NeuroFrance 2025

¹Integrative Neuroscience and Cognition Center, CNRS UMR 8002, Paris, France

What is the difference in our brain activity when an external stimulus is either perceived consciously or not ? One possibility is that it is just a matter of degree: non-conscious processing could just be an attenuated form of the same network activations that relate to conscious processing, and there would be a continuum between the two. This is what is described in classical models of perception and decision-making: sensation is a continuum, and we just place an arbitrary criterion on this continuum to make a decision of whether we have perceived a stimulus or not. In this talk I will present several behavioural and neuroimaging evidence that suggest a very different picture. Indeed, across different types of stimuli, across different tasks and using different types of measures (behavioural, fMRI, EEG, MEG, intracranial recordings), we consistently observed dynamics that could be better described as “bifurcations”, in which there can be two possible equilibria in the activity for the same stimulation, and hence two types of processing. Indeed, we showed that, when stimulating at threshold, exactly the same stimulation can either trigger late and sustained activity in a wide network of areas, or fail to do so and remain local. Interestingly, these dynamics can also be observed when no decision making is requested on the stimulus, suggesting that they are not just reflecting a postperceptual decision criterion. Instead, these two types of processing seem to match whether stimulus processing is associated withconscious experience or not. We are now trying to model these brain dynamics using classical models from system dynamics to be able to better understand how conscious peception is formed in the brain, and to build tools that could help us improve our diagnosis of patients with disorders of consciousness based on the response of their brains to external stimulation.