21 Scientists have studied how visual space is mapped in the cerebral cortex for decades under the assumption that the map is equal for lights and darks. Recent work, however, demonstrates that visual brain maps are dark-centric and, just as stars rotate around black holes in the Universe, lights rotate around darks in the brain representation of visual space. Published in the May 5, 2016 issue of Nature, work by Dr. Jens Kremkow and his collaborators in Dr. Jose Manuel Alonso’s laboratories demonstrates that visual brain maps are dark-centric.* The primary visual cortex has the most detailed representation of visual space and is the main recipient of eye inputs through the visual thalamus. In the first description of its functional architecture, Hubel and Wiesel demonstrated that the cortical map of visual space coexisted with other maps for eye input and stimulus orientation. Neurons responding to inputs from the left and right eyes segregated in the visual cortex to form a map of alternating stripes resembling a zebra pattern. Other scientists would discover a map with a pinwheel pattern and additional maps for stimulus features related to motion and depth. Though the maps for visual space and eye input were thought to originate from the segregation of thalamic afferents in the visual cortex, the other maps’ origin remained unclear. Dr. Kremkow and his colleagues indicate that the organization of all maps originates from an arrangement of thalamic afferents that minimizes differences in spatial position, eye input, and light/dark polarity among neighboring cortical neurons. The organization of visual space for both monocular and binocular vision is more precise for darks than lights. This surprising dark-centric organization could be a consequence of a size distortion for lights that originates at the photoreceptor, the very first neuron in the visual pathway. These findings explain why visual acuity is commonly measured with dark characters on light backgrounds and why visual resolution is lower for lights. * A similar result was reported in the same issue of Nature by Kuo-Sheng Lee, et al., of David Fitzpatrick’s laboratory at the Max Planck Florida Institute for Neuroscience. Scientists Discover a Surprising Central Role for Dark Stimuli in Brain Visual Maps Dr. Jens Kremkow Dr. Jose Manuel Alonso
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