A partial restoration of sight is possible in individuals blind from birth, thanks to the most recent advances in research. However, a group of researchers of the Mind/Brain Center of the University of Trento and of the University of Montréal in Canada have discovered that the functional reorganization of the brain happens in individuals who, for a long period, experienced a long sense deprivation, which could potentially impede complete sight restoration.
The researchers, including were able to study a case of a patient, visually impaired since birth, whose sight was restored during her adult life, following an artificial corneal implant (Boston Keratoprothesis) surgery in one eye. It is known that visual cortex maintains a certain degree of plasticity, with the capacity of the brain to tune its activity according to the experience it perceives, even in individuals visually impaired since birth. But the authors of the paper that describes this results discovered that, even months after the surgery, the visual cortex* does not restore its complete normal functioning.
* The visual cortex is the part of the occipital lobe responsible for the processing of the electric inputs coming from the eye.
In blind individuals, the occipital cortex responds to stimuli coming from other sense organs, such as hearing and touching, thus partially compensating the loss of sight. This challenges the sight restoration of individuals who undergo a transplantation, because the cortex – after its reorganization – may not be able to process visual inputs any longer, as per the researchers.
To better understand the importance of this phenomenon researchers examined the 50-year-old Canadian female patient through a set of behavioural and neurophysiological tests. They monitored, before and after the surgery, the changes of the sight and the brain anatomy, as a response to visual and sound stimuli. Therefore the team of researchers used the functional MRI to record the brain activations of the patient during the performance of specific visual and hearing tasks and then compared them with the activations of individuals with normal sight and individuals blind since birth, while performing the same tasks.
Before the surgery, the patient presented a structural and functional reorganization of the occipital areas typical of individuals with a long sense deprivation. Therefore the possibility of a partial recovery of the previous functions, after the sight restoration in adult age was proved. Considering the significant recent advances in the technological solutions that allow for the sight restoration, these results play a significant role in the clinical implications to foresee the possible results of transplantations in patients to be operated.
The study suggests that the eye surgery may achieve good results, also in adults severely visually impaired since childhood. However, it is important to warn that the observed restoration in the visual cortex, in terms of minor response to sound stimuli and the gradual increase of response to visual stimuli and the density of the brain, is not complete. Indeed seven months after the surgery, some areas continue to respond weakly to sound stimuli, despite the simultaneous response to visual inputs. This overlap may be the reason why some features of sight, in spite of the gradual improvements, still remain below standard seven months after the transplantation.
The clinical implications are twofold: The results of this research pave the way for the systematic clinical use of the pre-surgery MRI as a prognosis tool regarding the efficacy of the transplantation. Further, they open up ways for specific rehabilitation programmes after sight-restoration surgery.
The research “Tracking the evolution of cross modal plasticity and visual functions before and after sight-restoration” by Giulia Dormal, Olivier Collignon et. al. was published in the Journal of Neurophysiology.
The study was financed by the Canada Research Chair Program, Canadian Institutes of Health Research, Saint-Justine Foundation, the European Research Council, Veronneau Troutman Foundation, Fonds de recherche en ophtalmologie de l’Université de Montréal, PAI/UIAP grant PAI/33 and the Belgian National Fund for Scientific Research.