Abstract

Phase-amplitude coupling (PAC) between brain oscillations is thought to be an underlying neural mechanism of memory consolidation. Oscillation coupling may become weaker with greater age, possibly explaining natural memory decline across the lifespan, as suggested by studies of PAC during non-rapid-eye-movement sleep. Theta-gamma PAC (TGC) during wake is correlated with stronger encoding and better recall. However, it is unclear how TGC during rapid-eye-movement (REM) sleep correlates with memory or changes with age. I aimed to find TGC during REM sleep (REM TGC) affecting sleep-dependent memory consolidation that changes with age-related memory decline. We recorded scalp electroencephalography of good sleeping younger and older adults. Oscillatory data was extracted from filtered electroencephalography signals. Before sleep, participants learned a declarative memory or non-memory control task, then retested the respective task after sleep to measure memory consolidation. Memory consolidation was better in younger, compared to older, adults. REM TGC strength, measured by a modulation index, was not different between age groups nor task nights. Faster gamma coupling in a frontal channel was positively correlated with and predicts improvements in memory consolidation in younger adults. Slower gamma coupling in a central channel was positively correlated with memory consolidation in older adults. Our results suggest REM TGC strength is stable across the lifespan. However, the strength of faster TGC in younger and of slower TGC in older adults may improve memory consolidation. These results uncover more about how REM sleep and REM TGC changes across the lifespan, in relation to memory.


Keywords: rapid eye movement sleep, theta-gamma phase-amplitude coupling, sleep-dependent memory consolidation, aging