Movement-related potentials during development: a replication and extension of relationships to age, motor control,...

Three age groups of normals (children, preadolescents, and adults) and a group of mentally retarded adults performed a noncued button press task from which averaged movement-related potentials (MRPs) were derived. MRP wave shapes replicated our previously reported modal waveform types, except for the preadolescents, who showed no modal MRP. The normal groups showed a developmental shift in the prevalence of waveforms with the retarded differing from normal adults. The modal child waveform had a large amplitude positive-negative-positive form; the retarded had a uniphasic positive form; while normal adults showed the usual negative form. Major MRP types among children could not be attributed to differences in sampling or number of the trials averaged, or to trial-to-trial MRP variability. Background EEG activity did not differ in different modal MRP types. Modal child MRPs showed an initial peak positivity at Fz, and a late peak at Cz. The retarded had a sustaining central positivity developed by midepoch. MRP positivity and negativity were related to age, inhibition of extraneous eye movement (EM), and IQ. In children, greater cognitive proficiency is associated with adult-like MRP. The results suggest that positivity, in part, reflects a subject's efforts at inhibiting movement extraneous to the instructed task.