我們的視覺世界光線水平有一個巨大的范圍，比視網(wǎng)膜中的神經(jīng)元能夠表達(dá)的輸出信號的范圍大100倍,。然而,，我們在從黑暗的電影院到明亮的陽光下等相差很大的光線條件下仍然能夠看到東西。這其中的部分原因可能是因為,，錐形光受體能夠使自己的平均輸出適應(yīng)環(huán)境光照條件?，F(xiàn)在，研究人員在錐形雙極細(xì)胞和神經(jīng)節(jié)細(xì)胞之間發(fā)現(xiàn)了第二種自適應(yīng)機制,。兩個自適應(yīng)機制是互補的,，當(dāng)光線水平提高時，主導(dǎo)點（dominant site）會從視網(wǎng)膜回路切換到錐形自適應(yīng)機制,。
原始出處:
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: [email protected]).
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.
