Revealing the neural computations that distinguish imagination from reality

Our brain is able to turn external signals coming into our senses into a vivid and coherent experience of reality. At the same time, our brain is also able to generate sensory experience in the absence of external signals via imagination. Contrary to our intuition, our experience of reality is not an objective reflection of the external world, since the brain has no direct access to that. Instead, what we perceive as reality is an inference that the brain makes about its own activity, which is both externally driven (by sensory input) and internally driven (by imagination). Recent research has shown that imagining something leads to similar patterns of brain activity as perceiving that same thing in reality. This raises the question; how does the brain determine whether activity represents reality or imagination? I hypothesize that to distinguish imagination and reality, the brain relies on a perceptual reality monitoring process where higher-order brain regions infer perceptual reality when sensory signals are strong enough and there is low cognitive control. I propose to test this idea by answering three complementary questions: (a) how does sensory processing influence reality judgements? (b) how does cognitive control influence reality judgements? and (c) how are different signals integrated and evaluated to form reality judgements? To answer these questions, I will use a novel psychophysical paradigm to experimentally induce confusions between imagery and perception in healthy participants. I will precisely characterize neural processes during these confusions by combining state-of-the-art techniques (high-field fMRI, MEG and tRNS), with advanced computational methods (multivariate decoding and Bayesian modelling). The results of this project will increase our fundamental understanding of core cognitive processes such as perception and memory and will provide a novel perspective on disorders of reality monitoring such as psychosis.