Resting-State Functional Organization of the Brain in Blindness and Sight Recovery
Creators: name: Nadvar, Negin
Publisher: name: My University
Year: 2023
Subjects: subject: resting-state functional connectivity
subject: blindness
subject: sight restoration
subject: Argus II
subject: fMRI
subject: Biomedical Engineering
subject: FOS: Medical engineering
subject: Engineering

description: Reorganization of the human brain after blindness is well-documented, however, subsequent sight restoration can lead to adaptation that is not as well understood. Successful sight restoration therapy must integrate functionally with the visual system for perception to occur. Thus, our study is strongly motivated by the need to understand brain plasticity after regaining vision. In this thesis, I evaluated use of functional magnetic resonance imaging (fMRI) resting-state functional connectivity (rsFC) for vision studies from two angles: 1) from a methodology perspective, I explored the importance of proper data preprocessing on the resulting rsFC outcome, 2) from a neuroscientific perspective, I examined utility of rsFC as a potential metric of blindness and sight restoration. It has been shown that choice of analysis pipelines can impact the research findings. Therefore, replication studies that aim to reproduce the previously published results are critically necessary. In the first venue of my research, I verified reproducibility of a well-cited published study on ocular blindness using rsFC. By using the original dataset, I utilized another widely used software package to investigate how applying different implementations of the original pipeline or a more rigorous preprocessing stream can alter the outcomes. These alternative workflows changed the distribution of the whole-brain rsFC and functional network densities, reducing the overlap with the original results. Remarkably, the largest rsFC effects appeared to primarily belong to certain connection pairs, irrespective of the pipeline used, likely demonstrating immunity of the larger effects and likely the true results against suboptimal processing. This may highlight the significance of results verification across different computational streams in search of the true findings. Functional outcome of using Argus II, as the only retinal prosthesis with FDA approval that has been clinically used, can provide an exceptional opportunity to explore brain’s potential for plasticity upon reintroduction of (artificial) vision. Considerable variability in visual performance has been reported across Argus II recipients that remains unexplained. A previous experiment used fMRI to measure tactile-evoked cross-modal responses in visual cortex and reported no significant group-level results between blind and Argus II groups, possibly due to variability in activation baseline across individuals. The rsFC can potentially overcome this issue by providing a more stable metric. Numerous studies have used rsFC to assess cortical reorganization after blindness, nevertheless, it has rarely been utilized to study sight recovery. In this study, four resting-state runs from 10 sighted, 10 blind, with severe retinitis pigmentosa, and 7 Argus II subjects were included. The whole-brain ROI-ROI rsFC and some graph theory functional network measures were calculated and compared at the group level. Some quantities decreased after blindness but were not reversed by vision restitution, including visual-visual rsFC, visual-frontal rsFC, and some network measures. On the other hand, significant reduction was observed in visual-somatosensory, visual-auditory, visual-motor, and visual-association rsFC after blindness that were all returned to the level of sighted individuals in Argus II recipients. These rsFC measures can potentially serve as biomarkers for blindness and sight restoration, in the absence of or as a complement to the behavioral indices. The proposed metrics can enhance our understanding of variable outcomes among the receivers of sight restorative technologies and enable tracking rehabilitative progress. Future investigation with a larger number of test subjects for this rare condition can further unveil the profound ability of our brain to reorganize, following vision restoration.