Cardiorespiratory Fitness May Protect Memory for Poorer Sleepers

Exercise and Protection from Age-Related Cognitive Decline

In this chapter, we review the cross-sectional evidence in healthy human subjects for physical activity and cardiorespiratory fitness to offer neuroprotection and moderate cognitive decline in older age. The role of exercise training on cognition in healthy older adults and those diagnosed with mild cognitive impairment (MCI) is also discussed, including the evidence from neuroimaging studies that document changes to brain structure and function after a period of exercise training and improved fitness. Finally, in reference to animal models, the potential neurophysiological mechanisms for physical activity and exercise to impact human brain health are highlighted.

Does Cardiorespiratory Fitness Protect Memory from Sleep Deprivation?

INTRODUCTION

Animal studies have demonstrated that physical exercise can protect memory from the effects of sleep deprivation (SD). We examined whether having a high cardiorespiratory fitness (V̇O 2peak ) is associated with an enhanced capacity to encode episodic memory after one night of SD.

METHODS

Twenty-nine healthy young participants were allocated into either an SD group ( n = 19) that underwent 30 h of uninterrupted wakefulness, or a sleep control (SC) group ( n = 10) that followed a regular sleep routine. Following either the SD or SC period, participants were asked to view 150 images as the encoding part of the episodic memory task. Ninety-six hours after viewing the images, participants returned to the laboratory to perform the recognition part of the episodic memory task, which required the visual discrimination of the 150 images previously presented from 75 new images introduced as distractors. Cardiorespiratory fitness (V̇O 2peak ) was assessed with a bike ergometer graded exercise test. Group differences in memory performance were assessed with independent t tests and associations between V̇O 2peak and memory with multiple linear regression.

RESULTS

The SD group showed a significant increase in subjective fatigue (mean difference [MD] [standard error {SE}] = 38.94 [8.82]; P = 0.0001) and a worse capacity to identify the original 150 images (MD [SE] = -0.18 [0.06]; P = 0.005) and discriminate them from distractors (MD [SE] = -0.78 [0.21] P = 0.001). When adjusted for fatigue, higher V̇O 2peak was significantly associated with better memory scores in the SD (R 2 = 0.41; β [SE] = 0.03 [0.01]; P = 0.015) but not in the SC group ( R2 = 0.23; β [SE] = 0.02 [0.03]; P = 0.408).

CONCLUSIONS

These results confirm that SD before encoding impairs the capacity to create robust episodic memories and provide preliminary support to the hypothesis that maintaining high levels of cardiorespiratory fitness could have a protective effect against the disruptive effects of sleep loss on memory.

Acute evening high-intensity interval training may attenuate the detrimental effects of sleep restriction on long-term declarative memory

Recent evidence shows that a nap and acute exercise synergistically enhanced memory. Additionally, human-based cross-sectional studies and animal experiments suggest that physical exercise may mitigate the cognitive impairments of poor sleep quality and sleep restriction, respectively. We evaluated whether acute exercise may offset sleep restriction's impairment of long-term declarative memory compared to average sleep alone. A total of 92 (82% females) healthy young adults (24.6 ± 4.2 years) were randomly allocated to one of four evening groups: sleep restriction only (S5, 5-6 h/night), average sleep only (S8, 8-9 h/night), high-intensity interval training (HIIT) before restricted sleep (HIITS5), or HIIT before average sleep (HIITS8). Groups either followed a 15-min remote HIIT video or rest period in the evening (7:00 p.m.) prior to encoding 80 face-name pairs. Participants completed an immediate retrieval task in the evening. The next morning a delayed retrieval task was given after their subjectively documented sleep opportunities. Long-term declarative memory performance was assessed with the discriminability index (d') during the recall tasks. While our results showed that the d' of S8 (0.58 ± 1.37) was not significantly different from those of HIITS5 (-0.03 ± 1.64, p = 0.176) and HIITS8 (-0.20 ± 1.28, p = 0.092), there was a difference in d' compared to S5 (-0.35 ± 1.64, p = 0.038) at the delayed retrieval. These results suggest that the acute evening HIIT partially reduced the detrimental effects of sleep restriction on long-term declarative memory.