Dissecting the circuit for blindsight to reveal the critical role of pulvinar and superior colliculus

In patients with damage to the primary visual cortex (V1), residual vision can guide goal-directed movements to targets in the blind field without awareness. This phenomenon has been termed blindsight, and its neural mechanisms are controversial. There should be visual pathways to the higher visual cortices bypassing V1, however some literature propose that the signal is mediated by the superior colliculus (SC) and pulvinar, while others claim the dorsal lateral geniculate nucleus (dLGN) transmits the signal. Here, we directly test the role of SC to ventrolateral pulvinar (vlPul) pathway in blindsight monkeys. Pharmacological inactivation of vlPul impairs visually guided saccades (VGS) in the blind field. Selective and reversible blockade of the SC-vlPul pathway by combining two viral vectors also impairs VGS. With these results we claim the SC-vlPul pathway contributes to blindsight. The discrepancy would be due to the extent of retrograde degeneration of dLGN and task used for assessment.

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To collect the data in this study, we used the custom codes for Tempo for Windows (v. 10.34, Reflective Computing, USA) and used Spike2 (v.7.10c, Cambridge Electronic Design, Ltd., UK).
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April 2018
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No power calculations were performed to determine sample sizes. The sample sizes were determined by the possible number of behavioral task repeat per day and the experimental schedule, which was determined with reference to the former studies (e.g. Kinoshita et al., 2012. Nature) Data exclusions No data were excluded from the analysis.

Replication
Replication of the results was confirmed in two of two monkeys. Experiments of two monkeys were conducted in another institutes. Randomization In the VGS task, location and contrast of the saccade target was pseudo-randomly chosen from a set of target conditions.

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The investigators were not blinded in muscimol injection and dox administration experiments. A blinding was not relevant because the task control was conducted not by manually but by the script for TEMPO system.
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Two male macaque monkeys (Macaca fuscata and Macaca mulatta, body weight 6.8 and 9.0 kg) were used in this study. Monkey-H is the same animal used in the previous study (ref. 20). The third animal, Monkey-A, which was used only for the immunohistochemistry in this study, is the same animal used in another study (ref. 21).

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All macaque monkeys used in this study were supplied from a domestic breeding farm.

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