More than 40 million blind people worldwide reach this condition after many years of slow and progressive retinal degeneration. Very little is however known about whether the brain of blind people would be able to process artificial or restored visual inputs. New hope for blind people has been generated by the development of sophisticated prostheses or new light-responsive elements. These are aimed at replacing the disrupted retinal function and feeding restored visual signals to the brain.
Retinitis Pigmentosa is a hereditary illness of the retina that progressively leads to complete blindness. A team from the University of Pisa in Italy, led by Elisa Castaldi and Maria Concetta Morrone, has studied patients affected by the disease to determine the brain’s ability to process visual information after many years of total blindness.
A group of patients was assessed by measuring their perceptual and brain responses before and after the implantation of a prosthetic implant. The implant senses visual signals and sends them to the brain via the stimulation of the axons of retinal ganglion cells. The researchers used functional magnetic resonance imaging to determine that patients’ brain activity increased when they learned to recognize unusual visual stimuli such as flashes of light. This change in brain activity, observed at both the cortical and thalamic level, needed extensive training over a long period to become established. Their brain response to visual stimuli increased the more the patient practiced, and this led to an improved perception of the visual stimuli using the implant. In other words, the brain needs to learn to see again.
The results show that the brain undergoes plastic changes to re-learn how to make use of the new artificial visual signals after the implantation of a prosthetic device. These signals are probably uncharacteristic compared to normal visual signals received from the eyes. This residual plasticity of the sensory circuitry of the adult brain after many years of deprivation can be utilized in the development of new prosthetic implants.