Endogenous Pacemakers Flashcards
(3 cards)
One strength of the role of endogenous pacemakers in the sleep wake cycle that there were supporting evidence
Supporting evidence for the role of endogenous pacemakers in the sleep/wake cycle is provided by the French cave explorer, Michael Siffre (1975) who spent 205 days
underground in a cave and lacked any cues about when it was day or night. During the study a sleep/wake cycle was evident, but this varied from 24 hours to 48 hours. This suggests that the SCN can maintain a free-running sleep/wake cycle, but that exogenous zeitgebers are required to keep this at 24 hours.
However, it is difficult to obtain volunteers to take part in longitudinal research involving sleep
disruption, so samples are small or include participants who are interested in the research or
have time to spare. Such participants may have sleep-wake cycles that are different to those
who don’t volunteer which limits the population validity of such research.- not typical
Evidence supporting the role of the SCN as an endogenous pacemaker
Evidence supporting the role of the SCN as an endogenous pacemaker is provided by Morgan (1995) who selectively bred a strain of hamsters with an abnormal circadian rhythm
of 20 hours. SCN neurons were transplanted into normal hamsters (with a biological rhythm of 24 hours), which then displayed the same abnormal rhythm. This study provides strong evidence for the importance of the SCN in maintaining biological circadian rhythms. However, many studies, including Morgan’s, use non-human
animals. Despite mammals sharing basic brain physiology, such
as the role of hypothalamic structures such as the SCN, caution
must be taken when extrapolating findings to humans. The
endogenous pacemakers responsible for maintaining biological rhythms may differ between species. For example, an animal’s sensitivity to light and their nocturnal/diurnal habits affect the
way they respond to exogenous zeitgebers. This means any
findings for non-human animals may not be generalisable to humans.
It is biologically deterministic to assume that our sleep/wake cycle is controlled by endogenous pacemakers.
It is biologically deterministic to assume that our sleep/wake cycle is controlled by endogenous pacemakers. The theory implies that at night when SCN activity is high, more melatonin is released and we have no choice but to fall asleep. However, humans have the
free will to decide when exactly to sleep. For example, we can adopt behaviours, such as consuming caffeine, to delay the onset of sleep. Compared to other species, the pre-frontal cortex of the human brain offers the ability to suppress such biological urges. Ultimately, the
theory may be considered to be an example of soft determinism, as we have a degree of choice of when to sleep but eventually must give in to underlying endogenous mechanisms.
