Neural basis of visual perception

Which aspects of the neural signal most likely carry the behaviorally relevant visual information? What are the correct proxies to evaluate the validity of numerous computational strategies that have been proposed to underlie visual perception? These two questions can be tackled by testing the following hypothesis: if a computational strategy correctly captures the rules underling visual perception, then stimulation of visual areas according to such rules should allow one to elicit a visual percept. In other words, it should be possible to directly transfer meaningful visual information onto cortical areas and elicit a visual percept. Testing this hypothesis is a 2-step process requiring behavioral training and cortical recordings/stimulation of neurons with fluorescent and optogenetic tools. The technology for optogenetic stimulation at fast time scales (milliseconds) and tens of microns spatial resolution is becoming increasingly available. However, combining it with fluorescent read-out methods at similar resolutions in-vivo, while the animal is performing in a behavioral task represents a major technical challenge. This project aims at integrating available cutting-edge imaging and stimulation technology to overcome such technical challenges.

Behavioral training of mice

When trying to modify or induce a visual percept via optogenetic stimulation, one needs a reliable and quantitative method to read-out the animal’s visual percept. A promising proxy is the change in probability of detecting a target stimulus while the animal is engaged in a visual discrimination task. But what are the behavioral tasks a mouse can be trained on? What are the optimal training methods? Can we adopt the same training paradigms used for primates? To tackle these questions we are developing automated, high-throughput, behavioral setups which will allow us to test in parallel several training strategies, and through a refinement process to select the most effective ones. The animals’ performance during such optimization process will also provide a rich dataset for regressive models of animals’ behavior in visual discrimination tasks.

Functional connectivity of mouse visual areas

Several brain areas have been identified in humans that are involved in the processing of visual information; it is through the collective activity of populations of neurons in these regions that visual percepts arise. However, the specific coding mechanisms that translate such activations into a visual percept are still largely unknown. Traditionally, to tackle these problems electrophysiological experiments have been performed in cats or monkeys. Only recently, major advances in optical and genetic techniques (optogenetics) have made the mouse a powerful animal model for the study of vision. Because these developments are so recent, little is known about the response properties of neurons in primary and higher visual areas of the mouse, their functional connectivity, and how the visual signal is processed as it traverses these areas. This project aims to understand these functional mechanisms of visual processing in the context of the underlying cortical anatomy and in particular of the layered structure of these visual cortical areas.

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