Abstract: PURPOSE: To investigate the retinotopic properties and the top-down information transmission characteristics of the optic radiation (OR) sub-bundles.
METHODS: 7T retinotopy dataset from Human Connectome Project (HCP) was used to reconstruct the OR. Specifically, OR segmentation into sub-bundles was performed according to the retinotopic map of the primary visual cortex (V1). To suppress the influence of gray matter (GM) signals, white matter (WM) masks set to different degrees of restraint were used. The OR sub-bundles were confined within the spaces of these masks, which were ranked as level 1, level 2, and level 3 sub-bundles. The population receptive field (pRF) model was then applied to evaluate the retinotopic properties of these sub-bundles. Moreover, the consistency of the pRF properties of level 1 sub-bundles with those of V1 sub-fields at the endpoint of the sub-bundles was evaluated. Correlation analysis was performed to evaluate the relationships of the pRF parameters of level 2 and 3 sub-bundles with those of the level 1 sub-bundles. In addition, we applied the HCP working memory dataset to evaluate the activation of the foveal and peripheral OR sub-bundles and its correlation with those of the foveal and peripheral V1 and lateral geniculate nucleus (LGN) sub-fields.
RESULTS: The results showed that the pRF properties of differentially constrained sub-bundles exhibited the standard retinotopic properties, and the pRF properties of the level 1 sub-bundles were in good agreement with those of V1 sub-fields. Moreover, the pRF parameters of level 2 and 3 sub-bundles were significantly correlated with level 1- pRF parameters, indicating that OR sub-bundle evaluation was GM-free. Notably, the OR sub-bundles activation under the 2bk task was significantly stronger than that under the 0bk task. The activation differences between 2bk and 0bk of foveal and peripheral OR sub-bundles were significantly correlated with those of the corresponding V1 sub- fields, but not with those of the corresponding LGN sub-fields.
CONCLUSIONS: The findings demonstrated that the blood oxygen level-dependent (BOLD) signals of OR sub-bundles can encode high-fidelity visual information, indicating the feasibility of assessing WM functional activity at the tract sub-bundles level. Moreover, OR not only transmits visual information from bottom to up, but also engages top-down cognitive processes, such as visual working memory.

Key words: population receptive field (pRF), white matter, optic radiation (OR), blood oxygen level-dependent (BOLD), working memory