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Cambridge Neuroscience Public Lecture: Light, clocks and sleep: the discovery of a new photoreceptor within the eye

Public Lecture in Neuroscience: Tuesday 20th March, Babbage Lecture Theatre, Cambridge

Russell Foster is Professor of Circadian Neuroscience and Head of the Nuffield Laboratory of Ophthalmology at the University of Oxford. As part of the Cambridge Science Festival, The Cambridge Neuroscience Seminar and in conjunction with The British Neuroscience Association, Russell delivered a talk entitled 'Light, clocks and sleep: the discovery of a new photoreceptor within the eye' in the Babbage Lecture Theatre on The New Museums Site in Cambridge. For those of you who missed the talk, it can be viewed on the Cambridge Neuroscience website and on The British Neuroscience Association website. 


Until the late 1990’s it seemed inconceivable to most vision biologists that there could be an unrecognised class of light sensor within the eye. After all, the eye was the best understood part of the central nervous system. One hundred and fifty years of research had explained how we see: Light is detected by the rods and cones of the retina and their responses are assembled into an “image” by inner retinal neurones, followed by advanced visual processing in the brain. This representation of the eye left no room for an additional class of ocular photoreceptor. However, work in a variety of animals, including mice and humans, overturned this conventional view of the eye. We now know that the rods and cones are not alone.

Most organisms possess a 24h biological (circadian) clock, which acts to ‘fine-tune’ physiology and behaviour to the varying ecological demands of the day/night cycle. Such a clock is only useful if biological time remains synchronised to solar time, and the daily change in the gross amount of light (irradiance) at dawn or dusk provides the most reliable indicator of the time of day. In mammals the “master clock” is located within small paired nuclei at the base of the brain called the suprachiasmatic nuclei (SCN).  The SCN receive direct retinal projections which adjust the clock to the light/dark cycle, and eye loss in mammals blocks this completely. We were interested in how the eye detects light to provide this re-setting signal. Surprisingly, we found that visually blind mice, with genetic defects in the rods and cones, could still use their eyes to regulate the clock. These, and a host of subsequent experiments including studies in humans with genetic defects of the eye, showed that the processing of light information by the circadian and classical visual systems is different and that the mammalian eye contains an additional non-rod, non-cone photoreceptor based upon a small number of photosensitive retinal ganglion cells (pRGCs). The pRGCs have unusual light-sensing properties and use a remarkable light sensitive molecule called “melanopsin” for this task. We also know that these pRGCs do a lot more than regulate the clock, and are involved in a host of other irradiance detecting tasks that regulate sleep, alertness, hormonal rhythms and even pupil constriction. As a result these findings the clinical diagnosis of blindness is being revised. We now appreciate that eye loss will plunge an individual into a world that lacks both vision and a sense of time.

A bit about Russell Foster...

Russell Foster is Professor of Circadian Neuroscience and Head of the Nuffield Laboratory of Ophthalmology at the University of Oxford. He also holds a Fellowship at Brasenose College. In recognition of his research achievements he has been awarded the Honma prize (Japan), Cogan Award (USA), the Zoological Society Scientific Medal (UK), the Edrige-Green Medal (UK), Jesse Mole Lecture and Medal (UK), and Choyce Medal (UK). In May 2008 he was elected a Fellow of the Royal Society. Russell Foster’s research interests span the neurosciences but are currently focused upon two broad themes. The first relates to how environmental light is detected and processed by vertebrate photoreceptors.  The second line of research relates to how circadian rhythms and sleep are generated and their disruption in mental illness and neurodegenerative disease. He has over 180 peer reviewed publications with multiple publications in Science and Nature. In parallel with his research activities, Russell chairs and participates in multiple committees, he is a member of Council for BBSRC, a member of the Governing Council of the Sainsbury-Wellcome Centre for Neural Circuits and Behaviour, a Board member of the UK Research Integrity Office (RIO) and is a Faculty member of the Lundbeck Institute of Neuroscience in Denmark.  Russell is a strong proponent of the public awareness of science, and in June 2010 was appointed Chair of the Cheltenham Science Festival. With Leon Kreitzman he has published ‘Rhythms of Life’ (2005) and the sequel ‘Seasons of Life’ (2009). His new book with Stephen Lockley, “Sleep” will be published by Oxford University Press on the 22nd March 2012.

Posted on 26/03/2012

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