Prefrontal and parieto-occipital neural signatures of evidence accumulation and response to computerised Cognitive Behavioural Therapy in depression.

Computerised Cognitive Behavioural therapy (CBT) is an effective psychological intervention for mild to moderate depression. While CBT aims to correct maladaptive cognitive biases and ensuing disadvantageous decision-making, our current understanding of its mechanisms of change and associated neural substrates remains limited. Preliminary behavioural evidence has shown that the process of evidence accumulation (EA), indexing the efficiency of decision dynamics, is impaired in depression. However, little is known about the role of EA in the context of CBT for depression. In this study we recruited 37 (18 females) unmedicated depressed subjects. Participants attended two task-based functional resonance imaging sessions before and two months after completing an online self-help CBT-based intervention. We fitted a hybrid reinforcement learning drift diffusion model to the probabilistic reversal learning task data and investigated accumulator-like brain activity as a function of computerised CBT. We found that at baseline, responders, compared to nonresponders, exhibited weaker left prefrontal and parieto-occipital EA neural signatures, which subsequently increased in proportion to the sustained symptomatic improvement observed following computerised CBT. We thus provide novel evidence that attenuated EA neural signatures in the left prefrontal and parieto-occipital cortical areas are associated with response to computerised CBT in depression. Crucially, the observed increase of accumulator-like brain activity following computerised CBT warrants further investigation in future experimental work probing neurocomputational mechanisms of change in CBT.