Vertical meridian representation on the prelunate gyrus in area V4 of macaque

The representation of the lower quadrant in area V4 is presently thought to extend along the prelunate gyrus from a foveal representation laterally al l the way to the dorsal end of the superior temporal sulcus. However, sever al studies suggest the possibility of a more complex organization. To see i f the visuotopic organization on the crown of the gyrus was relatively homo geneous or instead contained inhomogeneities indicative of more complex org anization, we recorded from a grid of points over the prelunate gyrus. Rece ptive-field size and scatter in the region are large, making it difficult t o infer topography from simple inspection of receptive-field sequences. We developed an averaging procedure using data from all recording sites to det ect an inhomogeneity in topography with respect to the vertical meridian. W ith this procedure, we found a vertical meridian representation just medial to the medial end of the lateral sulcus. We also found a significant diffe rence in the incidence of orientation sensitivity on either side of the mer idian representation. The results show that the crown of the prelunate gyru s cannot be described as a single homogeneous region, but instead contains at least two different sub-regions adjoining along a shared representation of the vertical meridian. (C) 2001 Elsevier Science Inc.