Functional organization and plasticity of the visual cortex in mammals

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Brain plasticity is necessary not only for learning and memory but also to allow the brain to rapidly adapt to changes in the environment or to injuries. Complex behavior of mammals relies on the cooperation between multiple brain areas, particularly at the cortical level where neuronal networks are engaged or disengaged in reaction to external or endogenous stimuli. In the visual system, the cortical analysis occurs first at the level of the primary visual cortex and continues in higher-order areas through serial and parallel streams. All visual areas contain a representation (partial or complete) of the visual world and are organized in a topographic way (visuotopic maps). Further, in some species, a functional sub-organization can be observed in cortical areas (e.g. modules of ocular dominance, orientation). It is through the concerted activity of these distributed networks that an animal is able to interpret a visual scene, integrate its information with other sensory modalities, all in order to adopt the proper visuomotor behaviour. The overall goal of this research program aims to determine how brain networks can be modulated by sensory experience and how they can adapt to insults. As a first step, my lab will focus on the comparative study of the structure-function of the visual cortex in species (mice, rabbits and tree shrews) with specific cortical characteristics (functional maps organized in modules vs. a salt and pepper organization). We will determine how the environment changes the visual brain’s connectivity and functioning and if it can promote recovery from lesions by reinstating plasticity. Environmental enrichment (EE) is a powerful implement to modulate and enhance plasticity. We hypothesize that enrichment will induce a large-scale functional refinement of visuotopic maps and cortical modules as well as an increase in the coupling (cross-correlation) between the different areas of the cortical visual network. We also hypothesize that EE will facilitate network reorganization following an insult to one of its component. We will take advantage of mapping techniques developed recently in the laboratory. Optical brain imaging (intrinsic and voltage-sensitive dyes) will be used to visualize the activity of the visual areas as well as the functional connectivity between them in resting and stimulus- induced states before and after the enrichment of their environment. A range of visual stimuli varying in their complexity will be used to highlight specific sensitivity to stimulus types within the visual cortical network. These experiments will be made in conjunction with electrophysiological recordings and complemented by fMRI studies. Experiments will be performed using animals placed in an enriched milieu either in adulthood or during their development. The proposed program will contribute to our understanding of the impact of environment on brain connectivity and function and increase our knowledge on neuronal plasticity. The combination of brain imaging, optogenetic, and electrophysiology to study the development, structure and function of the neocortex in a phylogenetic context will provide an innovative multidisciplinary training environment.