Periodic Reporting for period 1 - DistriBrainRep (Studying brain representations as a distributed process: from neural code to behavior) Reporting period: 2019-06-15 to 2021-06-14 Summary of the context and overall objectives of the project Daily situations expose us to a continuous and rich stream of information (sights, sounds, verbal information etc.) that changes momentarily. This information must be processed and integrated with our prior knowledge of the world in order to create a comprehensible experience of our environment. For example, being confined to your house without being able to visit friends would not make sense unless you integrate the knowledge of an ongoing pandemic and recall its implications; understanding why you woke up with a headache and why your friend is not answering your calls necessitates the integration of knowledge of events that took place the previous night at the pub. How this integration of information is achieved by the human brain is a fundamental question in cognitive neuroscience, which also has implication onto medical conditions in which this integration is impaired. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far One potential way of tackling this question is by non-invasively studying the brains of human participants while they watch movies. This is a useful approach because movies simulate information present in our everyday lives and require us to integrate information in order to comprehend the movie narrative. Under the Marie Skłodowska Curie fellowship, I developed a novel method for studying brain activity evoked by movie watching, which sheds light on the way our brains incorporate the ongoing stream of experiences with our prior knowledge to make sense of evolving events.My novel approach for studying naturalistic integration of information takes inspiration from the vast knowledge gained in the field of spatial navigation in rodents. While a rat is navigating a maze, its brain “replays” the route travelled so far, to help the rat keep track of its position. My findings from movie-watching data indicate that the human brain uses a similar mechanism to keep track of evolving experiences and interpret them. To illustrate this, let’s consider the well-known sentence “We will always have Paris” from the movie “Casablanca”. To understand the meaning of this sentence while we perceive it, our brains must integrate this sentence with relevant information displayed throughout the movie (e.g. that the protagonists first fell in love in Paris and must now separate). Indeed, I found that at the end of each movie scene, the brain replays information from past scenes. But, significantly, out of the vast information conveyed to us during the movie, only information that is directly relevant to the current scene is replayed at the end of this scene (e.g. to understand the “Casablanca” example given above, the brain does not need to replay irrelevant information, such as that the male protagonist had letters of transit obtained from murdered German couriers). This suggests that the human brain can selectively replay relevant past information in order to interpret ongoing experiences. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) These findings illuminate the neural mechanism that enables us to make sense of unfolding events in our daily lives, and more generally – hint onto how we can learn from past experience. As such, these findings have the potential to combine a line of animal- and human-related findings into a unified framework of naturalistic information processing, and thus provide a leap in our understanding of a variety of cognitive processes, from spatial navigation to reasoning and problem solving – all of which require the integration of current with past information. Gaining such an understanding could assist in understanding clinical conditions in which the integration of current and past information may be impaired (e.g. dementia), or conditions characterized by incorrect interpretation of experiences (e.g. mental illnesses characterized by an impaired perception of reality).