the patients in the higher SW sleep group (44%); the patients were well matched for age, sex, disease duration, and other variables.

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The normative value for SW sleep is about 15%-20%, although people spend less time in SW sleep as they age. The study subjects were in their mid-60s on average, so the 14% cut point wasn’t too far off from what might be considered typical.

More SW sleep in PD was associated with better performance on measures of global function, attention/working memory, executive function, and language comprehension. Patients in the low SW group, for instance, performed 0.25 standard deviations below the normative mean on attention/working memory tests, while subjects in the high SW group performed 0.5 standard deviations above, meaning that they outperformed people in their age group who didn’t have PD. These differences were statistically significant.

It raises the question of what can be done to help PD patients sleep better. “I’m interested in exercise to improve sleep, and we have some primary data that show it’s helpful for sleep in general but also SW sleep,” said Dr. Amara. Sodium oxybate (Xyrem) might also help, but for now, it’s a controlled substance approved only for narcolepsy. “We might have to branch out and try something novel,” she said.

Dr. Amy Amara

The next step is to “see if we can use SW sleep to predict who might have cognitive declines and find interventions to [prevent] it,” she said.

Patients in the study had been diagnosed with PD for a mean of about 7 years. People in the high SW group were on lower amounts of levodopa equivalents, however, the investigators controlled for that, as well as for the fact that women tend to spend more time in SW sleep than men. There were no differences between the groups in measures of movement problems and of subjective scores of sleep quality and daytime sleepiness.

People with high SW sleep fell asleep sooner than did those in the low SW groups, about 9 minutes versus 20 minutes. There was no correlation between visual-spatial function and SW sleep, but visual-spatial function did correlate with the amount of time spent in rapid eye movement sleep, suggesting that dreaming might be important for visual-spatial function, Dr. Amara said.

The work was funded by the National Institutes of Health. Dr. Amara had no relevant disclosures.

aotto@frontlinemedcom.com