Homonymous lateral hemianopia (HLH) is characterized by loss of vision in half the visual field, and is the most common neurovisual disorder following stroke.
Numerous behavioral and neuroanatomical studies have focused on the phenomenon of blindsight, corresponding to patients' unconscious residual visual capacities in the blind hemifield. Cohort studies of patients have highlighted different types of blindsight, and a low occurrence of the phenomenon initially described: (1) type 1 blindsight (≈12%), unconscious visual abilities; (2) type 2 blindsight, visual abilities associated with sensations in the blind field (≈18%); (3) blindsense, sensations in the blind field without visual abilities (≈30%); and (4) no blindsight (≈40%). The heterogeneity of these blindsight abilities in the HLH population is closely related to patients' neuroanatomical and functional profiles.
In particular, resting-state functional imaging (r-fMRI) and default mode network analysis have highlighted a significant correlation between the degree of inter-hemispheric connection (between the healthy and injured hemispheres) and the rate of spontaneous visual field recovery. To our knowledge, this degree of functional connectivity has not yet been studied in relation to blindsight abilities. However, this functional MRI measurement tool represents a potential predictive factor for patients' residual performance in their blindsight field, in order to assess the level of visuo-cognitive impairment and, ultimately, to adapt care.
Subjects aged 18 and over
with homonymous visual field amputation sequelae of a retrochiasmatic lesion of vascular origin (stroke), including the occipital region (primary visual cortex, optic radiations, associated occipital areas)
Requires follow-up brain MRI as part of treatment
Able to perform experimental tasks on computer
Severe neuropsychological disorders (language, memory, attention, vigilance, reasoning)
Severe ophthalmological disorders or visual acuity below 3/10 prior to stroke
Progressive ophthalmological disorders (cataract or glaucoma) likely to bias measurements
Major psychiatric or behavioral disorders making care impossible
Patients over 18 years of age with homonymous lateral hemianopia undergoing cerebral MRI for follow-up and rehabilitation following stroke
Case-only
Cross-sectional
Not listed
Description of resting-state functional MRI measurement of the degree of Resting State Functional Connectivity (RSFC) between left and right hemisphere regions.
Comparison of the degree of inter-hemispheric Resting State Functional Connectivity between the four patient groups: absence of blindsight, type I blindsight, type II blindsight and blindsense.
Correlation between inter-hemispheric functional connectivity and blindsight performance
Resting-state functional MRI measurement of the degree of RSFC between left and right hemisphere regions of interest. Blindsight performance assessed by measuring the sensitivity of discrimination of spatial orientation (horizontal/vertical) of lines presented in the patient's blind field (blindsight).
Density and intensity of visual and attentional default networks in each type of blindsight
Calculation (Graph Theory) of neural network matrices, weighted and created on the basis of correlations of activations in different brain regions during resting-state functional MRI measurement .
Blindsight performance according to the laterality of the lesion (left or right hemisphere)
Blindsight performance assessed by measuring the sensitivity of discrimination of spatial orientation (horizontal/vertical) of lines presented in the patient's blind field (blindsight)
Correlation between the level of inter-hemispheric functional connectivity and blindsight performance
Resting-state functional MRI measurement of the degree of Resting State Functional Connectivity (RSFC) between left and right hemisphere regions of interest, blindsight performance assessed by measuring the sensitivity of spatial orientation discrimination (horizontal/vertical) of lines presented in the blindsight field.
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