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Keith A. Schneider; High-resolution imaging of the human thalamus and superior colliculus during binocular rivalry. Journal of Vision 2009;9(8):271. doi: 10.1167/9.8.271.
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Introduction. Binocular rivalry is known to suppress the eye-specific layers of the lateral geniculate nucleus (LGN) in humans, but the spatial resolution has been insufficient to discriminate between the magnocellular (M) and parvocellular (P) sections. It is also unknown whether the perceptual alternations during binocular rivalry, and hence our awareness, are reflected in the activity of the pulvinar or superior colliculus. Therefore we employed high-resolution functional magnetic resonance imaging (fMRI) to study binocular rivalry in these structures.
Methods. Subjects' brains were scanned with a 3 T MRI scanner and a multi-channel head coil. The spatial resolution was enhanced beyond the hardware limits of the scanner using a post-processing super-resolution technique. Subjects viewed stimuli through anaglyph glasses to isolate each eye. Alternating hemifield flickering checkerboard stimuli were used to determine the eye dominance of each voxel in the subcortical structures. To induce binocular rivalry, subjects were shown a rapidly rotating stimulus consisting of two full-field orthogonal gratings independently presented to each eye. The subjects indicated the perceptually dominant grating via key presses. The amplitude of the perceptual modulations were determined through the average fMRI response time-locked to the subjects' perceptual responses.
Results. Binocular rivalry modulated the activity in each of the subcortical structures. In the LGN, the sign of the modulation was related to the laminar structure of the nucleus, with but no differences were observed between voxels belonging to the M or P sections.
Conclusions. The phenomenon of binocular rivalry can be measured throughout the human visual system, including the subcortical visual nuclei, suggesting that these structures contribute to our awareness. No special role in binocular rivalry could be attributed to either the M or P sections of the LGN.
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