Fig. 2.

Response magnitude changes in a visuotopically correspondent portion of MT after V1 deactivation in the owl monkey. (a and b) Magnitude (a) and orientation polar (b) maps produced by using full-field gratings at four orientations. The magnitude map shows the overall strength of orientation response (light = stronger; dark = less strong). The polar map contains information about both orientation preference (color) and magnitude of orientation selectivity (brightness) (see the color key below d). (c and d) Magnitude (c) and orientation polar (d) maps after V1 deactivation with muscimol. Reduced activation is apparent after V1 deactivation. Brackets highlight an area of increased activation outside the predeactivation boundaries of MT, perhaps resulting from a decrease in lateral inhibition in the area adjacent to that affected by deactivation. (e and f) Time courses of intrinsic signal strength to 8 s of stimulation (indicated by the solid black line above the x axis) using a 0° full-field drifting grating for the small square regions [red square in b and green square in d, which are the regions of interest (ROIs)] on the maps before and after V1 deactivation, respectively. The plots are polynomial fits of the average data points (squares) from 10 trials. The control ROI plot (e) shows a typical intrinsic response curve; the optical reflectance decreased with stimulus onset, dipped to its lowest point ≈7 s after onset, and then rebounded. On the graphs, the x axis shows time in s, and the y axis shows the change (in 10^–4) in the ROI relative to the blank (ΔR/R). The control ROI peak magnitude ΔR/R (dR/R) = –0.119 ± 0.017% (mean ± SD). The post-blocking ROI plot (f) does not show any stimulation-related response, and the optical reflectance appears to remain constant during stimulation, as indicated by the ROI peak magnitude ΔR/R = –0.008 ± 0.027%.