🧠 neuroscience

Cholinergic and noradrenergic modulation of perceptual decision making and learning

This study demonstrates that acetylcholine and noradrenaline modulate perceptual decision making not by altering the weighting of sensory evidence, but by specifically regulating the rate at which top-down prior expectations are updated in response to new evidence during the learning process.

Original authors: Dias Maile, A. A., Andronova, E., Ball, F., Aravitska, D., Dannenberg, L. K., Schnitzler, A., O'Reilly, J. X., Jocham, G.

Published 2026-06-25

📖 3 min read☕ Coffee break read

CC BY 4.0

Original authors: Dias Maile, A. A., Andronova, E., Ball, F., Aravitska, D., Dannenberg, L. K., Schnitzler, A., O'Reilly, J. X., Jocham, G.

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine your brain is like a detective trying to solve a mystery in a foggy room. To figure out what's happening, the detective has two main sources of information:

The Foggy Clues (Bottom-up Evidence): These are the messy, noisy sensory details you see right now. They are often unclear, like seeing a shadow that might be a person or just a coat rack.
The Detective's Notebook (Top-down Expectations): This is what the detective has learned from past cases. It's a set of "best guesses" or expectations built up over time.

Usually, your brain has to balance these two. Sometimes you trust the clues more; sometimes you trust your notebook more. Scientists wanted to know: Do two specific chemicals in the brain—Acetylcholine and Noradrenaline—help you weigh the clues against the notebook while you are making a decision? Or, do they help you update your notebook when you learn something new?

To find out, researchers gave 62 healthy volunteers one of three things: a placebo (a fake pill), a drug that blocks Acetylcholine (biperiden), or a drug that blocks Noradrenaline (propranolol). Then, they played a game where the participants had to make guesses based on both visual clues and what they had learned previously.

Here is what they found, using a simple analogy:

The "Notebook" vs. The "Clues"
Think of your brain's "Notebook" as a weather forecast you've been keeping. If the forecast says "sunny" but you look outside and see rain, you have to decide whether to trust the forecast or your eyes.

The Result: The drugs did not change how much the participants trusted the visual clues (the rain outside). Whether they took the drug or not, they still looked at the evidence the same way.
The Real Change: The drugs did change how quickly they updated their "Notebook" (the forecast) based on new results.

How the Two Drugs Acted Differently

The Noradrenaline Blocker (Propranolol):
Imagine this drug acts like a filter that only lets you learn from "good news." When the participants got a reward (a "win"), they updated their notebook very quickly. But if they didn't get a reward, they didn't change their mind as fast. It was like a student who only pays attention when they get an A, but ignores the feedback when they get a B.
The Acetylcholine Blocker (Biperiden):
This drug acted like a "super-learner" who changes their mind too easily. Whether the outcome was a win or a loss, the participants updated their beliefs very fast. The problem was that they changed their minds so quickly that their "Notebook" became unstable. They couldn't hold onto a consistent belief for long because they were reacting too strongly to every single new piece of information.

The Big Takeaway
The study concludes that these two chemicals aren't the ones deciding how much to trust the sensory clues right now. Instead, they are the editors of your notebook. They control how fast and how much you update your past expectations when you encounter new evidence.

Noradrenaline seems to help you update your expectations specifically when things go well (reward).
Acetylcholine seems to help you update your expectations based on all outcomes, but if you block it, you might become too jumpy and unstable in your beliefs.

In short, these chemicals don't change how you see the world in the moment; they change how quickly you rewrite your story of what the world is like based on what happens next.

Technical Summary: Cholinergic and Noradrenergic Modulation of Perceptual Decision Making and Learning

Problem Statement
Perceptual decision making fundamentally relies on the integration of noisy bottom-up sensory evidence with top-down prior expectations derived from past experiences. While acetylcholine and noradrenaline have been hypothesized to shape these computations, a critical ambiguity remains: do these neuromodulators directly influence the weighting of sensory evidence versus prior expectations during the decision-making process itself, or do they instead modulate the learning process that generates these expectations? Disentangling the role of these neurotransmitters in immediate evidence weighting versus the updating of beliefs during learning is essential for understanding the neural mechanisms of adaptive behavior.

Methodology
To address this question, the study employed a within-subject crossover design involving 62 healthy participants. Participants performed a perceptual decision-making task designed to require the integration of sensory evidence with learned expectations. Crucially, the reliability of both the sensory evidence and the prior expectations was varied independently within the task.

The study utilized pharmacological manipulation to isolate the contributions of specific neurotransmitter systems:

Acetylcholine: Modulated via biperiden, a muscarinic acetylcholine receptor antagonist.
Noradrenaline: Modulated via propranolol, a $\beta$ -adrenoceptor antagonist.
Control: A placebo condition.

The experimental design allowed the researchers to observe how blocking these receptors affected the participants' ability to update beliefs based on new evidence and how these changes influenced final choices.

Key Contributions and Results
The study provides empirical evidence distinguishing the effects of cholinergic and noradrenergic blockade on the learning versus decision-making components of the task. The key findings include:

Accelerated Belief Updating: Both biperiden and propranolol led to a faster updating of current beliefs in response to new evidence compared to the placebo condition.
Specificity of Noradrenergic Effects: Under propranolol (noradrenergic blockade), the accelerated updating was specific to reward outcomes.
Broad Cholinergic Effects and Stability: Under biperiden (cholinergic blockade), faster updating occurred in response to both reward and non-reward outcomes. This broad sensitivity resulted in less stable beliefs, suggesting that intact cholinergic signaling is necessary for maintaining belief stability against non-rewarding evidence.
Independence from Sensory Weighting: Notably, neither drug affected the degree to which choices were governed by the strength of the sensory evidence. This indicates that the observed effects were not due to a change in how sensory input was weighted during the decision itself.

Significance and Claims
The paper concludes that acetylcholine and noradrenaline do not primarily shape perceptual decision making by altering the immediate weighting of sensory evidence against priors. Instead, the findings suggest that these neuromodulators guide perceptual decision making by modulating the updating of top-down prior expectations in response to new bottom-up evidence during the learning phase. Specifically, the study posits that these systems regulate how quickly and under what conditions (reward vs. non-reward) an agent revises their internal model of the environment, thereby influencing the stability and adaptability of future decisions.

Technical Summary: Cholinergic and Noradrenergic Modulation of Perceptual Decision Making and Learning

More like this