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

• Published in: Brain (London, England : 1878) England : 1878), 2006-07, Vol.129 (7), p.1822-1832
• Main Authors: Leh, Sandra E., Johansen-Berg, Heidi, Ptito, Alain
• Format: Article
• Language: English
• Subjects: Adult; Attention; Biological and medical sciences; Blindness, Cortical - physiopathology; blindsight; Brain Mapping - methods; brain plasticity; Diffusion Magnetic Resonance Imaging - methods; diffusion tensor imaging (DTI) tractography; Female; hemispherectomized subjects; Hemispherectomy; Humans; Investigative techniques, diagnostic techniques (general aspects); Male; Medical sciences; Nerve Fibers - physiology; Nervous system; Neurology; Neuronal Plasticity; Parietal Lobe - physiopathology; Pyramidal Tracts - physiopathology; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Superior Colliculi - physiopathology; superior colliculus; Vascular diseases and vascular malformations of the nervous system; Visual Fields; Visual Pathways - physiopathology
• ISSN: 0006-8950; 1460-2156
• DOI: 10.1093/brain/awl111

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’.