Washington, November 21 : Georgia Tech researchers have found that the brain of a patient with macular degeneration, the leading cause of blindness in the elderly, reorganises its neural connections in response to the disease.
Writing about their study in the journal Restorative Neurology and Neuroscience, the researchers say that when patients with macular degeneration focus on using another part of their retina to compensate for their loss of central vision, the brain shows increased activity.
In macular degeneration, damage to the retina causes patients to lose their vision in the center of their visual field. Patients with the disease make up for this loss by focusing with other parts of their visual field.
The team revealed that it was with the aid of Magnetic Resonance Imaging (MRI) that they could observe an increased brain activity when patients used their preferred retinal locations.
"Our results show that the patient's behaviour may be critical to get the brain to reorganize in response to disease. It's not enough to lose input to a brain region for that region to reorganize; the change in the patient's behaviour also matters," said Eric Schumacher, assistant professor in Georgia Tech's School of Psychology.
Studies conducted in the past have produced conflicting results, with some supporting and some rejecting the suggestion that the primary visual cortex, the first part of the cortex to receive visual information from the eyes, reorganises itself.
Schumacher and his graduate student Keith Main joined forces with researchers from the Georgia Tech/Emory Wallace H. Coulter Department of Biomedical Engineering and the Emory Eye Center to test whether the patients' use of other areas outside their central visual field, known as preferred retinal locations, to compensate for their damaged retinas drives, or is related to, this reorganization in the visual cortex.
During the study, the researchers presented 13 volunteers with a series of tests designed to visually stimulate their peripheral regions, and measure brain activity with functional magnetic resonance imaging.
The team observed that when patients visually stimulated the preferred retinal locations, they increased brain activity in the same parts of the visual cortex that were normally activated when healthy patients focused on objects in their central visual field.
Based on that observation, the researchers came to the conclusion that the brain had reorganized itself.
According to them, the parts of the visual cortex that process information from the central visual field in patients with normal vision were reprogrammed to process information from other parts of the eye, parts that macular degeneration patients use instead of their central visual areas.
Though studies involving other tasks have shown that the brain can reorganize itself, Schumacher and his colleagues claim that theirs is the first study to directly show that this reorganization in patients with retinal disease is related to patient behaviour.
The researchers are currently studying how long this reorganization takes, and whether it can be fostered through low-vision training.