Figure 12.

Schematic illustrating simple (a), intermediate (b), and complex (c) motor-posterior parietal networks. Nondivergent, homotopic projections from PPC to M1 are hypothesized for tree shrews (as in a) and divergent projections from movement domains in different areas in PPC to M1 are hypothesized for the macaque monkey (c). For example, when a given domain in M1 is deactivated via cooling (e.g., X in grasp domain in M1), in a simple nondivergent network (a) stimulation of a similar domain in PPC would result in no movements. A very complex network consisting of divergent and convergent connectivity from multiple domains and multiple cortical fields (c) would have a different motor output, perhaps including domain switching or modified movements. We hypothesize that galagos have networks of intermediate complexity (b).