Improving longer-term memory via wakeful rest in health and amnesia: evidence for memory consolidation
Alber, Jessica Lynne
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A short wakeful rest immediately after new learning boosts verbal memory retention over several minutes. This memory boost is observed both in healthy people and in patients with amnesia, including patients with amnestic mild cognitive impairment (aMCI) and mild Alzheimer’s Disease (AD). Wakeful resting is hypothesized to boost memory by protecting the memory consolidation (strengthening) process from interfering sensory stimulation. The effect of a short wakeful rest immediately after new learning has, to this stage, been tested only over standard retention intervals (≤1 hour). The objectives of this PhD project were to: 1.) examine whether a short wakeful rest immediately after learning boosts memory over a longer retention interval (7 days) in healthy older adults (Experiment 1, Experiment 2) and aMCI/mild AD patients (Experiment 3) 2.) investigate whether intentional rehearsal is necessary and sufficient to boost memory during wakeful rest, over both short-term (15-minute) and long-term (7-day) delays (Experiment 4, 5 and 6) 3.) compare the effect of a short post-learning rest on retention as assessed via cued recall, free recall and recognition, both over short delays (15 minutes) and long delays (7 days and 4 weeks) (Experiments 4,5 and 7) 4.) examine whether a short wakeful rest immediately after learning boosts retention of real-life-like stimuli (face/name paired associates) in healthy older adults and aMCI/mild AD patients (Experiment 8, Experiment 9) In order to accomplish these aims, several samples of healthy adults and amnesic patients were tested, utilising a range of experimental designs. In all experiments, the learning of new material was followed immediately (i) by a brief wakeful rest, or (ii) by a cognitively demanding task. A delayed memory test took place after a range of intervals. The results demonstrate a pronounced memory enhancement over 15-30 minutes and 7 days in aMCI/mild AD patients via a short post-learning wakeful rest. A similar, albeit less pronounced 7-day memory benefit via post-learning wakeful rest was found in healthy older adults. Moreover, it was found that post-learning wakeful resting boosted 7-day recognition memory in healthy older adults, even when the learned material could not be rehearsed intentionally. Although intentional rehearsal did provide a 7-day memory improvement in healthy older adults, the present results indicate that it is not necessary in order to enhance long-term recognition memory via wakeful resting. The long-lived memory benefit gained via post-learning wakeful rest was shown to last at least 4 weeks in healthy adults, and free recall tests were more sensitive to the post-learning delay manipulation than cued recall tests. Finally, healthy controls and aMCI/mild AD patients who were able to learn face/name pairs showed enhanced 30-minute retention of these stimuli following wakeful rest conditions. The present findings demonstrate that both clinical and non-clinical populations are able to retain more new information over long periods, if the time interval immediately after new learning is devoid of further sensory stimulation. These results contribute to a growing body of literature stipulating that minimizing sensory stimulation frees early memory consolidation resources, allowing for superior offline consolidation of verbal material over a standard (≤1 hour) interval. The findings of this thesis extend this hypothesis over (i) a longer interval and (ii) to real-life-like stimuli, and these results are examined in light of memory consolidation theory. Implications of the premise of retroactive interference as a mechanism of longer-term forgetting are discussed.