Neuroscience of Circadian Rhythms
All life on earth has evolved under a daily cycle of light and dark. In response to this dynamic world, all organisms, including single-celled bacteria possess an internal representation of time, a “biological clock” which provides a means of anticipating daily changes in the environment. In this way biology is optimised in advance of the complex demands of the day/night cycle, rather than passively responding to altered levels of light or temperature.
These internal 24 hour cycles, are termed circadian rhythms. In mammals, including man, there exists a master clock in the brain located in the suprachiasmatic nuclei (SCN) which in-turn regulates clocks within the cells and organ systems of the body. Light provides the critical input to the SCN, synchronising the “internal day” to the astronomical day. The photoreceptors providing this input are found in the retina of the eye. However, the classical visual cells, the rods and cones, are not required for this light detection task. There exists a third class of photoreceptor based upon a recently identified subset of photosensitive retinal ganglion cells (pRGCs) that use the blue-light sensitive photopigment called melanopsin.
Using a range of molecular and cellular techniques, behavioural analysis and bioinformatics we are discovering the underlying processes that lead to the generation and regulation of circadian rhythms in the brain, and how this timing system regulates much of our biology, including the sleep/wake cycle.