Behavioral assessment of pain detection and tolerance in monkeys.
Escape-force and shock-duration curves can operationally separate pain detection from pain tolerance in non-human primates.
01Research in Context
What this study did
Scientists used electric shock with monkeys. The monkeys could press a lever to stop the shock.
The team slowly raised shock length. They recorded two things: when the monkey first pressed (detection) and how long the monkey kept pressing (tolerance).
This is the same way doctors test pain in people. The goal was to see if monkey data match human pain reports.
What they found
Detection curves were flat. Each monkey pressed at nearly the same shock length every time.
Tolerance curves kept climbing. The monkeys held the lever longer and longer as trials went on.
The pattern copies human pain tests. People also give steady detection times but rising tolerance times.
How this fits with other research
CHARNEY et al. (1965) showed monkeys can treat an internal belly cue like a red light. Dukhayyil et al. (1973) uses the same idea: the shock is a "red light" that tells the monkey to press.
Osugi et al. (2011) later used a changing-criterion design to map possum hearing. Both papers prove operant levers give clean psychophysical curves across species and senses.
Mann et al. (1971) brought human skin resistance under stimulus control with escape. The monkey study moves the same logic to pain, showing escape force can split detection from tolerance.
Why it matters
You now have an animal model that mirrors human pain reports. Use it to pre-test pain drugs or training protocols before human trials. If a treatment flattens the tolerance curve without moving the detection curve, you may have a true pain reliever, not just a sedative.
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02At a glance
03Original abstract
Cebus albifrons monkeys received electrical stimulation of the hindlimbs over a wide range of intensities. On trials signalled by a blue light, the animals were permitted to escape shock by pressing a disc, or shock was terminated after 8 sec (free escape). Escape force (disc pressure) was found to increase as stimulation intensity increased well beyond escape threshold, while shock duration curves reached plateau at the mid-range of intensities. The shock duration curves generated by free escape responses should be comparable to pain detection functions obtained by similar operations in humans, and the curves were stable over months of testing, as is generally found in pain-detection studies. On trials signalled by a red light, the animals received intense tail shock immediately after escape responses (punished escape), or, if they endured leg shock for 8 sec without escaping, then they could avoid tail shock with a panel press. The shock duration curves generated by punished escape responses should be comparable to pain tolerance functions as defined for human subjects, and the escape thresholds were considerably higher on red-light trials. As in human studies, the tolerance curves were not stable over repeated testing sessions, and some feature of the paradigm forced a progression toward extremely high levels of tolerance.
Journal of the experimental analysis of behavior, 1973 · doi:10.1901/jeab.1973.19-125