PSYA3 - Endogenous pacemakers and Exogenous zeitgebers

A natural study into residents in the Arctic Circle found that in the summer months when the sun didn’t set they still sleep for 7 hours a day. This suggests that there are other factors than light that act as zeitgebers, such as social life and clocks.

An Infradian rhythm is a biological bodily rhythm that is longer than a day but shorter than a year. The most obvious example is the female menstrual cycle which may be controlled by hormones or pheromones. Hormones are internal chemical substances such as FSH and LSH. Pheromones are odourless and invisible chemicals that we release into the air that can be detected by others.

McClintock found that women who live together such as, nuns or girls at boarding school, have correlated menstrual cycles. He claimed that this was due to pheromones that we release that trigger each others cycle. This shows that the endogenous pacemaker controlling the menstrual cycle is affected by external zeitgebers such as pheromones. This is very similar to the way sleep-wake cycle is affected by light.

Case studies such as the blind man and the cave study are not very scientific as they only have one participant. It is hard to control all the variables and you cannot generalise the results. But studies on the sleep-wake cycle and the menstrual cycle all show that the endogenous pacemaker is affected by external zeitgebers. This is an example of nature-nurture interaction, as the innate pacemaker is affected by the environment.

This study of endogenous pacemakers is an example of biological reductionism as it explains sleep-waking using biological pacemakers in the brain. As research shows that these can be affected by external zeitgebers, you cannot explain biological rhythms just using biological pacemakers.