---
title: "Volatility Priors: A Modifiable Brain Target Behind Delusions"
slug: schizophrenia-volatility-priors-delusions-treatment-target
category: health
category_label: "Health"
author: "BrainWavePost Staff"
date: 2026-08-19
tags: ["schizophrenia", "delusions", "paranoia", "computational psychiatry", "CBT for psychosis", "predictive processing", "neuroscience"]
read_time_minutes: 10
canonical_url: https://brainwavepost.com/article/schizophrenia-volatility-priors-delusions-treatment-target
source: BrainWavePost
---

# Volatility Priors: A Modifiable Brain Target Behind Delusions

*Health · 2026-08-19 · BrainWavePost Staff · 10 min read*

> Researchers have linked persecutory delusions to an inflated expectation that the world is chaotic and unpredictable — a computational quantity called a volatility prior. A randomized trial then showed that this expectation, and the caudate activity tied to it, can be shifted by psychological therapy. Here is exactly what the evidence supports, and one widely repeated claim it does not.

> **Health journalism, not medical advice** _(note)_
>
> This article explains published research. It is not diagnostic or treatment guidance, and nothing here should be used to start, stop or change any medication or therapy. Decisions about psychosis treatment belong with a qualified clinician.

Ask why someone holds a belief that seems, from outside, obviously untrue, and the usual answers reach for content: what the belief says, where the idea came from. Computational psychiatry asks a different question — not what the belief is about, but how the brain decides when to change its mind at all.

That reframing has produced one of the more concrete candidate targets in psychosis research: the volatility prior. Informally, it is a person's standing assumption about how fast the world changes. A high volatility prior means expecting the rules to keep shifting, so any single piece of evidence is treated as potentially stale and beliefs are revised sharply and often. A low one means expecting stability, so surprises get absorbed slowly. [1][2]

## Where the delusion link was established

The clearest cross-sectional evidence comes from Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, where Sheffield, Suthaharan, Leptourgos and Corlett tested belief updating in 42 people with schizophrenia and 44 control participants using a three-option probabilistic reversal learning task — a game in which the winning option silently changes, so the experimenter can measure how a person handles an unstable environment. Choices were fitted with a Hierarchical Gaussian Filter, a Bayesian model that separates out how much volatility a participant expected in the first place. [1]

- Paranoia was significantly associated with an elevated win-switch rate — abandoning an option even after it paid out — and with elevated prior beliefs about volatility, both within the schizophrenia group and across the whole sample. [1]
- The relationship was specific: it tracked paranoia, not unusual thought content generally, and not anxiety measures. [1]
- There was a significant indirect effect of paranoia on the relationship between volatility priors and worry, linking the computational parameter to the worry-based models of how persecutory delusions are maintained. [1]

This sits on top of a decade of predictive-processing work in psychosis, including the Science paper showing that Pavlovian-conditioned hallucinations arise from overweighting perceptual priors, and the wider Biological Psychiatry review setting out the predictive coding account of psychotic symptoms. [3][4]

## The part that makes it a treatment target

A correlation with symptom severity is interesting. A quantity that moves when someone gets better is a target. That is what a Vanderbilt-led randomized clinical trial, published in JAMA Network Open in June 2025, set out to test. [2]

Sixty-two adults aged 18 to 65 with a schizophrenia spectrum or delusional disorder diagnosis and an active persecutory delusion — persistent for at least three months, held with more than 50% conviction — were randomized 1:1 to eight weeks of manualized cognitive behavioural therapy for psychosis (CBTp) or to befriending therapy, conversation and activity focused on neutral topics. Both arms continued standard care. Volatility priors were measured with the same reversal-learning task and model, alongside PSYRATS delusion severity and fMRI activation in the striatum and prefrontal cortex. [2]

- **62** — participants randomized to CBTp (32) or befriending (30) [2]
- **d = 0.52** — decrease in volatility priors after treatment (P = .006) [2]
- **d = 1.50** — decrease in delusion severity on PSYRATS (P < .001) [2]

## What the trial found

- Volatility priors decreased following treatment across both groups: F(1,112) = 7.7, P = .006, Cohen d = 0.52 (95% CI 0.15–0.90). [2]
- Delusion severity also decreased across both groups, and considerably more strongly: F(1,112) = 59.7, P < .001, Cohen d = 1.50 (95% CI 1.00–1.90). [2]
- Activation in the caudate nucleus and prefrontal cortex significantly decreased after treatment, in the 35 participants (57%) who completed fMRI. [2]
- Decreased caudate activation was associated with decreased volatility priors: F(1,58.3) = 16.6, P < .001, d = 1.07 — and that association held after controlling for antipsychotic medication (F(1,53) = 13.77, P < .001). [2]

> This randomized clinical trial found that elevated volatility priors and associated activation in the caudate nucleus were amenable to change. Volatility priors could be a potential target for intervention in psychosis.
>
> — Sheffield JM, et al., JAMA Network Open (2025) [2]

> **One widely repeated claim the paper does not support** _(info)_
>
> Summaries of this work often say that delusion severity fell in step with volatility expectations — that as volatility priors dropped, symptoms dropped with them. The trial explicitly tested that and did not find it: the decrease in volatility priors was not associated with clinical improvement in PSYRATS scores (F(1,102.8) = 1.8, P = .18, d = 0.26, 95% CI −0.12 to 0.65). Both measures moved during treatment; their changes did not track each other. The target claim rests on modifiability, not on a demonstrated coupling to symptom change. [2]

## Why that distinction matters

The trial delivers something genuinely useful: a computational parameter and a specific brain region that shift over eight weeks of talking therapy, with the neural and computational changes tracking each other and surviving adjustment for medication. That is a mechanistic handle where psychiatry has had very few. [2]

What it does not yet deliver is proof that pushing volatility priors down is what makes people better. Because both arms improved and both showed the parameter fall, the design cannot attribute the change to CBTp specifically, and the null correlation means the causal chain from volatility prior to symptom relief remains a hypothesis. A follow-on trial explicitly testing the role of belief updating in persecutory delusions is registered and recruiting; until it reports, treat the mechanism as promising and unproven. [2][7]

## The clinical backdrop

Schizophrenia affects roughly 1 in 300 people worldwide according to the World Health Organization, and persecutory delusions are among its most common and most distressing features — the trial's own framing is that they are “common, distressing, and difficult to treat.” [1][2][5]

Psychological therapy already has a place in guidelines: NICE guideline CG178 recommends CBT for adults with psychosis and schizophrenia, and Cochrane has reviewed CBT plus standard care against other psychosocial treatments, finding the evidence base limited in quality. In a July 2025 exceptional surveillance review, NICE considered adding metacognitive therapy as an option for CG178 and decided not to update the guideline at that point. Better mechanistic targets are wanted precisely because current psychological treatments help meaningfully but not universally. [6][8][9]

## What to watch next

1. Whether a therapy designed to lower volatility expectations directly outperforms one that does not — the test the current trial could not run. [2]
2. Whether volatility priors predict who responds, rather than only shifting alongside response. [2]
3. Whether the caudate finding replicates in a larger imaging sample; only 35 participants here had usable fMRI. [2]
4. Whether the effect is specific to persecutory beliefs, as the cross-sectional data suggest, or generalises across delusional content. [1]

## Sources and further reading

- [1] Sheffield JM, Suthaharan P, Leptourgos P, Corlett PR — 'Belief Updating and Paranoia in Individuals With Schizophrenia', Biological Psychiatry: Cognitive Neuroscience and Neuroimaging 2022;7(11):1149–1157: https://doi.org/10.1016/j.bpsc.2022.03.013
- [2] Sheffield JM, Sloan AF, Corlett PR, et al. — 'Prior Expectations of Volatility Following Psychotherapy for Delusions: A Randomized Clinical Trial', JAMA Network Open 2025;8(6):e2517132: https://doi.org/10.1001/jamanetworkopen.2025.17132
- [3] Powers AR, Mathys C, Corlett PR — 'Pavlovian conditioning-induced hallucinations result from overweighting of perceptual priors', Science 2017;357(6351):596–600: https://doi.org/10.1126/science.aan3458
- [4] Sterzer P, Adams RA, Fletcher P, et al. — 'The Predictive Coding Account of Psychosis', Biological Psychiatry 2018;84(9):634–643: https://pubmed.ncbi.nlm.nih.gov/30007575/
- [5] World Health Organization — Schizophrenia fact sheet: https://www.who.int/news-room/fact-sheets/detail/schizophrenia
- [6] NICE — Clinical guideline CG178, 'Psychosis and schizophrenia in adults: prevention and management': https://www.nice.org.uk/guidance/cg178
- [7] ClinicalTrials.gov — NCT04748679, the registration record for the randomized trial: https://clinicaltrials.gov/study/NCT04748679
- [8] Jones C, Hacker D, Xia J, et al. — 'Cognitive behavioural therapy plus standard care versus standard care plus other psychosocial treatments for people with schizophrenia', Cochrane Database of Systematic Reviews 2018;11:CD008712: https://doi.org/10.1002/14651858.CD008712.pub3
- [9] NIMH — Schizophrenia statistics: https://www.nimh.nih.gov/health/statistics/schizophrenia

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