Proceedings of the Royal Society B: Biological Sciences
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Contribution of human melanopsin retinal ganglion cells to steady-state pupil responses

Sei-ichi Tsujimura

Sei-ichi Tsujimura

Department of Information Science and Biomedical Engineering, Kagoshima University, Kagoshima, Japan

[email protected]

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Kazuhiko Ukai

Kazuhiko Ukai

Department of Applied Physics, School of Advanced Science and Engineering, Waseda University, Tokyo, Japan

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,
Daisuke Ohama

Daisuke Ohama

Department of Information Science and Biomedical Engineering, Kagoshima University, Kagoshima, Japan

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Atsuo Nuruki

Atsuo Nuruki

Department of Information Science and Biomedical Engineering, Kagoshima University, Kagoshima, Japan

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Kazutomo Yunokuchi

Kazutomo Yunokuchi

Department of Information Science and Biomedical Engineering, Kagoshima University, Kagoshima, Japan

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    The recent discovery of melanopsin-containing retinal ganglion cells (mRGCs) has led to a fundamental reassessment of non-image forming processing, such as circadian photoentrainment and the pupillary light reflex. In the conventional view of retinal physiology, rods and cones were assumed to be the only photoreceptors in the eye and were, therefore, considered responsible for non-image processing. However, signals from mRGCs contribute to this non-image forming processing along with cone-mediated luminance signals; although both signals contribute, it is unclear how these signals are summed. We designed and built a novel multi-primary stimulation system to stimulate mRGCs independently of other photoreceptors using a silent-substitution technique within a bright steady background. The system allows direct measurements of pupillary functions for mRGCs and cones. We observed a significant change in steady-state pupil diameter when we varied the excitation of mRGC alone, with no change in luminance and colour. Furthermore, the change in pupil diameter induced by mRGCs was larger than that induced by a variation in luminance alone: that is, for a bright steady background, the mRGC signals contribute to the pupillary pathway by a factor of three times more than the L- and M-cone signals.

    Footnotes

    This paper is dedicated to the memory of our friend and co-author, Kazuhiko Ukai, who made a significant contribution to this project before he passed away on 1st November 2009.

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