EEG correlates of impaired attention performance under secobarbital and chlorpromazine in the monkey

The effects of secobarbital and chlropromazine upon behavior in a continuous, rapidly presented successive (go-no go) discrimination ("attention") task were evaluated in six Macaca mulatta monkeys. Simultaneous monitoring of EEG activity from epidural and subcortical electrodes permitted an evaluation of the nature of altered central nervous system events during erroneous performance (errors of omission) on this task. The computer-assisted analysis of pre-stimulus and post-stimulus EEG frequency activity (baseline crossings) suggests that the best measure of attentive behavior from the pre-stimulus EEG is percentage of beta 2 (25-40 cps) activity. No difference could be observed between drugs or among cerebral placements in this regard. This was determined by comparing measures of EEG frequency, pooled for a given test period, with performance from the same test period. On a trail-by-trail basis. however, the beta 2 measure in the pre-stimulus epoch failed to ditinguish correct responses from errors of omission. Separation between correct responses and errors of omission is possible if comparisons are made between the changes in percentage of beta 2 activity in the pre-stimulus vs. post-stimulus occurs with correct positive trials and the smallest change with correct negative trials. For secobarbital, no difference could be detected between correct and incorrect positive trials. For chlorpromazine, however, there was significantly less change in beta 2 for incorrect positive than for correct positive trials. The results were interpreted in terms of the hypothesis that secobarbital produces errors by depression of the general level of activation whereas chlorpromazine acts by reducing the sensory input which is necessary for correct discrimination performance.