Sleep and memory
Walker has written about the effects of sleep on student learning and recommends a rethink around the idea of end-of-semester exams that encourage cramming, even all-nighters. He has changed his own teaching to avoid final exams, splitting his courses up into thirds to spread the assessment load.
Sleep before learning
Sleep is an active process that improves memory. When we are awake the hippocampus experiences and learns things in the real world, as a short-term location for new memories. It is also limited in capacity. It deals with this by shifting memories into other locations, namely the cortex, during sleep. You can test this using daytime naps and Walker compared a 90 minute ‘nap’ with a ‘no-nap’ group, after they performed a taxing 100 face-name pair task. Later that day, another intense learning task was performed, to see if learning had declined. Those that napped actually increased their ability to learn, while those that stayed awake showed a decline, the difference being a staggering 20%. It would appear that light, Stage 2 NREM sleep and short sleep spindles led to greater retention. It would appear that sleep refreshes our ability to learn, especially the later period of a night’s sleep. Getting up too early and shortening your sleep period seems to be deleterious to learning. This seems to decline with age.
Sleep after learning
What about after one has learnt something? Consolidation of memories has been posited for 2000 years, but it was Jenkins and Dallenbach (1924), who tested forgetting of verbal facts over eight hours, either awake or asleep. This has been replicated many times and forgetting in the group that was awake is greater, the benefits of sleep being 20-40% greater for the sleep groups.
REM and NREM sleep was then discovered in the 1950s and the link between consolidation of memory and deep NREM was established, with MRI evidence indicating that memories literally move from the hippocampus to the neocortex during sleep. It would appear that your cache of memories gets cleared and stored every night, leaving you ready for the next day’s learning. Sleep can also improve learning by recovering memories you lost while learning. It seems to rescue memories. Motor skills are also consolidated and enhanced during sleep.
Stimulating learning during sleep
Sleepers stimulated by electrical voltage pulses during deep NREM. The sleepers felt nothing but doubled their ability to recall facts learnt just before going to sleep. Quiet auditory tones synchronised with brain waves, from speakers next to the bed, have also been found to have an effect, namely a 40% improvement on recall.
Sleep to forget
When two groups were presented with words to remember but told to remember some (tagged R) and forget others (tagged F), the group that had a 90 minute nap had actively remembered more R words and forgotten more F words. It would seem that sleep is quite intelligent or active in what it selects as memories to be stored.
Sleep and emotions
Emotions or the affective side of learning are also influenced by sleep. The brain does reprocess or modulate emotions through sleep. Sleep deprivation encourages high emotional responses including aggression, bullying and behavioural problems in children.
Walker has been criticised for being slapdash with his data and references in his book. He has responded and apologised for some of its weaknesses.
Walker’s book and TED talk popularised sleep research and although he has been criticised for some inaccuracies, the benefits of sleep are now well known, especially among teachers and parents, worried by the rise in late night screen time.
Walker, M., 2017. Why we sleep: Unlocking the power of sleep and dreams. Simon and Schuster.
Stickgold, R. and Walker, M.P., 2013. Sleep-dependent memory triage: evolving generalization through selective processing. Nature neuroscience, 16(2), pp.139-145.
Walker, M.P. and van Der Helm, E., 2009. Overnight therapy? The role of sleep in emotional brain processing. Psychological bulletin, 135(5), p.731.
Walker, M.P. and Stickgold, R., 2004. Sleep-dependent learning and memory consolidation. Neuron, 44(1), pp.121-133.
Walker, M.P. and Stickgold, R., 2006. Sleep, memory, and plasticity. Annu. Rev. Psychol., 57, pp.139-166.
Jenkins, J.G. and Dallenbach, K.M., 1924. Obliviscence during sleep and waking. The American Journal of Psychology, 35(4), pp.605-612.
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