Profound Contrast Adaptation Early in the Visual Pathway

Summary has investigated slow contrast adaptation in the primate retina, and that found substantially less adaptation than Prior exposure to a moving grating of high contrast led to a substantial and persistent reduction in the in the salamander. We describe here new observations that sharply clarify the picture in the primate visual pathcontrast sensitivity of neurons in the lateral geniculate nucleus (LGN) of macaque. This slow contrast adapta- way and have major implications for psychophysical studies: neurons in magnocellular LGN (M cells), but tion was potent in all magnocellular (M) cells but essentially absent in parvocellular (P) cells and neurons not those in parvocellular LGN (P cells), show strong contrast adaptation that originates in the retina. that received input from S cones. Simultaneous recordings of M cells and the potentials of ganglion cells driving them showed that adaptation originated in gan- Results glion cells. As expected from the spatiotemporal tuning of M cells, adaptation was broadly tuned for spatial Aftereffects of Adaptation to High-Contrast Stimuli frequency and lacked orientation selectivity. Adapta- We studied the responses of single neurons in LGN tion could be induced by high temporal frequencies of anesthetized macaque before, during, and through to which cortical neurons do not respond, but not by recovery from adaptation to contrast modulation of diflow temporal frequencies that can strongly adapt cor- ferent stimuli. Our initial experiments were prompted tical neurons. Our observations confirm that contrast by observations in ganglion cells (Baccus and Meister,