Effects of methamphetamine and scopolamine on variability of response location.
Methamphetamine and scopolamine make monkeys switch levers more even while total presses drop.
01Research in Context
What this study did
Scientists gave monkeys two drugs: methamphetamine and scopolamine. The monkeys worked on fixed-ratio and fixed-interval lever schedules. The team watched how often the monkeys switched levers, not just how fast they pressed.
What they found
Both drugs made the monkeys change levers more often. Higher doses made the pattern even less predictable. At the same time, the drugs slowed the overall number of presses.
How this fits with other research
Hearst (1960) first showed methamphetamine slows fixed-ratio lever pressing in monkeys. Goldman et al. (1979) kept the same setup but added the twist: rate drops while variability rises.
McMillan (1979), published the same year, found d-amphetamine and caffeine also cut fixed-interval pressing. That paper looked only at rate; Goldman et al. (1979) shows variability can climb even while rate falls.
Davison et al. (1989) later used methadone in pigeons on alternating FR-FI schedules. The birds shifted from ratio to interval control, showing drugs can reveal hidden schedule effects. The 1979 study opens the same window by tracking lever switches.
Why it matters
If you run drug-behavior studies, watch variability, not just speed. A drop in responses can hide a jump in unpredictability. Track location, sequence, or timing to catch these shifts. This keeps your baseline clean and your data honest.
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02At a glance
03Original abstract
Methamphetamine and scopolamine were studied in monkeys responding under a multiple fixed-ratio fixed-interval schedule of reinforcement. A response on any one of six levers could satisfy the schedule requirements. Variability of response location was evaluated in terms of switches, where a switch was defined as a response on one lever followed by a response on a different lever. Under baseline conditions the fixed-ratio schedule generated a high rate of responding and a low level of variability, while the fixed-interval schedule generated a low rate of responding and a high level of variability. Both methamphetamine (0.1 to 0.5 mg/kg) and scopolamine (2.4 to 240 microgram/kg) decreased overall response rate and increased variability of response location in each component of the multiple schedule with increasing doses of drug. At lower doses both drugs were found to decrease rate without affecting response variability.
Journal of the experimental analysis of behavior, 1979 · doi:10.1901/jeab.1979.32-255