Effects of long sleep time and irregular sleep\u2013wake rhythm on cognitive function in older people

Masato Okuda,Norio Ozaki,Akito Shimouchi,Kunihiro Iwamoto,Kozue Takeda,Seiko Miyata,Fumihiko Yasuma,Akiko Noda,Honoka Nakashima

doi:10.1038/s41598-021-85817-y

Masato Okuda, Norio Ozaki + Show 7 more

Open Access

https://doi.org/10.1038/s41598-021-85817-y

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Abstract

Sleep disturbances and cognitive decline are common in older adults. We aimed to investigate the effects of the total sleep time (TST) and sleep–wake rhythm on executive function and working memory in older adults. In 63 older participants, we measured the TST, wake after sleep onset (WASO), and sleep timing (midpoint between bedtime and wake-up time) using actigraphy. Executive function was evaluated with the trail making test B (TMT-B) and Wisconsin card sorting test (WCST). The number of back task (N-back task) was used to measure working memory. Participants with a TST ≥ 8 h had a significantly lower percentage of correct answers (% correct) on the 1-back task than those with a TST < 8 h. The % correct on the 1-back task was significantly correlated with the TST, WASO, and sleep timing. Multiple regression analyses revealed that the TST and sleep timing were significant factors of the % correct on the 1-back task. The TMT-B score was significantly correlated with the sleep timing. Category achievement on the WCST was significantly correlated with the standard deviation of the sleep timing. Therefore, a long sleep time and an irregular sleep–wake rhythm could have adverse effects on executive function and working memory in older people.

Highlights

Sleep disturbances and cognitive decline are common in older adults
We evaluated the total sleep time (TST), sleep efficiency, and wake after sleep onset (WASO)
Our findings suggest that a long sleep time and an irregular sleep–wake rhythm are involved in declines in executive function and working memory in older people

Summary

Introduction

We aimed to investigate the effects of the total sleep time (TST) and sleep–wake rhythm on executive function and working memory in older adults. The % correct on the 1-back task was significantly correlated with the TST, WASO, and sleep timing. A long sleep time and an irregular sleep–wake rhythm could have adverse effects on executive function and working memory in older people. The role of the sleep–wake rhythm in cognitive function has not been completely evaluated in community-dwelling older people free from dementia-related disorders. The different domains of cognitive function have been widely assessed with the trail making test B (TMT-B)[12], Wisconsin card sorting test (WCST)[13], and number of back task (N-back task)[14, 15]. A long sleep time and an irregular sleep–wake rhythm may have a negative impact on the different domains of cognitive function

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