Oral drug self-administration in rhesus monkeys: interactions between drug amount and fixed-ratio size.
Under fixed-ratio schedules, upping the number of drug deliveries per ratio boosts reinforcing power even as the ratio grows.
01Research in Context
What this study did
Scientists let rhesus monkeys drink a drug solution by pressing a lever. Each press followed a fixed-ratio schedule. The team changed two things: how many drug deliveries the monkey got after finishing the ratio, and how big the ratio was.
They used a tandem FR-N setup. The monkeys worked for oral drug, not IV. The goal was to see how the amount of drug per ratio altered its own reinforcing power.
What they found
When the monkeys got more drug deliveries for the same ratio, they pressed more. Drug deliveries went up. When the ratio itself got bigger, deliveries dropped.
The key point: more deliveries per fixed ratio boosted reinforcing strength, even if the ratio number rose.
How this fits with other research
Locurto et al. (1980) saw a similar flip. Small FR5 plus stimulants hurt accuracy. Large FR20/50 plus the same drugs helped accuracy by removing ratio strain. Both studies show ratio size can reverse drug effects.
Doughty et al. (2002) looked at reinforcer size under DRL, not FR. Larger food rewards sped responding and ruined DRL efficiency. Jason et al. (1985) found the opposite direction under FR: more drug per ratio increased responding. Schedule type decides whether bigger reward helps or hurts.
Pliskoff et al. (1967) first titrated reward size by count using brain stimulation. Jason et al. (1985) copied the count idea with oral drug deliveries, moving the method from brain stimulation to drug reinforcement.
Why it matters
If you thin reinforcement by raising the ratio, keep the amount per delivery the same or increase it. Clients will stay engaged because the bigger payoff counters the extra work. Watch for schedule type: DRL plus larger reward can backfire, but FR plus larger reward keeps responding strong.
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02At a glance
03Original abstract
During daily 3-hr sessions, 5 rhesus monkeys drank drug solutions and water that were concurrently available. The drug solutions were: 1 milligram per milliliter (mg/mL) pentobarbital (2 monkeys), 1 mg/mL pentobarbital plus 0.5% ethanol (1 monkey), 1 mg/mL pentobarbital plus 1% ethanol (1 monkey), and 8% ethanol (1 monkey). The drug solution and water were available under identical two-component tandem fixed-ratio continuous-reinforcement N schedules. Two variables were manipulated: the size of the fixed-ratio component and the number of liquid deliveries (N) in the second component. Deliveries of the drug solution maintained higher rates of responding than did deliveries of the drug vehicle, water. The number of drug deliveries per session increased with increases in the number of deliveries per fixed ratio and decreased with increases in fixed-ratio size. Analysis of the results in terms of the proportion of deliveries to responses showed that the number of drug deliveries per session was directly related to the size of this quotient. Finally, when fixed-ratio size was repeatedly doubled, the following orderly relationship emerged: The greater the number of available drug deliveries per fixed ratio, the less was the percent decrease in the number of fixed ratios completed per session. It was concluded that increases in the number of liquid deliveries per fixed ratio resulted in increases in reinforcing efficacy.
Journal of the experimental analysis of behavior, 1985 · doi:10.1901/jeab.1985.44-377