| Area 21a of cat cortex is one of several visual areas located in the middle of lateralsuprasylvian gyrus that were defined by anatomical connections and retinotopicorganization. A number of studies have investigated the corticocortical connections ofthis area. These results indicate that area 21a receives its principal excitatory input fromarea 17 and appears to be involved in form and pattern analysis rather than motionanalysis. In this study we have shown an organization of orientation in cat area 21ausing intrinsic signal optical imaging, and then compared them with orientation map incat visual area 17. Human and some other mammalians show greater behavioral sensitivity to verticaland horizontal grating stimuli than to those obliquely oriented (usually referred to as the'oblique effect'). Evidences from single-neuron electrophysiology, evoked-potentialstudies and optical imaging studies have demonstrated that more neurons in the visualcortex area 17 of cats and V1 of monkeys respond preferentially to vertical andhorizontal orientations than oblique ones. But the neural mechanism underlying thisperceptual asymmetry remains unclear. Therefore, to explore if there is an oblique effectoutside area 17, we examined the intrinsic signals in the cortex area 21a of cats usingoptical imaging and visual evoked potential (VEP) when it responded to differentorientation gratings. Experiments were performed on 25 adult cats. Using the intrinsic signal opticalimaging, we found the functional orientation map in area 21a for the first time. Themaps elicited by gratings of similar orientations, but opposite directions of motion (180oapart), were very similar to each other. Two orthogonal grating activated complementarypatterns of the maps. These results suggest that area 21a, like area 17 and 18, has anorientation functional columnar organization. We measured the amount of cortical space activated by differently oriented gratingin area 21a and 17 using optical imaging of intrinsic signals. On average, the area of the 20å¤æ—¦å¤§å¦åšå£«å¦ä½è®ºæ–‡ 第一部分exposed area 21a preferentially activated by vertical and horizontal grating was 25.8%larger than that by grating at oblique ones. Meanwhile the difference in area 17 was only5.2%. Thus, the orientation oblique effect in area 21a was more significant than that inarea 17. The similar results were observed in the amplitude of the VEP in area 21a. The present study for the first time observed the orientation column maps and theoblique effect in extrastriate visual area 21a in addition to area 17. Area 21a must sharesome similarities of the organization of area 17 and modulate certain properties(including orientation selectivity) of area 17. |
