Purpura K, Tranchina D, Kaplan E, Shapley R M
Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021.
Vis Neurosci. 1990 Jan;4(1):75-93. doi: 10.1017/s0952523800002789.
The responses of monkey retinal ganglion cells to sinusoidal stimuli of various temporal frequencies were measured and analyzed at a number of mean light levels. Temporal modulation tuning functions (TMTFs) were measured at each mean level by varying the drift rate of a sine-wave grating of fixed spatial frequency and contrast. The changes seen in ganglion cell temporal responses with changes in adaptation state were similar to those observed in human subjects and in turtle horizontal cells and cones tested with sinusoidally flickering stimuli; "Weber's Law" behavior was seen at low temporal frequencies but not at higher temporal frequencies. Temporal responses were analyzed in two ways: (1) at each light level, the TMTFs were fit by a model consisting of a cascade of low- and high-pass filters; (2) the family of TMTFs collected over a range of light levels for a given cell was fit by a linear negative feedback model in which the gain of the feedback was proportional to the mean light level. Analysis (1) revealed that the temporal responses of one class of monkey ganglion cells (M cells) were more phasic at both photopic and mesopic light levels than the responses of P ganglion cells. In analysis (2), the linear negative feedback model accounted reasonably well for changes in gain and dynamics seen in three P cells and one M cell. From the feedback model, it was possible to estimate the light level at which the dark-adapted gain of the cone pathways in the primate retina fell by a factor of two. This value was two to three orders of magnitude lower than the value estimated from recordings of isolated monkey cones. Thus, while a model which includes a single stage of negative feedback can account for the changes in gain and dynamics associated with light adaptation in the photopic and mesopic ranges of vision, the underlying physical mechanisms are unknown and may involve elements in the primate retina other than the cone.
在多个平均光照水平下，测量并分析了猴视网膜神经节细胞对不同时间频率的正弦刺激的反应。通过改变固定空间频率和对比度的正弦波光栅的漂移速率，在每个平均水平上测量时间调制调谐函数（TMTF）。神经节细胞时间反应随适应状态变化而出现的改变，与在人类受试者以及用正弦闪烁刺激测试的海龟水平细胞和视锥细胞中观察到的变化相似；在低时间频率下观察到了 “韦伯定律” 行为，但在较高时间频率下未观察到。时间反应通过两种方式进行分析：（1）在每个光照水平下，TMTF 由一个由低通和高通滤波器级联组成的模型拟合；（2）对于给定细胞，在一系列光照水平上收集的 TMTF 族由一个线性负反馈模型拟合，其中反馈增益与平均光照水平成正比。分析（1）表明，一类猴神经节细胞（M 细胞）在明视觉和中间视觉光照水平下的时间反应比 P 神经节细胞的反应更具相位性。在分析（2）中，线性负反馈模型相当好地解释了在三个 P 细胞和一个 M 细胞中观察到的增益和动力学变化。从反馈模型中，可以估计灵长类视网膜中视锥通路暗适应增益下降一半时的光照水平。该值比从分离的猴视锥细胞记录估计的值低两到三个数量级。因此，虽然一个包含单级负反馈的模型可以解释在明视觉和中间视觉视觉范围内与光适应相关的增益和动力学变化，但其潜在的物理机制尚不清楚，可能涉及灵长类视网膜中除视锥细胞之外的其他成分。
