Abstract
Albinism is a congenital disorder where misrouting of the optic nerves at the chiasm gives rise to abnormal visual field representations in occipital cortex. In typical human development, the left occipital cortex receives retinal input predominantly from the right visual field, and vice-versa. In albinism, there is a more complete decussation of optic nerve fibers at the chiasm, resulting in partial representation of the temporal hemiretina (ipsilateral visual field) in the contralateral hemisphere. In this study, we characterize the receptive field properties for these abnormal representations by conducting detailed fMRI population receptive field mapping in a rare subset of participants with albinism and no ocular nystagmus. We find a nasal bias for receptive field positions in the abnormal temporal hemiretina representation. In addition, by modelling responses to bilateral visual field stimulation in the overlap zone, we found evidence in favor of discrete unilateral receptive fields, suggesting a conservative pattern of spatial selectivity in the presence of abnormal retinal input.
Highlights
Albinism is a congenital disorder associated with misrouting of the optic nerves during embryogenesis, which leads to abnormal retinotopic organization in sub-cortical and cortical visual areas (Carroll, Jay, McDonald, & Halliday, 1980; Creel, Witkop, & King, 1974; Hedera et al, 1994; Morland, Hoffmann, Neveu, & Holder, 2002)
Responses to nasal and temporal hemiretina stimulation were modelled independently, and population receptive field (pRF) estimates obtained for each condition
We observed clear lateralization of visual field representations, with the nasal hemiretina represented in the contralateral hemisphere and the temporal hemiretina represented in the ipsilateral hemisphere, as expected (Figure 2)
Summary
Albinism is a congenital disorder associated with misrouting of the optic nerves during embryogenesis, which leads to abnormal retinotopic organization in sub-cortical and cortical visual areas (Carroll, Jay, McDonald, & Halliday, 1980; Creel, Witkop, & King, 1974; Hedera et al, 1994; Morland, Hoffmann, Neveu, & Holder, 2002). A single case study in a green monkey (Guillery et al, 1984) and more recently human functional MRI (fMRI) studies (Hoffmann, Tolhurst, Moore, & Morland, 2003; Kaule et al, 2014; Morland et al, 2002) suggest the presence of overlapping representations of ipsilateral and partial contralateral visual fields on the same cortical territory, in agreement with model (2); an interleaved representation While these recent advances shed light on the topographic organization of the albinotic visual cortex, relatively little is known about the nature of these abnormal representations. The presence or absence of evidence for dual receptive fields would inform how abnormal retinal input is integrated to produce stereoscopic vision and to what degree are retinotopic representations plastic in the abnormally developed visual cortex
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