Pentobarbital self-administration in rhesus monkeys: drug concentration and fixed-ratio size interactions.
Stronger reinforcers can cancel out the response-slowing effect of higher fixed-ratio requirements.
01Research in Context
What this study did
Scientists let rhesus monkeys press a lever to give themselves pentobarbital, a sedative.
They changed two things: how strong the drug dose was and how many presses the monkey had to make.
The team watched how fast the monkeys pressed and how many drug deliveries they earned.
What they found
Response speed and total drug deliveries made an upside-down U.
Medium drug levels produced the most work; weak or very strong levels produced less.
When the required presses were high, stronger drug doses helped the monkeys keep working.
How this fits with other research
WALLETHOMAS et al. (1963) saw the same upside-down U in pigeons given pentobarbital under FR 30. Their birds also worked hardest at moderate doses, showing the pattern holds across species.
Zimmerman (1969) showed that bigger food reinforcers shorten the pause after reinforcement under FR schedules. Baer et al. (1984) now show that bigger drug reinforcers can offset the suppressive effect of larger ratios, extending the magnitude idea from food to drugs.
Northup et al. (1991) mixed cocaine and food under FR and progressive-ratio schedules. They also found an inverted-U for magnitude and saw cocaine maintain higher breakpoints than food. The new monkey data line up: stronger reinforcers, whether cocaine or pentobarbital, can push animals through tougher response costs.
Why it matters
For BCBAs, the study is a reminder that reinforcer strength and response cost trade off. If a client stalls when the task gets big, try boosting the payoff before you lower the demand. A stronger reinforcer—more tokens, longer iPad time, a better snack—may keep the response going without changing the ratio itself.
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02At a glance
03Original abstract
Performances of three rhesus monkeys were reinforced by the oral delivery of pentobarbital and studied as functions of fixed-ratio size and drug concentration. Pentobarbital solutions and water were concurrently available on identical reinforcement schedules from separate liquid-delivery systems during 3-hour sessions. Under a fixed-ratio 16 schedule of drug availability, a descending series of drug concentrations was tested (4, 2, 1, 0.5, 0.25, 0.125, and 0.0625 mg/ml, followed by a retest at 4 mg/ml). Partial concentration series beginning with the highest concentration were repeated with fixed-ratios of 32 and 64, with a fixed-ratio 128 for two monkeys, and with fixed-ratio 256 for one. At each fixed-ratio value, response rate and number of drug deliveries were inverted U-shaped functions of pentobarbital concentration. Drug intake (mg/kg/session) increased directly with drug concentration. As the fixed-ratio size was increased, the number of liquid deliveries decreased. For each drug concentration, when the numbers of drug deliveries at fixed-ratios of 32, 64, and 128 responses were plotted as percentages of those obtained at fixed-ratio 16, the following orderly relationship emerged: the higher the drug concentration, the less that drug deliveries were decreased by increases in fixed-ratio size. This relationship indicates an increase in reinforcing efficacy with increases in pentobarbital concentration.
Journal of the experimental analysis of behavior, 1984 · doi:10.1901/jeab.1984.42-37