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  • Laboratory studies have shown that total sleep

    2018-10-26

    Laboratory studies have shown that total sleep deprivation for 24–72h impairs the performance of many tasks [1,6,7]. So, it is possible that the lack of sleep may affect a basic cognitive process, such as attention, working memory or executive functions, crucial for the execution of a broad range of activities. Some studies have provided evidence of an effect of total sleep deprivation on attention [8], while others have documented and effect on executive functions [9]. However, conflicting results about the effects of total sleep deprivation on working memory have been found, since a dexamethasone acetate in this cognitive process has been observed in some studies, while no effect has been observed in other papers [10,11]. Several papers have demonstrated that total sleep deprivation affects verbal working memory, while other papers have failed to demonstrate an effect on visuospatial working memory [1]. Nevertheless, sleep deprivation affects performance on verbal and visuospatial tasks, which require the participation of phonological and visuospatial components of working memory [12]. On the other hand, partial sleep deprivation is a reduction in the number of hours a person normally sleeps at night, and this condition becomes chronic when it occurs over the course of several consecutive days [13,14]. This condition occurs commonly during weekdays in people working or studying on a morning shift, because they have to wake up early to go to work or school, but they tend to go to bed late due to occupational, social or recreational activities [1,2,14]. This chronic sleep reduction produces subjective feelings of sleepiness, tiredness, irritability, and lack of concentration [15,16]. Although many people are exposed to chronic partial sleep deprivation, its effects on basic cognitive processes are less known. An effect of sleep reduction on attention has been observed [8,17,18], but there are few studies documenting effects on working memory [19,20]. Working memory is a basic cognitive process that maintains a limited amount of information during a brief period, in order to organize, differentiate, and use this information [21,22]. Working memory has several components: phonological storage, visuospatial storage, an episodic component, and a central executive. The first two components are involved in storing information, while the last two components are related to the regulation and use of the stored information. The phonological component focuses on processing auditory information related to speech, reading, language comprehension, and vocabulary acquisition [23,24]. The visuospatial component is responsible for processing visual information, including both images and the location and placement of objects in space [23–25]. The episodic component is involved in the integration and transfer of information between the other stores of working memory [23,26,27]. The central executive is a component that selects relevant information and directs it to each memory subsystem [28]. Each component of working memory require the participation of different brain structures; the phonological component is related to the posterior parietal cortex of the left hemisphere [29], the visuospatial component is related to the medial frontal gyrus, the superior frontal sulcus and the intraparietal sulcus [29,30], and the central executive is related to the ventrolateral prefrontal cortex [31]. Different tasks have been used to evaluate working memory. One of these is the N-Back task, in which participants are presented with a stream of stimuli, and they have to decide for each event whether it matches the one presented N items before. This task has been used in many studies to evaluate working memory, because its design fits well with the working memory concept as expressed by Baddeley [22]. Also, this task has been used extensively in the fields of neuroscience, clinical and aging research [32–34]. Some concerns have been raised about the validity of the N-Back task as a working memory test, because it has low correlations (r=0.20) with other working memory tasks [35]. Nevertheless, high correlations (r=0.67, r=0.80) between N-Back and other working memory tasks have been found when a confirmatory factor analysis is used, that includes hierarchical latent factors that model task-specific, paradigm-specific and construct variance [36,37].