Patients with macular degeneration, who lose the center of their visual field, learn to shift their gaze and “look” at things indirectly. Neurons in the deprived part of the visual cortex also adjust their activity. A new study suggests these adjustments may be the brain’s response to a loss of visual input, and not a process of rewiring that could take decades.
Nancy Kanwisher, Daniel D. Dilks and colleagues at the Massachusetts Institute of Technology, Harvard University and the National Institute of Mental Health had previously shown that when patients with macular degeneration shift their eyes, the portion of visual cortex called the foveal cortex, which normally responds to what’s directly ahead, begins responding to stimuli from the new location, called the preferred retinal locus.
It was unclear whether neurons in the foveal cortex were switching to the new, preferred location or could function in a more versatile way. Reporting in the March 4 Journal of Neuroscience, the scientists show that neurons in the fovea take any work they can get. Using functional magnetic resonance imaging in two patients with macular degeneration, the researchers found that the fovea responded to both the preferred retinal location and a second area not habitually used.
“The foveal cortex can take information from perhaps anywhere, and that reorganization is not driven by long-term prior use but may be a much quicker response,” says Dilks.