Fifty-seventh annual meeting of the American association of physicists in medicine
TH-CD-207-06: Development of a Wide-View Retinotopic Mapping to Quantify Age Effects On Visual Cortex
Neural degeneration in normal aging can lead to functional changes in the visual cortex. However, the visual stimuli used in previous studies only covered a narrow, central visual field. The goals of this study were to 1) establish a practical, low-cost visual screen system inside a clinical MRI system; 2) investigate effects of normal aging with the wide-view to include central and peripheral visual areas.
Five elderly (60.6±3.4 y.o.) and five young (26.6±3.0 y.o.) normal volunteers were scanned at 3T. Visual stimulations (checkerboard animations) were projected to a customized plastic screen inside the magnet bore. Retinotopic BOLD fMRI was performed using the posterior half of a 12-channel head coil to image the occipital lobe without obstructing subjects’ vision to achieve visual simulation from 0∼90° of the visual field. MRI data were processed in Freesurfer for a two-sample unpaired group analysis with significance level p<0.05.
Boundaries of complete visual cortex areas were delineated with retinotopic fMRI and the wide-view stimulus system. With a small ring stimulus in the central visual field, older subjects showed significantly reduced neural activity (p<0.05) compared to younger subjects in the central vision region of the primary visual cortex. However, with the ring-stimulus expanded to the periphery (visual angle 45°∼90°), older subjects had significantly more activation (p<0.05) in central visual cortex areas than young subjects but significantly weaker responses (p<0.05) in periphery visual cortex areas.
Our results demonstrated that wide-view retinotopic mapping could be used to quantify age-related changes in the visual cortex. Central visual areas of healthy older subjects exhibited weaker BOLD activity for central stimulation and stronger signal for periphery stimulation, indicating potential central vision loss and neural reorganization with age. Future studies will correlate fMRI with visual field tests to investigate neural alterations in glaucoma patients.