Abstract
In Prosimian primates, New World monkeys, and Old World monkeys microstimulation with half second trains of electrical pulses identifies separate zones in posterior parietal cortex (PPC) where reaching, defensive, grasping, and other complex movements can be evoked. Each functional zone receives a different pattern of visual and somatosensory inputs, and projects preferentially to functionally matched parts of motor and premotor cortex. As PPC is a relatively small portion of cortex in most mammals, including the close relatives of primates, we suggest that a larger, more significant PPC emerged with the first primates as a region where several ethologically relevant behaviors could be initiated by sensory and intrinsic signals, and mediated via connections with premotor and motor cortex. While several classes of PPC modules appear to be retained by all primates, elaboration and differentiation of these modules likely occurred in some primates, especially humans.
Highlights
The dorsal stream of sensorimotor processing involves several cortical regions that are especially enlarged and differentiated in primates
The dorsal stream of visuomotor processing included projections of a specific array of extrastriate visual areas into posterior parietal cortex (PPC), which in turn relayed to motor, premotor, and prefrontal areas of frontal cortex (Ungerleider and Mishkin, 1982)
The contributions to PPC primarily come from a collection of visual areas (Boussaoud et al, 1990; Kaas and Morel, 1993, Born and Bradley, 2005; Kaskan and Kaas, 2007) that are especially involved in processing information about visual motion
Summary
The dorsal stream of sensorimotor processing involves several cortical regions that are especially enlarged and differentiated in primates. Our own studies have provided new evidence for somewhat different functional subdivisions of PPC, as well as anatomical evidence that functionally compatible zones of PPC and motor and premotor cortex are directly interconnected, and share cortical somatosensory and thalamic connections.
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