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Year : 2021  |  Volume : 48  |  Issue : 1  |  Page : 33-37

To study the association between daytime sleepiness and cognition as tested by stroop test in Indian medical students

1 Department of Physiology, ESIC Medical College and Hospital, Faridabad, Haryana, India
2 Department of Community Medicine, ESIC Medical College and Hospital, Faridabad, Haryana, India
3 Department of Physiology, ESIC Medical College and Hospital, MIA, Alwar, Rajasthan, India

Date of Submission10-Sep-2020
Date of Acceptance21-Feb-2021
Date of Web Publication5-May-2021

Correspondence Address:
Dr. Shilpa Khullar
Department of Physiology, ESIC Medical College and Hospital, NH-3, NIT, Faridabad, Haryana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jss.jss_89_20

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Context: Human populations have undergone a steady constant decline in sleep hours attributable to changes in environmental and social circumstances. Excessive daytime sleepiness has been associated with a decreased capacity to perform daily activities and cognitive decline all over the world particularly among students. Aim: The aim of our study was to see the association between excessive daytime sleepiness and cognitive function in Indian medical students. Settings and Design: It was a cross-sectional study conducted in a Government Medical College located in the Delhi/NCR region. Materials and Methods: The study included 60 healthy young volunteers in the 18–30 years age group of both sexes. The students were assessed for daytime sleepiness using the Epworth Sleepiness Scale (ESS). Color–Word Stroop Test was used to assess cognition in both the groups. Statistical Analysis: Data were expressed as mean ± standard deviation and analyzed using SPSS Software Version 21. Results: The average score of the ESS scale of the participants was 7.33 ± 2.20. In the Stroop Test, the reaction time of congruent trial and incongruent trial was 24.81 ± 7.76 and 31.15 ± 8.03 s, respectively. No significant correlation was seen between the ESS score and parameters of the “Stroop Test.” Conclusion: The reaction time of the incongruent trial was significantly higher as compared to the congruent trial (P < 0.05) in the Stroop Task. No significant correlation was seen between the ESS score and Stroop Test results.

Keywords: Cognition, daytime sleepiness, Epworth Sleepiness Scale, troop task

How to cite this article:
Khullar S, Singh M, Das S, Kamya. To study the association between daytime sleepiness and cognition as tested by stroop test in Indian medical students. J Sci Soc 2021;48:33-7

How to cite this URL:
Khullar S, Singh M, Das S, Kamya. To study the association between daytime sleepiness and cognition as tested by stroop test in Indian medical students. J Sci Soc [serial online] 2021 [cited 2022 Dec 5];48:33-7. Available from: https://www.jscisociety.com/text.asp?2021/48/1/33/315459

  Introduction Top

In the last decades, excessive daytime sleepiness and poor quality of sleep have been increasingly recognized as symptoms that must be identified and managed early because of their high prevalence in the general population, their numerous and potentially serious consequences, and their association with the majority of sleep disorders.[1] Excessive daytime sleepiness refers to uncontrollable dozing off and drowsiness during the daytime, leading to the inability to remain alert and cautious in performing important daily activities.[2] Excessive daytime sleepiness can be caused in a large proportion by the poor quality of sleep and can directly affect the 3 behavior and job performance of the individuals.[3],[4] The prevalence of excessive daytime sleepiness would be 12%–16% among the general population.[5],[6] and approximately one-third of adults report it as some form of insomnia during the course of a year.[7]

Among university students, sleep disturbances have been observed to be widely prevalent.[8],[9] New social and academic environment, excessive use of social media,[10],[11] and unhealthy lifestyle choices are some of the factors attributed to sleep problems among undergraduate medical students.[12] In addition to these factors, they generally do not have an adequate quality of life due to their high academic load, hospital shifts, and long hours of night study, which may even upset their quality of sleep and increase the risk of excessive daytime sleepiness.[13],[14]

Among the many consequences of this worrying finding, poor sleep quality has been associated with an increased risk of burnout, psychoactive substance use, anxiety, and depression.[15],[16] Moreover, numerous studies have shown a negative impact of daytime sleepiness and poor sleep quality on the academic performance of medical university students.[17],[18],[19] Indeed, hours of sleep acquired before examination time has been identified as a predictor of examination scores among medical students, also excessive daytime sleepiness before examinations has been shown to correlate with worse academic achievement.[20]

In our study, we have studied the cognitive function of subjects using the “Stroop Test” or “Stroop Effect” named after psychologist John Ridley Stroop who first identified the phenomenon in his PhD work in the 1930s. Several articles have made reference to this formative work, establishing it as a widely used test in cognitive psychology.[21]

With more people getting less sleep and given the growing rates of dementia in aging population globally,[22] it is vital that science advances our understanding of the effects of sleep loss on cognitive and emotional functioning.

The association between sleep factors and cognition has been explored in worldwide research with conflicting reports, necessitating further exploration in the field of sleep physiology. Keeping in mind the paucity of data on this subject in the Indian context, we undertook this study to examine how daytime sleepiness is a determinant of cognitive function as assessed by the “Stroop test.”

  Subjects and Methods Top

Study design

This was a cross-sectional study.

The study was conducted in the Department of Physiology of a Government Medical College located in Delhi/NCR over a period of 2 months between June and July 2019.

It had a total of 60 subjects of both sexes aged between 18 and 30 years. The purpose of the study was explained to all the subjects and written informed consent was obtained from each of them. The project was started after obtaining clearance from the Institutional Ethical Committee following approval of the project from ICMR.

Subject selection

The subjects were selected from MBBS students studying in 1st and 2nd years. The following inclusion and exclusion criteria were followed:

Inclusion criteria

Healthy young adults of both the sexes aged between 18 and 30 years with normal eyesight or corrected normal eyesight with normal color vision were included in the study.

Exclusion criteria

  1. History of any chronic medical illness
  2. Physical disability
  3. Neurological disorders
  4. Subjects with color blindness.

Epworth Sleepiness Scale

Daytime sleepiness was assessed using the Epworth Sleepiness Scale (ESS).[2] It is a simple, self-administered questionnaire with having a total of 8 items. It has good internal validity and reliability and is a low-cost and effective measure of assessing sleepiness in adults. The questionnaire asks the subject to rate his or her probability of falling asleep on a scale of 0–3 for eight different situations that most people engage in during their daily lives, though not necessarily every day. The scores for the eight questions are added together to obtain a single number.

Sleepiness is assessed using a 4-point Likert scale referring to an individuals' likelihood of dozing off in that situation

0 = would never doze off

1 = slight chance of dozing

2 = moderate chance of dozing

3 = high chance of dozing.

The maximum score possible is 24, with higher scores reflecting higher levels of sleepiness.

Interpretation of the Epworth Sleepiness Scale score

0–10 = normal range of sleepiness in healthy adults

11–14 = mild sleepiness

15–17 = moderate sleepiness

18–24 = severe sleepiness.

Stroop test

Before conducting the Stroop test, the subject was asked to relax for 5 min. After detailed history and physical examination, the subjects were first familiarized with the test, by doing a trial run. In the online version of the Stroop test, each subject was presented with a series of colored words (black, blue, green, and red). These words appeared in different colors, sometimes matching the word (e.g., word blue written in blue-congruent/Stroop facilitation) and sometimes not matching the word (e.g., the word blue written in red-incongruent/Stroop interference.[23] The task of the subject was to indicate as quickly as possible whether the color in which the word is written matches the word itself or not. Most people respond faster and more accurately to the congruent trial as compared to the incongruent trial. The correctness of response of the subject was calculated in percentage and average reaction time (in sec) for the congruent and incongruent trials was calculated in seconds.[24]

Statistical analysis

All statistical analyses were done using SPSS software version 21 for windows (SPSS, INC, Chicago, IL). The results have been presented as mean ± standard deviation and in percentages. A correlation was done between the ESS score along with the parameters of the Stroop test – % correctness of the response for the congruent and incongruent trials. P ≤ 0.05 was considered significant.

  Results Top

The study was conducted in the Department of Physiology of a medical college and multispecialty hospital located in the Delhi/NCR region. The aim of the study was to study the association between daytime sleepiness and cognition in young healthy Indian adults aged between 18 and 30 years.

A total of 60 subjects were included in the study taking into consideration various inclusion and exclusion criteria. The average age of the subjects was between 19.30 ± 0.89 years. Out of 60 subjects, 35 (58.3%) were male and 25 (41.6%) were female. The average ESS score for all the participants was found to be 7.33 ± 2.20.

The results of the Stroop test conducted are presented in [Table 1]. The reaction time of the incongruent trial was significantly higher compared to the congruent trial (P = 0.02). However, no statistically significant difference was seen in the percentage of correctness of response between the congruent and incongruent trials (P > 0.05).
Table 1: Results of the Stroop test

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A correlation was done between the ESS scores with the different parameters of the Stroop test for the congruent as well as incongruent trials. However, no significant correlation was seen, as depicted in [Table 2].
Table 2: Correlation between Epworth Sleepiness Scale score and various parameters of Stroop test

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  Discussion Top

The aim of our study was to see the association between daytime sleepiness as assessed by ESS Score and cognition as tested by Stroop Test in young Indian adults. The study included 60 subjects of both sexes aged between 18 and 30 years. College students are more likely to exhibit irregular sleep patterns; hence, we chose to work with students of a medical college and multispecialty hospital located in the Delhi/NCR region. The students selected were belonged to a similar educational background as education is also an important factor acting as a strong predictor of Stroop performance. In all age-dependent groups, less-educated healthy participants showed slower color-naming rates and needed more time to complete the color task. They also presented a greater interference effect, as they provided poorer performances on the Color–Word task than those who were highly educated.[24]

The subjects had a mean ESS score of 7.33 ± 2.20. This indicates that most of the subjects had normal levels of sleepiness, with only 6.7% of the subjects falling into the category of mild Sleepiness (ESS score >11). The reaction time of the incongruent trial was higher in comparison to the congruent trial. No significant correlation was seen between ESS scores and results of the Stroop Test.

There are numerous studies establishing the hypothesis that Stroop interference – the cost of performing one task in the presence of another – is a general, quick, frequently used, and highly specific index of cognitive flexibility for assessing brain dysfunction as well as research applications.[25]

With respect to the Stroop effect, it is likely that several factors are involved, including nonspecific performance affects of practice (e.g., stimulus encoding, response execution, and color name facility) that impact both control and interference conditions.[25]

A study conducted by El Hangouche et al.[26] in the year 2018 concluded that poor night sleep quality and daytime sleepiness correlated with each other and led to cognitive decline and poor academic achievement in medical students.

A cross-sectional study by Anderson et al. too claims decrements in selected executive function which includes cognition, associated with decreased sleep duration and subjective daytime sleepiness.[27]

A cross-sectional self-administered questionnaire-based study by Abdulghani et al. on medical students using ESS indicates a significant relationship between abnormal ESS scores, total sleeping hours, and academic performance.[19]

There are some studies which have documented results contradictory to our study. The Stroop test showed no significant increase in time taken to complete or the number of mistakes made in each set. This indicates that acute sleep deprivation was not detrimental to students' cognitive ability.[25]

A recent study done on medical students in the year 2019 showed that medical students have a high prevalence of excessive daytime sleepiness (EDS) (52.3%) compared to others that may be due to their hectic and excessive workload causing them to study until late at night. In a similar study done in Kerala on 349 medical students, the prevalence of excessive daytime sleepiness was found to be 25.5%. Similar findings have been reported by a study done in Chennai where the prevalence was found to be 30.5%. Their results are also consistent with a study done abroad in Brazil and Malaysia. However similar to us, some studies did not find EDS in medical students.[28]

A study was conducted on 30 Nepalese medical students in the year 2014. Their age was comparable to ours (23.1 ± 2.8 years). The time taken to read the incongruent card was longer as compared to the congruent card (P < 0.001). Their study like similar studies suggested that language proficiency could affect the results of the Stroop test.[29] Nepalese students being nonnative English speakers similar to our subjects find it more difficult to read incongruent trial made for English speakers and the interference increases. Their findings have also been supported by similar studies that have shown that interference is more if the second language is a nondominant one.[30] Hence, their result indicates that as selective attention and task difficulty increase, the interference percentage also increases. In addition, it also indicates that the English version of the Stroop test cannot assess the selective attention for non-English-speaking population.

Our findings of change in reaction time in congruent and incongruent trials are similar to those of Cain et al.[31] They have reported slower reaction time in incongruent trials as compared to congruent trials. This indicates a global slowing of the mental processes following sleep deprivation and daytime sleepiness. Similar findings have been reported by various other authors using different parameters.[32],[33],[34]

The results of a study done by Cain et al. suggested that the degree to which an executive function is affected by sleep deprivation may depend on the particular executive function studied and the degree to which it is subserved by the prefrontal cortex.[31] Similar to our results, incongruent trials showed the slowest response (reaction time), the congruent trial showed the fastest response, and the neutral trial had intermediate reaction time. There was a significant main effect of time awake on the error rate of the response.

Neuroimaging studies have shown that several cortical areas are activated during the performance of the Stroop test. Much of the focus of neuroimaging studies during the Stroop task has been on activation of the dorsolateral prefrontal cortex and anterior cingulate cortex.[34]

Correlation studies were done between the ESS score and the different parameters of the Stroop test for both the congruent and incongruent trials. However, we were not able to see any significant findings in the correlational analysis, which may be primarily due to the insufficient power of our study. The probable reason for this could be the small sample size. Since the STS project needs to be completed within a period of 2 months as per directions of ICMR, we were not able to include a large number of subjects in this study. Various studies have been able to establish the correlation between sleepiness and cognitive decline,[12],[19],[27],[34],[35],[36] while some studies have not been able to do so[37] like our study.

Early interventional programs for sleep hygiene of subjects like lifestyle changes can be advised to subjects with sleep deprivation and excessive daytime sleepiness to reduce the chances of subsequent cognition-related morbidity and mortality. Although more studies are needed to validate this inference, our findings provide important guidance to navigate future studies in this area. Theories and hypotheses of how sleep deprivation affects neurocognitive abilities are evolving rapidly as both the ranges of cognitive effects from sleep loss and the neurobiology of sleep-wake regulation are better understood. Further studies of neurocognitive deficits in human disorders are needed as they impact large segments of the population.

Limitations of the study

The major limitation of the study was the small sample size. Thus, a broad generalization of the results to the larger population cannot be done. Our sample size consisted of a representative sample of a single medical school. Therefore, the results are not generalizable to the whole student population in all medical colleges of India. The ESS score in the study is self-reported which cannot be assessed objectively.

  Conclusion Top

On studying the parameters of the Stroop test, the reaction time of the incongruent trial was seen to be significantly higher as compared to the congruent trial. However, no statistically significant difference in the percentage of correctness of response was seen on the comparison between the congruent and incongruent trials. No significant correlation was seen between the ESS scores with different parameters of the Stroop Test.

  Acknowledgment Top

The authors thank the Indian Council for Medical Research which supported the study through its Short-Term Studentship program for undergraduate medical students.

Financial support and sponsorship

Conducted under STS Scheme of ICMR for MBBS students.

Conflicts of interest

There are no conflicts of interest.

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  [Table 1], [Table 2]


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