Evolution of Parietal-Frontal Networks in Primates
Posterior parietal cortex (PPC) of macaque monkeys is known to contain at least four action specific modules or domains: grasping, body defense, looking, and reaching. Similar action-specific domains have also been demonstrated by microstimulation within primary motor cortex (M1) and premotor cortex (PMC). We used microstimulation methods to identify as many as nine action-specific domains of PPC in prosimian galagos and New World owl and squirrel monkeys and functionally matched domains in M1 and PMC. Domains in PPC are widely interconnected, but each domain has connections focused on functionally matched domains in PMC and M1. Functional imaging studies suggest that at least some of the macaque domains exist in humans. PPC domains use visual and somatosensory information to decide on the optimal action, while PMC and M1 domains may use PPC inputs and other sources of information to confirm or alter the PPC decision. We suggest that early primates had a greatly expanded PPC with domains for basic, adaptive, and complex behaviors, while the nonprimate ancestors of primates had little PPC, and this cortex had only a weak effect on motor behavior.
