2026 ECNP Congress

PS02-2133

Cognitive mechanisms of behavioural activation: early reduction in aversive Pavlovian bias mediates anhedonia improvement in clinical settings

Lioba Chiara Sophie Berndt — D. Crawley, R. Tymchyk, A. Hall, J. Onysk, T. Erdmann, E. Wimmer, I. Berwian, Q. Huys · University College London, Division of Psychiatry and Queen Square Institute of Neurology, London, United Kingdom

2026 ECNP Congress

Introduction

Behavioural Activation (BA) is a frontline, evidence-based treatment for major depressive disorder, with psychotherapies showing moderate meta-analytic effects (d=0.34) [1]. However, remission rates of around 56% indicate that many patients do not achieve full recovery, with anhedonia being a known predictor of poor treatment response [2]. A better understanding of the cognitive mechanisms engaged by BA could help improve and better target treatment. Conceptually, BA is thought to work by strengthening maladaptively low appetitive Pavlovian biases and reducing maladaptively high aversive Pavlovian biases: the automatic tendencies to approach reward and withdraw from threat that interfere with goal-directed behaviour. While laboratory studies have begun to support this view [3], whether these reinforcement learning mechanisms operate in real-world clinical settings, and whether they drive symptom recovery, remains untested.

Aims

We investigated whether BA modifies Pavlovian biases early in treatment (3 weeks), specifically whether it increases appetitive and decreases aversive Pavlovian bias, and whether such changes are associated with improvements in global depressive symptoms and with a particular focus on anhedonia.

Methods

In a randomised controlled observational study conducted within the UK NHS Talking Therapies service, 152 participants with low mood were allocated to complete an affective Go/No-Go task either before starting BA (control; n=78) or during early BA (active; n=74). Assessment timepoints were randomised between subjects, without affecting therapy start date or delivery. Pavlovian parameters, capturing appetitive bias (reward anticipation facilitating action) and aversive bias (threat anticipation inhibiting action), were quantified using computational modelling [4]. Symptom change was assessed using the Temporal Experience of Pleasure Scale (TEPS) as the primary measure of anhedonia, alongside broader depression measures (e.g., PHQ-9). Between-group differences in Pavlovian parameters were assessed using FDR-corrected t-tests, and mediation analysis was tested using bootstrapped regression.

Results

Anhedonia improved significantly in the active group (p=0.047; d=0.53) but not in controls, while global depressive symptom severity improved in both groups, suggesting a specific early effect of BA on hedonic functioning. Compared to controls, participants undergoing BA showed a significant shift in Pavlovian biases (pFDR=0.012; d=0.65), with and increase in appetitive bias and a decsrease in aversive bias, while the control group showed the opposite pattern. Most importantly, the reduction in aversive Pavlovian bias statistically mediated the observed improvement in anhedonia (β=−1.77; p=0.036; bootstrap p=0.028).

Conclusions

This study provides the first evidence from a realistic clinical setting that BA engages reinforcement learning mechanisms, modifying Pavlovian biases early in treatment. The specificity of effects to anhedonia points to a precise cognitive mechanism through which BA may restore hedonic engagement by overcoming automatic aversive inhibition that has become entrenched. Notably, these effects were detectable using brief online cognitive tasks delivered within routine NHS care, demonstrating that such assessments can serve as scalable mechanistic biomarkers of treatment response, with broader implications for personalising and stratifying psychological therapies.

References

  1. Leichsenring, F., Steinert, C., Rabung, S., Ioannidis, J. P. A., 2022. The efficacy of psychotherapies and pharmacotherapies for mental disorders in adults: an umbrella review and meta-analytic evaluation of recent meta-analyses. World Psychiatry 21(1), 133-145.
  2. McMakin, D. L., Olino, T. M., Porta, G., Dietz, L. J., Emslie, G., Clarke, G., Wagner, K. D., Asarnow, J. R., Ryan, N. D., Birmaher, B., Shamseddeen, W., Mayes, T., Kennard, B., Spirito, A., Keller, M., Lynch, F. L., Dickerson, J. F., Brent, D. A. 2012. Anhedonia Predicts Poorer Recovery Among Youth With Selective Serotonin Reuptake Inhibitor Treatment–Resistant Depression. J Am Acad Child Adolesc Psychiatry 51(4). 404-411.
  3. Huys, Q. J. M., Russek, E. M., Abitante, G., Kahnt, T., & Gollan, J. K. (2022). Components of Behavioral Activation Therapy for Depression Engage Specific Reinforcement Learning Mechanisms in a Pilot Study. Computational psychiatry, 6(1), 238-255.
  4. Guitart-Masip, M., Huys, Q. J. M., Fuentemilla, L., Dayan, P., Duzel, E., Dolan, R. J. 2012. Go and no-go learning in reward and punishment: Interactions between affect and effect. NeuroImage. 62(1). 154-166.