Three-dimensional structure and evolution of primate primary visual cortex.

In this study, three-dimensional reconstructions of primate primary visual cortex (V1) were used to address questions about its evolution. The three-dimensional shape of V1 in anthropoids is significantly longer and narrower than in strepsirrhines. This difference is an effect of clade and is not due to differences in activity pattern or V1 size. New measurements of V1 volume were also provided in order to reassess V1 size differences between strepsirrhines and anthropoids. It was found that for a given lateral geniculate nucleus (LGN) volume, anthropoids have a significantly larger V1 than strepsirrhines do. This is important since LGN is the principal source of V1's input. Finally, independent contrasts analysis was used to examine the scaling of V1 relative to LGN, the rest of cortex, and the rest of the brain. It was confirmed that V1 scales with positive allometry relative to LGN. A number of possible explanations for scaling are discussed. V1 scaling may have to do with the tendency of large brains to be more compartmentalized than small brains, or V1 scaling might reflect the geometry of information representation.