%A Song,Zhuoyi
%A Zhou,Yu
%A Juusola,Mikko
%D 2016
%J Frontiers in Computational Neuroscience
%C
%F
%G English
%K photoreceptor,light adaptation,Random Photon Absorption Model (RandPAM),sublinear summation,quantum-gain-nonlinearity,photon sampling,multi-photon-hits
%Q
%R 10.3389/fncom.2016.00061
%W
%L
%N 61
%M
%P
%7
%8 2016-June-24
%9 Hypothesis and Theory
%+ Mrs Zhuoyi Song,Centre for Mathematics, Physics and Engineering in the Life Sciences and Experimental Biology (CoMPLEX), University College London,London, UK,zhuoyi.song@shef.ac.uk
%+ Mrs Zhuoyi Song,Department of Biomedical Science, University of Sheffield,Sheffield, UK,zhuoyi.song@shef.ac.uk
%#
%! Photoreceptorsâ€™ Early Gain Control Arises from Quantal Sampling
%*
%<
%T Random Photon Absorption Model Elucidates How Early Gain Control in Fly Photoreceptors Arises from Quantal Sampling
%U https://www.frontiersin.org/article/10.3389/fncom.2016.00061
%V 10
%0 JOURNAL ARTICLE
%@ 1662-5188
%X Many diurnal photoreceptors encode vast real-world light changes effectively, but how this performance originates from photon sampling is unclear. A 4-module biophysically-realistic fly photoreceptor model, in which information capture is limited by the number of its sampling units (microvilli) and their photon-hit recovery time (refractoriness), can accurately simulate real recordings and their information content. However, sublinear summation in quantum bump production (quantum-gain-nonlinearity) may also cause adaptation by reducing the bump/photon gain when multiple photons hit the same microvillus simultaneously. Here, we use a Random Photon Absorption Model (RandPAM), which is the 1st module of the 4-module fly photoreceptor model, to quantify the contribution of quantum-gain-nonlinearity in light adaptation. We show how quantum-gain-nonlinearity already results from photon sampling alone. In the extreme case, when two or more simultaneous photon-hits reduce to a single sublinear value, quantum-gain-nonlinearity is preset before the phototransduction reactions adapt the quantum bump waveform. However, the contribution of quantum-gain-nonlinearity in light adaptation depends upon the likelihood of multi-photon-hits, which is strictly determined by the number of microvilli and light intensity. Specifically, its contribution to light-adaptation is marginal (â‰¤ 1%) in fly photoreceptors with many thousands of microvilli, because the probability of simultaneous multi-photon-hits on any one microvillus is low even during daylight conditions. However, in cells with fewer sampling units, the impact of quantum-gain-nonlinearity increases with brightening light.