Unconscious vision: new insights into the neuronal correlate of blindsight using diffusion tractography.

Full Abstract

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'.

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Author information

Author/s: Leh, Sandra E (SE); Johansen-Berg, Heidi (H); Ptito, Alain (A);

Affiliation: Cognitive Neuroscience Unit, Montreal Neurological Institute and Hospital, McGill University Montreal, Canada.

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: Brain : a journal of neurology (Brain), published in England. (Language: eng)

Reference: 2006-Jul; vol 129 (issue Pt 7) : pp 1822-32

Dates: Created 2006/06/28; Completed 2006/08/03; Revised 2007/11/15;

PMID: 16714319, status: MEDLINE (last retrieval date: 12/26/2008)

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adult
Attention
Blindness, Cortical - physiopathology
Brain Mapping - methods
Diffusion Magnetic Resonance Imaging - methods
Female
Hemispherectomy
Humans

Male
Nerve Fibers - physiology
Neuronal Plasticity
Parietal Lobe - physiopathology
Pyramidal Tracts - physiopathology
Superior Colliculi - physiopathology
Visual Fields
Visual Pathways - physiopathology

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