Variable-ratio schedules of timeout from avoidance: effects of d-amphetamine and morphine.
Drug impact hinges on whether the behavior earns relief or something else, not on how often the behavior occurs.
01Research in Context
What this study did
Rats worked on a two-lever avoidance box. Pressing one lever postponed mild shock. Pressing the other lever earned a brief timeout from the whole setup.
The schedule for timeout was variable-ratio: the number of presses needed changed each time. The team then gave injections of d-amphetamine or morphine to see which lever the rats preferred.
What they found
d-Amphetamine made the timeout lever skyrocket. The rats pressed it far more often, yet they still avoided shock just fine.
Morphine did the opposite. Timeout presses dropped, but shock avoidance stayed steady or even rose. Same box, same rats, different drug, opposite story.
How this fits with other research
Davison et al. (1995) swapped cocaine for d-amphetamine and saw the same timeout boom, proving the effect is not just one stimulant.
Elsmore et al. (1994) ran timeout plus food side-by-side. Morphine again cut timeout presses while leaving food alone, showing the drug picks the reinforcer, not the response.
Rincover et al. (1975) first showed morphine can split escape and avoidance in monkeys. The 1991 paper extends that idea to timeout, a milder form of relief.
Why it matters
If you ever consult on cases using medication, remember: a stimulant may spike behaviors that earn breaks, while an opioid might suppress them. Check which responses your client uses to escape tasks. A simple rate count can hide these opposite shifts.
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02At a glance
03Original abstract
Rats were trained on concurrent schedules in which pressing one lever postponed shock and pressing the other lever produced periods of signaled timeout from avoidance on variable-ratio schedules. These procedures generated high rates of timeout-reinforced responding and provided a baseline for studying the effects of drugs on behavior maintained by different types of negative reinforcement (shock postponement vs. timeout). Morphine (2.5 to 10.0 mg/kg) reduced behavior maintained by timeout at doses that increased or had no effect on avoidance responding. In contrast, d-amphetamine (0.125 to 2.0 mg/kg) produced large increases in timeout responding at doses that had minimal effect on avoidance in rats trained on variable-interval and variable-ratio schedules. Thus, the event-dependent effects of morphine, observed in previous studies in which timeout responding was maintained at low rates by interval schedules, were replicated with high timeout rates maintained by variable-ratio schedules. The effects of d-amphetamine could also be described as "event dependent" because timeout responding was stimulated more than avoidance regardless of the maintenance schedule or baseline rate.
Journal of the experimental analysis of behavior, 1991 · doi:10.1901/jeab.1991.56-193