What cortical areas are responsible for blindsight in hemianopic patients?

Sánchez-López, Javier; Cardobi, Nicolò; Pedersini, Caterina A.; Savazzi, Silvia; Marzi, Carlo Alberto

doi:10.1016/j.cortex.2020.08.007

Cited by 11 publications

(19 citation statements)

References 74 publications

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“…Two blindsight positive patients (P6, P8) showed retained fMRI signal in the blindsight test zone using both MP and pRF techniques, albeit not completely normal. This is consistent with previous studies ( Papanikolaou et al, 2014 ; Schneider et al, 2019 ; Sanchez-Lopez et al, 2020 ), and suggests that both methods can reveal preserved visual processing in hemianopia beyond SAP. Interestingly, the blindsight stimulus in both patients overlapped the border of preserved and absent signal, raising the possibility that fMRI sensitivity may simply reflect better resolution than perimetry at the border zones of field loss.…”

Section: Discussionsupporting

confidence: 93%

“…However, this type of test, while critical for practical issues such as suitability for driving, does not reveal any non-conscious vision that is often present in patients with hemianopia ( Stoerig and Cowey, 1989 , 1992 , 1997 ; Weiskrantz, 1993 , 1996 ; Tomaiuolo et al, 1997 ; Tamietto and de Gelder, 2008 ; Ajina et al, 2015 ; Ajina and Bridge, 2018 , 2019 ; Danckert et al, 2019 ; Sanchez-Lopez et al, 2020 ). The definition of regions of the VF as “blind” based on perimetric measures additionally does not reflect the finding that stimulation within this blind field can lead to neural activity in the visual areas of the brain ( Barbur et al, 1993 ; Morland et al, 2001 ; Bridge et al, 2008 ; Radoeva et al, 2008 ; Tinelli et al, 2013 ; Papanikolaou et al, 2014 ; Schneider et al, 2019 ; Sanchez-Lopez et al, 2020 ). Disadvantages of SAP therefore consist of its low spatial specificity, the high performance and attention required by the participant, the fact that it only captures conscious vision and its limited flexibility in testing stimuli.…”

Section: Introductionmentioning

confidence: 99%

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Visual Field Reconstruction in Hemianopia Using fMRI Based Mapping Techniques

Bridge

Carvalho

Cornelissen

et al. 2021

Front. Hum. Neurosci.

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PurposeA stroke that includes the primary visual cortex unilaterally leads to a loss of visual field (VF) representation in the hemifield contralateral to the damage. While behavioral procedures for measuring the VF, such as perimetry, may indicate that a patient cannot see in a particular area, detailed psychophysical testing often detects the ability to perform detection or discrimination of visual stimuli (“blindsight”). The aim of this study was to determine whether functional magnetic resonance imaging (fMRI) could be used to determine whether perimetrically blind regions of the VF were still represented in VF maps reconstructed on the basis of visually evoked neural activity.MethodsThirteen patients with hemianopia and nine control participants were scanned using 3T MRI while presented with visual stimulation. Two runs of a dynamic “wedge and ring” mapping stimulus, totaling approximately 10 min, were performed while participants fixated centrally. Two different analysis approaches were taken: the conventional population receptive field (pRF) analysis and micro-probing (MP). The latter is a variant of the former that makes fewer assumptions when modeling the visually evoked neural activity. Both methods were used to reconstruct the VF by projecting modeled activity back onto the VF. Following a normalization step, these “coverage maps” can be compared to the VF sensitivity plots obtained using perimetry.ResultsWhile both fMRI-based approaches revealed regions of neural activity within the perimetrically “blind” sections of the VF, the MP approach uncovered more voxels in the lesioned hemisphere in which a modest degree of visual sensitivity was retained. Furthermore, MP-based analysis indicated that both early (V1/V2) and extrastriate visual areas contributed equally to the retained sensitivity in both patients and controls.ConclusionIn hemianopic patients, fMRI-based approaches for reconstructing the VF can pick up activity in perimetrically blind regions of the VF. Such regions of the VF may be particularly amenable for rehabilitation to regain visual function. Compared to conventional pRF modeling, MP reveals more voxels with retained visual sensitivity, suggesting it is a more sensitive approach for VF reconstruction.

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Visual Field Reconstruction in Hemianopia Using fMRI Based Mapping Techniques

Bridge

Carvalho

Cornelissen

et al. 2021

Front. Hum. Neurosci.

View full text Add to dashboard Cite

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“…Using a complementary approach, Sanchez-Lopez et al. (2020) have studied the neuroanatomical bases of the unconscious above-chance performance and of the phenomenological aspects that may be associated.…”

Section: Altered Residual Functioning: a Multidimensional Spectrum Of...mentioning

confidence: 99%

“…Finally, the cortical thickness of the intact hemisphere was greater in patients showing above-chance performance than in those at chance. Along those lines, it would be highly interesting to use a similar approach as Sanchez-Lopez and colleagues (2020) and study the neuro-anatomical correlates of different patterns of responses while taking into account both objective and subjective perception in the blind VF using the SAS, as well as factoring in the delay from the lesion acquisition.…”

Section: Altered Residual Functioning: a Multidimensional Spectrum Of...mentioning

confidence: 99%

The nature of blindsight: implications for current theories of consciousness

Derrien

Garric

Sergent

et al. 2022

Neuroscience of Consciousness

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Blindsight regroups the different manifestations of preserved discriminatory visual capacities following the damage to the primary visual cortex. Blindsight types differentially impact objective and subjective perception, patients can report having no visual awareness whilst their behaviour suggests visual processing still occurs at some cortical level. This phenomenon hence presents a unique opportunity to study consciousness and perceptual consciousness, and for this reason, it has had an historical importance for the development of this field of research. From these studies, two main opposing models of the underlying mechanisms have been established: (a) blindsight is perception without consciousness or (b) blindsight is in fact degraded vision, two views that mirror more general theoretical options about whether unconscious cognition truly exists or whether it is only a degraded form of conscious processing. In this article, we want to re-examine this debate in the light of recent advances in the characterization of blindsight and associated phenomena. We first provide an in-depth definition of blindsight and its subtypes, mainly blindsight type I, blindsight type II and the more recently described blindsense. We emphasize the necessity of sensitive and robust methodology to uncover the dissociations between perception and awareness that can be observed in brain-damaged patients with visual field defects at different cognitive levels. We discuss these different profiles of dissociation in the light of both contending models. We propose that the different types of dissociations reveal a pattern of relationship between perception, awareness and metacognition that is actually richer than what is proposed by either of the existing models. Finally, we consider this in the framework of current theories of consciousness and touch on the implications the findings of blindsight have on these.

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“…This in itself underscores the value of additional personalized measurements to characterize the patient-specific visual field loss. Many reports of anatomical lesion definitions of HVFL provide only a cursory outline of the lesion location, pointing to the occipital cortex or the occipital pole (Fujino et al, 1986;Sanchez-Lopez et al, 2020). However, there is a drive for personalized approaches to treatment and constant improvements in imaging technology are likely to facilitate this (Hinman et al, 2016).…”

Section: Perimetry and Anatomical Mrimentioning

confidence: 99%

Linking Multi-Modal MRI to Clinical Measures of Visual Field Loss After Stroke

et al. 2022

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Loss of vision across large parts of the visual field is a common and devastating complication of cerebral strokes. In the clinic, this loss is quantified by measuring the sensitivity threshold across the field of vision using static perimetry. These methods rely on the ability of the patient to report the presence of lights in particular locations. While perimetry provides important information about the intactness of the visual field, the approach has some shortcomings. For example, it cannot distinguish where in the visual pathway the key processing deficit is located. In contrast, brain imaging can provide important information about anatomy, connectivity, and function of the visual pathway following stroke. In particular, functional magnetic resonance imaging (fMRI) and analysis of population receptive fields (pRF) can reveal mismatches between clinical perimetry and maps of cortical areas that still respond to visual stimuli after stroke. Here, we demonstrate how information from different brain imaging modalities—visual field maps derived from fMRI, lesion definitions from anatomical scans, and white matter tracts from diffusion weighted MRI data—provides a more complete picture of vision loss. For any given location in the visual field, the combination of anatomical and functional information can help identify whether vision loss is due to absence of gray matter tissue or likely due to white matter disconnection from other cortical areas. We present a combined imaging acquisition and visual stimulus protocol, together with a description of the analysis methodology, and apply it to datasets from four stroke survivors with homonymous field loss (two with hemianopia, two with quadrantanopia). For researchers trying to understand recovery of vision after stroke and clinicians seeking to stratify patients into different treatment pathways, this approach combines multiple, convergent sources of data to characterize the extent of the stroke damage. We show that such an approach gives a more comprehensive measure of residual visual capacity—in two particular respects: which locations in the visual field should be targeted and what kind of visual attributes are most suited for rehabilitation.

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What cortical areas are responsible for blindsight in hemianopic patients?

Cited by 11 publications

References 74 publications

Visual Field Reconstruction in Hemianopia Using fMRI Based Mapping Techniques

Visual Field Reconstruction in Hemianopia Using fMRI Based Mapping Techniques

The nature of blindsight: implications for current theories of consciousness

Linking Multi-Modal MRI to Clinical Measures of Visual Field Loss After Stroke

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