To directly relate responses to the spatial pattern of light, we generated a “partial field flash” stimulus in which only a portion of the screen was transiently brightened or darkened. To compare responses across conditions, we defined a response strength metric as the mean response amplitude KU-57788 concentration to

light increments and decrements and set the sign of this metric, by convention, to be negative for cells that hyperpolarized to light (Figures S1F and S1G, Supplemental Experimental Procedures). This analysis showed that cells with RF centers inside the flash region hyperpolarized to brightening and depolarized to darkening, while cells with RF centers outside this region responded with opposite polarity (Figures 1C and 1D). Thus, individual cells produced responses of opposite polarities to center and surround stimulation, as well as to decrements and increments. Behavioral responses

to motion of rotating square-wave gratings display a contrast frequency optimum between 5–10 Hz (Tammero et al., 2004; Clark et al., 2011). To assess whether surround responses were sufficiently fast to shape signals relevant to motion vision, we presented brief “partial field flashes” (Figures 1E and 1F). For flashes lasting 200 ms, cells responded with opposite polarity to center and surround stimulation. Both response types were biphasic and largely differed in amplitude rather than kinetics (Figure 1F). selleck The response shape was consistent with kernels extracted from L2 responses to dynamically varying noise stimuli (Clark et al., 2011). Thus, surround Tolmetin inputs influence L2 responses even to rapid stimuli, on timescales that impact motion detection. We next examined how L2 responses vary as a function of the extent of center and surround stimulation by presenting circles and annuli, of either contrast polarity, around identified RF centers (Figures 2 and S2). As expected from an antagonistic center-surround RF, responses to large circles

were weaker than those to small circles (Figures 2A–2D, S2A, and S2B). In addition, annuli with sufficiently large internal radii so as to reduce center stimulation (4° and above) produced inverse responses (Figures 2E, 2F, and S2C–S2F). We infer that surround effects become stronger than center effects approximately 5° away from the RF center and extend radially to more than 15°. We next quantified the effects of surround stimulation by computing response amplitudes as a function of the spatial extent of the stimulus (Figures 2C, 2D, S2E, and S2F; as described in S1F). This analysis showed that the relative effect of surround stimulation differed between increments and decrements. For increments, amplitudes of responses to large circles were ∼50% smaller than responses to small circles (p < 10−4), while for decrements they were not statistically significantly different (Figures 2C and 2D). We next tested whether L2 responses reflect linear spatial integration.