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Contribution of the retino-tectal pathway to visually guided saccades after lesion of the primary visual cortex in monkeys

Authors

  • Rikako Kato,

    1. Department of Developmental Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan
    2. The Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), Kawaguchi, Japan
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  • Kana Takaura,

    1. Department of Developmental Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan
    2. The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
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    • Present address: Laboratory for Adaptive Intelligence, RIKEN Brain Science Institute, Wako, Japan.

  • Takuro Ikeda,

    1. Department of Developmental Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan
    2. The Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), Kawaguchi, Japan
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    • Present address: Center for Neuroscience Studies, Canadian Institutes of Health Research Group in Sensory-Motor Systems, Department of Physiology, Queen’s University, Kingston, ON, Canada.

  • Masatoshi Yoshida,

    1. Department of Developmental Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan
    2. The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
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  • Tadashi Isa

    1. Department of Developmental Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan
    2. The Core Research for Evolutionary Science and Technology (CREST), Japan Science and Technology Agency (JST), Kawaguchi, Japan
    3. The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
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Dr T. Isa, 1Department of Developmental Physiology, as above.
E-mail: tisa@nips.ac.jp

Abstract

Previous reports on ‘blindsight’ have shown that some patients with lesions of the primary visual cortex (V1) could localize visual targets in their scotoma with hand and/or eye movements without visual awareness. A role of the retino-tectal pathway on residual vision has been proposed but the direct evidence for this still remains sparse. To examine this possibility, we inactivated the superior colliculus (SC) of unilateral V1-lesioned monkeys using microinjections of muscimol, and analysed the effects on visually guided saccades. Following muscimol injections into the contralesional SC, the monkeys performed the visually guided saccade task with relatively minor deficits. The effects of ipsilesional SC inactivation were more severe. After injections, the monkeys failed to localize the target within the visual field represented at the injection site on the SC map. The effects of ipsilesional SC inactivation may result from sensory deficits, motor deficits or a combination of both. To examine these possibilities, we tested the effects of SC inactivation on the motor system by investigating spontaneous saccades. After inactivation of the ipsilesional SC, spontaneous saccades toward the injection site were not abolished, suggesting that impairment of visually guided saccades following inactivation of the ipsilesional SC could not be explained solely by a motor deficit and was primarily due to a visual deficit, presumably by interfering with processing in the superficial layer. We conclude that the retino-tectal pathway plays an essential role in residual vision after V1 lesion. The results suggest that this pathway may be involved in mediating unconscious vision in blindsight patients.

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