Delineating the Neural Correlates of Visual Awareness through the Integration of Multimodal Neuroimaging and Noninvasive Electrical Neuromodulation

Abstract

In recent years, there has been a push to develop a fundamental theory of consciousness in the neuroscience community. However, to date, the physical mechanisms underlying conscious awareness remain unclear. The major aim of this dissertation was to delineate neural correlates of consciousness through the integration of multimodal functional neuroimaging and noninvasive electrical neuromodulation. To this extent, we utilized simultaneous EEG-fMRI imaging to investigate both the electrophysiological and hemodynamic correlates of visual awareness during binocular rivalry. Binocular rivalry is a classic visual phenomenon in which one’s perception spontaneously fluctuates between two different images that are presented simultaneously to the viewer, one to each eye. These random alternations in visual awareness occur despite the static dichoptic input, making binocular rivalry a promising framework for the study of brain networks involved in consciousness. In addition, we evaluated the feasibility of using transcranial direct/alternating current stimulation to modulate behavioral and electrophysiological correlates of rivalry and visual perception in general. Our findings point to the existence of multiple neural networks operating independently during rivalry for its resolution. Differential patterns of activation in fronto-parietal networks and across the default mode network were associated with both subjective changes in visual awareness and maintaining perceptual stability during rivalry. Collectively, our findings suggest that suppression of eye-specific neural activity during rivalry is mainly due to bottom-up processing in early visual cortex, while fronto-parietal activity appears more generalized and predominantly related to attentional processes and conscious awareness of changes in sensory information.