Steady-state assessment of impulsive choice in Lewis and Fischer 344 rats: between-condition delay manipulations.
Run one delay per day, not climbing delays inside one session, to see true strain or individual differences in impulsive choice.
01Research in Context
What this study did
Ahlborn et al. (2008) compared two ways of running delay-discount tests with rats.
One group got longer and longer delays inside the same daily session.
Another group got each delay on a different day.
They tracked how often Lewis rats and Fischer 344 rats picked a small, quick reward over a big, late one.
What they found
The strain difference showed up under both setups.
Between-day delays gave cleaner, less extreme data for the Fischer rats.
Within-session climbing delays made the same rats look more impulsive than they really are.
How this fits with other research
Haynes et al. (2022) used the within-session climb and still saw the classic preference flip.
Their result looks opposite, but both papers agree the method works if you want to watch choice reverse in real time.
Hughes et al. (2022) took the steady-state idea and squeezed it into one fast session so brain scientists can inject drugs between trials.
Skrtic et al. (1982) ran the first rat delay study; J et al. simply swapped when the delays appear to cut carry-over noise.
Why it matters
If you test delay discounting in any organism, the rule is the same: keep the delay constant within a session and swap conditions across days.
You will get steadier data and avoid painting your subject as more impulsive than they are.
Try it next time you run a concurrent-chains protocol with kids or rats — run one delay per day and watch the curve smooth out.
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02At a glance
03Original abstract
Previous research has shown that Lewis rats make more impulsive choices than Fischer 344 rats. Such strain-related differences in choice are important as they may provide an avenue for exploring genetic and neurochemical contributions to impulsive choice. The present systematic replication was designed to determine if these findings could be reproduced using a procedure less susceptible to within- or between-session carry-over effects that may have affected previous findings. Specifically, delays to the larger-later food reinforcer were manipulated between conditions following steady-state assessments of choice, and the order of delays across conditions was mixed. The results confirmed previous findings that Lewis rats made significantly more impulsive choices than Fischer 344 rats. Fischer 344 rats' preference for the larger-later reinforcer, on the other hand, was less extreme than reported in prior research, which may be due to carry-over effects inherent to the commonly used technique of systematically increasing delays within session. Previously reported across-strain motor differences were reproduced as Lewis rats had shorter latencies than Fischer 344 rats, although these latencies were not correlated with impulsive choice. Parallels between reduced dopamine function in Lewis rats and clinical reports of impulse-control disorders following treatment of Parkinson patients with selective D2/D3 dopamine agonists are discussed.
Journal of the experimental analysis of behavior, 2008 · doi:10.1901/jeab.2008.90-333