CLINICAL REVIEWSleep loss, learning capacity and academic performance
Introduction
Sleep is an active, repetitive and reversible behaviour serving several different functions, such as repair and growth, learning or memory consolidation, and restorative processes: all these occur throughout the brain and the body.1, 2 Thus, during sleep behavioural, physiological and neurocognitive processes occur: these very processes are susceptible to be impaired by the absence of sleep.
Sleep loss is, in fact, one of the most striking problems of modern society.3 Very often, to cope with our many daily interests, we prefer to sacrifice some sleep time, in the hope that this will not induce dangerous effects but will enable us to carry out several other activities. Unfortunately, this is not true and sleep deprivation has various consequences, such as sleepiness and impairments in neurocognitive and psychomotor performance.4, 5 More specifically, in their classic meta-analysis, Pilcher and Huffcut4 claimed that sleep-deprived individuals functioned at a level that is comparable with the ninth percentile of non-sleep-deprived subjects. These decrements in neurobehavioural functioning after sleep restriction or deprivation are well known and common to all people6, 7 even though some individual differences in vulnerability to sleep loss have been shown.8
The last few years have seen an increasing literature on the relationship between sleep, memory and learning capacity (e.g. Ref.9). Recent findings have shown that sleep plays an important role in learning processes and memory consolidation,10, 11 although no direct relationships were found between different kinds of memory, such as procedural or declarative memory, and different sleep stages, such as REM or NREM sleep.12 These studies clearly show that sleep deprivation can impair learning and memory for both motor procedural (e.g. Ref.10) and declarative memory systems (e.g. Ref.13).
It is well known that the integrity of learning and memory processes are fundamental in school achievement and academic performance, particularly in individuals like children and adolescents who are in a particular developmental phase.14, 15, 16, 17, 18 At this stage in life, adolescents suffer from increasing school, family and social pressure and from an environmentally induced delay of sleep timing,19, 20, 21 together with changes of intrinsic regulatory (both circadian and homeostatic) processes.22 Taken together, these altered sleep patterns lead to a marked increase in sleepiness23 that usually facilitates cognitive, emotional, behavioural and academic failure.22 Surprisingly, not much data exists regarding the specific effects of inadequate sleep and sleepiness on daytime functioning in children.17 Nevertheless, some experimental evidence reinforces the common belief that disrupted or poor sleep is usually followed by inefficient daytime behaviour and variability in performance. Within these activities, academic performance and/or school achievement should be carefully taken into consideration. As recently pointed out in some literature reviews,24, 25, 26 learning abilities and consequent academic performance are particularly dependent on sleep patterns and sleepiness levels. These impairments in neurocognitive functioning can be observed in several kinds of learners: from school to university students, so that the consequent ability to learn from lessons or from practical activities, such as laboratory work, very often proves to be drastically reduced.
The aim of this review is to focus on the effects of sleep deprivation/fragmentation on ‘day-after’ learning capacity and academic performance. In order to discuss these issues, we will briefly introduce the most recent findings on the relationships between sleep and learning-memory processes. Then, we will turn our attention to the studies showing the relationship between sleep patterns and schedules on academic performance and learning. Finally, we will discuss studies investigating the effects of induced sleep loss on academic performance and neurobehavioural functioning, with particular attention to learning capacity.
Section snippets
The relationship between sleep and learning-memory processes
For almost a century, several studies showed the beneficial effects of sleep on memory functioning in animals and humans for different types of learning materials.9, 27, 28 Recent studies in molecular genetics, neurophysiology, and cognitive and behavioural neuroscience have strengthened the idea that sleep may play an important role in learning and memory, although the extent of this role remains hotly debated.29 In fact, there is still poor understanding as regards which aspects of memory
Sleep patterns/schedules and academic performance
As seen in the previous section, sleep has a relevant facilitating role in learning and memory processes. Conversely, sleep deprivation and/or fragmentation usually impairs these functions. In the following, we will review the most relevant contributions in the literature investigating the effects of sleep patterns and schedules on academic performance of school and university students. It should be stressed that most of these studies correlated sleep-wake patterns with subjective (self- or
Effects of imposed sleep loss on learning and academic performance
Results from studies investigating the effects of different sleep patterns and schedules on academic performance showed that students who sleep poorly, with an elevated sleep fragmentation (i.e., reduced sleep quality), with later bedtimes and early awakenings, usually tend to offer a decreased academic performance and a reduced neurobehavioural functioning.14, 25, 26 However, the studies seen so far are only ‘naturalistic’ correlative ones: in this section we shall more deeply review those
Conclusions
The studies discussed here allow us to draw some conclusions. As a first observation, regardless of the theoretical framework adopted (dual process hypothesis or sequential processing hypothesis), both REM and NREM sleep seem necessary for learning and memory: thus, for an efficient consolidation of both (declarative) knowledge and (procedural) skills, the worst risk is sleep loss or fragmentation.
Moreover, it was shown that an increasing daytime sleepiness, as a consequence of poor sleep
Acknowledgements
We wish to thank Giancarlo La Camera, Ph.D. (NIH, Bethesda, USA) and Caterina Cinel, Ph.D. (University of Essex, UK) for their invaluable help in collecting some of the bibliographic material.
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