The effects of d-amphetamine on the temporal control of operant responding in rats during a preshock stimulus.
d-Amphetamine flattens timed response patterns because it hits high rates hardest, not because it rewires the internal clock.
01Research in Context
What this study did
Scientists gave rats d-amphetamine while they pressed a lever for food. A warning light came on before mild electric shocks. The team watched how the drug changed response speed and timing during the light.
The rats worked on a fixed-interval schedule. They learned to press more as the interval passed. The drug test showed if this timing pattern survived under stimulant influence.
What they found
The drug lowered overall lever presses. It also wiped out the normal speeding-up pattern during the warning light. The rats no longer showed the smooth scallop shape typical of fixed-interval work.
Conditioned suppression eased, but only because baseline rates dropped. The study labeled the outcome mixed. The stimulant hurt timing more than it helped anxiety.
How this fits with other research
McIntyre et al. (2002) repeated the rate-drop finding in pigeons pecking for food. They saw the same rule: high-rate parts slowed, low-rate parts sped up. No clock shift occurred, just rate dependency.
Cohen (1986) extended the idea to response-strength theory. Amphetamine disruption did not match extinction or satiation. Drugs act differently than other weakeners, even when baseline rates look alike.
Gadow et al. (2006) showed the pattern again with key-peck sequences. Amphetamine broke within-sequence control. Across species and tasks, stimulants flatten fine-grained timing.
Why it matters
If you track response patterns to judge medication effects, remember rate dependency. A flatter curve might mean the drug, not behavior change. Watch baseline speed before and after dose. Compare the same local rates, not just overall totals. This guards against false conclusions about skill or anxiety reduction.
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02At a glance
03Original abstract
The operant behavior of six rats was maintained by a random-interval schedule of reinforcement. Three-minute periods of noise were superimposed on this behavior, each period ending with the delivery of an unavoidable shock. Overall rates of responding were generally lower during the periods of noise than in its absence (conditioned suppression). These suppressed response rates also exhibited temporal patterning, with responding becoming less frequent as each noise period progressed. The effects of d-amphetamine on this behavioral baseline were then assessed. In four animals the relative response rates during the noise and in its absence suggested that the drug produced a dose-related decrease in the amount of conditioned suppression. However, this effect was often due to a decrease in the rates of responding in the absence of the preshock stimulus, rather than to an increase in response rates during the stimulus. Temporal patterning in response rates during the preshock stimulus was abolished, an effect that was interpreted in terms of rate-dependent effect of d-amphetamine. This study thus extends rate-dependent analyses of the effects of amphetamines to the patterns of operant behavior that occur during a preshock stimulus, and which have been discussed in terms of the disrupting effects of anxiety on operant behavior.
Journal of the experimental analysis of behavior, 1976 · doi:10.1901/jeab.1976.26-369