Abstract
Purpose :
Long-term plasticity of the visual system has remained difficult to demonstrate. Most attempts have focused on investigating reorganization upon central visual loss. Here we performed an observational cross-sectional study on individuals with Retinitis Pigmentosa (RP) as a genetically-determined model of peripheral visual loss to test the hypothesis of long-term plasticity.
Methods :
A total of 37 participants from three age- and gender-matched groups were studied: RP (n=12); full-field healthy Control group (FFCnt, n=13); artificial scotoma healthy Control group (ASCnt, n=12). Exclusion criteria included visual field diameter < 5° and/or visual acuity < 0.2. MRI data were acquired using a 3T Siemens Magnetom TrioTim scanner with a 12-channel birdcage head coil. The protocol consisted of two high-resolution T1-weighted 3D MPRAGE sequences and four functional MRI runs (two polar angle and two eccentricity).
Population receptive fields (pRF) responses were described by a 2D gaussian and explained variance (R2) was used as a quantitative measure of the goodness-of-fit of the modeling. We used an artificial scotoma approach and pRF size to probe long-term plasticity.
The study was approved by the Ethics Commission of the University of Coimbra, in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants.
Results :
ANCOVA on mean pRF size showed a significant interaction between visual area (V1,V2,V3) and eccentricity (RP: F(2,642)=11.91, p<0.001; FFCnt: F(2,834)=10.79, p<0.001). Explained variance of pRF signals along the calcarine sulcus was preserved only in RP but not in artificial scotoma suggesting long-term plasticity. A repeated measures ANOVA on R2 showed a significant interaction between eccentricity and group (F(12.2,415.2)=4.75, p<0.001). R2 was consistently lower in ASCnt (exact binomial test p<0.001), and higher in FFCnt groups as supported by the main effect of the group (p<0.001). Regression Analysis of mean pRF size vs eccentricity in the Calcarine Sulcus of RP and ASCnt showed a significant difference between slopes (F(1,296)= 15.01, p<0.001) due to an increase in pRF size in more eccentric locations in RP.
Conclusions :
We found evidence for reorganization in RP based on pRF enlargement in the periphery and preserved explained variance as compared to the artifical scotoma control, suggesting long term visual cortical plasticity.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.