Exogenous zeitgeibers explained
External cues act as zeitgeibers
(Klein and Wegmann)
These cues may influence/ entrain biological rhythms (endogenous pacemakers)
Light suppresses the production of melatonin from the pineal gland which influences peoples sleep/ wake cycle
Vetter et al- Exogenous zeitgeibers
Vetter et al. (2011) demonstrated that natural light is a superior exogenous zeitgeber for entraining human circadian rhythms compared to artificial office light. A 5-week study showed participants exposed to warm artificial light adjusted to dawn, while those under blue-enriched light remained desynchronized, highlighting that light composition influences sleep-wake cycles.
Burgess et al (2003) Exogenous zeitgeibers
Burgess et al. (2003) demonstrated that exposure to artificial bright light acts as a powerful exogenous zeitgeber, shifting the human circadian rhythm to adjust for jet lag. Participants exposed to continuous bright light before east-west flights shifted their sleep-wake cycles by 2.1 hours, significantly reducing time needed to adjus
Campbell and Murphy (1998)
Campbell and Murphy (1998) demonstrated that light acts as a powerful exogenous zeitgeber for human sleep-wake cycles, even when not detected by the eyes. By shining a light on the back of participants’ knees, researchers shifted their circadian rhythms by up to 3 hours, suggesting light affects peripheral skin receptors, not just the eyes
Miles et al- (1977) Research against Exogenous zeitgeibers
Miles et al. (1977) studied a man blind from birth with a 24.9-hour circadian rhythm, showing that, despite exposure to social cues (exogenous zeitgebers like meal times), his sleep-wake cycle remained abnormal. This study demonstrates that social cues alone are insufficient to entrain the sleep-wake cycle to 24 hours without light cues, suggesting an over-reliance on external factors in some theories.
Morgan (1955)
bred hamsters so that they had circadian rhythms of 20 hours rather than 24. SCN neurons from these abnormal hamsters were transplanted into the brains of normal hamsters, which subsequently displayed the same abnormal circadian rhythm of 20 hours, showing that the transplanted SCN had imposed its pattern onto the hamsters. This research demonstrates the significance of the SCN and how endogenous pacemakers are important for biological circadian rhythms.
Decoursey et al (2000)
Destroyed the SCN in 30 chipmunks. Their sleep/wake cycles disappeared, and most were killed by predators because they were active when they should have been asleep.
How the SCN works detailed 1
. Specialized light-sensitive cells in the retina (containing melanopsin) detect light and pass this information directly to the SCN.
. The SCN receives direct information about light levels from the environment via the optic nerve.
. The SCN passes information about light levels to the pineal gland
. When light levels fall, the SCN triggers the pineal gland to increase the production of the hormone melatonin.
. Melatonin increases, making us feel sleepy and inhibiting the brain mechanisms that keep us awake.
Describe the role of defence mechanisms according to the psychodynamic approach
• help the ego manage the conflict between the id and the superego
• provide compromise solutions (usually unconscious) to deal with unresolvable conflict
• provide a strategy to reduce anxiety (which weakens the ego’s influence)
• use of examples, eg through the use of denial/displacement/repression, to describe the role of
defence mechanisms.
What is meant by meta analysis
. • meta-analysis is the process where researchers collect and collate a wide range of previously
conducted research on a specific area
• collated research is reviewed together
• combined data/effect size is often statistically tested to provide an overall conclusion.
Turk et al (2002)
Discovered a patient who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere
Peterson et al (1988)
Used brain scans to show wernickes area active during listening tasks and bricks area active during reading tasks, proving distinct areas for language
Elbert et al
Concluded that capacity for neural reorganisation is much greater in children than in adults, meaning that neural
Elbert et al
Concluded that capacity for neural reorganisation is much greater in children than in adults, meaning that neural regeneration is less effective in older brains
