Enhancement of progressive-ratio performance by chlordiazepoxide and phenobarbital.
Motivation to work follows an inverted-U curve - moderate drug doses increase effort, but too much or too little reduces it.
01Research in Context
What this study did
Researchers gave pigeons two common drugs: chlordiazepoxide and phenobarbital.
The birds worked on progressive-ratio schedules where each reward cost more pecks than the last.
They measured how many pecks the birds would do before quitting - called the breaking point.
What they found
Both drugs made the birds work harder, but only at middle doses.
Too little drug did nothing. Too much drug also did nothing.
The sweet spot was 20 mg/kg for chlordiazepoxide and 40 mg/kg for phenobarbital.
How this fits with other research
WALLER et al. (1962) found similar results with pentobarbital on fixed-ratio schedules. Both studies show barbiturates can boost ratio performance.
Northup et al. (1991) extended this work by comparing cocaine versus food rewards. They also found the inverted-U pattern - more reward first helps, then hurts.
Clarke et al. (1998) tested the same progressive-ratio setup but changed step sizes. They found step size affects how many ratios birds try, not the final breaking point.
Why it matters
This shows that motivation isn't fixed - it can be chemically enhanced. For your clients, this means environmental factors like medication timing could affect how hard they're willing to work in therapy. Consider tracking response effort across sessions to spot natural variations in motivation.
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02At a glance
03Original abstract
The key pecking of two pigeons was reinforced with food on a progressive-ratio schedule, which required an increasing number of responses for each successive reinforcement: 8, 16, 24, 32, etc. When the subject failed to complete the next ratio in the sequence within 60 min, the session terminated. The number of responses in the final completed ratio was defined as the "breaking point". After the breaking point had stabilized (60 sessions), it served as a baseline to assess the effects of varying doses (5 to 80 mg/kg) of chlordiazepoxide and phenobarbital, administered intramuscularly 30 min before the sessions. Both drugs increased the breaking point. The dose-effect curves were inverted U-shaped, with maximum enhancement of performance occurring at 20 mg/kg for chlordiazepoxide and at 40 mg/kg for phenobarbital. A comparable enhancement was not obtained during a non-drug "probe" session, which was conducted after the subjects' body weights had been temporarily reduced from 80% to 70% of their free-feeding weights. The drug-induced enhancement of breaking point was related to the initial values of the performance and may represent a reduction in the aversiveness of the schedule.
Journal of the experimental analysis of behavior, 1972 · doi:10.1901/jeab.1972.17-287