Functional symmetry of the primary visual pathway evidenced by steady-state visual evoked potentials

The primary visual pathway exhibits a symmetrical anatomical structure, initially arising from the left and right retinas, passing through the lateral geniculate nucleus, and finally projecting to the left and right primary visual cortices. However, to our knowledge, studies based on scalp EEG have not provided adequate evidence of the functional symmetry of the primary visual pathway, as the usual visual ERP is often related to other higher-level brain areas. Steady-state visual evoked potentials (SSVEPs) can be considered as the direct response of the primary visual pathway to a repetitive stimulus, with a very limited correlation with responses of higher-level brain areas. Therefore, SSVEPs can be used to evaluate the functional symmetry of the primary visual pathway. In this study, we draw a comparison among the powers and distributions of SSVEPs of different frequencies when the left or right eye alone is stimulated, and when both the eyes are stimulated together. Our results indicate that the primary visual pathway is almost symmetrical in generating SSVEPs from either eye and that there is some functional interaction between the left and right primary visual pathways.