Outline and Evaluate Research into Circadian Rhythms

Outline and Evaluate Research into Circadian Rhythms A circadian rhythm is a biological rhythm that occurs over a 24-hour cycle. For example, the sleep/wake cycle; we are at out most alert at 10am, we have the best coordination at 2:30pm, out fastest reaction time is at 3:30pm, and our deepest sleep is at 2am. Our circadian rhythms occur due to light and melatonin. Light sensitive cells in our eyes send messages about the levels of light, in our environment to the suprachiasmatic nucleus. This manages our circadian rhythms and is found in the optic chiasm. During the day we have two sleep drive dips: 2-4am and 2-3pm. This is when there is a lack of light. Melatonin is also used to regulate these rhythms. The release of this hormone is controlled by the pineal gland. It releases melatonin when it is dark, making you feel tired, and inhibits when it is light, so you feel awake. Light signifies daytime and sends messages through the SCN to the pineal gland, to produce or stop producing melatonin. Siffre showed how circadian rhythms work, by spending extended periods of time in a cave. He had no natural light exposure and no exposure to sound. He emerged believing that he had spent 6 months there, but it had been 7. His rhythm set to 25 hours, but he woke up and fell asleep on a regular cycle. This shows how our natural cycle may be longer than 24 hours, but we have adapted based on daily tasks such as mealtimes and daylight. There is supporting evidence by Aschoff and Weaver, who got participants to spend four weeks in a world war two bunker with no natural light. All experienced a circadian rhythm between 24 and 25 hours, except one person who had a 29-hour rhythm. This supports the case study from Siffre, and the conclusion that we do not naturally have a 24-hour cycle. Despite this, there are problems with the evidence provided. Both studies used extremely small samples, meaning it is hard to generalise the results to the whole population, thus lacking population validity. Furthermore, there may be individual differences involved, which mean the participants reacted to the changes in atypical ways. As such, factors like age and gender may have significant impacts on our circadian rhythms. Furthermore, the research has practical application the shift work. It has been found that this has led to a desynchronization of circadian rhythms, leading to cognitive and physiological effects. It is shown that shift workers suffer a concentration lapse at 6am, increasing the likelihood of accidents. In addition, they are more likely to suffer from heart disease as a result of the stress of adjusting their sleep/wake cycle. Thus, the research has many implications on maintaining worker productivity, and safety in the workplace. Furthermore, it also has application to pharmacokinetics. Understanding circadian rhythms can help determine the best time to administer drug treatments. For example, the risk of heart attack is greater in the morning, so drugs can be taken at night, but not released until dusk, when they are most effective. This means there are peak times for giving drugs, and dosage which increase their efficiency.