Society for Neuroscience 2005

T.Okamoto1*; K.Ikezoe4; H.Tamura4; M.Watanabe3; I.Fujita4; K.Aihara1,2
1. ERATO, JST, Tokyo, Japan
2. IIS, Univ. of Tokyo, Tokyo, Japan
3. Grad. Sch. Eng., Univ. of Tokyo, Tokyo, Japan
4. Cog. Neurosci., Osaka Univ., Osaka, Japan

In orientation map of the striate cortex (V1), orientation preferences of neurons change smoothly clockwise or counterclockwise around pinwheel centers. In a previous study, we made a prediction on the basis of a geometric model of V1 orientation map that the degree of extra-receptive field contextual modulation is greater for neurons with a larger distance from its nearest pinwheel center (Okamoto et al. SFN 2003). This topography of contextual modulation derives from a characteristic distribution pattern of neurons preferring iso- and cross-orientation; at a cortical site distant from a pinwheel center, as one moves from the site farther way, relative areas of domains preferring iso-orientation and those preferring cross-orientation change periodically. This tendency becomes weaker for a cortical site near a pinwheel center. The computational model is based on an idealized, honeycomb-like arrangement of orientation preferences. Here we addressed whether orientation maps from monkey V1 exhibit the distribution pattern of orientation preferences predicted by our model. By using intrinsic optical imaging techniques, we obtained orientation maps from V1 in anesthetized monkeys (Macaca fuscata). We measured relative areas of domains with iso- and cross-orientation preferences as a function of the distance from a cortical site under analysis. The same procedure was then repeatedly applied to other cortical sites with different distances from the nearest pinwheel center. The overall distribution pattern of preferred orientation as a joint function of the distance from a given site and the distance from that site to its nearest pinwheel center was consistent with the one predicted from the idealized orientation map. The results indicate that our model captures the topographic nature of monkey V1, and lend a support for our prediction on contextual modulation.