Final Report Summary - HIGHERVISION (The function of higher-order cortical and thalamic pathways during vision)
When interacting with the environment we depend on our perception of the world around us. Visual perception relies on information flow from the eye to the visual cortex, where it is relayed and transformed via a series of cortical processing stages. Most research so far has focused on feedforward processing of visual information. However, perception is highly dependent on the context in which a given stimulus occurs, such as the surrounding environment and the animal’s behavioural state, its knowledge, expectations and actions. Using state-of-the-art methodology combining in vivo imaging, electrophysiology, animal behaviour, virtual reality, genetic tools and optogenetics, we studied how neural circuits in the cerebral cortex and thalamus integrate such non-sensory, contextual information with visual signals, and the mechanisms by which context and an animal’s prior knowledge influence visual processing: (1) We determined how visual context, namely information about the wider visual scene, is integrated by neurons in visual cortex. We found that contextual synaptic interactions are functionally specific, suited for facilitating the detection of edges and contours in the environment which is crucial for interpreting the visual scene. (2) We studied how behavioural context influences visual processing, in particular how the read-out of visual information in the cerebral cortex is changed during learning when visual stimuli become behaviourally relevant to an animal. We found that processing of relevant visual information is improved by learning and dynamically adjusted depending on the behavioural context. Moreover, we could identify several cellular and circuit mechanisms of this improved visual coding induced by learning. (3) We have focused on the role of higher-order thalamocortical circuits in conveying contextual information to the cortex. We have investigated the anatomical and functional organization of these circuits and found that they serve as a major secondary visual pathway. This pathway can integrate contextual and sensory information for instance to inform visual cortex about visual stimuli that are not predicted by the animal’s own actions. Together, our work establishes fundamental principles underlying cortical processing and thalamocortical communication during vision.