Mechanism For Effects Of Aging On Sleep-dependent Memory Consolidation

Sleep not only has important physiological significance,but also plays a vital role in human cognitive processes.Studies have shown that post-learning sleep helps to keep and improve memory compared with an equal-length wake interval,this can be called sleep-dependent memory consolidation(SDC).With aging,older adults’ memory are gradually impaired;and also accompany by impaired sleep function,such as decreased sleep time,increased sleep fragments,decreased sleep efficiency and reduced slow wave sleep.Thus,the changes of SDC with aging have aroused widespread concern among researchers.Although a large number of studies suggest that SDC is impaired during aging,the results are not consistent due to the influences of memory type,sleep stage,and memory retrieve.In addition,studies have shown that emotion can facilitate memory consolidation,that is,compared with neutral memory,emotional memory can not only get a deeper degree encoding can also be retrieved better.In recent years,results suggest that sleep has a greater effect on emotional memory consolidation than neutral memory consolidation,and has a delay effect with time.However,the sleep-dependent emotional memory consolidation mechanism affected by aging has not yet been elucidated.Previous studies generally supported that older adults have positivity effect,and within memory,attention,decision-making and other areas,older adults tend to pay attention to positive stimulus and avoid negative stimulus.However,whether there is the same positivity effect in SDC with aging has not been studied yet.In view of this,we conducted the following three studies:Study 1 applied a meta-analysis to explore the age effect in SDC.After study selection,15 articles containing 22 studies examining age-related changes in SDC were included in the present meta-analysis.First,we compared the differences in SDC between young and older adults;and then examine the age differences in SDC inspecific memory types;finally,we further explore the origination of the age differences by testing the age-related differences separately for the sleep and wake condition.The results show that older adults have a decline in SDC relative to young adults across memory types.Moreover,this age-related degradation in the sleep-dependent beneficial effect is mainly manifested in declarative memory relative to procedural memory.Study 2 investigated the positivity effect of SDC with aging from the aspect of positive stimulus bias.The results shown that post-learning sleep benefited emotional memory consolidation,for young adults,sleep promoted the neutral memory consolidation,but for older adults,sleep selectively facilitated the positive memory consolidation,suggesting that there was positivity effect of SDC with aging.We also found a significantly negative correlation between the proportions of deep sleep and the negative memory retention in young adults,but this was not significant in older adults,suggesting that the positive emotional bias of SDC in older adults may be related to the impaired functional connection between deep sleep and negative memory.Study 3 aimed to investigate the SDC in older adults from the perspective of negative stimulus avoiding.The results shown that post-learning sleep,compared with post-learning wake increased the forgotten rate of the negative pictures’ spatial location related to neutral pictures for young adults,whereas decreased the forgotten rate of the negative pictures’ spatial location related to neutral pictures for older adults.The results suggested that there was negative emotional circumvention phenomenon: because older adults refused the negative emotion of the picture,they paid more attention to remember the location of the pictures,whereas young adults paid more attention to the negative emotion of the pictures rather than the locations,contributing to the differences between the two valence memories after sleep.Combined,compared with young adults,the effect of sleep to promote memory consolidation was impaired in older adults,and age difference of SDC was mainly manifested in declarative memory;For SDC,there was positivity effect in older adults.This study first quantified the SDC effect with aging,and further examined emotion influence on SDC in older adults.It provides a theoretical basis for the investigation of neural mechanisms underlying SDC and cognitive intervention researches for older adults,as well as enriched theories of SDC.