Much progress has been made in understanding the neural bases of cognitive functions related to selective attention, memory, or decision making in humans using functional brain mapping techniques and in the macaque as the prototypical animal model for human brain function using single-cell physiology and other invasive techniques. These studies have almost exclusively focused on sensory and higher-order processing areas of the cerebral cortex. In contrast, relatively little is known about the role of thalamic nuclei such as the lateral geniculate nucleus (LGN) in perception and cognition. Traditionally, the LGN has been viewed as the gateway to primary visual cortex, which conveys the visual information faithfully from the retina to cortex without much modulation. The goal of the proposed research is to challenge this traditional view by investigating the functional role of the LGN in perceptual functions related to visual awareness and in cognitive functions related to selective attention. The central hypothesis that motivates this research is that the LGN plays an important role beyond that of a relay nucleus as a gatekeeper in visual attention and awareness. FMRI and behavioral studies in non-impaired and dyslexic subjects are proposed to address the following questions: 1) Can neural correlates of conscious perception be identified as early as in the parvocellular, or magnocellular parts of the LGN?; 2) What is the neural mechanism by which selective attention controls gain in the human LGN, and is this gain control confined to the magnocellular LGN?; 3) Are visual processing abnormalities and attentional deficits in dyslexic subjects associated with a functional disorganization of the magnocellular LGN? In the human brain, it has proven difficult to study subcortical nuclei because of spatial resolution and signal-to-noise limitations of brain mapping techniques. The proposed research will use innovative high- and super-resolution imaging techniques in humans to overcome some of these issues. The cerebral cortex depends critically on the information that it receives from the thalamus, since it receives very little else. Understanding cortical functioning depends on understanding the thalamic inputs that are the necessary first step in cortical processing. ? ? ?
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