我们的视觉世界光线水平有一个巨大的范围，比视网膜中的神经元能够表达的输出信号的范围大100倍。然而，我们在从黑暗的电影院到明亮的阳光下等相差很大的光线条件下仍然能够看到东西。这其中的部分原因可能是因为，锥形光受体能够使自己的平均输出适应环境光照条件。现在，研究人员在锥形双极细胞和神经节细胞之间发现了第二种自适应机制。两个自适应机制是互补的，当光线水平提高时，主导点（dominant site）会从视网膜回路切换到锥形自适应机制。
原始出处:
Nature 449, 603-606 (4 October 2007) | doi:10.1038/nature06150; Received 27 June 2007; Accepted 6 August 2007; Published online 12 September 2007
Light adaptation in cone vision involves switching between receptor and post-receptor sites
Felice A. Dunn1, Martin J. Lankheet4 & Fred Rieke2,3
Program in Neurobiology and Behavior,
Howard Hughes Medical Institute and,
Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195, USA
Functional Neurobiology and Helmholtz Institute, Utrecht University, 3584 CH Utrecht, The Netherlands
Correspondence to: Fred Rieke2,3 Correspondence and requests for materials should be addressed to F.R. (Email: rieke@u.washington.edu).
We see over an enormous range of mean light levels, greater than the range of output signals retinal neurons can produce. Even highlights and shadows within a single visual scene can differ 10,000-fold in intensity—exceeding the range of distinct neural signals by a factor of 100. The effectiveness of daylight vision under these conditions relies on at least two retinal mechanisms that adjust sensitivity in the 200 ms intervals between saccades1. One mechanism is in the cone photoreceptors (receptor adaptation)2, 3, 4, 5 and the other is at a previously unknown location within the retinal circuitry that benefits from convergence of signals from multiple cones (post-receptor adaptation)6, 7. Here we find that post-receptor adaptation occurs as signals are relayed from cone bipolar cells to ganglion cells. Furthermore, we find that the two adaptive mechanisms are essentially mutually exclusive: as light levels increase the main site of adaptation switches from the circuitry to the cones. These findings help explain how human cone vision encodes everyday scenes, and, more generally, how sensory systems handle the challenges posed by a diverse physical environment.
