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Circadian Rhythms and Its Effect on Memory

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Circadian Rhythms have been known to influence learning and memory. Morning types and evening types of behaviour has been studied and it has been found that why some people are more alert in the mornings or afternoons is due to the circadian rhythms of the body. Cultural and social cues also affect the circadian rhythms and in this study, it has been shown that these factors affect Singaporeans in as much as anyone from around the world. A test on memory was given to participants once in the morning and another in the evening to if there is any significance between each individual score and relates it to their type. The results for the morning types were inconsistent with the research done by other people, which could be due to certain confounding factors such as participant size however, this research has come to the conclusion that the test results should differ according to when they are most active

Circadian Rhythms and its Effect on Memory

Friday nights are one of the nights where you will find many people thronging towards bars and night spots to relax and a have break after the long week at work. Sundays however, reveals the opposite. Ask any adult why this is so and they would probably attribute it to the fact that many of them need to wake up early the next day to beat the rush hour traffic in the morning for work. Whether it is having the energy to party late into the night or trying to remember your way to work in the early morning traffic, there are underlying biological and psychological factors that are at work.

Our sleeping patterns are based on circadian rhythms, which is a roughly 24-hour cycle in the biochemical, physiological or behavioral processes of living entities which is regulated by light and dark cues from the environment. Not only do they regulate some of our bodily functions, studies have shown that they do play a role in memory and learning and according to Roth and Sweatt (2008), chemicals released during sleep actually promotes long term memory in mice while disruptions in the circadian rhythms actually cause them to forget learned responses. The study suggest that though circadian rhythms are known to be involved in creating good memory, it might actually be the way certain chemicals are changed to create this from happening. In another study, Nesca and Koulack (1994) did a study which proved that sleeping directly after studying does indeed improve memory recall of the things studied before sleep.

Some people claim that they are more alert during the early hours of the day or during the evening time. This claim could be due to the sleeping habits and lifestyles of each individual that cause them to see significant cognitive capacities at different times of the day. A Study by Diaz-Morales (2007) has indicated in his study that Morning and Evening types have distinct personality traits that affect their behaviour and thought patterns. It was suggested that it could be due to the entraining cause by environmental and social cues, people become either one of the types based on cultural and social influences in their lives. Sleeping habits also play a role in causing us to choose when most people choose to do activities. Duffy et. al. (2001) correlated a person's preference and habitual waking time to the person's circadian period. Because during different stages of the circadian period a person's body will release hormones or chemicals, like melatonin, to help with sleeping and body temperature also rises and falls according to these stages. When a person sleeps, in relation to this period, it affects mental performance when he wakes up.

Many studies have linked memory, cognition and learning to be closely tied to the circadian rhythms in people's bodies (Nesca & Koulack, 1994; Gritton H. J., Sutton B. C., Martinez V., Sarter M. & Lee M. T., 2009) and it has been said that people learn better during certain times of the day. This could be due to the fact that people's alertness varies with the times of the day due to our biological reactions within our bodies (Matchock L. R. & Mordkoff T. J., 2009) From previous studies done in other parts of the world, participants who underwent a short test to determine whether they were Morning Types or Evening Types did do better during the times dependant on which type they were. Since it has been proven that our circadian rhythms are affect by social and cultural cues as well (Diaz-Morales, 2007) will people from Singapore show the same results? Will the environment in Singapore change how our bodies react to daily environmental cues which affect the circadian rhythms in our us or are they similar across the board.

The aim of this study is to see if there is a difference in mental performance between Morning Types and Evening Types by comparing their AM and PM performance on memory there by reaffirming the theory that people have different peak mental alertness dependant on the time of the day; with Morning Types performing better in the morning test and Evening Types performing better in the evening test.




A total of 43 people participated in this study with 21 people categorized as Morning Types and 22 people as Evening Types. Their ages ranged from 10 years of age to 59 years of age. The participants were randomly selected from friends and family members who knew the researchers. After they agreed to participate in this study, they were asked if they considered themselves as morning types or evening types to place them in the groups used to test the hypothesis.


The experiment consisted of asking individuals to remember lists of words early in the morning or in the evening. Two different lists of words comprising of 21 common words were used; seven words are three letters long, seven are five letters long, seven are more than five letters long. The words used were common nouns and verbs. The lists can be found in Appendix A for the morning test and Appendix B for the evening test.


The participants were separated into 2 different groups; Group 1 reported that they were morning types; Group 2 reported that they were evening types. Each participant was tested twice, once in the morning within 630am to 830am and once in the evening between 730pm to 930pm. Which test was conducted first was dependant on the availability of the participant. The participant was seated at a table and the following instructions were read to them: "In the experiment, your task is to try and remember words. I will give you a sheet of paper



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