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Area summation functions of macaque V3 neurons



Conference Title

Society of Neuroscience Annual Meeting


Society of Neuroscience


Washington, D.C. / November 15-19, 2008

Publication Date / Copyright Date



Although the anatomical organization of V3 has been extensively investigated, much less is known about the quantitatively analyzed receptive-field properties of individual V3 neurons (Gegenfurtner et al, 1997). Because V3, like V2 and MT, receives direct feed forward input from V1 and also from V2, certain RF properties of subgroups of V3 neurons may be substantially different from others. To examine this possibility, we measured the area summation function of each V3 neuron after determining unit’s orientation/direction tuning and spatial frequency tuning. All units viewed the central 5-6 degrees. Stimulus was circular drifting high-contrast (80%) sine wave gratings. As previously reported (Gegenfurtner et al, 1997), the orientation tuning of V3 neurons was on the average, similar or slightly broader than in V2. Also the optimal spatial frequency and spatial resolution were slightly lower in V3 than in V2. We found distinct subgroups of V3 neurons that substantially differed in area summation properties. About one-third of the sampled units exhibited excitatory summation over large areas (5-10 degrees RF centers) and had no or little surround suppression. Another one-third had extremely small RF centers (one degree or less) and showed nearly complete surround suppression. The remaining samples of V3 neurons had summation properties that are similar to the area summation properties that were previously reported (i.e., RF center sizes were about 3-5 degrees and surround suppression was moderate, Gegenfurtner et al, 1997). Neurons with similar summation properties tended to be clustered, but these summation properties were not systematically related to their orientation or spatial frequency tuning properties. These results suggest that V3 contains subgroups of neurons that distinctly differ in their abilities to integrate signals over extended space.



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