Spatial frequency preference maps of primate visual cortex revealed by optical imaging of intrinsic signals

Abstract

Electrophysiological studies designed to determine the geometry of spatial frequency (SF) preference in primate primary visual cortex (V1) have reported either columnar or laminar differences. In this study we used optical imaging to examine the cortical organization of SF preference in bush babies and owl monkeys using sine wave gratings of a range of SFs at 4 orientations. Both species are nocturnal but owl monkeys have a cutoff behavioral acuity of 10 c/deg whereas bush babies have a cutoff acuity of 5 c/deg. In spite of these behavioral differences both species showed the same basic tangential organization of SF preference within V1. As expected, the range of SFs close to the area centralis was shifted to higher SFs in comparison to the range of SFs seen at more eccentric locations. Examination of the activation patterns produced by the extremes of the SF range showed that these were different and revealed clusters of activation within neighboring territories. In some regions, however, high and low SFs overlapped. Iso-SF domains were generally smaller and had a different appearance than iso-orientation domains, although color-coded maps of SF preference did reveal pinwheel-like structures in some regions in both species. Comparison of maps of SF and orientation preference in the same animal suggested that these maps are largely independent. Our data supports a V1 model in which spatial frequency is mapped continuously across cortex in the form of multiple SF processing domains. (Supported by EY01778, S10RR13947, EY08126, HD15052)