Background: Partial sleep deprivation is common among young adults today. Though multiple studies have stressed on the benefits of having a good sleep, medical students often compromise their sleep due to academic targets and stress. This can lead to changes in attention and cognition. The effects of acute partial sleep deprivation of a single night have been studied less and studies in the past in Indian context have shown controversial results that reaction time is decreased following acute partial sleep deprivation. Purpose: The purpose of the study was to evaluate the effects of a single night of partial sleep deprivation on the cognitive status and alertness of medical students in the Indian context and to find out the change in auditory event-related potential (AERP) and psychomotor vigilance of medical students following a single night of partial sleep deprivation. Methods: The study was a before–after experimental trial conducted among 20 medical student volunteers of a tertiary care hospital of eastern India. Baseline psychomotor vigilance task measured by unprepared serial reaction time, and AERP measured by P300, were assessed at baseline (after normal sleep) and after four hours of sleep deprivation (intervention). Results: It was seen that median RT had increased from 320.4 ms to 337.6 ms after acute partial sleep deprivation (P < .001). P300 and lapses (P < .05) were also found to increase significantly (P < .05), while there was significant decrease in correctness (P < .01). Conclusion: The study concluded that cognition is affected, including alertness and latency, following partial sleep deprivation even for a single night and contradicted earlier results of Indian studies stating variable effect on psychomotor vigilance. Keywords Sleep deprivation, cognition, reaction time higher P300 amplitude and smaller latencies for subjects with Introduction a higher educational level. A higher cognitive reserve may compensate for neurocognitive deficits. Much less is known Sleep is a fundamental body requirement for a healthy life. about the effect of PSD on the cognitive status and behavioral Still, millions of people across the world are sleep-deprived. functions of this group. Moreover, studies in the past in the Sleep deprivation has been observed to have a detrimental Indian context have shown controversial results that reaction effect on the physical and mental health and abilities 2–4 11 time (RT) is decreased following acute PSD. Hence, this of an individual, and it decreases attention span and study was conducted with an aim to evaluate the effects of performance. This finally involves various social, financial, PSD on the cognitive status and alertness of medical students and health-related costs. Partial sleep deprivation (PSD) or in the Indian context, and validate the earlier results. sleep restriction is a common condition that affects more than one-third of normal adults due to various factors including professional demands, social and domestic responsibilities, 2,7 and sleep disorders. Effects of total sleep deprivation and a more common form of sleep deprivation, that is, acute PSD, Department of Physiology, AIIMS, Bhubaneswar, Odisha, India have been extensively studied and demonstrated via various 7,8 AIIMS, Bhubaneswar, Odisha, India cognitive tests to produce decline in cognitive function. Corresponding author: Medical students, comprising one of the most intelligent Priyadarshini Mishra, Department of Physiology, AIIMS, Bhubaneswar, Sijua, sections of the society, often compromise their sleep to Patrapada, Odisha 751019, India. perform well in academics. Findings of Pergher et al showed E-mail: email@example.com Creative Commons CC BY: This article is distributed under the terms of the Creative Commons Attribution 4.0 License (http://www. creativecommons.org/licenses/by/4.0/) which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage). 58 Annals of Neurosciences 27(2) Before the study, participants were allowed to sleep for Methods 3 nights in the laboratory to avoid bias due to unfamiliar surroundings during sleep. Before the study was started, The study was conducted in the Department of Physiology, of a tertiary care center of eastern India, during May to July participants were instructed to avoid stimulants like caffeine 2018, after permission from Institute Ethics Committee. It was and also to avoid day time naps. Auditory event-related 12,13 a form of experimental study design (before and after study), potential (ERP) (P300) and psychomotor vigilance task where subjects served as their own controls. Intervention (PVT) were carried out on the subjects at 9:00 am on the that was given was a single night of PSD. Participants were day following a night of normal sleep, which was considered allowed to sleep for only 4 h (2–6 am). They were tested baseline. Each of the subjects then underwent PSD for a twice, once following a night of normal sleep (baseline) and single night in the laboratory. Following this acute partial again following a night of PSD (intervention). Considering deprivation of night sleep, their P300 and PVT were estimated unprepared serial RT as the primary variable for reference the next day at 9:00 am (Figure 1). that determines psychomotor of an individual, and based on P300 was measured in quiet surroundings using 9 15 the results of a study conducted in India where the mean RT Neuropack (Nihon Kodhen) as per the guidelines of the during baseline was 200.59 ± 34.59 ms and after intervention International Federation of Clinical Neurophysiologists. was 155.59 ± 36.24 ms, an effect size as drawn from this Event-related evoked potentials (P300) were recorded with correlation of 0.5 (being before and after) as 1.27 using with Ag/Ag Cl electrodes from standard locations using G*Power 3.1 software, and sample size was calculated as 10–20 International system. the electrodes were placed 11 at 5% level of significance with statistical power of 95%. at Fz, Cz, Pz (active electrodes at frontal, vertex, and An additional sample of 20% was taken into account during parietal areas), FPz (ground electrode on the forehead), and recruitment considering the chances of drop-out mid-way A1, A2 (reference electrode behind the ear lobules). The during the study, and thus fixed as 14. recordings were obtained in response to standard auditory All students in each year of Bachelor of Medicine and “odd-ball paradigm” where a frequent and a rare stimuli were Bachelor of Surgery (MBBS) were informed about details given randomly. The skin electrode contact impedance was of the study through a common e-mail and invited for kept below 5Ω. The subjects were instructed to press a participation. Those who gave consent were given a chance button on the response pad with the thumb of their to participate in the study. A brief clinical history was taken dominant hand on hearing Auditory 1 (target, rare) among and examination performed for all students showing their the frequently occurring stimuli delivered by headphones. willingness to participate in the study. Students with history During the recording session, subjects were instructed to fix of medical, neurological, hearing, or sleep related disorder, his/her eyes on a particular spot on the wall in front in order were excluded from the study. The remaining volunteers were to avoid electro-oculographic artifacts due to eye movements. given a sleep diary to be maintained for 2 weeks and their Signals were averaged for 20 trials. The P300 wave was self-ratings of quality of sleep were also assessed using the identified as the most robust positive wave between 200 Pittsburgh Sleep Quality Index (PSQI). Final selection of and 400 ms after stimulus recognition. The peak latency and subjects was done on the basis of average PSQI scores (scores amplitude (base to peak) of the waveform was recorded and from 0 to 5 indicated good quality of sleep and from 6 to 21 saved in the computer. Later these were entered in an MS indicated poor quality of sleep) and sleep diary. Volunteers Excel worksheet for data analysis. having poor quality of sleep at night and having less than 7 16 PVT by the PEBL software version 0.14 (Shane Mueller hours of sleep at night, as evidenced from sleep diary and August 2010) was utilized for PVT. The subject was seated PSQI, were excluded from the study. comfortably asked to respond as soon as possible to red circle appearing in the center of the screen by pressing “Space Bar” on computer keypad. The red circle usually keeps on Day 2 Day Day coming in the interval of 2–10 s. The unprepared serial RT Day 3 1 2 Night was calculated in milliseconds. The total task duration was 10 min. Scores for PVT were noted under the following heads: Measure Single average RT, number of lapses or errors of omission (RT > 500 Measurement ment of night of Single of Psychom partial night of ms), number of sleep responses (RT > 30 s), and number of psychomotor otor sleep normal vigilance and vigilance too fast responses/errors of commission. deprivatio sleep P300 and Data were entered onto a worksheet of MS Excel 2016, P300 and imported to Stata version 12.1 SE. Data were presented either as categorical or continuous variables. Appropriate statistical tests were applied for analysis of the data. A P value of .05 was set as statistically significant. P300 amplitude and latency and auditory PVT data were compared using matched Figure 1. Study Design: Each Participant Underwent a 3-Day, Protocol pair nonparametric tests (two-tailed sign test). Ethical Mishra et al. 59 clearance was obtained from the Institute Ethics Committee prior to the study. Results A total of 28 students expressed their consent to participate in the study and approached the investigators in response to the common e-mail sent. However, after maintaining the daily diary, it was seen that six students did not have adequate sleep that was considered for inclusion (>7 h). Two more students were excluded from the study because of poor quality of sleep (PSQI scores >6). Rest of the students were found to have a good quality of sleep ranging from 0 to 5 and were thus included in the study. Thus, a final total of 20 students were Figure 2. P300 (Latency) Before and After Acute Partial Sleep Dep- included in the experiment and were considered for analysis rivation Among Study Participants (n = 20) (n = 20). Median age of the study population was found to be 21.5 years (IQR: 21, 23 years). The study participants were predominantly males (n = 19, 95%). Considering a small sample size of 20, nonparametric tests were used for analysis. Two-tailed sign test was used to compare the values before and after PSD. It was seen that the median average RT had increased from 320.4 ms to 337.6 ms after acute PSD, which was found to be very highly significant (P < .001). Statistically significant increase in P300 and lapses (P < .05) with highly significant decrease in correctness (P<0.01) were also seen among the study participants (see Table 1). Table 1. Effect of Partial Sleep Deprivation Among Study Partici- pants (n = 20) Figure 3. Comparison of Average Reaction Time (RT) Before and Sl Pre-test Value Post-test Value After Acute Partial Sleep Deprivation Among Study Participants No. Component Median (IQR) Median (IQR) P Value (n = 20) 1. P300 303.5 (284.0, 309.5 (297.5, .0414* (latency 321.0) 337.0) in ms) P300 25.89 (16.64, 21.78 .16 (amplitude 31.39) (17.93,27.63) in μV) 2. RT 320.4 (315.0, 337.6 (326.6, .0004*** 332.3) 354.6) Too fast 1.0 (0.0, 2.0) 2.0 (1.0, 3.0) .1185 Lapse 1.5 (0.0, 2.5) 3.0 (2.0, 4.0) .0127* Correct 118.0 (117.0, 117 (115,117) .0013** 119.5) Note: *Significant at .05 levels. ** Highly significant at .01 level. *** Very highly significant at .001 levels. P300 = auditory event-related potential; RT Figure 4. Comparison of Too Fast Responses (TOOFAST) Before = average reaction time, Too fast = number of too fast responses in PVT, and After Acute Partial Sleep Deprivation Among Study Participants Lapse = number of lapses (RT > 500 ms), Correct = number of correct (n = 20) responses. 60 Annals of Neurosciences 27(2) our study revealed that PSD affects executive function and RTs in medical students. The brain is affected by sleep or its deprivation. Synaptic plasticity and strength require sleep, as a consequence of which cognitive abilities such as learning and memory (especially long term ) are impaired following its 15,19,17 deprivation. PSD, acutely and on a chronic basis, have been shown to have effects on cognition in many animal and 4,7,16,20–23 human studies. Short periods of sleep restriction, say even an hour, after cognitive learning, can impair formation of memory. In a study conducted among medical students elsewhere in northern India, the P300 latency and amplitude were Figure 5. Comparison of Lapses (LAPSE) Before and After Acute found to decrease significantly as compared to the test Partial Sleep Deprivation Among Study Participants (n = 20) values at baseline. RT also showed a significant decrease in the test condition as compared to the baseline values. The study demonstrated that PSD produces variable effects on the cognitive status of medical students as reflected by the decrease in P300 amplitude and latency. Alertness of medical students seemed to show an improvement as reflected by the decrease in RT. This was contrasting to our study, where RT and latency of P300 was found to be significantly more in comparison to be baseline, signifying decrease in alertness and attention. The possible reasons may be inclusion of students with only good quality sleep in the current study and more controlled environment during the study. Nap is often considered to be a powerful public health tool, and can reduce sleep-related accidents and improve performance. In a study trying to demonstrate the minimum Figure 6. Comparison of Number of Correct Responses (COR- effective duration of afternoon nap that could counteract RECT) Before and After Acute Partial Sleep Deprivation Among acute PSD, it was seen that among the various durations Study Participants (n = 20) of nap that can improve alertness and alertness following PSD, a 10 minute nap was the most effective among short nap durations that were considered in the study. In another Discussion study it was seen that nappers were able to tolerate frustration significantly longer than non-nappers. The latter reported The difference in P300 was found to be marginally significant, feeling more impulsive after a 60 minute period. Day with increase in PSD (Table1 and Figure 2). There were no time napping was avoided in the current study. Thus, these significant differences between the amplitudes. The RT was medical students can be told about this 10-minute nap, which found to be significantly high with increased number of can be taken after the acute PSD during day time during lapses and decreased number of correct responses in case of lunch break, and even during the night time for increasing PSD (Table 1, Figures 3, 4, 5 and 6). the attention span. However, chronic sleep deprivation needs Medical students have a rigorous curriculum and a to be avoided, and awareness created among the students, highly competitive environment for academic excellence. In since it decreases long-term memory function as seen from many situations, either during examinations or night duties, various studies. their sleep gets compromised. Acute PSD is more common than complete sleep deprivation in students. Educational background is a critical experience which develops over Conclusion a period of time. The impact of formal education on 10,17,18 cognitive ability has been explored in certain studies. The PVT and AERP were found to be significantly affected Higher education builds a cognitive reserve which can help by acute PSD in the medical students. The RT and P300 were compensate for conditions which affect neurocognition. found to increase significantly as was the number of lapses Pergher et al. found higher P300 amplitudes and observed (P < .05), while there was a highly significant decrease in smaller P300 latencies for individuals that were more educated correctness (P < .01) post intervention (sleep deprivation). compared to less educated ones. Though the cognitive reserve This showed that a single night of PSD was also able to have is considered to be higher in students with formal education, effects on cognition levels among medical students. Mishra et al. 61 Acknowledgments 10. Stern Y, Gurland B, Tatemichi TK, et al. Influence of education and occupation on the incidence of Alzheimer’s disease. 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Annals of Neurosciences – SAGE
Published: Apr 1, 2020