On Melatonin Suppression from Polychromatic and Narrowband Light

Click to increase image sizeClick to decrease image size

Authors' Response

Victoria L. Revell¹ and Debra J. Skene²

¹Faculty of Life Sciences, University of Manchester, Manchester, UK

²Human Chronobiology Group, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, UK

Dear Editor,

We are pleased that are our recent data (Revell & Skene, 2007) have generated interest from Bullough and colleagues, and we would like the opportunity to reply to their letter. They state that our findings confirm studies by their laboratory demonstrating that multiple photopigments contribute to non‐image‐forming (NIF) responses. This is not strictly correct. In our paper, we clearly state that the stimulatory effect of the additional wavelengths present in our polychromatic light could be via the stimulation of visual photopigments and/or via melanopsin regeneration. It is not possible to distinguish which of these phenomena are responsible for the observed increased effectiveness of the polychromatic light at suppressing nocturnal melatonin. Animal data already exist (Mure et al., 2007) showing that melanopsin photoreversal can influence NIF responses to light. While we are encouraged to learn that their model (Rea et al., 2005) predicts our observed results, we believe that the model will need to be modified to take account of melanopsin photoreversal. In addition, future models will also need to be adjusted as the relative contribution of rods, cones, and melanopsin to NIF responses under light conditions differing in irradiance, duration, and spectral composition is elucidated.