Rate-dependent effects of drugs: modification by discriminative stimuli of the effects of amobarbital on schedule-controlled behavior.
Stimulus shifts can shrink or swell the rate changes amobarbital causes on fixed-interval schedules.
01Research in Context
What this study did
Pigeons pecked a key on a fixed-interval schedule. Every few minutes they got food.
The birds first got amobarbital alone. Later, lights changed color during odd minutes to see if the drug effect shifted.
What they found
Amobarbital raised peck rates most when baseline rates were low. The boost shrank when rates were already high.
Adding a new light color twisted the size of the drug boost in tricky ways. The same dose did not always lift rates by the same amount.
How this fits with other research
Garcia (1974) ran the same rate-dependency test with pentobarbital and d-amphetamine under two-key conjunctive schedules. The low-rate boost showed up again, proving the rule holds across schedule shapes.
WALLER et al. (1962) saw amobarbital lift pecking that had been shut down by a pre-time-out red light. Their FR study is an early hint that stimuli can gate drug effects.
McAuley et al. (1986) later found d-amphetamine shortened pauses in rats under FI. The drug still followed rate dependency, but it also wrecked the birds' sense of time, showing the rule can coexist with other disruptions.
Why it matters
If you run drug-behavior sessions, remember that a simple stimulus change can flip the size of a drug effect. Track baseline rates minute-by-minute and watch for added cues. A red light, a beep, or a room change could turn a small dose into a big swing. Always pair your data sheets with a log of any new stimuli that day.
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02At a glance
03Original abstract
Food-deprived pigeons responded under a 10-min fixed-interval schedule of food presentation. During even-numbered minutes of the schedule, the discriminative stimuli were the same as those present when food was delivered. During odd-numbered minutes there was either a change in keylight color or a change in overhead illumination, either for the entire duration of the odd-numbered minutes, or for 3-sec after each response. Responding during even-numbered minutes showed the usual pattern of positive acceleration; responding during odd-numbered minutes was similarly graded, but rates were much lower. The response-rate-increasing effects of amobarbital were inversely related to control rates of responding for both even- and odd-numbered minutes. However, when the stimulus change during odd-numbered minutes was either keylight color or a change from a darkened to a brightly illuminated chamber, increases in responding were considerably less than predicted on the basis of the effects on responding during even-numbered minutes. When the stimulus change was from a darkened to a dimly illuminated chamber, control rates of responding changed little, but increases in responding during odd-numbered minutes after amobarbital were considerably greater, and of the approximate order expected on the basis of control rate.
Journal of the experimental analysis of behavior, 1970 · doi:10.1901/jeab.1970.14-167