Effects of scopolamine on repeated acquisition of radial-arm maze performance by rats.

Scientists gave rats a daily eight-arm maze task. Each day the rats had to learn which four arms now held food. The team injected scopolamine before some sessions. Scopolamine blocks brain acetylcholine, a chemical tied to learning.

They also tested methyl-scopolamine, a form that barely enters the brain. This check shows if effects come from brain action or body side issues.

Scopolamine slashed choice accuracy. Errors jumped from about 20 % to 60 % within the first half of each session. Learning inside the session almost stopped.

Methyl-scopolamine did nothing. The trouble was in the brain, not the gut.

Martens et al. (1989) ran a close cousin study. They gave humans diazepam and used the same "learn-a-new-chain-each-day" design. Diazepam also wrecked new learning while sparing old chains. Both papers show that repeated-acquisition tasks are sensitive to different brain drugs across species.

NEVIN et al. (1963) looked at chlorpromazine and amphetamine in rats under avoidance schedules. Like scopolamine, chlorpromazine cut responding. The pattern links low response rates to several drug classes, but only scopolamine was tested on within-session learning.

Hatton et al. (2005) flipped the question: they asked if chlordiazepoxide speeds up extinction. It did, once several sessions had passed. Scopolamine blocks acquisition; chlordiazepoxide speeds loss. Together they map how drugs can hurt forming or help removing behavior.

If you work with clients on new skill sequences, remember that acetylcholine systems power rapid within-session adjustments. Medications with anticholinergic side effects—common allergy or mood drugs—may quietly flatten learning curves. Track session-by-session accuracy, not just final mastery, to spot this. When you see flat early-trial scores that bloom after the med wears off, consider a pharmacist consult.