Circadian rhythms (In Our Time)

Broadcaster: BBC Radio 4                                            radio

Year: 2015

Genre: Discussion


Review by Emma Sterling

“Circadian rhythms are a biological version of a clock inside humans and all other animals, plants and quite possibly in almost every living cell…These rhythms are a response to the most predictable condition of life on earth, that is, dark at night and bright during the day.”

“Circadian rhythms are one of the best examples of how genes relate to behaviour.”

In this episode of his series In Our Time (41 minutes), Melvyn Bragg talks with Professors Russell Foster, Debra Skene and Steve Jones about circadian rhythms, what they are and how they affect behaviour in humans and other organisms.

The programme includes a brief explanation about the subcellular process involved in circadian rhythms. In humans this takes place in what is described as the ‘master pacemaker’, formally known as the suprachiasmatic nuclei (SCN). This is a group of 50,000 cells located in the hypothalamus that are essential for producing the rhythm. Approximately 12-14 genes and their protein products are involved in the molecular feedback loop with an oscillation of approximately 24 hrs. In some individuals these oscillations are slightly longer, in others slightly less. These differences can affect whether that person is a morning or evening person. Other factors that can affect these oscillations include polymorphisms in the genes that control this process, and external factors such as food, drink and caffeine but none of the aforementioned are as important as light.

The hours of sleep required has changed as we have evolved. Humans require less sleep than other primates; for example chimpanzees need about 12 hours sleep as day on average. In addition, there is a difference between African clocks and European clocks with African clocks being more rigid and European clocks being more labile-set to move with the seasons.

The experts also discuss various experiments with humans, mice and plants that have demonstrated how light and receptors in the eye affect the circadian rhythms. Additionally, Professor Russell Foster, in particular, emphasised the link between sleep and mental illness. Genes that control circadian rhythms have been linked to the affected genes in mental illnesses such as schizophrenia and bipolar.

You might also be interested in this interview (3 mins) with Leicester Professor Bambos Kyriacou expert about the work of his team using Drosophila melanogaster as a model organism for studying circadian rhythms.

A longer (14 minute) version is also available.

For further reading on the genetic link between sleep and mental illness see:




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