Michael-Paul Schallmo, Ph.D. - US grants

? DESCRIPTION (provided by applicant): The context in which a stimulus appears can have a profound effect on how it is perceived and processed by the human brain. For example, the neural response to a visual stimulus is often suppressed when seen in a cluttered background. This effect is termed surround suppression, and its magnitude depends on the similarity of visual features between the center and surrounding stimuli. It is not yet clear what neural mechanism(s) underlie this effect, or how they may be divided in to separate processing stages. It is also not clear how differences in the spatial and functional properties of different suppression mechanisms might give rise to the various forms of spatial context effects observed in human vision. Using psychophysics, functional MRI, and electroencephalography, this project seeks to define three distinct mechanisms that contribute to surround suppression, each with different functional properties. A range of different stimulus and optical display configurations will be used to separately quantify the perceptual and neural response during short-range, mid- range, and long-range suppression. This will provide insight into the neural underpinnings of spatial context effects that play an important role in a number of visual processes including edge detection and figure-ground segmentation. Differentiating these mechanisms may also elucidate contextual processing strategies conserved across many brain systems, and how such processes may become disrupted in clinical conditions such as schizophrenia, autism spectrum disorder, and amblyopia.

Abstract Psychosis is a serious mental disorder involving disruptions in neural processing that are poorly understood. In addition to disrupted cognition, abnormal sensory processing is also found in psychosis, including distorted perception and hallucinations. This proposal will apply tools from visual neuroscience in order to gain insight into the neural basis of abnormal visual perception in psychosis. Because visual neural circuits are well- understood in animal models, we will be able to test a very specific hypothesis about the nature of visual circuit disruptions in psychosis; that this disorder is associated with abnormally weak early visual gain control. Gain control is a neural process that prevents responses to strong visual stimuli from becoming too large. It is known that in psychosis, some visual illusions are perceived as weaker than in healthy adults due to abnormally weak gain control. We will use a visual paradigm designed to tap into particular neural circuits in combination with EEG, in order to pinpoint the neural basis of this visual abnormality. In addition, we will acquire longitudinal measures of visual gain control and psychosis symptoms, in order to test the hypothesis that weaker gain control is associated with clinical deterioration. Finally, using functional MR spectroscopy, we will examine the role of glutamate in occipital cortex during visual processing in psychosis. This work will elucidate the pathophysiological mechanisms of psychosis, thereby facilitating the development of more precisely targeted, etiologically-based treatments.