Effects of d-amphetamine and caffeine on schedule-controlled and schedule-induced responding.

The team gave rats two common stimulants: caffeine and d-amphetamine.

They watched how the drugs changed lever pressing on a fixed-interval schedule.

They also counted laps of schedule-induced licking, the extra drinking that pops up between food deliveries.

Both drugs slowed the rats down.

Lever pressing dropped, and the compulsive licking almost stopped.

The slowdown was biggest for rats that had been pressing or licking the fastest before the drug.

Hearst (1960) first showed that d-amphetamine cuts fixed-ratio output; the new study adds fixed-interval and adjunctive behavior to the list.

Sanders (1969) mixed diazepam with the same drug and saw rates go both up and down. The clean drop seen here hints that diazepam, not the amphetamine, drove the messy pattern.

Hymowitz (1981) later found that diazepam boosts punished pressing and licking. Together the three papers draw a simple line: amphetamine suppresses, diazepam restores.

If you run drug-behavior studies, remember that baseline speed sets the size of the effect. A hyperactive animal will look calmer after stimulants, while a slow animal may barely change. When you see mixed results across labs, check whether sedatives or anxiety meds were also on board.