Food-deprivation level alters the effects of morphine on pigeons' key pecking.
Hunger level decides whether morphine speeds or slows pigeon key-peck — same dose, opposite effect.
01Research in Context
What this study did
Scientists gave pigeons morphine and watched them peck a key for food.
The birds worked on two schedules: fixed-ratio (every 30 pecks) and fixed-interval (first peck after 5 min).
Before sessions, some birds were a little hungry, others very hungry.
The team changed the morphine dose and the hunger level to see how each mix changed peck rate.
What they found
Low hunger: even tiny morphine doses slowed the birds down.
High hunger: the same low doses sped the birds up, but high doses still slowed them.
The dose-response curve slid left or right depending on how hungry the pigeon was.
How this fits with other research
Noordenbos et al. (2012) saw the same slide with apomorphine, but they swapped hunger for reward size. Smaller rewards made the drug stronger — a clean conceptual twin.
Leslie (1977) had already shown that hungrier rats press more during scary signals. L et al. extend that idea: hunger also decides whether a drug helps or hurts pressing.
Spangler et al. (1984) found only slowdowns with morphine in monkeys. The birds show both speed-ups and slowdowns. The gap comes from task type: shock discrimination versus food key-peck, plus added hunger as a dial.
Why it matters
If a client on pain medication suddenly works faster or slower, check meal times before you tweak the program. A skipped lunch can flip the effect of the same dose. Track hunger level like you track data points — it may be the hidden variable behind "inconsistent" performance.
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02At a glance
03Original abstract
Four pigeons pecked response keys under a multiple fixed-ratio 30 fixed-interval 5-min schedule of food presentation. Components alternated separated by 15-s timeouts; each was presented six times. Pigeons were maintained at 70%, 85%, and greater than 90% of their free-feeding weights across experimental conditions. When response rates were stable, the effects of morphine (0.56 to 10.0 mg/kg) and saline were investigated. Morphine reduced response rates in a dose-dependent manner under the fixed-ratio schedule and at high doses under the fixed-interval schedule. In some cases, low doses of morphine increased rates under the fixed-interval schedule. When pigeons were less food deprived, reductions in pecking rates occurred at lower doses under both schedules for 3 of 4 birds compared to when they were more food deprived. When pigeons were more food deprived, low doses of morphine increased rates of pecking in the initial portions of fixed intervals by a greater magnitude. Thus, food-deprivation levels altered both the rate-decreasing and rate-increasing effects of morphine. These effects may share a common mechanism with increased locomotor activity produced by drugs and with increased drug self-administration under conditions of more severe food deprivation.
Journal of the experimental analysis of behavior, 1998 · doi:10.1901/jeab.1998.69-295