Naturalistic Movies and Encoding Analysis Redefine Areal Borders in Primate Visual Cortex

Accurate definition of the borders of cortical visual areas is essential for the study of neuronal processes leading to perception. However, data used for definition of areal boundaries has suffered from issues related to resolution, uniform coverage, or suitability for objective analysis, leading to ambiguity. Here, we present a novel approach that combines widefield optical imaging, presentation of naturalistic movies, and encoding model analysis, to objectively define borders in the primate extrastriate cortex. We applied this method to test conflicting hypotheses about the third-tier visual cortex, where areal boundaries have remained controversial. The results support a hypothesis whereby an area contains representations of both the upper and lower contralateral quadrants (DM) is located immediate anterior to V2, and unveil pronounced tuning preferences in the third-tier areas. High-density electrophysiological recordings with a Neuropixels probe confirm these findings. Our encoding-model approach offers a powerful, objective way to disambiguate areal boundaries. ### Competing Interest Statement The authors have declared no competing interest.