Cortical networks for ethologically relevant behaviors in primates.

Parietal-frontal networks in primate brains are central to mediating actions. Physiological and anatomical investigations have shown that the parietal-frontal network is consistently organized across several branches of primate evolution that include prosimian galagos, New World owl and squirrel monkeys, and Old World macaque monkeys. Electrical stimulation with 0.5-sec trains of pulses delivered via microelectrodes evoked ethologically relevant actions from both posterior parietal cortex (PPC) and frontal motor cortex (FMC). Reaching, grasping, defensive, and other complex movement patterns were evoked from domains that had a characteristic organization in both FMC and PPC. Although a PPC domain (e.g. reaching) may be connected with other PPC domains (e.g. grasping and defensive), its connections with FMC are preferential for a matching domain (reaching). Similarly, electrical stimulation of a PPC domain and concurrent optical imaging of FMC, showed activation patterns consistent with the preferential connectivity of PPC and FMC domains. The evidence for similar arrangements of interconnected functional domains in PPC and FMC of members of three major branches of the primate radiation suggests that the parietal-frontal networks emerged early in the evolution of primates. The small size of PPC in the close relatives of primates including lagomorphs, rodents, and tree shrews, suggests a limited involvement of PPC in motor behavior before archaic primates emerged. However, functional domains may have evolved in motor cortex before the emergence of archaic primates.