The monkey's prefrontal cortex functions in motor programming

A new experimental approach is presented which resulted in clarification of the specific functions of the monkey’s prefrontal cortex. Monkeys with chronically implanted transcortical nonpolarizable electrodes were trained on delayed response (DR) and visual delayed matching-to-sample (DMS) tasks. The onset of the trial for each group depended upon on-line computer detection of one of the specified events: FN – surface-negative steady potential shifts (SPS) from principalis cortex; MN – a similar SPS from precentral cortex; FB – near baseline SP from principalis cortex; LEM – rightward eye deviations; and YC – controls, with intertrial intervals yoked to those of other monkeys. Monkeys were trained with 1-s cue presentations. on successive delays of 2 to 12 s. The DR acquisition rate by the FN group was substantially faster than that of any other group, as indicated by its mean error that was only 17.24 percent the YC group’s error. The MN and LEM monkeys acquired the task at the same rates as the YCs, while the FB monkeys were the slowest learners. The correct DR performance transferred to testing with constant intertrial intervals (without preconditions). Subsequent on-line tests with brief (0.1 s) cue duration showed high DR performance by the FN, but not by other groups. No similar rapid learning was found with the DMS task. The findings from this, and other experiments, suggest that the major function of principalis cortex is the selection, or programming of delayed spatial choice responses. The view seems consonant with interpretations for the role of the human prefrontal cortex.