Sleep is defined as the rest for the mind and body which the receptivity to external stimuli and bodily movement decreases. Sleep is a reversible, active and repetitive behavior serving different functions, for instance memory or learning consolidation, growth and repair and restorative processes. The consolidation during sleep enhances qualitative and quantitative changes of memory representations. Through particular patterns of electric field potential oscillations and neuromodulators activity, rapid eye movement (REM) sleep and slow-wave sleep (SWS) support the synaptic consolidation and system consolidation respectively.
According to Czeisler (2015), the optimum sleep duration for adolescences or students are 8 hours or more, in order to have a better academic performance. According to Center for Disease Control and Prevention (CDC) (2014), it stated that there are approximately 50-70 billion of people suffering from sleep deprivation. Sleep deprivation is defined as lack of sleep, it can cause daytime sleepiness, weight loss or gain, fatigue and others. It also antagonistically influences the cognitive and brain function. Lack of sleep causes negative effects, for instance poor concentration and academic performance on adolescences and children. The researchers concluded that there is a negative association between individual task performance or academic performance and sleep deprivation. This is because sleep deprivation causes students perform poorly on memory, problem-solving tasks, attention and this antagonistically influenced their academic performance Thus, sleep is important for brain functioning and stores memories which lead to a better academic performance.
Therefore, this literature review will focus on how sleep affects academic performance. This literature review will first discuss about how sleep affects memory and lead to a better academic performance. Then, it will discuss about how sleep quality and duration affects academic performance.
2. The relationship between sleep and memory
2.1 The mechanism of sleep and memory
The cyclic occurrence of non-rapid eye movement (NREM) and rapid eye movement (REM) which includes slow wave sleep (SWS) are used to characterize sleep. In humans, the REM and SWS sleep controls the late and early part of nocturnal sleep respectively. Early part of sleep (SWS) has an advantage on the consolidation of declarative memories; whereas later part of sleep (REM) has an advantage on non-declarative memory, for instance emotional a procedural memory. The memories that are encoded into a temporary store are redistributed and reactivated into a long-term store during the SWS. The system consolidation of SWS depends on a dialogue between hippocampus under-top-down and neocortex that usually controlled by neocortical slow oscillations. REM sleep promotes synaptic consolidations that are supported by electrophysiological and molecular events. The REM sleep can disconnection the memory system and stabilized the transformed memories without disturbing the synaptic consolidation. Thus, the SWS and REM have different functions to develop memory consolidation which can lead to a better academic performance.
2.2 Sleep and memory enhances better academic performance
Sleep plays a significant role in consolidation of memory. The cognitive process whereby recognition, learning and experiences are recalled is known as memory. The daytime naps and nocturnal sleep is used to enhance and stabilized the memory processes. Different stages of sleep enhances different types of memories. The SWS improves declarative memories; whereas the REM improves non-declarative memories.
According to Ashworth et al. (2014), the result from sleep-dependent memory consolidation was assessed by using the actigraph (monitor sleep), Tower of Hanoi cognitive puzzle (implicit task) and animal name (explicit task) showed that there was an increment in performance of 25% and 14% on the Tower of Hanoi task and non-word learning task respectively after sleep in children. The increment performance on Tower of Hanoi task maybe because children are consolidating explicit aspect of the task and thus sleep is essential for consolidation memory in children in order to have a better academic performance. Furthermore, the result of an actigraph from a study showed that bad sleepers performed worst in the prospective memory task as compared to good sleepers (Fabbri et al. 2013). The good and bad sleepers were defined by using Total Sleep Time (TST), Sleep Efficiency (ES), Sleep Onset Latency (SOL), Number of Awakenings( NA>5) and Wake After Sleep Onset (WASO). According to Potkin and Bunney (2012), the result assessed from paired-associate test showed that an increment of 20.6% in declarative memory. It is also demonstrated that, the increment can only be observed in participants that are assigned to sleep condition not in no sleep conditions.
3. Sleep quality and academic performance
Sleep quality has an impact on cognitive performance and is itself impacted by numerous factors, for instance stress. A good sleep quality enhances concentration and memory, less stress and good mood. The consequences of poor sleep quality is daytime sleepiness. Poor sleep quality can affects student’s behavioral performance and cognitive functioning. Many studies stated that there are relationship between quality sleep, timing of sleep and sleep quantity in academic performance and learning abilities.
According to Gilbert and Weaver (2010), the result concluded from the Sleep Quality Score (GSQ) on the Pittsburgh Sleep Quality Index (PSQI) showed there were approximately 70% of non-depressed students had poor sleep quality score. There were 557 undergraduate students participated in this study. It also stated that 415 non-depressed students showed there is a relationship between poor sleep quality and lower academic performance. This study also proved that, there is a negative association between grade point average (GPA) and GSQ on the PSQI. The range for GSQ are 0-21, the higher the GSQ, the poorer the sleep quality and consequence affects the academic performance. In addition, according to Ahrberg et al. (2012), the result assessed by correlation analyses by using the PSQI, stress and grades stated that there was an interrelationship between stress, sleep quality and academic performance before the exam. It also stated that, there were 59%, 29% and 9% of students that had poor sleep quality (PSQI>5) before, after and during the exam respectively. A study with 385 adolescents aged form 13-18 years old was carried out by Short et al. (2013), showed that sleep quality was positively associated with poor consequences by using the recorded students sleep patterns and self-made questionnaire. For instance, it will recede daytime alertness, more depressed mood and poor academic performance.
4. Sleep duration and academic performance
The prevalent problems in adolescents and children are poor sleep quality, sleepiness and insufficient sleep. There is a relationship between this problems and memory, school performance and learning. According to National Sleep Foundation (2015), the recommendations sleep duration for children, adolescents and young adults are 9-11 hours, 8-10 hours and 7-9 hours respectively.
The result of a study assessed from analysis of covariance (ANCOVA) and compared between different variables and students total sleep duration stated that lower school grades, lesser behavioral persistence, more tiredness and inferior positive attitude towards life was due to the sleeping duration less than average, which is 8 hours for each night (Perkinson-Gloor et al. 2013). This study also stated that the average sleep duration of participants was 8.36 hours. In this study, it showed students with short sleep duration (<8 hours) are related to lower school grades in German language and Mathematics as compared to students with longer sleep duration (>8 hours). This study concluded that students with short sleep duration (<8 hours) were more tired and diminished the memory process which lead to a poor academic performance. Furthermore, according to Battammam et al. (2012), the result assessed by the self-made questionnaire and Epworth Sleepiness Scale (ESS) (to assess daytime sleepiness) showed that there is a negative association between increased daytime sleepiness, decreased night sleep time and late bedtimes on weekends and weekdays and academic performance in medical students. It also stated that, there were 72% (295 students) had 'average' academic performance (GPA<3.75) and 28% (115 students) had 'excellent' academic performance (GPA'3.75). The 'average' group had higher percentage of student had daytime sleepiness and higher ESS score (>10). On the contrary, the ‘excellent’ group had lower ESS score (<10) and increased in total sleep time on weekdays. Thus, it showed that there is a relationship between increased in total sleep time and academic performance. Another study carried out by Li et al. (2012) based on school-based intervention, national cross-sectional survey and a proposed cohort study showed that there is a positive association between daytime sleepiness and insufficient sleep with poor school or academic performance. It also showed that the percentage of predominance daytime sleepiness was 64.4%. This indicated that daytime sleepiness (short sleep duration) caused impairment in attention, academic performance, memory and learning motivation. 5. Discussion There are many studies showed that, there is an interrelationship between different sleep variables and memory and academic performance. In this literature review, the relationship between sleep and memory which lead to a better academic performance, sleep quality and sleep duration and academic performance were discussed with the used of up to date studies. All of the articles collected were taken from year 2010 onwards. Most of the studies had positive consequences. Therefore, it showed that there is a relationship between sleep and memory which lead to a better academic performance, relationship between sleep quality and academic performance and relationship between sleep duration and academic performance. Nevertheless, majority of the studies reviewed had limitations. Small sample size is one of the limitations that arise from most of the studies. Small sample size will produce false-positive results, cannot used to conclude the results obtained to a larger population and it will usually over-estimate the significance of an associations. Thus, small sample size is a problem for most of the studies. Therefore, in future research a large sample size is needed, so that the results obtained can be used to generalize to a bigger population. Another limitation is the disease status of a participant. Those participants with dementia or AD are not able to precisely recall their sleep-related factors and disease history that was possessed by self-reported (Xu et al. 2010). Thus, in future research, the sleep-related factors, for instance polysomnography and neurobiological disease need to be measured objectively, in order to determine the sleep duration of each participants. Furthermore, inaccurately self-reported by the participants is also one of the limitations that arise from most of the studies. According to BaHammam et al. (2012), it stated that there might be some of the students inaccurately reported their wake or sleep habits. Therefore, by using the actigraphy measurements, a defined validation of self-reported sleep duration is conducted with it. ur text in here...
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