We humans are extraordinarily visual organisms, indeed a third of our cerebral cortex is devoted to processing visual information. The main starting point for much of this processing is a large region at the back of the brain called primary visual cortex, which holds a maplike representation of the visual world. This region connects to at least thirty other regions of the brain, each of which processes a different kind of visual information. Although most research focuses on the "forward" processing of visual information from primary visual cortex up to these higher stages of the visual brain, in fact it has been known for decades that there are at least as many connections that go in the other direction, from high visual areas "backward" down to primary visual cortex. Yet, the role of these "backward" connections in visual perception is not well understood. This proposal asks what those "backward" visual connections do, by investigating a surprising new phenomenon reported very recently by the PI's lab. In this new phenomenon, brain imaging (specifically, functional magnetic resonance imaging, or fMRI) was used to show that high-level information about the shape of an object represented presented in the peripheral visual field is present the center of the maplike representation in primary visual cortex. This finding is surprising because this information is in the "wrong" part of the visual map, so this information must be coming from higher level parts of the visual system, via the "backward" connections. This proposal uses fMRI, as well as behavioral methods and a method called transcranial magnetic stimulation (TMS) that allows us to disrupt this maplike representation, to ask why this "feedback" representation is found in visual cortex, whether it plays a causal role in visual perception, and exactly where it is within the maplike part of visual cortex.
This research is relevant to public health because it will tell us how the visual cortex works in humans. Disorders of vision are catastrophic, and we cannot help people with visual disorders without understanding how their brains process visual information. In particular, this work will be important for the future development of a neural prosthesis for people suffering from visual impairments, as well as for developing new training strategies for helping people recover from certain types of central visual disorders.
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