Steady potential shifts and facilitated learning of delayed response in monkeys

Abstract

Monkeys with implanted nonpolarizable cortical and eye electrodes were trained on a delayed response task, in which the presentation of each trial was contingent upon on-line computer detection of specified events for each of three groups: SP—surface-negative steady potential (SP) shifts from left prefrontal cortex; LEM—eye movements to the right of approximately 40°; and YC—controls tested with intertrial intervals yoked to those generated by experimental monkeys under the on-line condition. The mean number of sessions and total errors to 90% correct performance, through successively longer delays, indicated significantly faster learning and greater transfer of performance levels by SP monkeys compared to the other two groups ( P = 0.018). During on-line testing on 12-s delayed response trials containing brief cues of 100, 200, and 500 ms, only the SP monkeys were capable of maintaining near-criterion performance. Electrocorticograms, recorded during on-line training, show no systematic relation of steady potential shifts with eye movements but indicate hemispheric asymmetry of prefrontal cortical processes related to attention. The results provide evidence that steady potential shifts, used as independent variables in the present situation, reflect increased neural excitability of prefrontal cortex mediating higher attentive states.