Many disorders of the visual system impair spatiotemporal processing. It is thought that this is due to abnormalities in the cortical network. In primate cortex, visual information is encoded in multiple functionally specialized areas which are connected to hierarchical processing streams, specialized for object recognition and spatial relationships. The structure and physiology of the synaptic circuits that underlie these functions are incompletely understood. Recent advances in labeling, recording and manipulating the activity of distinct types of neurons suggest that the mouse visual system in a suitable model for unraveling the underlying network. An important question is whether the mouse visual cortex is similar to that of primates and contains multiple modularly organized areas that are linked to distinct processing streams. If so, another important question is how these modules, areas and processing streams work together to create a unified representation of the world that can be flexibly changed by internal representations of the world to optimally guide behavioral goals.

To investigate these questions we are employing a combination of anatomical, physiological and optogenetic techniques. For delineating area maps we are studying the regional distribution of molecular markers and use topographic mapping of connections and physiological recording of visual receptive fields. Multi-color viral tracing methods are employed to study the anatomical organization of cortical streams and areal hierarchies. Single unit recordings with electrode arrays are used to determine whether the areas are connected to different streams that process distinct visual information. To study the neuronal composition of feedforward and feedback circuits between lower and higher cortical areas we are using neuronal tracers and cell-type specific markers of excitatory and inhibitory neurons. For determining the mechanisms of synaptic transmission in interareal circuits we are using laser photo stimulation of channelrhodopsin labeled feedforward and feedback connections and whole cell recording of synaptically connected inhibitory and excitatory neurons in brain slices.

The results show that mouse visual cortex contains at least 11 visual areas, which are linked to distinct hierarchically organized streams that preferentially process spatial and temporal information. Our findings demonstrate that the mouse and primate visual systems share fundamental similarities, suggesting that the mouse is a suitable model for mechanistic studies of neurological disorders in humans.

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