In a series of studies, we combined advanced behavioural methods with state-of-the-art fMRI techniques to assess changes in the underlying neural circuitry in healthy human adults as well as in patients with a wide range of ophthalmological and neurological disorders. We used high-resolution neuroimaging and biologically-inspired computational models to assess the properties of the visual cortex. Specifically, we used functional MRI to estimate the portion of the visual field to which a group of neighbouring neurons in the visual cortex responds to, which is known as its population receptive field (pRF). Despite the exceptional challenges we had to face during most of the action’s period due to the ongoing Covid-19 pandemic, we were able to successfully achieve the main objectives of the action.
In one of the projects, we used fMRI to map visual representations in patients with retinitis pigmentosa (RP)–a rare genetic disorder that involves the loss of peripheral retinal cells. We tested the impact of task-related attentional feedback on the dynamic of the underlying neural circuitry (pRFs) in the primary visual cortex (V1) of these patients. Our results show that while the visual system of patients with retinal lesions is intact and largely unresponsive in cortical regions that do not receive retinal inputs, attentional feedback results in brain activity in the lesion projection zone (LPZ) of these patients. Specifically, we show that the attention-related activation of the LPZ in these patients is (1) not spatially-specific and affects both hemispheres of the brain; and (2) associated with atypically large visual pRFs in the V1-LPZ. We propose that these results reflect the influence of top-down signals from extrastriate areas in V1, which are typically regulated by the presence of retinal inputs. We are working on the manuscript related to this project that will be submitted to a peer-reviewed journal in the next few months.
Then, in another project, we examined the neural substrates of training-induced recovery of conscious vision in patients with stroke-induced cortical blindness. Specifically, we linked the changes in visual sensitivity to changes in the underlying neural circuitry measured using fMRI. Overall, our results reveal that visual recovery relies on spared, perilesional V1 cortex that is functionally impaired, but can be brought back “online” using intensive training. Moreover, we show that training increased the coverage of the blind field, which was mediated by the enlargement of V1 pRFs covering the blind field. These findings indicate that a certain level of baseline V1 responsiveness is required for training to effectively induce recovery of conscious vision. The results of this project provide novel and vital insights regarding the neural mechanisms by which visual rehabilitation training restores perceptual functions in the blind field of patients with cortical damage. This project was recently accepted for publication in Nature Communications (currently in press).
Moreover, the beneficiary collaborated on another project, in which he helped design fast and efficient testing protocols to optimise the time required for the behavioural assessment of visual functions in patient populations. The beneficiary was also responsible of the design and set-up of a fully-equipped testing room at the Spinoza Centre for Neuroimaging.
Although the dissemination and exploitation of the results was considerably limited due to the COVID-19 crisis, we were able to disseminate some of our results at several scientific conferences and workshops (4 international; 2 national). The beneficiary was invited to present the results of his research to group of scientists twice, and co-organised a public outreach event–the Weekend of Science–in Amsterdam. The results of the project can be exploited by scientists, to help develop biologically-inspired computational models of visual dynamics, as well as clinicians, to improve current visual rehabilitation therapies.
