Effects Of Sleep Deprivation And Nap On Working Memory Tasks

The concept of sleep deprivation originated from the description for the sleep loss,which caused by the continuous working period.Gradually,it forms an independent concept.Sleep deprivation refers to a state of multiple deficits of cognitive performance resulting from total sleep loss or partial sleep loss,along with a series of psychological and physiological dysfunction,such as vigilance,memory,emotional processing,decision making,etc.Working memory is a system to maintain and process information during the cognitive processing.At present,the research on the effects of sleep deprivation on performance of working memory has some inconsistent results.Some studies showed that the performance of working memory decreased after sleep deprivation,while others did not find significant changes of the working memory performance after sleep deprivation.On the other hand,many studies show that the nap is an effective way to resist the adverse effects of sleep deprivation.Taking a nap after sleep deprivation is a short period of sleep,typically lasts for 15-30 min.Some studies showed that the nap can relieve fatigue and improve the cognitive function after sleep deprivation,while other studies showed that it is in vain.Therefore,the present study attempted to explore the issues mentioned above by conducting two experimental studies.Study 1 used the traditional behavior method to investigate the different working memory performance after 36 h of total sleep deprivation.The experiment adopted the paradigm of OSPAN(Operation Span)working memory task.The OSPAN paradigm can be divided into simple and complex working memory task.The former named as Letter task,including the stage of working memory maintenance and the stage of simple processing(arrow pointing),the latter task includes the stage of maintenance and complex processing(equation judgment),which named as the OSPAN task.Additionally,the two different processing stage are also studied as two independent task conditions,which named as Arithmetic task and Baseline task separately.This paradigm offered the possibility to explore the reasons why there were so many studies showing the inconsistency in the effects of sleep deprivation on working memory.The results showed: the accuracy and reaction time of OSPAN task and arithmetic condition did not change obviously after 36 h of total sleep deprivation;while the accuracy of the Letter task significantly decreased.In other words,the performance of the complex OSPAN working memory task and the complex processing stage after 36 h of total sleep deprivation had been maintained the same performance as the stage before sleep deprivation.Study 2 combined the technique of f MRI(functional magnetic resonance imaging)and the same experiment paradigm as mentioned in the study 1.It aimed to reveal the neural mechanism of the effects of 36 h of total sleep deprivation on simple and complex working memory task from the perspective of large-scale brain networks.Additionally,another part of 30 min nap was added behind the 36 h of total sleep deprivation.For the results,on the behavioral level,this experiment drew a consistent conclusion with the Study 1 after 36 h of sleep deprivation.On the other hand,we did not find any restorative effects after 30 min nap;While on the neurological level,we explored the effects of sleep deprivation and 30 min of nap on the interaction of frontoparietal control network(FPC),default mode network(DMN)and dorsal attention network(DAN).Independent component analysis(ICA)was firstly conducted to obtain the three networks.By comparing their activation and functional connectivity among the three networks,we found:(1)the activation of FPC is significantly increased during the OSPAN task after sleep deprivation,but performed decreased trend during the other three tasks.There is no obvious change after 30 min nap.The activation of DMN demonstrates opposite changes on the complex and simple working memory tasks.That is to say,decreased activation was found during the OSPAN task and Arithmetic task,while increased activation was found during the Letter task.For the DAN,it shows a significantly decreased activation during the OSPAN task and Arithmetic condition.Then we do not reveal any obvious changes after 30 min nap.(2)For the functional connectivity of each other,we only find the connectivity of DMN-DAN was obviously decreased after sleep deprivation.(3)the changes of DMN-DAN connectivity is positively correlated with the performance of Letter task,which shows that this functional connectivity can be used as a reliable indicator to predict the performance of simple working memory.But the correlation becomes tight after 30 min nap,demonstrating that the 30 min of nap do not cause the restorative effect to some extent.In summary,our study revealed the effects of 36 h of total sleep deprivation and 30 min of nap on simple-complex working memory tasks from the perspective of large-scale brain networks by using the f MRI.It provides new neuroimaging evidence for the argument issues as we mentioned above.The results are important for understanding of the neural mechanism on which sleep deprivation and nap impact the cognitive performance and developing effective intervention strategy against sleep deprivation.