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Annette E Allen, Riccardo Storchi, Robert Bedford, Franck P Martial, Robert J Lucas; A melanopsin contribution to the representation of spatial patterns in the mouse visual system. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4140.
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© ARVO (1962-2015); The Authors (2016-present)
The discovery of melanopsin, a new photoreceptor in the mammalian retina, has revolutionized our understanding of how changes in background light intensity are measured to drive sub-conscious responses such as circadian photoentrainment. As yet it has not altered our view of how more conventional visual tasks such as detecting spatial patterns are undertaken. Responsibility for that aspect of vision remains solely attributed to rods and cones. Here, we set out to define the spatiotemporal resolution of melanopsin vision in visually intact mice.
We have modified a commercially available projection system so that each of the R, G and B channels is instead a combination of up to five, independently controlled wavelengths (λmax 405, 455, 525, 561, 630nm). With this stimulus, we have adapted a psychophysical method (receptor silent substitution) to produce patterned stimuli that are only visible to only rods and cones, only melanopsin, or all photoreceptors. We have used multi-channel recording electrodes to record light-evoked activity in the dorsal lateral geniculate nucleus (dLGN) of urethane anaesthetised Opn1mwR mice; these mice display a long-wavelength shifted spectral sensitivity of green cones, which allows us to achieve maximal contrast for each photopigment.
We find that melanopsin can support the representation of spatial patterns in ~20% of dLGN neurons. Receptive fields of individual dLGN neurons arising from either melanopsin alone, or rods and cones, are spatially contiguous. However, melanopsin is important in maintaining the representation of spatial patterns over longer time frames. By using natural images and simulated head/eye movements, we show that the dLGN relies upon melanopsin to avoid ‘fade out’ of coarse spatial patterns under periods of relative visual fixation. We have modelled the temporal contribution of melanopsin using an autoregressive exogenous model, with which we explored the spatiotemporal contribution of melanopsin in the dLGN.
Visual responses arising exclusively with melanopsin are detectible at the level of the dLGN at relatively modest contrasts, and on a physiologically relevant spatial and temporal scale. Our data imply that melanopsin makes a distinct contribution to encoding spatial patterns, and allows a reappraisal of the circuits and processes responsible for spatial vision.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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