Circadian rhythms

• Biological rhythms are patterns of change in the body that form cyclical rhythms
• endogenous pacemakers are internal biological clocks
• exogenous zeitgebers are external cues that entrain our biological rhythms
• Circadian rhythms are biological rhythms that are subject to a 24 hour period such as the sleep/wake cycle
• The sleep/wake cycle is governed by the exogenous zeitgeber of light
• the sleep/wake cycle is governed by the endogenous pacemaker of the superchiasmatic nucleus (SCN)
• The superchiasmatic nucleus (SCN) is located above the optic chiasm which provides information from the eye regarding the exogenous zeitgeber of light
• Siffre's (1962) cave study aimed to investigate the free running biological rhythm of the sleep/wake cycle
• Siffre (1962) self-isolated in a cave in the alps deprived of any natural light
• Siffre (1962) emerged from the cave in mid September thinking it was early August
• Siffre (1962) found his free running biological rhythm ran for around 25 hours
• Although Siffre (1962) showed some variation in his sleep wake cycle, his study shows biological rhythms are entrained by exogenous zeitgebers
• Aschoff and Wever (1976) kept participants in a WWII bunker deprived of natural light
• Aschoff and Wever (1976) found all but one participant's (29 hours) sleep wake cycle remained around 24-25 hours without the exogenous zeitgeber of light
• Aschoff and Wever (1976) shows biological rhythms are entrained by the exogenous zeitgeber of light
• Folkard (1985) had 12 participants live in a cave deprived of natural light for 3 weeks
• Folkard (1985) had participants go to bed when a clock read 11:45 and get up when it read 7:45
• Folkard (1985) had researchers slowly speed up the clock over the course of the study so a 24 hour day passed in 22 hours unbeknownst to participants
• Folkard (1985) found only one participant adjusted to the speeding up of the sleep/wake cycle
• Folkard's (1985) study suggests that the free running biological rhythm of the sleep/wake cycle cannot be overridden by exogenous zeitgebers
• Circadian rhythms strength; real world application as it can help psychologists understand the consequences of desynchronisation when it comes to night shift work EG Boivin (1996) found night shift workers experience a loss in concentration around 6AM showing employers how they can best improve worker productivity
• Circadian rhythms strength; real world application as medical treatments such as chromotherapeutics has developed understanding into how medication impacts circadian rhythms allowing understanding into when best administer them
• Circadian rhythm research weakness; lacks generalisability as research such as Siffre uses an extremely limited sample that lacks representativeness