Functional cerebral reorganization of visual scene processing in age-related macular degeneration patients

International audienceAge-related macular degeneration (AMD) represents an interesting way to study cortical reorganization after a peripheral lesion of the visual system, as well as the link between cortical activation and visual function. In AMD, the processing of fine details in a visual scene, or high spatial frequencies (HSF), is impaired in patients' residual vision, while the processing of global shapes, or low spatial frequencies (LSF), is relatively well-preserved. The present fMRI study aimed to investigate the residual abilities and functional cerebral reorganization of spatial frequency processing in visual scenes in AMD patients.AMD patients and normally sighted elderly participants performed a categorization task under fMRI, using large black and white photographs of scenes (indoors vs. outdoors, with a visual angle of 24x18 degrees) filtered in LSF, HSF, and non-filtered scenes. The study also explored the effect of luminance contrast on spatial frequency processing. Contrast across scenes was either unmodified, or equalized using a root-mean-square contrast normalization in order to increase contrast in HSF scenes.Results showed that performances were lower for HSF than for NF and LSF scenes, for both AMD patients and controls. However, the selective deficit in the categorization of HSF scenes was more pronounced in AMD patients than in control participants, and was associated with lower activity in the occipital cortex and the parahippocampal place area, a distant cerebral region specialized for scene recognition. Increasing the contrast of HSF scenes improved the processing in the residual vision and spurred activation of the occipital cortex for AMD patients.Therefore, a deficit in processing HSF in scenes exists in AMD patients, in association with an absence of activation in the occipital cortex, but also in a distant scene selective region. Functional brain changes may explain why AMD patients exhibit greater difficulty with details processing even in their residual vision. The deficit can be partially restored by enhancing luminance contrast. These findings may lead to new perspectives for rehabilitation procedures for the residual vision of AMD patients