A2 Biopsychology - Endogenous Pacemakers and Exogenous Zeitgebers

Question 1

Describe an endogenous pacemaker.

Answer 1

An internal pacemaker that regulates the s/w cycle. In humans, this is the suprachiasmatic nucleus (SCN); a bundle of nerve cells in the hypothalamus.

SCN receives information on light from the optic chasm (which sits just below the SCN) and sends information to the pineal gland which produces melatonin to make us sleepy. This occurs even when our eyes are shut and not receiving light.

Question 2

Evaluate endogenous pacemakers.

Answer 2

DeCoursey et al (2000) destroyed the SCN of 30 chipmunks and found that their s/w cycle disappeared. Most were killed by predators as a result. This shows that the SCN is crucial in keeping the s/w cycle as the chipmunks were awake when they should’ve been asleep.
(-) ethical issues as most of the chipmunks were killed
(-) problems generalising to humans.
(+) application to chronotherapeutics as the SCN keeps our s/w cycle steady

Question 3

Describe exogenous zeitgebers

Answer 3

Light is an external factor which can reset the SCN through the process of entrainment and keeps the s/w cycle at 24 hrs and not 25. Regular mealtimes and other daily routines also help to keep the s/w cycle at 24hrs and not the natural 25.

Question 4

Evaluate exogenous zeitgebers.

Answer 4

(+) Campbell and Murphy (1998) found that when ppts were woken up at different points in the night and had light shone on the backs of their knees, their s/w cycle was disrupted by up to 3 hrs.
(-) Study is yet to be replicated so poor reliability
(-) Study doesn’t tell us anything about all of the other exogenous zeitgebers
(-) Some researchers say that some light could have entered the ppts’ eyes which is a major confounding variable and severely lowers the validity of the study and therefore the supporting evidence for light being a powerful exogenous zeitgeber.
(+) chronotherapeutic light can help ppl with depression/SAD
(+) Real world application to mobile phones, laptops etc
(-) Laughton Miles says that exogenous zeitgebers are probably exaggerated; boy blind from birth had a s/w cycle of 24.9 hrs and this couldn’t be changed by regular mealtimes/ daily routines