Brain Advance Access originally published online on May 19, 2006
Brain 2006 129(7):1822-1832; doi:10.1093/brain/awl111
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Unconscious vision: new insights into the neuronal correlate of blindsight using diffusion tractography
1 Cognitive Neuroscience Unit, Montreal Neurological Institute and Hospital, McGill University Montreal, Canada 2 Centre for Functional Magnetic Resonance Imaging of the Brain, Department of Clinical Neurology, University of Oxford Oxford, UK
Correspondence to: Alain Ptito and Sandra Leh, Neuropsychology/Cognitive Neuroscience Unit, Montreal Neurological Institute, 3801 University Street, Montreal, Quebec, Canada, H3A 2B4 E-mail: alain.ptito{at}mcgill.ca; sandra{at}bic.mni.mcgill.ca
The existence of several types of unconscious vision, or ‘blindsight’, has convincingly been demonstrated in numerous studies, and their neuronal correlates have been hypothesized according to the nature of the residual vision observed. We used diffusion tensor imaging (DTI) tractography to demonstrate an association between the presence of ‘Type I’- blindsight or ‘attention blindsight’ and reconstructed superior colliculi (SC) fibre tracts in hemispherectomized subjects, in support of the hypothesis that this subcortical structure plays a pivotal role in this type of blindsight. Before the DTI study, ‘Type I’ blindsight was identified in two of four hemispherectomized subjects by using a spatial summation effect paradigm, an indirect behavioural method, in which subjects were unaware of a stimulus presented in their blind visual field and were required to respond to an identical stimulus presented simultaneously in their intact field. SC tracts were then reconstructed in six control subjects, the two hemispherectomized subjects with blindsight and the two hemispherectomized subjects without blindsight. Whereas control subjects demonstrated mainly ipsilateral connections to visual association areas, parietal cortex, prefrontal areas and to an area close to the frontal eye fields, hemispherectomized subjects with blindsight showed ipsi- and contralateral connections from the SC to visual association areas, primary visual areas, parietal areas, prefrontal areas and to the posterior part of the internal capsule. In contrast, no projections from the SC on the hemispherectomized side were observed in hemispherectomized subjects without blindsight, in support of a key role of this structure in ‘Type-I’ or ‘attention blindsight’.
Key Words: blindsight; diffusion tensor imaging (DTI) tractography; superior colliculus; hemispherectomized subjects; brain plasticity
Abbreviations: DTI, diffusion tensor imaging; FEF, frontal eye fields; FMRIB, functional MRI of the brain; MNI, Montreal Neurological Institute; SC = superior colliculi
Received January 11, 2006. Revised March 29, 2006. Accepted March 30, 2006.
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