Time to choose: impact of intertrial interval on selecting between methamphetamine and food reinforcement in male and female rats.
A 20-second intertrial interval makes rats choose methamphetamine over food almost every time.
01Research in Context
What this study did
MD'Agostino et al. (2025) let rats pick between methamphetamine and food. They changed how long the rat waited between choices. The short wait was 20 seconds. The long wait was 90 seconds.
They watched if the rat took more drug or more food when the wait changed.
What they found
When the wait was short, rats chose the drug almost every time. When the wait was long, they often picked food instead.
The change was big and happened for both male and female rats.
How this fits with other research
Christopher et al. (1991) saw the same wait-time lever. They kept the lever in view during the wait. Long waits then slowed learning. MR kept the lever out of view, so the wait itself, not the lever, drove the choice shift.
Chiviacowsky et al. (2013) bundled nine sugar pellets quickly and rats became patient. MR shortened the wait between trials and rats became impulsive for drug. Both studies show that how fast you deliver stuff changes what the rat wants.
Madden et al. (2003) proved that lights and tones can control cocaine taking. MR adds that plain timing—just the gap—can do the same job for methamphetamine.
Why it matters
If you run a drug-vs-food assay, lock the intertrial interval before you start. A 20-second gap will give you high drug preference; 90 seconds will give you more food picks. Pick the gap that matches the question you are asking. Do not let the gap drift across sessions or your data will swing.
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02At a glance
03Original abstract
<h4>Rationale</h4>A central component of substance use disorder is the maladaptive choice of the drug over natural reinforcers. Compared to other drugs of abuse, methamphetamine (METH) choice has received limited study.<h4>Objective</h4>We sought to characterize the role of intertrial interval on METH choice behavior.<h4>Methods</h4>We examined the choice of METH versus food, across multiple METH doses (0.05-0.2 mg/kg/infusion), between male and female rats, employing a fixed ratio (FR1) reinforcement schedule with intertrial intervals (ITIs) of 20 and 600 s. Rats learned to lever-press for either the METH or the food reinforcer during separate, alternating training sessions. Rats then underwent choice testing, where both levers were presented for 25 discreet trials per session. Lastly, under a progressive ratio (PR) schedule, breakpoints for METH and food were assessed during separate, alternating sessions.<h4>Results</h4>METH choice was substantially higher when using the 20 s versus 600 s ITI. When the 20 s ITI was used, choice was dose- but not sex-dependent. When using the 600 s ITI, choice was influenced by dose and sex, with female rats in the higher dose group choosing METH more than other groups. PR breakpoints were higher for METH than for food, and this effect was more pronounced among female rats. METH choice was positively correlated with the ratio of METH/food breakpoints.<h4>Conclusion</h4>Reinforcement schedule parameters, namely ITI, during discrete choice testing can markedly influence METH choice behavior; thus, this should be carefully considered during experiment design and selected based on overarching study aims.
, 2025 · doi:10.1007/s00213-025-06750-w