Effects of d-amphetamine on speaking in isolated humans.

The effects of oral d-amphetamine, 5--20 mg were studied in isolated humans who produced speech monologues during experimental sessions. Drug effects were studied under double-blind conditions by making repeated observations within each subject after placebo or active drug. In the first experiment, d-amphetamine 15 mg was studied in 4 isolated subjects who had received instructions that they should talk some of the time during experimental sessions. All subjects spoke more after active drug than after placebo. In the second experiment, d-amphetamine 5--20 mg was studied in 4 subjects who were instructed to talk, but who also earned points under a fixed interval 5 min schedule by speaking (i.e. by closure of a voice operated relay). Point delivery did not generally influence patterns of speech over time. Reliable drug produced increases in amount of talking were observed in 3 of 4 subjects. Adjective checklist self report scores indicating a stimulant drug effect were also sensitive to effects of d-amphetamine. Under controlled laboratory conditions, an increase in speaking is a reliable behavioral effect of d-amphetamine in isolated humans producing speech monologues.