Cortical field potentials were recorded by electrodes implanted on the surface and at 2.0-3.0 mm depth in various cerebral cortices in monkeys performing self-paced movements of various body parts. It was found that surface-negative, depth-positive potential (readiness potential) occurred about 1.0 s before every movement in the premotor (PMC), motor (MC), somatosensory (SSC) and posterior parietal (PPC) cortices, and supplementary motor area (SMA). The readiness potential is considered to be responses due to superficial thalamo–cortical projections. It was indicated by electric stimulation and morphological studies that the readiness potential of the ventral premotor cortex (PMCv), facial part of MC, SSC and PPC originated mainly in the area X, VPLo, LP and pulvinar nuclei in the thalamus respectively. Further it was indicated by the resection studies of the cerebellum that the readiness potential in the PMCv and MC originated in the cerebello–thalamo–cortical responses. In order to study how preparative activities in the PPC for hand movements activated the forelimb muscle, we recorded activities induced in the muscle after electric stimulation of the MC and PPC, and also measured conduction time of nerve impulses between the PPC – PMCv, PMCv – MC, and PPC – MC respectively, by electric stimulation. It was found that excitatory activities in the PPC could be transmitted to the forelimb muscle without passing through the PMCv and MC. It is possible that many cortices producing readiness potential – motor areas in broad sense – could be simultaneously activated to initiate self-paced movements through parallel processing.