Pentobarbital and d-amphetamine effects on concurrent performances.
Drug effects swing from helpful to harmful when reinforcement schedules run side-by-side, so always watch the task context.
01Research in Context
What this study did
Bacotti (1979) gave lab animals two levers at once. One lever paid off after a set number of presses (FR). The other paid off after a set time passed (FI).
The team then injected either pentobarbital (a downer) or d-amphetamine (an upper). They watched how the drugs changed the way the animals split their time between the two levers.
What they found
The drugs did not simply speed up or slow down everything. Pentobarbital sometimes helped FR performance and hurt FI performance. Amphetamine did the opposite, and the flip depended on how long the FI timer was set.
In short, the same drug could help or hurt depending on which schedule the animal was working on at that moment.
How this fits with other research
Llewellyn et al. (1976) ran almost the same drugs on a single long FI schedule. They also saw that amphetamine first raised, then lowered, response rates as the dose went up. Pentobarbital only moved responding around inside the interval. Bacotti (1979) adds the FR side and shows the drug story changes when two schedules run together.
Sievert et al. (1988) swapped cocaine for amphetamine and kept pentobarbital. Under FI and RI schedules, cocaine made all response rates look the same. Pentobarbital just slowed everything. Bacotti (1979) agrees that pentobarbital is mostly a brake, but shows the brake can help FR when FI is present at the same time.
Dougherty et al. (1996) and Lancioni et al. (2000) later used concurrent schedules to teach pigeons and rats to tell pentobarbital from saline. They got clean dose-response curves. Bacotti (1979) is the earlier proof that concurrent schedules themselves are sensitive to small drug changes, setting up those later discrimination studies.
Why it matters
If you ever consult on cases where clients take stimulants or sedatives, remember: the same med can help one skill and hurt another when both run close in time. Watch the task, not just the drug. When you see odd gains in one area paired with new losses in another, check if the two tasks run on different reinforcement schedules before you blame the dose.
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02At a glance
03Original abstract
The effects of pentobarbital and d-amphetamine were studied in pigeons responding under several concurrent fixed-ratio variable-interval and concurrent fixed-ratio fixed-interval schedules of food presentation. Drug effects were compared with different fixed ratios, fixed and variable intervals, changeover delays, and with the schedules operating singly. Doses of d-amphetamine that increased or did not affect responding under the interval schedules decreased responding under the fixed-ratio schedule, whereas doses of pentobarbital that increased responding under the fixed-ratio schedule decreased or eliminated responding under the interval schedules. These effects depended both on the schedule of food delivery and the parameters of schedules arranged concurrently. Pentobarbital increased responding under the fixed-ratio schedule with 4-minute and 10-minute interval schedules arranged concurrently, but not with 1.5-minute schedules. d-Amphetamine decreased concurrent ratio and interval responding with the 1.5-minute interval schedules, but either increased or did not affect responding with the longer intervals. Changes in the parameter of one schedule altered responding controlled by that schedule and also other concurrent performances. As a consequence, the effects of drugs on each behavior were altered.
Journal of the experimental analysis of behavior, 1979 · doi:10.1901/jeab.1979.31-141