How the circadian rhythm affects performance?
How many of you from time to time waking up have thought “I am ready to conquer the world!” or going to bed “I am so tired to do anything”? It is evident that in both these cases the main thing in common is the sleep-wake cycle.
In this Neuroscience project, we attempt to answer the fascinating question of whether there exists an explicit correlation between the circadian rhythm, chronotype of the person (“morning person” or “owl”) and brain performance in the human body, or whether these two phenomena are not directly related.
Brain performance is an essential factor in any person’s life quality. Moreover, productivity is, in general, the hottest topic in nowadays society, since modern busy lifestyles demand us to be as productive human beings as possible every day, each day. Therefore, it is only a natural desire to explore brain efficiency in all possible ways, and during this project, we are addressing circadian rhythms.
The most natural hypothesis would be that “morning people” are more productive in the morning and “owls”, in contrast, are more efficient in the evening. We will check these hypotheses and maybe we will be lucky to find other unexpected connections between the circadian rhythm and brain productivity? What if we will manage to find some secret keys to brain superpower? Well, let us dive in!
The lifestyle we lead strongly correlates with our circadian rhythm, which is a natural, internal process responsible for our physical, mental and behavioral changes during a daily cycle. The circadian rhythm controls a release of certain hormones and neurotransmitters, it has an impact on our sleep and wake cycle, energy and stress levels, metabolism and appetite, arousal and alertness . The circadian rhythm is controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus and is influenced by light and darkness. Information received from the optic nerves about incoming light SNC send alert signals to the brain. When a light intake decreases, the SNC contrariwise send relaxation signals to the brain . This is the reason why people who work in shifts find it difficult to sleep during the day and work at night. However, the influence of the circadian rhythm can be different for a “night owl” or a “morning person”.
At the moment, many researchers are interested in studying how the cognitive abilities of the brain change according to the time of day. Studies showed that a simply delaying school start to 8.30 a.m. (one additional hour of sleep) could lead to an economic gain of $83 billion to the US economy within a decade! . With the rapid development of modern technologies, people are becoming more independent of natural lightness. The prolonged effect of artificial light has a negative effect on circadian rhythms, shifting them. This can lead to irritability, depression, and anxiety.
To conduct the experiments we used the site Human Benchmark, which aims to measure different aspects of brain performance. Human Benchmark provides six different tests to measure brain abilities.
- Number Memory Test requires to remember the longest number.
The average person can only remember 7 digit numbers reliably, but it’s possible to do much better using mnemonic techniques.
2. Reaction Time Test evaluates the visual reflexes.
In addition to measuring your reaction time, this test is affected by the latency of your computer and monitor. Using a fast computer and low latency / high framerate monitor will improve your score.
3. Verbal Memory Test requires to keep as many words in short term memory as possible.
The number of words you need to remember grows continually until you can’t keep them in your head anymore.
4. Visual Memory Test requires to memorize the squares.
Every level, a number of tiles will flash white. Memorize them, and pick them again after the tiles are reset! Levels get progressively more difficult, to challenge your skills.
5. Hearing Test aims to determine high-frequency hearing loss.
High-frequency hearing loss is common and tends to progress with age. This test is best performed with decent headphones at a moderate volume.
6. Typing Test checks how many words can be typed per minute by a person.
This is a simple test of typing speed, measuring words per minute, or WPM. The recorded score is WPM * Accuracy.
To gather the data we ask responders to take the abovementioned tests twice a day — in the morning after waking up, and in the evening before going to bed. We ask them to repeat experiments for three days in a row. To avoid misrepresentations responders were asked to get familiar with tests and site interface beforehand. We also collect information about the responders’ chronotype. Experiments were held in wintertime.
We were able to gather the data from 27 responders. 16 of them defined themselves as “morning person” and 11 of them chose “owl” as their chronotype. As it was expected, not all participants were consistent with taking tests two times a day 3 days in a row. Sometimes responders forgot to take the test in the morning or in the evening. Sometimes they did not manage to take tests for 3 days or vice versa took tests for more than 3 days. Nevertheless, we gathered all the data that was given to us, which resulted in 132 instances. Among these 132 instances, 77 belong to “morning people” (33 times tests were taken in the morning and 44 times in the evening) and 55 belong to “owls” (28 and 27 times for morning and evening respectively).
According to the Human Benchmark, the average person can only remember 7 digit numbers. We can observe that people who took this test were able to remember 9 digit numbers on average. Still, the maximum number that was remembered contains 12 digits. The boxplots demonstrate that “morning people” remember more digit numbers in the morning, while “owls” remember more digit numbers in the evening, which agrees with our hypothesis.
Morning-morning person: maximum-12, minimum-8, upper hinge-11, lower hinge-9, median-10.
Morning-owl: maximum-11, minimum-6, upper hinge-10, lower hinge-7, median-8.5.
Evening-morning person: max-12, min-5, upper hinge-10.5, lower hinge-7.5, median-9.
Evening-owl:max-12, min-6, upper hinge-11, lower hinge-8, median-9.5.
The average reaction time is 284 milliseconds according to the site statistics. In our case, we have got that the average reaction time is about 350 milliseconds. The results of this test depend on many factors such as the latency of the computer and monitor and touchpad sensitivity. 30ms is currently a typical lag for a desktop/laptop. Based on this we cannot observe particular patterns at this plot. According to the site, mobile device ‘taps’ tend to be a bit slower than clicks. For example, we can observe that for the particular person the reaction time was more than 1000 milliseconds, which may be a consequence of one of the problems listed above.
Morning-morning person: max-552, min-258, median-364.5.
Morning-owl: max-542, min-273,median-357.
Evening-morning person: max-593, min-243, median-412,5.
Evening-owl: max-653, min-266, median-336.
According to the Human Benchmark, the average number of words that a person can keep in short-term memory is about 25. In our case, the conducted experiment shows that the average number of words is near 40. The maximum number of words that a person remembered is 105. Most importantly, the boxplot shows that “morning people” remember more words in the morning, while “owls” — in the evening.
Morning-morning person: maximum-82, minimum-25, upper hinge-65.5, lower hinge-41.5, median-55.
Morning-owl: maximum-48, minimum-14, upper hinge-38.5, lower hinge-22, median-28.5.
Evening-morning person: max-53, min-12, upper hinge-43.5, lower hinge-24.5, median-32.5.
Evening-owl:max-105, min-20, upper hinge-69, lower hinge-33, median-53.
According to the statistics given on the Human Benchmark, the mode for the Visual Memory test is 9 level, meaning that the average person can memorize the arrangement of 9 white tiles.
In our experiments, we also obtained a mode 9 among all responders. Additionally, we can observe from the boxplot that for “morning person” performance was better in the morning than in the evening. What is more, “owls” performed significantly better on the Visual Memory test in the evening than in the morning.
Morning-morning person: max-11, min-7, up hinge-10, low hinge-8, median-9.
Morning-owl: max-10, min-7, up hinge-9.5, low hinge-7.5, median-8.5.
Evening-morning person: max-11, min-6, up hinge-10, low hinge-7, median-8.5.
Evening-owl:max-12, min-8, up hinge-11, low hinge-9, median-10.
Human Benchmark states that the average person is able to hear the high-frequency sound of approximately 19000Hz. Our experiments confirmed these statistics. Nevertheless, we were not able to establish dependencies between circadian rhythms, chronotypes and hearing abilities. However, it is quite interesting that “owls” from our dataset, in general, hear better than “morning people” despite the time of the day.
It is worth to be mentioned that the Hearing Test is highly dependent on the technical equipment of the responder, which probably results in a lack of correlations.
Morning-morning person: max-22220, min-13026,median-18250.
Morning-owl: max-22313, min-12766, median-19292.
Evening-morning person: max-22187, min-14968, median-18715.
Evening-owl:max-22272, min-14774, median-20105.
According to the Human Benchmark, the mode for typing test is approximately 38 words per minute, which is quite similar to the most popular result among our responders — 36 words per minute. Similarly to the Hearing Test, there are also no correlations that seemed to be presented between circadian rhythms, chronotypes and typing abilities of the person. However, in contrast to the Hearing Test, the “morning people” from our dataset, in general, type better than “owls” despite the time of the day.
Morning-morning person: maximum-60, minimum-6,median-35.5.
Morning-owl: maximum-61, minimum-6, median-26.
Evening-morning person: maximum-72, minimum-7, median-35.5.
Evening-owl: maximum-60, minimum-8, median-22.5.
To sum up, during the experiments we were able to establish the dependencies between circadian rhythms, chronotypes, and productivity in three tests: Number Memory, Verbal Memory, and Visual Memory. For these 3 tests, our initial hypothesis holds: “morning people” are more productive in the morning and “owls” perform better in the evening. However, for the 3 other tests, Reaction Time, Hearing and Typing, no correlations between circadian rhythms, chronotypes and productivity seem to be present.
The authors would like to thanks all the responders for their time and effort.
The authors would like to acknowledge the financial support given to them by Dora Plus scholarships and the University of Tartu through tuition waivers.
Roles in the project
Note: majority of the work were done by us in a pair at the library, hence there was no distinct division of the tasks. This project was a truly team effort.
Tetiana Shtym: Introduction, Motivation, Background, Methods sections, Data Gathering, Data Analysis (Number Memory, Reaction Time, Verbal Memory), Visualisation of the Data
Yana Halas: Introduction, Motivation, Background, Methods sections, Data Gathering, Data Analysis (Visual Memory, Hearing Test, Typing Test), Conclusion