Injury to the primary visual cortex (V1) leads to the loss of visual experience. Nonetheless, careful testing shows that certain visually guided behaviours can persist even in the absence of visual awareness1,2,3,4. The neural circuits supporting this phenomenon, which is often termed blindsight, remain uncertain4. Here we demonstrate that the thalamic lateral geniculate nucleus (LGN) has a causal role in V1-independent processing of visual information. By comparing functional magnetic resonance imaging (fMRI) and behavioural measures with and without temporary LGN inactivation, we assessed the contribution of the LGN to visual functions of macaque monkeys (Macaca mulatta) with chronic V1 lesions. Before LGN inactivation, high-contrast stimuli presented to the lesion-affected visual field (scotoma) produced significant V1-independent fMRI activation in the extrastriate cortical areas V2, V3, V4, V5/middle temporal (MT), fundus of the superior temporal sulcus (FST) and lateral intraparietal area (LIP) and the animals correctly located the stimuli in a detection task. However, following reversible inactivation of the LGN in the V1-lesioned hemisphere, fMRI responses and behavioural detection were abolished. These results demonstrate that direct LGN projections to the extrastriate cortex have a critical functional contribution to blindsight. They suggest a viable pathway to mediate fast detection during normal vision.
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We thank A. Maier and D. McMahon for comments on the manuscript; S. Smirnakis, R. Berman, R. Wurtz, B. Richmond, S. Guderian and M. Fukushima for discussions; C. Zhu and H. Merkle for magnetic resonance coil construction; K. Smith, N. Phipps, J. Yu, G. Dold, D. Ide and T. Talbot for technical assistance; D. Sheinberg for developing visual stimulation software; and members of the Brian Wandell laboratory for developing and sharing mrVista software. This work was supported by the Intramural Research Programme of the NIMH, the NINDS, and the NEI.
The authors declare no competing financial interests.
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Schmid, M., Mrowka, S., Turchi, J. et al. Blindsight depends on the lateral geniculate nucleus. Nature 466, 373–377 (2010). https://doi.org/10.1038/nature09179
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