Effects of acute and chronic morphine on delay discounting in pigeons.

Bigham et al. (2013) gave pigeons choices between a small food reward now or a larger one later. They first tested the birds sober to see each bird's baseline preference. Then they gave the birds morphine in two ways: a single shot (acute) or daily doses for several weeks (chronic). After each drug condition they ran more choice trials. Finally they watched what happened when the drug was stopped (withdrawal).

One dose of morphine made the birds pick the small-quick reward more often. Daily morphine produced mixed results; some birds stayed impulsive, others returned toward baseline. When the drug was removed, every bird flipped: they now preferred the big delayed reward, even if they had to wait. The withdrawal effect outlasted the drug sessions by days.

Lerner et al. (2012) ran a similar pigeon study but used nicotine instead of morphine and tested memory, not delay choices. Both papers show that acute and chronic drug regimens can be compared within single subjects. Bordi et al. (1990) also gave pigeons drugs (diazepam, pentobarbital, amphetamine) and saw mixed, bird-specific changes in key-peck rates, matching the mixed chronic morphine data here.

Renda et al. (2015) looks contradictory at first: working-memory training in rats did NOT change their delay discounting, hinting that impulsive choice is hard to budge. Yet K et al. show withdrawal clearly shifted preference. The difference is method: training a cognitive skill is not the same as removing a drug that alters reward value. The rat paper warns us that not every intervention touches discounting; the pigeon paper shows that drug history can.

Miller (1976) showed pigeons' choices follow matching-law equations, meaning we can predict their moves from reinforcer value. K et al. add a pharmacologic twist: morphine withdrawal suddenly increases the value of the large delayed reward, a measurable swing you could plug into those same equations.

If you work with clients who use opioids, expect impulsive choices while the drug is on board and a possible swing toward patience during withdrawal. The pigeon data suggest the withdrawal phase, not the high, is when individuals may over-value distant rewards — a risky window if that 'big reward' is another dose. Monitor timing of drug screens or reinforcement schedules accordingly; what looks like improved self-control may be a temporary pharmacologic after-effect.