Differential effects of cocaine and pentobarbital on fixed-interval and random-interval performance.
Cocaine makes response rates uniform across schedule segments, pentobarbital just slows everything down — a useful behavioral metric for drug class comparison.
01Research in Context
What this study did
Sievert et al. (1988) gave two drugs to lab subjects working on fixed-interval and random-interval schedules. They watched how cocaine and pentobarbital changed the speed and pattern of lever presses.
The team compared the same person before and after each drug. No extra rewards or punishments were added.
What they found
Cocaine made response rates almost the same across all parts of both schedules. High-rate segments slowed down and low-rate segments sped up, so everything flattened into one steady pace.
Pentobarbital simply slowed every segment. It did not flatten the pattern; it just lowered the volume, like turning down a radio.
How this fits with other research
Barber et al. (1977) and Llewellyn et al. (1976) already showed that pentobarbital slows high rates and can raise low rates. Sievert et al. (1988) confirm that part, but add the new twist: cocaine erases the ups and downs entirely.
Dworkin et al. (1989) looks like a contradiction at first. They found pentobarbital can increase punished responding while cocaine increases non-punished responding. The difference is the task: I et al. added punishment history. When punishment is in the mix, pentobarbital can look stimulatory, but on plain schedules it still just slows things down.
Scull et al. (1973) first mapped cocaine’s effect on FI pauses in rats. L et al. extend that work by showing cocaine also unifies the whole response-rate curve, not just the pause.
Why it matters
If you ever consult on cases where medication changes coincide with behavior shifts, watch the pattern, not just the speed. Cocaine-like drugs may flatten naturally variable work bursts, while sedative drugs simply reduce output. Use moment-to-moment rate plots to spot which drug class is at play and to time teaching trials when response patterns are most stable.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Plot within-session response rates; if bursts flatten under a new med, flag a possible stimulant effect.
02At a glance
03Original abstract
Reports have indicated that the behavioral effects of a drug can be related to the nondrug control rate of behavior in the absence of the drug. To investigate the purported relationship between control rate and drug rate, squirrel monkeys were trained under a fixed-interval 300-s schedule of stimulus-shock termination, a procedure that engendered a wide range of response rates. A light illuminated the experimental chamber during the fixed interval, and the first lever press after 300 s had elapsed terminated the light for 30 s and precluded an electrical stimulus to the tail. Following acute intramuscular administration of cocaine (0.03-0.56 mg/kg), overall rate increased and different control rates of responding, during different parts of the fixed interval, converged toward a common rate. Subsequently, the schedule was changed to a multiple fixed-interval 300-s random-interval 300-s schedule; performance during the random-interval component was characterized by steady responding at a uniformly high rate. Analysis of fixed-interval and random-interval performances following acute cocaine administration revealed convergence of response rates toward a common, uniform rate. Pentobarbital (0.3-10.0 mg/kg) only decreased overall rate, and different control rates of responding during the fixed interval did not converge toward a common rate. The results indicate that this type of analysis can be useful in comparing pharmacological agents from different classes and that the rate at which responding becomes uniform can provide a quantitative behavioral end point for characterizing drug effects on behavior.
Journal of the experimental analysis of behavior, 1988 · doi:10.1901/jeab.1988.49-411