Functional and Structural Organization of Human Visual Cortex in Retinitis Pigmentosa

Abstract

Purpose: Retinitis Pigmentosa (RP) is an inherited retinal disease characterized by progressive degeneration of photoreceptors, leading to peripheral vision loss with central vision being affected in later stages. Symptoms onset age varies from infancy to adulthood, making RP an interesting model to study visual cortical adult plasticity. In contrast with previous studies, which have mainly covered central vision loss, we aim to determine the influence of peripheral retinal dystrophy on visual cortical function and structure using magnetic resonance imaging (MRI).

Methods: Brain images of 5 RP subjects (2 males; mean age 49.60±10.60 years; mean disease duration 30.40±14.29 years) and 9 age- and gender-matched healthy controls were acquired with a 3 Tesla scanner and analyzed with BrainVoyager®. First, retinotopy was applied to delineate individual visual cortical areas. The second functional MRI stimulus consisted in a random sequence of two checkerboard rings (presented at central and paracentral visual fields), during passive viewing and a one-back visual memory task (OBT). Stimuli were presented monocularly.

Results: RP patients presented a reduction in visual acuity (p=0.001), retinal thickness (p<0.000), and visual field (p≤0.008) of both eyes, which is consistent with longterm loss of photoreceptor cells even in the central retina. Results showed a posterior-to-anterior displacement of cortical activation in RP (p≤0.043) for paracentral and peripheral visual stimulation, which was more prominent in the left hemisphere. Moreover, RP participants showed increased cortical activation for visual areas V1 dorsal (p=0.036) and V3 dorsal (p=0.002) in the right hemisphere, and V1 ventral (p=0.037) in the left hemisphere, when contrasting the OBT with the passive viewing condition. Additionally, cortical thickness was decreased in dorsal visual area V3 (p=0.029) for RP subjects.

Conclusions: These results suggest functional reorganization at the lesion projection cortical zone and demonstrate adult functional reorganization of visual processing in striate and extrastriate cortices of RP patients, possibly caused by changing or unmasking of feedback signals from higher order cortical areas involved in attention. Despite the limited sample size, these outcomes are critical to assist the development of future visual recovery methods for RP patients.

Keywords: 755 visual cortex • 650 plasticity • 702 retinitis