Abstract
Introduction
In young adults, sleep spindles are theorized to represent memory consolidation. Spindle density may be especially prominent when young adults encode information that has future relevance. Older adults, on the other hand, show reduced capacity for future thinking and deficits in sleep-dependent memory consolidation. To advance these literatures, we investigated whether the process of mentally simulating the future (versus remembering the past) was associated with subsequent alterations to sleep microarchitecture in young and older adults.
Methods
64 healthy adults aged 18–84 completed a polysomnography adaptation night followed by two in-laboratory experimental nights. On both nights, participants completed the Modified Future Crovitz Test (MFCT) in which they mentally simulated only future events or remembered only past events (night order counterbalanced). To quantify the extent of future/past thinking, we conducted linguistics analyses on tense (future/past) using LIWC 2015 software.
Results
On the future-thinking night, young adults with greater future-tense MFCT scores showed significantly greater spindle density across frontal, midline, and central sites (r=.42 to r=.51), even when controlling for age, gender, and total word count (all ps < .01). The opposite was true for middle-to-older aged adults; greater future-tense MFCT scores were associated with less spindle density across midline and central sites after controlling for age, gender, and word count (r=-.44 to r=-.46, ps<.05). However, while spindle density decreased, frontal slow oscillations increased in older adults with greater future-tense MFCT scores (r=.39, p<.05). On the past-thinking night, spindle density and slow oscillations were unrelated to past-tense or future-tense MFCT scores for either age group.
Conclusion
Age-related deficits in memory consolidation may be due to impaired tagging of information as having future relevance, or impaired physiological responses during sleep to wake-based tagging. Addressing encoding—spindle interactions may inform why cognitive functioning declines in some adults more than others.
Support
Sleep Research Society Foundation
Episodic memory and future thinking during early childhood: Linking the past and future