On the Evolution of the Frontal Eye Field: Comparisons of Monkeys, Apes, and Humans

This chapter compares the location, extent, and boundaries of the frontal eye field (FEF) in prosimians, New World monkeys, Old World monkeys, apes, and humans. We are particularly interested in understanding how the location of FEF in humans relates to that in other primate species. We consider whether FEF should be understood as a collection of distinct areas or as a single area with multiple modules that can be of different sizes (and locations) in different species according to lifestyle and habitat. We also consider how the size and location of FEF is a matter of operational definition with resolution specified by the various techniques applied, making comparison across species, especially humans, challenging. Locating FEF is challenged further by the variation of sulcal morphology across species and individuals. Nevertheless, in all investigated primate species FEF appears to be located at the transition zone between premotor area 6 and prefrontal area 8 in a cortical region with significant sulcal variation where it is bordered caudally (in premotor cortex) and rostrally (in prefrontal cortex) by areas also contributing to visually guided gaze behavior. We highlight current areas of uncertainty. In particular, lacking information about precise boundaries, we do not know whether the size and modularity of FEF scales across species with overall neocortical area, or with the complexity of visual and other sensory systems, or with changes in associated subcortical circuits, or with the complexity of the musculature used for visually guided behaviors, or with the complexity of cognitive control over gaze behavior.