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Derrien D, Garric C, Sergent C, Chokron S. The nature of blindsight: implications for current theories of consciousness. Neurosci Conscious 2022; 2022:niab043. [PMID: 35237447 PMCID: PMC8884361 DOI: 10.1093/nc/niab043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Revised: 11/08/2021] [Accepted: 01/13/2022] [Indexed: 11/16/2022] Open
Abstract
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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Affiliation(s)
- Diane Derrien
- Integrative Neuroscience and Cognition Center, UMR 8002, CNRS & Université de Paris, Paris 75006, France
- Institut de Neuropsychologie, Neurovision, NeuroCognition, Fondation Ophtalmologique Rothschild, Paris 75019, France
| | - Clémentine Garric
- Inserm, CHU Lille, U1172—LilNCog (JPARC)—Lille Neuroscience & Cognition, University of Lille, Lille 59000, France
| | - Claire Sergent
- Integrative Neuroscience and Cognition Center, UMR 8002, CNRS & Université de Paris, Paris 75006, France
| | - Sylvie Chokron
- Integrative Neuroscience and Cognition Center, UMR 8002, CNRS & Université de Paris, Paris 75006, France
- Institut de Neuropsychologie, Neurovision, NeuroCognition, Fondation Ophtalmologique Rothschild, Paris 75019, France
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2
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Linton P. V1 as an egocentric cognitive map. Neurosci Conscious 2021; 2021:niab017. [PMID: 34532068 PMCID: PMC8439394 DOI: 10.1093/nc/niab017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 05/21/2021] [Accepted: 06/08/2021] [Indexed: 01/20/2023] Open
Abstract
We typically distinguish between V1 as an egocentric perceptual map and the hippocampus as an allocentric cognitive map. In this article, we argue that V1 also functions as a post-perceptual egocentric cognitive map. We argue that three well-documented functions of V1, namely (i) the estimation of distance, (ii) the estimation of size, and (iii) multisensory integration, are better understood as post-perceptual cognitive inferences. This argument has two important implications. First, we argue that V1 must function as the neural correlates of the visual perception/cognition distinction and suggest how this can be accommodated by V1's laminar structure. Second, we use this insight to propose a low-level account of visual consciousness in contrast to mid-level accounts (recurrent processing theory; integrated information theory) and higher-level accounts (higher-order thought; global workspace theory). Detection thresholds have been traditionally used to rule out such an approach, but we explain why it is a mistake to equate visibility (and therefore the presence/absence of visual experience) with detection thresholds.
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Affiliation(s)
- Paul Linton
- Centre for Applied Vision Research, City, University of London, Northampton Square, London EC1V 0HB, UK
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3
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Ajina S, Jünemann K, Sahraie A, Bridge H. Increased Visual Sensitivity and Occipital Activity in Patients With Hemianopia Following Vision Rehabilitation. J Neurosci 2021; 41:5994-6005. [PMID: 34035137 PMCID: PMC8276743 DOI: 10.1523/jneurosci.2790-20.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 02/22/2021] [Accepted: 03/26/2021] [Indexed: 11/21/2022] Open
Abstract
Hemianopia, loss of vision in half of the visual field, results from damage to the visual pathway posterior to the optic chiasm. Despite negative effects on quality of life, few rehabilitation options are currently available. Recently, several long-term training programs have been developed that show visual improvement within the blind field, although little is known of the underlying neural changes. Here, we have investigated functional and structural changes in the brain associated with visual rehabilitation. Seven human participants with occipital lobe damage enrolled in a visual training program to distinguish which of two intervals contained a drifting Gabor patch presented within the blind field. Participants performed ∼25 min of training each day for 3-6 months and undertook psychophysical tests and a magnetic resonance imaging scan before and after training. A control group undertook psychophysical tests before and after an equivalent period without training. Participants who were not at ceiling on baseline tests showed on average 9.6% improvement in Gabor detection, 8.3% in detection of moving dots, and 9.9% improvement in direction discrimination after training. Importantly, psychophysical improvement only correlated with improvement in Humphrey perimetry in the trained region of the visual field. Whole-brain analysis showed an increased neural response to moving stimuli in the blind visual field in motion area V5/hMT. Using a region-of-interest approach, training had a significant effect on the blood oxygenation level-dependent signal compared with baseline. Moreover, baseline V5/hMT activity was correlated to the amount of improvement in visual sensitivity using psychophysical and perimetry tests. This study, identifying a critical role for V5/hMT in boosting visual function, may allow us to determine which patients may benefit most from training and design adjunct interventions to increase training effects.SIGNIFICANCE STATEMENT Homonymous visual field loss is a common consequence of brain injury and is estimated to affect more than 230,000 people in the United Kingdom. Despite its high prevalence and well-described impact on quality of life, treatments to improve visual sensitivity remain experimental, and deficits are considered permanent after 6 months. Our study shows that behavioral changes following vision rehabilitation are associated with enhanced visually-evoked occipital activity to stimuli in the blind visual field. Unlike previous behavioral studies, we observe clinical changes that are specific to the trained region of vision. This lends significant weight to such training paradigms and offers a mechanism by which visual function can be improved despite damage to the primary visual pathway.
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Affiliation(s)
- Sara Ajina
- Department of Neurorehabilitation and Therapy Services, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, United Kingdom
- Wellcome Centre for Integrative Neuroimaging, Functional MRI of the Brain, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, United Kingdom
| | - Kristin Jünemann
- Wellcome Centre for Integrative Neuroimaging, Functional MRI of the Brain, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, United Kingdom
- Division of Clinical Psychology and Sexual Medicine, Department of Psychiatry, Social Psychiatry and Psychotherapy, Hannover Medical School, 30635 Hannover, Germany
| | - Arash Sahraie
- School of Psychology, University of Aberdeen, Kings College, Old Aberdeen AB24 3FX, United Kingdom
| | - Holly Bridge
- Wellcome Centre for Integrative Neuroimaging, Functional MRI of the Brain, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, United Kingdom
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4
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Elshout JA, Bergsma DP, van den Berg AV, Haak KV. Functional MRI of visual cortex predicts training-induced recovery in stroke patients with homonymous visual field defects. NEUROIMAGE-CLINICAL 2021; 31:102703. [PMID: 34062384 PMCID: PMC8173295 DOI: 10.1016/j.nicl.2021.102703] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2020] [Revised: 05/17/2021] [Accepted: 05/18/2021] [Indexed: 12/28/2022]
Abstract
Damage to the visual brain typically leads to vision loss. Vision loss may be partially recovered with visual restitution training (VRT) Cortical responses to visual stimulation do not always lead to visual awareness. A mismatch between Humphrey and neural perimetry predicts training outcome. This finding has important implications for better rehabilitation strategies.
Post-chiasmatic damage to the visual system leads to homonymous visual field defects (HVDs), which can severely interfere with daily life activities. Visual Restitution Training (VRT) can recover parts of the affected visual field in patients with chronic HVDs, but training outcome is variable. An untested hypothesis suggests that training potential may be largest in regions with ‘neural reserve’, where cortical responses to visual stimulation do not lead to visual awareness as assessed by Humphrey perimetry—a standard behavioural visual field test. Here, we tested this hypothesis in a sample of twenty-seven hemianopic stroke patients, who participated in an assiduous 80-hour VRT program. For each patient, we collected Humphrey perimetry and wide-field fMRI-based retinotopic mapping data prior to training. In addition, we used Goal Attainment Scaling to assess whether personal activities in daily living improved. After training, we assessed with a second Humphrey perimetry measurement whether the visual field was improved and evaluated which personal goals were attained. Confirming the hypothesis, we found significantly larger improvements of visual sensitivity at field locations with neural reserve. These visual field improvements implicated both regions in primary visual cortex and higher order visual areas. In addition, improvement in daily life activities correlated with the extent of visual field enlargement. Our findings are an important step toward understanding the mechanisms of visual restitution as well as predicting training efficacy in stroke patients with chronic hemianopia.
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Affiliation(s)
- J A Elshout
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
| | - D P Bergsma
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
| | - A V van den Berg
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
| | - K V Haak
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands.
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5
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LeDoux JE, Michel M, Lau H. A little history goes a long way toward understanding why we study consciousness the way we do today. Proc Natl Acad Sci U S A 2020; 117:6976-6984. [PMID: 32170012 PMCID: PMC7132279 DOI: 10.1073/pnas.1921623117] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Consciousness is currently a thriving area of research in psychology and neuroscience. While this is often attributed to events that took place in the early 1990s, consciousness studies today are a continuation of research that started in the late 19th century and that continued throughout the 20th century. From the beginning, the effort built on studies of animals to reveal basic principles of brain organization and function, and of human patients to gain clues about consciousness itself. Particularly important and our focus here is research in the 1950s, 1960s, and 1970s involving three groups of patients-amnesia, split brain, and blindsight. Across all three groups, a similar pattern of results was found-the patients could respond appropriately to stimuli that they denied seeing (or in the case of amnesiacs, having seen before). These studies paved the way for the current wave of research on consciousness. The field is, in fact, still grappling with the implications of the findings showing that the ability to consciously know and report the identity of a visual stimulus can be dissociated in the brain from the mechanisms that underlie the ability to behave in a meaningful way to the same stimulus.
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Affiliation(s)
- Joseph E LeDoux
- Center for Neural Science, New York University, New York, NY 10003;
- Department of Psychology, New York University, New York, NY 10003
- Department of Psychiatry, New York University Langone Medical School, New York, NY 10003
- Department of Child and Adolescent Psychiatry, New York University Langone Medical School, New York, NY 10003
- Emotional Brain Institute, Nathan Kline Institute, Orangeburg, NY 10962
| | - Matthias Michel
- Consciousness, Cognition & Computation Group, Université Libre de Bruxelles, B1050 Bruxelles, Belgium
- Center for Mind, Brain and Consciousness, New York University, New York, NY 10003
| | - Hakwan Lau
- Department of Psychology, University of California, Los Angeles, CA 90095
- Brain Research Institute, University of California, Los Angeles, CA 90095
- Department of Psychology, University of Hong Kong, Hong Kong
- State Key Laboratory of Brain and Cognitive Sciences, University of Hong Kong, Hong Kong
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6
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Mazzi C, Savazzi S, Silvanto J. On the “blindness” of blindsight: What is the evidence for phenomenal awareness in the absence of primary visual cortex (V1)? Neuropsychologia 2019; 128:103-108. [DOI: 10.1016/j.neuropsychologia.2017.10.029] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 10/17/2017] [Accepted: 10/23/2017] [Indexed: 10/18/2022]
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7
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Does TMS on V3 block conscious visual perception? Neuropsychologia 2019; 128:223-231. [DOI: 10.1016/j.neuropsychologia.2017.11.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 10/07/2017] [Accepted: 11/10/2017] [Indexed: 11/22/2022]
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8
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Mazzi C, Savazzi S. The Glamor of Old-Style Single-Case Studies in the Neuroimaging Era: Insights From a Patient With Hemianopia. Front Psychol 2019; 10:965. [PMID: 31114532 PMCID: PMC6502964 DOI: 10.3389/fpsyg.2019.00965] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2018] [Accepted: 04/11/2019] [Indexed: 11/23/2022] Open
Affiliation(s)
- Chiara Mazzi
- Perception and Awareness (PandA) Lab, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.,National Institute of Neuroscience, Verona, Italy
| | - Silvia Savazzi
- Perception and Awareness (PandA) Lab, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.,National Institute of Neuroscience, Verona, Italy
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9
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Chabanat E, Jacquin-Courtois S, Havé L, Kihoulou C, Tilikete C, Mauguière F, Rheims S, Rossetti Y. Can you guess the colour of this moving object? A dissociation between colour and motion in blindsight. Neuropsychologia 2018; 128:204-208. [PMID: 30102905 DOI: 10.1016/j.neuropsychologia.2018.08.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 06/01/2018] [Accepted: 08/08/2018] [Indexed: 10/28/2022]
Abstract
Blindsight has been primarily and extensively studied by Lawrence Weiskrantz. Residual visual abilities following a hemispheric lesion leading to homonymous hemianopia encompass a variety of visual-perceptual and visuo-motor functions. Attention blindsight produces the more salient subjective experiences, especially for motion (Riddoch phenomenon). Action blindsight illustrates visuo-motor abilities despite the patients' feeling that they produce random movements. Perception blindsight seems to be the weakest residual function observed in blindsight, e.g. for wavelength sensitivity. Discriminating motion produced by isoluminant colours does not give rise to blindsight for motion but the outcome of the reciprocal test is not known. Here we tested whether moving stimuli could give rise to colour discrimination in a patient with homonymous hemianopia. It was found that even though the patient exhibited nearly perfect performances for motion direction discrimination his colour discrimination for the same moving stimulus remained at chance level. It is concluded that easily discriminated moving stimuli do not give rise to colour discrimination and implications for the 3 levels of blindsight taxonomy are discussed.
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Affiliation(s)
- E Chabanat
- Inserm UMR-S 1028, CNRS UMR 5292, ImpAct, Centre de Recherche en Neurosciences de Lyon, France; Université de Lyon, Université Claude Bernard Lyon 1, France.
| | - S Jacquin-Courtois
- Inserm UMR-S 1028, CNRS UMR 5292, ImpAct, Centre de Recherche en Neurosciences de Lyon, France; Université de Lyon, Université Claude Bernard Lyon 1, France; Service de rééducation neurologique, Pavillon Bourret, Hôpital Henry-Gabrielle, Hospices Civils de Lyon, 20, route de Vourles, Saint-Genis-Laval, France; Plate-forme 'Mouvement et Handicap', Hôpital Henry-Gabrielle et Hôpital Neurologique Neurologique Pierre Wertheimer, Hospices Civils de Lyon, 20, route de Vourles, Saint-Genis-Laval, France.
| | - L Havé
- Inserm UMR-S 1028, CNRS UMR 5292, ImpAct, Centre de Recherche en Neurosciences de Lyon, France; Université de Lyon, Université Claude Bernard Lyon 1, France.
| | - C Kihoulou
- Inserm UMR-S 1028, CNRS UMR 5292, ImpAct, Centre de Recherche en Neurosciences de Lyon, France
| | - C Tilikete
- Inserm UMR-S 1028, CNRS UMR 5292, ImpAct, Centre de Recherche en Neurosciences de Lyon, France; Université de Lyon, Université Claude Bernard Lyon 1, France; Service de Neuro-Cognition et Neuro-Ophtalmologie, Hôpital Neurologique Pierre Wertheimer, Hospices Civils de Lyon, 59 boulevard Pinel, 69677 Bron Cedex, France.
| | - F Mauguière
- Université de Lyon, Université Claude Bernard Lyon 1, France; Département de Neurologie Fonctionnelle et Epileptologie, Hôpital Neurologique Pierre Wertheimer, Hospices Civils de Lyon, France; Inserm UMR-S 1028, CNRS UMR 5292, NeuroPain, Centre de Recherche en Neurosciences de Lyon, France.
| | - S Rheims
- Université de Lyon, Université Claude Bernard Lyon 1, France; Département de Neurologie Fonctionnelle et Epileptologie, Hôpital Neurologique Pierre Wertheimer, Hospices Civils de Lyon, France; Inserm UMR-S 1028, CNRS UMR 5292, TIGER, Centre de Recherche en Neurosciences de Lyon, France.
| | - Y Rossetti
- Inserm UMR-S 1028, CNRS UMR 5292, ImpAct, Centre de Recherche en Neurosciences de Lyon, France; Université de Lyon, Université Claude Bernard Lyon 1, France; Service de rééducation neurologique, Pavillon Bourret, Hôpital Henry-Gabrielle, Hospices Civils de Lyon, 20, route de Vourles, Saint-Genis-Laval, France; Plate-forme 'Mouvement et Handicap', Hôpital Henry-Gabrielle et Hôpital Neurologique Neurologique Pierre Wertheimer, Hospices Civils de Lyon, 20, route de Vourles, Saint-Genis-Laval, France.
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10
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Zhan M, Engelen T, de Gelder B. Influence of continuous flash suppression mask frequency on stimulus visibility. Neuropsychologia 2018; 128:65-72. [PMID: 29763616 DOI: 10.1016/j.neuropsychologia.2018.05.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 05/09/2018] [Accepted: 05/11/2018] [Indexed: 12/16/2022]
Abstract
The continuous flash suppression (CFS) paradigm is increasingly used in consciousness research, but its mechanisms are still not fully understood. To better understand its temporal properties, we presented the CFS masks at 9 frequencies, and examined their influence on stimuli visibility, while taking into account the inter-individual variability and the change of CFS suppression as the experiment progressed. The frequencies consisted of fundamental frequencies of 3, 4 and 5 Hz, and their 2nd and 3rd harmonics, which included the 10 Hz frequency typically used in most of the CFS studies. We found that the suppression of stimulus awareness was stronger under 4, 6 and 8 Hz than 10 Hz. After controlling for inter-individual variability with mixed-effects analysis, we found that the number of seen trials was lower for the 4 Hz-basis frequencies than the 5 Hz ones, and was lower for the 2nd than 3rd harmonic. We propose that this may be caused by an interaction between the CFS masks and the ongoing sampling of the attentional mechanism. Examining individual data, we also found a habituation effect that the participants saw significantly more stimuli as the experiment progressed. Our results suggest that these factors need to be taken care of in future CFS studies in order to achieve optimal visual awareness suppression and ensure the generalizability of results.
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Affiliation(s)
- Minye Zhan
- Faculty of Psychology and Neuroscience, Department of Cognitive Neurosciences, Maastricht University, 6229EV Maastricht, The Netherlands
| | - Tahnée Engelen
- Faculty of Psychology and Neuroscience, Department of Cognitive Neurosciences, Maastricht University, 6229EV Maastricht, The Netherlands
| | - Beatrice de Gelder
- Faculty of Psychology and Neuroscience, Department of Cognitive Neurosciences, Maastricht University, 6229EV Maastricht, The Netherlands; Department of Computer Science, University College London, WC1E 6BT, UK.
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11
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Organization of area hV5/MT+ in subjects with homonymous visual field defects. Neuroimage 2018; 190:254-268. [PMID: 29627591 DOI: 10.1016/j.neuroimage.2018.03.062] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2018] [Revised: 03/05/2018] [Accepted: 03/26/2018] [Indexed: 11/21/2022] Open
Abstract
Damage to the primary visual cortex (V1) leads to a visual field loss (scotoma) in the retinotopically corresponding part of the visual field. Nonetheless, a small amount of residual visual sensitivity persists within the blind field. This residual capacity has been linked to activity observed in the middle temporal area complex (V5/MT+). However, it remains unknown whether the organization of hV5/MT+ changes following early visual cortical lesions. We studied the organization of area hV5/MT+ of five patients with dense homonymous defects in a quadrant of the visual field as a result of partial V1+ or optic radiation lesions. To do so, we developed a new method, which models the boundaries of population receptive fields directly from the BOLD signal of each voxel in the visual cortex. We found responses in hV5/MT+ arising inside the scotoma for all patients and identified two possible sources of activation: 1) responses might originate from partially lesioned parts of area V1 corresponding to the scotoma, and 2) responses can also originate independent of area V1 input suggesting the existence of functional V1-bypassing pathways. Apparently, visually driven activity observed in hV5/MT+ is not sufficient to mediate conscious vision. More surprisingly, visually driven activity in corresponding regions of V1 and early extrastriate areas including hV5/MT+ did not guarantee visual perception in the group of patients with post-geniculate lesions that we examined. This suggests that the fine coordination of visual activity patterns across visual areas may be an important determinant of whether visual perception persists following visual cortical lesions.
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12
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Abstract
Much remains to be understood about visual system malfunction following injury. The resulting deficits range from dense, visual field scotomas to mild dysfunction of visual perception. Despite the predictive value of anatomical localization studies, much patient-to-patient variability remains regarding (a) perceptual abilities following injury and (b) the capacity of individual patients for visual rehabilitation. Visual field perimetry is used to characterize the visual field deficits that result from visual system injury. However, standard perimetry mapping does not always precisely correspond to underlying anatomical or functional deficits. Functional magnetic resonance imaging can be used to probe the function of surviving visual circuits, allowing us to classify better how the pattern of injury relates to residual visual perception. Identifying pathways that are potentially modifiable by training may guide the development of improved strategies for visual rehabilitation. This review discusses primary visual cortex lesions, which cause dense contralateral scotomas.
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Affiliation(s)
- Stelios M Smirnakis
- Department of Neurology, Brigham and Women's Hospital, Boston, Massachusetts 02115.,Department of Neurology, Jamaica Plain Campus, Veterans Administration Boston Healthcare System, Boston, Massachusetts 02130.,Harvard Medical School, Boston, Massachusetts 02115;
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13
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Ajina S, Bridge H. Subcortical pathways to extrastriate visual cortex underlie residual vision following bilateral damage to V1. Neuropsychologia 2018; 128:140-149. [PMID: 29320715 PMCID: PMC6562274 DOI: 10.1016/j.neuropsychologia.2018.01.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 12/18/2017] [Accepted: 01/05/2018] [Indexed: 11/29/2022]
Abstract
Residual vision, or blindsight, following damage to the primary visual cortex (V1) has been investigated for almost half a century. While there have been many studies of patients with unilateral damage to V1, far fewer have examined bilateral damage, mainly due to the rarity of such patients. Here we re-examine the residual visual function and underlying pathways of previously studied patient SBR who, as a young adult, suffered bilateral damage restricted to V1 which rendered him cortically blind. While earlier work compared his visual cortex to healthy, sighted participants, here we consider how his visual responses and connections compare to patients with unilateral damage to V1 in addition to sighted participants. Detection of drifting Gabor patches of different contrasts (1%, 5%, 10%, 50% and 100%) was tested in SBR and a group of eight patients with unilateral damage to V1. Performance was compared to the neural activation in motion area hMT+ measured using functional magnetic resonance imaging. Diffusion tractography was also used to determine the white matter microstructure of the visual pathways in all participants. Like the patients with unilateral damage, patient SBR showed increased % BOLD signal change to the high contrast stimuli that he could detect compared to the lower contrast stimuli that were not detectable. Diffusion tractography suggests this information is conveyed by a direct pathway between the lateral geniculate nucleus (LGN) and hMT+ since this pathway had microstructure that was comparable to the healthy control group. In contrast, the pathway between LGN and V1 had reduced integrity compared to controls. A further finding of note was that, unlike control participants, SBR showed similar patterns of contralateral and ipsilateral activity in hMT+, in addition to healthy white matter microstructure in the tract connecting hMT+ between the two hemispheres. This raises the possibility of increased connectivity between the two hemispheres in the absence of V1 input. In conclusion, the pattern of visual function and anatomy in bilateral cortical damage is comparable to that seen in a group of patients with unilateral damage. Thus, while the intact hemisphere may play a role in residual vision in patients with unilateral damage, its influence is not evident with the methodology employed here. Bilaterally hemianopic patient SBR has neural patterns like unilateral patients. hMT+ activity increases with stimulus contrast and better stimulus detection. Like in unilateral patients, the pathway between LGN and hMT+ is intact in SBR.
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Affiliation(s)
- Sara Ajina
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, UK
| | - Holly Bridge
- Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, UK.
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14
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Intact hemisphere and corpus callosum compensate for visuomotor functions after early visual cortex damage. Proc Natl Acad Sci U S A 2017; 114:E10475-E10483. [PMID: 29133428 PMCID: PMC5715784 DOI: 10.1073/pnas.1714801114] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Unilateral damage to the primary visual cortex (V1) leads to clinical blindness in the opposite visual hemifield, yet nonconscious ability to transform unseen visual input into motor output can be retained, a condition known as "blindsight." Here we combined psychophysics, functional magnetic resonance imaging, and tractography to investigate the functional and structural properties that enable the developing brain to partly overcome the effects of early V1 lesion in one blindsight patient. Visual stimuli appeared in either the intact or blind hemifield and simple responses were given with either the left or right hand, thereby creating conditions where visual input and motor output involve the same or opposite hemisphere. When the V1-damaged hemisphere was challenged by incoming visual stimuli, or controlled manual responses to these unseen stimuli, the corpus callosum (CC) dynamically recruited areas in the visual dorsal stream and premotor cortex of the intact hemisphere to compensate for altered visuomotor functions. These compensatory changes in functional brain activity were paralleled by increased connections in posterior regions of the CC, where fibers connecting homologous areas of the parietal cortex course.
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Hadid V, Lepore F. From Cortical Blindness to Conscious Visual Perception: Theories on Neuronal Networks and Visual Training Strategies. Front Syst Neurosci 2017; 11:64. [PMID: 28912694 PMCID: PMC5583595 DOI: 10.3389/fnsys.2017.00064] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Accepted: 08/11/2017] [Indexed: 12/13/2022] Open
Abstract
Homonymous hemianopia (HH) is the most common cortical visual impairment leading to blindness in the contralateral hemifield. It is associated with many inconveniences and daily restrictions such as exploration and visual orientation difficulties. However, patients with HH can preserve the remarkable ability to unconsciously perceive visual stimuli presented in their blindfield, a phenomenon known as blindsight. Unfortunately, the nature of this captivating residual ability is still misunderstood and the rehabilitation strategies in terms of visual training have been insufficiently exploited. This article discusses type I and type II blindsight in a neuronal framework of altered global workspace, resulting from inefficient perception, attention and conscious networks. To enhance synchronization and create global availability for residual abilities to reach visual consciousness, rehabilitation tools need to stimulate subcortical extrastriate pathways through V5/MT. Multisensory bottom-up compensation combined with top-down restitution training could target pre-existing and new neuronal mechanisms to recreate a framework for potential functionality.
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Affiliation(s)
- Vanessa Hadid
- Département de Sciences Biomédicales, Université de MontréalMontréal, QC, Canada
| | - Franco Lepore
- Centre de Recherche en Neuropsychologie et Cognition (CERNEC), Département de Psychologie, Université de MontréalMontréal, QC, Canada
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16
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Bollini A, Sanchez-Lopez J, Savazzi S, Marzi CA. Lights from the Dark: Neural Responses from a Blind Visual Hemifield. Front Neurosci 2017; 11:290. [PMID: 28588445 PMCID: PMC5440595 DOI: 10.3389/fnins.2017.00290] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 05/08/2017] [Indexed: 12/24/2022] Open
Abstract
Here we present evidence that a hemianopic patient with a lesion of the left primary visual cortex (V1) showed an unconscious above-chance orientation discrimination with moving rather than static visual gratings presented to the blind hemifield. The patient did not report any perceptual experience of the stimulus features except for a feeling that something appeared in the blind hemifield. Interestingly, in the lesioned left hemisphere, following stimulus presentation to the blind hemifield, we found an event-related potential (ERP) N1 component at a post-stimulus onset latency of 180-260 ms and a source generator in the left BA 19. In contrast, we did not find evidence of the early visual components C1 and P1 and of the later component P300. A positive component (P2a) was recorded between 250 and 320 ms after stimulus onset frontally in both hemispheres. Finally, in the time range 320-440 ms there was a negative peak in right posterior electrodes that was present only for the moving condition. In sum, there were two noteworthy results: Behaviorally, we found evidence of above chance unconscious (blindsight) orientation discrimination with moving but not static stimuli. Physiologically, in contrast to previous studies, we found reliable ERP components elicited by stimuli presented to the blind hemifield at various electrode locations and latencies that are likely to index either the perceptual report of the patient (N1 and P2a) or, the above-chance unconscious performance with moving stimuli as is the case of the posterior ERP negative component. This late component can be considered as the neural correlate of a kind of blindsight enabling feature discrimination only when stimuli are moving and that is subserved by the intact right hemisphere through interhemispheric transfer.
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Affiliation(s)
- Alice Bollini
- Department of Neuroscience, Biomedicine and Movement, University of VeronaVerona, Italy
| | - Javier Sanchez-Lopez
- Department of Neuroscience, Biomedicine and Movement, University of VeronaVerona, Italy.,National Institute of NeuroscienceVerona, Italy
| | - Silvia Savazzi
- Department of Neuroscience, Biomedicine and Movement, University of VeronaVerona, Italy.,National Institute of NeuroscienceVerona, Italy
| | - Carlo A Marzi
- Department of Neuroscience, Biomedicine and Movement, University of VeronaVerona, Italy.,National Institute of NeuroscienceVerona, Italy
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17
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Visual deprivation selectively reshapes the intrinsic functional architecture of the anterior insula subregions. Sci Rep 2017; 7:45675. [PMID: 28358391 PMCID: PMC5372462 DOI: 10.1038/srep45675] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 02/28/2017] [Indexed: 12/17/2022] Open
Abstract
The anterior insula (AI) is the core hub of salience network that serves to identify the most relevant stimuli among vast sensory inputs and forward them to higher cognitive regions to guide behaviour. As blind subjects were usually reported with changed perceptive abilities for salient non-visual stimuli, we hypothesized that the resting-state functional network of the AI is selectively reorganized after visual deprivation. The resting-state functional connectivity (FC) of the bilateral dorsal and ventral AI was calculated for twenty congenitally blind (CB), 27 early blind (EB), 44 late blind (LB) individuals and 50 sighted controls (SCs). The FCs of the dorsal AI were strengthened with the dorsal visual stream, while weakened with the ventral visual stream in the blind than the SCs; in contrast, the FCs of the ventral AI of the blind was strengthened with the ventral visual stream. Furthermore, these strengthened FCs of both the dorsal and ventral AI were partially negatively associated with the onset age of blindness. Our result indicates two parallel pathways that selectively transfer non-visual salient information between the deprived “visual” cortex and salience network in blind subjects.
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18
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Mazzi C, Mazzeo G, Savazzi S. Markers of TMS-evoked visual conscious experience in a patient with altitudinal hemianopia. Conscious Cogn 2017; 54:143-154. [PMID: 28215463 DOI: 10.1016/j.concog.2017.01.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/24/2017] [Accepted: 01/24/2017] [Indexed: 11/29/2022]
Abstract
Transcranial magnetic stimulation (TMS) of the occipital and parietal cortices can induce phosphenes, i.e. visual sensations of light without light entering the eyes. In this paper, we adopted a TMS-EEG interactive co-registration approach with a patient (AM) showing altitudinal hemianopia. Occipital and parietal cortices in both hemispheres were stimulated while concurrently recording EEG signal. Results showed that, for all sites, neural activity differentially encoding for the presence vs. absence of a conscious experience could be found in a cluster of electrodes close to the stimulation site at an early (70ms) time-period after TMS. The present data indicate that both occipital and parietal sites are independent early gatekeepers of perceptual awareness, thus, in line with evidence in favor of early correlates of perceptual awareness. Moreover, these data support the valuable contribution of the TMS-EEG approach in patients with visual field defects to investigate the neural processes responsible for perceptual awareness.
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Affiliation(s)
- Chiara Mazzi
- Perception and Awareness (PandA) Laboratory, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy; National Institute of Neuroscience, Verona, Italy
| | - Gaetano Mazzeo
- Perception and Awareness (PandA) Laboratory, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy; National Institute of Neuroscience, Verona, Italy
| | - Silvia Savazzi
- Perception and Awareness (PandA) Laboratory, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy; National Institute of Neuroscience, Verona, Italy.
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19
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Ma G, Yang D, Qin W, Liu Y, Jiang T, Yu C. Enhanced Functional Coupling of Hippocampal Sub-regions in Congenitally and Late Blind Subjects. Front Neurosci 2017; 10:612. [PMID: 28119560 PMCID: PMC5222804 DOI: 10.3389/fnins.2016.00612] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 12/26/2016] [Indexed: 11/13/2022] Open
Abstract
The hippocampus has exhibited navigation-related changes in volume and activity after visual deprivation; however, the resting-state functional connectivity (rsFC) changes of the hippocampus in the blind remains unknown. In this study, we focused on sub-region-specific rsFC changes of the hippocampus and their association with the onset age of blindness. The rsFC patterns of the hippocampal sub-regions (head, body and tail) were compared among 20 congenitally blind (CB), 42 late blind (LB), and 50 sighted controls (SC). Compared with the SC, both the CB and the LB showed increased hippocampal rsFCs with the posterior cingulate cortex, angular gyrus, parieto-occpital sulcus, middle occipito-temporal conjunction, inferior temporal gyrus, orbital frontal cortex, and middle frontal gyrus. In the blind subjects, the hippocampal tail had more extensive rsFC changes than the anterior hippocampus (body and head). The CB and the LB had similar changes in hippocampal rsFC. These altered rsFCs of the hippocampal sub-regions were neither correlated with onset age in the LB nor the duration of blindness in CB or LB subjects. The increased coupling of the hippocampal intrinsic functional network may reflect enhanced loading of the hippocampal-related networks for non-visual memory processing. Furthermore, the similar changes of hippocampal rsFCs between the CB and the LB suggests an experience-dependent rather than a developmental-dependent plasticity of the hippocampal intrinsic functional network.
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Affiliation(s)
- Guangyang Ma
- Department of Radiology and Tianjin Key Laboratory of Functional Imaging, Tianjin Medical University General HospitalTianjin, China; Key Laboratory of Hormones and Development (Ministry of Health), Tianjin Key Laboratory of Metabolic Diseases, Tianjin Metabolic Diseases Hospital & Tianjin Institute of Endocrinology, Tianjin Medical UniversityTianjin, China
| | - Dan Yang
- Department of Radiology and Tianjin Key Laboratory of Functional Imaging, Tianjin Medical University General HospitalTianjin, China; Tianjin Central Hospital of Gynecology ObstetricsTianjin, China
| | - Wen Qin
- Department of Radiology and Tianjin Key Laboratory of Functional Imaging, Tianjin Medical University General Hospital Tianjin, China
| | - Yong Liu
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences Beijing, China
| | - Tianzi Jiang
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences Beijing, China
| | - Chunshui Yu
- Department of Radiology and Tianjin Key Laboratory of Functional Imaging, Tianjin Medical University General Hospital Tianjin, China
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20
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Losey DM, Stocco A, Abernethy JA, Rao RPN. Navigating a 2D Virtual World Using Direct Brain Stimulation. Front Robot AI 2016. [DOI: 10.3389/frobt.2016.00072] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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21
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Ajina S, Bridge H. Blindsight and Unconscious Vision: What They Teach Us about the Human Visual System. Neuroscientist 2016; 23:529-541. [PMID: 27777337 DOI: 10.1177/1073858416673817] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Damage to the primary visual cortex removes the major input from the eyes to the brain, causing significant visual loss as patients are unable to perceive the side of the world contralateral to the damage. Some patients, however, retain the ability to detect visual information within this blind region; this is known as blindsight. By studying the visual pathways that underlie this residual vision in patients, we can uncover additional aspects of the human visual system that likely contribute to normal visual function but cannot be revealed under physiological conditions. In this review, we discuss the residual abilities and neural activity that have been described in blindsight and the implications of these findings for understanding the intact system.
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Affiliation(s)
- Sara Ajina
- 1 Oxford Centre for Functional MRI of the Brain (FMRIB), Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Holly Bridge
- 1 Oxford Centre for Functional MRI of the Brain (FMRIB), Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
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22
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Elshout JA, van Asten F, Hoyng CB, Bergsma DP, van den Berg AV. Visual Rehabilitation in Chronic Cerebral Blindness: A Randomized Controlled Crossover Study. Front Neurol 2016; 7:92. [PMID: 27379011 PMCID: PMC4911356 DOI: 10.3389/fneur.2016.00092] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 06/03/2016] [Indexed: 01/22/2023] Open
Abstract
The treatment of patients suffering from cerebral blindness following stroke is a topic of much recent interest. Several types of treatment are under investigation, such as substitution with prisms and compensation training of saccades. A third approach, aimed at vision restitution is controversial, as a proper controlled study design is missing. In the current study, 27 chronic stroke patients with homonymous visual field defects were trained at home with a visual training device. We used a discrimination task for two types of stimuli: a static point stimulus and a new optic flow-discontinuity stimulus. Using a randomized controlled crossover design, each patient received two successive training rounds, one with high contrast stimuli in their affected hemifield (test) and one round with low-contrast stimuli in their intact hemifield (control). Goldmann and Humphrey perimetry were performed at the start of the study and following each training round. In addition, reading performance was measured. Goldmann perimetry revealed a statistically significant reduction of the visual field defect after the test training, but not after the control training or after no intervention. For both training rounds combined, Humphrey perimetry revealed that the effect of a directed training (sensitivity change in trained hemifield) exceeded that of an undirected training (sensitivity change in untrained hemifield). The interaction between trained and tested hemifield was just above the threshold of significance (p = 0.058). Interestingly, reduction of the field defect assessed by Goldmann perimetry increases with the difference between defect size as measured by Humphrey and Goldmann perimetry prior to training. Moreover, improvement of visual sensitivity measured by Humphrey perimetry increases with the fraction of non-responsive elements (i.e., more relative field loss) in Humphrey perimetry prior to training. Reading speed revealed a significant improvement after training. Our findings demonstrate that our training can result in reduction of the visual field. Improved reading performance after defect training further supports the significance of our training for improvement in daily life activities.
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Affiliation(s)
- Joris A Elshout
- Section of Biophysics, Department of Cognitive Neuroscience, Donders Centre for Neuroscience, Donders Institute for Brain, Cognition, and Behaviour, Radboud University Medical Centre , Nijmegen , Netherlands
| | - Freekje van Asten
- Department of Ophthalmology, Radboud University Medical Center , Nijmegen , Netherlands
| | - Carel B Hoyng
- Department of Ophthalmology, Radboud University Medical Center , Nijmegen , Netherlands
| | - Douwe P Bergsma
- Section of Biophysics, Department of Cognitive Neuroscience, Donders Centre for Neuroscience, Donders Institute for Brain, Cognition, and Behaviour, Radboud University Medical Centre , Nijmegen , Netherlands
| | - Albert V van den Berg
- Section of Biophysics, Department of Cognitive Neuroscience, Donders Centre for Neuroscience, Donders Institute for Brain, Cognition, and Behaviour, Radboud University Medical Centre , Nijmegen , Netherlands
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23
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Mather G, Battaglini L, Campana G. TMS reveals flexible use of form and motion cues in biological motion perception. Neuropsychologia 2016; 84:193-7. [PMID: 26916969 DOI: 10.1016/j.neuropsychologia.2016.02.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 02/01/2016] [Accepted: 02/21/2016] [Indexed: 10/22/2022]
Abstract
The perception of human movement is a key component of daily social interactions. Although extrastriate area MT+/V5 is closely associated with motion processing, its role in the processing of sparse 'biological motion' displays is still unclear. We developed two closed matched psychophysical tasks to assess simple coherent motion perception and biological motion perception, and measured changes in performance caused by application of TMS over MT+/V5. Performance of the simple motion discrimination task was significantly depressed by TMS stimulation, and highly correlated within observers in TMS conditions, but there was no significant decrement in performance of the biological motion task, despite low intra-observer correlations across TMS conditions. We conclude that extrastriate area MT+/V5 is an obligatory waypoint in the neural processing of simple coherent motion, but is not obligatory for the processing of biological motion. Results are consistent with a dual neural processing route for biological motion processing.
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Affiliation(s)
- George Mather
- School of Psychology, University of Lincoln, Brayford Pool, Lincoln LN2 1NB, UK
| | - Luca Battaglini
- Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy
| | - Gianluca Campana
- Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy; Human Inspired Technology Research Centre, University of Padova, Via Luzzati 4, 35122 Padova, Italy
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24
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Vadakkan KI. A framework for the first-person internal sensation of visual perception in mammals and a comparable circuitry for olfactory perception in Drosophila. SPRINGERPLUS 2015; 4:833. [PMID: 26753120 PMCID: PMC4695467 DOI: 10.1186/s40064-015-1568-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Accepted: 11/26/2015] [Indexed: 02/02/2023]
Abstract
Perception is a first-person internal sensation induced within the nervous system at the time of arrival of sensory stimuli from objects in the environment. Lack of access to the first-person properties has limited viewing perception as an emergent property and it is currently being studied using third-person observed findings from various levels. One feasible approach to understand its mechanism is to build a hypothesis for the specific conditions and required circuit features of the nodal points where the mechanistic operation of perception take place for one type of sensation in one species and to verify it for the presence of comparable circuit properties for perceiving a different sensation in a different species. The present work explains visual perception in mammalian nervous system from a first-person frame of reference and provides explanations for the homogeneity of perception of visual stimuli above flicker fusion frequency, the perception of objects at locations different from their actual position, the smooth pursuit and saccadic eye movements, the perception of object borders, and perception of pressure phosphenes. Using results from temporal resolution studies and the known details of visual cortical circuitry, explanations are provided for (a) the perception of rapidly changing visual stimuli, (b) how the perception of objects occurs in the correct orientation even though, according to the third-person view, activity from the visual stimulus reaches the cortices in an inverted manner and (c) the functional significance of well-conserved columnar organization of the visual cortex. A comparable circuitry detected in a different nervous system in a remote species-the olfactory circuitry of the fruit fly Drosophila melanogaster-provides an opportunity to explore circuit functions using genetic manipulations, which, along with high-resolution microscopic techniques and lipid membrane interaction studies, will be able to verify the structure-function details of the presented mechanism of perception.
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Affiliation(s)
- Kunjumon I Vadakkan
- Division of Neurology, Department of Medicine, University of Toronto, Sunnybrook health Sciences Centre, 2075 Bayview Ave. Room A4-08, Toronto, ON M4N3M5 Canada ; Neurosearch Center, 76 Henry St., Toronto, ON M5T1X2 Canada
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25
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Waves of awareness for occipital and parietal phosphenes perception. Neuropsychologia 2015; 70:114-25. [DOI: 10.1016/j.neuropsychologia.2015.02.021] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Revised: 02/10/2015] [Accepted: 02/16/2015] [Indexed: 10/24/2022]
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26
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Schmid MC, Maier A. To see or not to see--thalamo-cortical networks during blindsight and perceptual suppression. Prog Neurobiol 2015; 126:36-48. [PMID: 25661166 DOI: 10.1016/j.pneurobio.2015.01.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 01/05/2015] [Accepted: 01/14/2015] [Indexed: 11/15/2022]
Abstract
Even during moments when we fail to be fully aware of our environment, our brains never go silent. Instead, it appears that the brain can also operate in an alternate, unconscious mode. Delineating unconscious from conscious neural processes is a promising first step toward investigating how awareness emerges from brain activity. Here we focus on recent insights into the neuronal processes that contribute to visual function in the absence of a conscious visual percept. Drawing on insights from findings on the phenomenon of blindsight that results from injury to primary visual cortex and the results of experimentally induced perceptual suppression, we describe what kind of visual information the visual system analyzes unconsciously and we discuss the neuronal routing and responses that accompany this process. We conclude that unconscious processing of certain visual stimulus attributes, such as the presence of visual motion or the emotional expression of a face can occur in a geniculo-cortical circuit that runs independent from and in parallel to the predominant route through primary visual cortex. We speculate that in contrast, bidirectional neuronal interactions between cortex and the thalamic pulvinar nucleus that support large-scale neuronal integration and visual awareness are impeded during blindsight and perceptual suppression.
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Affiliation(s)
- Michael C Schmid
- Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society, Deutschordenstraße 46, Frankfurt a. M. 60528, Germany.
| | - Alexander Maier
- Vanderbilt University, Department of Psychology, 111 21st Avenue South, 301 Wilson Hall, Nashville, TN 37240, USA.
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27
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Mazzi C, Mancini F, Savazzi S. Can IPS reach visual awareness without V1? Evidence from TMS in healthy subjects and hemianopic patients. Neuropsychologia 2014; 64:134-44. [DOI: 10.1016/j.neuropsychologia.2014.09.026] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 09/09/2014] [Accepted: 09/15/2014] [Indexed: 10/24/2022]
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28
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Perez C, Chokron S. Rehabilitation of homonymous hemianopia: insight into blindsight. Front Integr Neurosci 2014; 8:82. [PMID: 25374515 PMCID: PMC4206079 DOI: 10.3389/fnint.2014.00082] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Accepted: 09/30/2014] [Indexed: 12/28/2022] Open
Abstract
Strong evidence of considerable plasticity in primary sensory areas in the adult cortex, and of dramatic cross-modal reorganization in visual areas, after short- or long-term visual deprivation has recently been reported. In the context of patient rehabilitation, this scientifically challenging topic takes on urgent clinical relevance, especially given the lack of information about the role of such reorganization on spared or newly emerged visual performance. Amongst the most common visual field defects found upon unilateral occipital damage of the primary visual cortex is homonymous hemianopia (HH), a perfectly symmetric loss of vision in both eyes. Traditionally, geniculostriate lesions were considered to result in complete and permanent visual loss in the topographically related area of the visual field (Huber, 1992). However, numerous studies in monkeys, and later, in humans, have demonstrated that despite destruction of the striate cortex, or even following a hemispherectomy, some patients retain a certain degree of unconscious visual function, known as blindsight. Accordingly, there have recently been attempts to restore visual function in patients by stimulating unconscious preserved blindsight capacities. Herein we review different visual rehabilitation techniques designed for brain-damaged patients with visual field loss. We discuss the hypothesis that explicit (conscious) visual detection can be restored in the blind visual field by harnessing implicit (unconscious) visual capacities. The results that we summarize here underline the need for early diagnosis of cortical visual impairment (CVI), and the urgency in rehabilitating such deficits, in these patients. Based on the research precedent, we explore the link between implicit (unconscious) vision and conscious perception and discuss possible mechanisms of adaptation and plasticity in the visual cortex.
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Affiliation(s)
- Céline Perez
- Neurology, Unité Fonctionnelle Vision et Cognition, Fondation Ophtalmologique Rothschild Paris, France
| | - Sylvie Chokron
- Neurology, Unité Fonctionnelle Vision et Cognition, Fondation Ophtalmologique Rothschild Paris, France ; Laboratoire de Psychologie de la Perception, Université Paris-Descartes, UMR 8242 CNRS Paris, France
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29
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Silvanto J. Is primary visual cortex necessary for visual awareness? Trends Neurosci 2014; 37:618-9. [PMID: 25442362 DOI: 10.1016/j.tins.2014.09.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 09/30/2014] [Indexed: 11/28/2022]
Abstract
Influential models propose that conscious experience of extrastriate activity requires the integrity of primary visual cortex (V1). A new study challenges this view by demonstrating that when V1 is lesioned, visual qualia can be induced when transcranial magnetic stimulation (TMS) is applied over the patients' ipsilesional hemisphere.
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Affiliation(s)
- Juha Silvanto
- Department of Psychology, Faculty of Science and Technology, University of Westminster, 115 New Cavendish Street, W1W 6UW, London, UK; Brain Research Unit, O.V. Lounasmaa Laboratory, School of Science, Aalto University, PO BOX 15100, 00076 Aalto, Finland.
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30
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Urbanski M, Coubard OA, Bourlon C. Visualizing the blind brain: brain imaging of visual field defects from early recovery to rehabilitation techniques. Front Integr Neurosci 2014; 8:74. [PMID: 25324739 PMCID: PMC4179723 DOI: 10.3389/fnint.2014.00074] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Accepted: 09/03/2014] [Indexed: 01/04/2023] Open
Abstract
Visual field defects (VFDs) are one of the most common consequences observed after brain injury, especially after a stroke in the posterior cerebral artery territory. Less frequently, tumors, traumatic brain injury, brain surgery or demyelination can also determine various visual disabilities, from a decrease in visual acuity to cerebral blindness. Visual field defects is a factor of bad functional prognosis as it compromises many daily life activities (e.g., obstacle avoidance, driving, and reading) and therefore the patient's quality of life. Spontaneous recovery seems to be limited and restricted to the first 6 months, with the best chance of improvement at 1 month. The possible mechanisms at work could be partly due to cortical reorganization in the visual areas (plasticity) and/or partly to the use of intact alternative visual routes, first identified in animal studies and possibly underlying the phenomenon of blindsight. Despite processes of early recovery, which is rarely complete, and learning of compensatory strategies, the patient's autonomy may still be compromised at more chronic stages. Therefore, various rehabilitation therapies based on neuroanatomical knowledge have been developed to improve VFDs. These use eye-movement training techniques (e.g., visual search, saccadic eye movements), reading training, visual field restitution (the Vision Restoration Therapy, VRT), or perceptual learning. In this review, we will focus on studies of human adults with acquired VFDs, which have used different imaging techniques (Positron Emission Tomography, PET; Diffusion Tensor Imaging, DTI; functional Magnetic Resonance Imaging, fMRI; Magneto Encephalography, MEG) or neurostimulation techniques (Transcranial Magnetic Stimulation, TMS; transcranial Direct Current Stimulation, tDCS) to show brain activations in the course of spontaneous recovery or after specific rehabilitation techniques.
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Affiliation(s)
- Marika Urbanski
- Service de Médecine et de Réadaptation Gériatrique et Neurologique, Hôpitaux de Saint-Maurice Saint-Maurice, France ; Inserm, U 1127, ICM FrontLab Paris, France ; CNRS, UMR 7225, ICM FrontLab Paris, France ; Sorbonne Universités, UPMC Univ Paris 06, UMRS 1127 Paris, France ; Institut du Cerveau et de la Moelle Épinière, ICM FrontLab Paris, France
| | - Olivier A Coubard
- The Neuropsychological Laboratory, CNS-Fed Paris, France ; Laboratoire Psychologie de la Perception, UMR 8242 CNRS-Université Paris Descartes Paris, France
| | - Clémence Bourlon
- Service de Médecine et de Réadaptation, Clinique Les Trois Soleils Boissise-le-Roi, France
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31
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Silvanto J. Why is "blindsight" blind? A new perspective on primary visual cortex, recurrent activity and visual awareness. Conscious Cogn 2014; 32:15-32. [PMID: 25263935 DOI: 10.1016/j.concog.2014.08.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 07/30/2014] [Accepted: 08/04/2014] [Indexed: 01/19/2023]
Abstract
The neuropsychological phenomenon of blindsight has been taken to suggest that the primary visual cortex (V1) plays a unique role in visual awareness, and that extrastriate activation needs to be fed back to V1 in order for the content of that activation to be consciously perceived. The aim of this review is to evaluate this theoretical framework and to revisit its key tenets. Firstly, is blindsight truly a dissociation of awareness and visual detection? Secondly, is there sufficient evidence to rule out the possibility that the loss of awareness resulting from a V1 lesion simply reflects reduced extrastriate responsiveness, rather than a unique role of V1 in conscious experience? Evaluation of these arguments and the empirical evidence leads to the conclusion that the loss of phenomenal awareness in blindsight may not be due to feedback activity in V1 being the hallmark awareness. On the basis of existing literature, an alternative explanation of blindsight is proposed. In this view, visual awareness is a "global" cognitive function as its hallmark is the availability of information to a large number of perceptual and cognitive systems; this requires inter-areal long-range synchronous oscillatory activity. For these oscillations to arise, a specific temporal profile of neuronal activity is required, which is established through recurrent feedback activity involving V1 and the extrastriate cortex. When V1 is lesioned, the loss of recurrent activity prevents inter-areal networks on the basis of oscillatory activity. However, as limited amount of input can reach extrastriate cortex and some extrastriate neuronal selectivity is preserved, computations involving comparison of neural firing rates within a cortical area remain possible. This enables "local" read-out from specific brain regions, allowing for the detection and discrimination of basic visual attributes. Thus blindsight is blind due to lack of "global" long-range synchrony, and it functions via "local" neural readout from extrastriate areas.
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Affiliation(s)
- Juha Silvanto
- University of Westminster, Faculty of Science and Technology, Department of Psychology, 309 Regent Street, W1B 2HW London, UK; Brain Research Unit, O.V. Lounasmaa Laboratory, School of Science, Aalto University, PO BOX 15100, 00076 Aalto, Finland.
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Kwon HG, Jang SH. Neural connectivity of the lateral geniculate body in the human brain: diffusion tensor imaging study. Neurosci Lett 2014; 578:66-70. [PMID: 24970751 DOI: 10.1016/j.neulet.2014.06.033] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Revised: 06/03/2014] [Accepted: 06/13/2014] [Indexed: 11/25/2022]
Abstract
A few studies have reported on the neural connectivity of some neural structures of the visual system in the human brain. However, little is known about the neural connectivity of the lateral geniculate body (LGB). In the current study, using diffusion tensor tractography (DTT), we attempted to investigate the neural connectivity of the LGB in normal subjects. A total of 52 healthy subjects were recruited for this study. A seed region of interest was placed on the LGB using the FMRIB Software Library which is a probabilistic tractography method based on a multi-fiber model. Connectivity was defined as the incidence of connection between the LGB and target brain areas at the threshold of 5, 25, and 50 streamlines. In addition, connectivity represented the percentage of connection in all hemispheres of 52 subjects. We found the following characteristics of connectivity of the LGB at the threshold of 5 streamline: (1) high connectivity to the corpus callosum (91.3%) and the contralateral temporal cortex (56.7%) via the corpus callosum, (2) high connectivity to the ipsilateral cerebral cortex: the temporal lobe (100%), primary visual cortex (95.2%), and visual association cortex (77.9%). The LGB appeared to have high connectivity to the corpus callosum and both temporal cortexes as well as the ipsilateral occipital cortex. We believe that the results of this study would be helpful in investigation of the neural network associated with the visual system and brain plasticity of the visual system after brain injury.
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Affiliation(s)
- Hyeok Gyu Kwon
- Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University, 317-1, Daemyung dong, Namku, Daegu 705-717, Republic of Korea.
| | - Sung Ho Jang
- Department of Physical Medicine and Rehabilitation, College of Medicine, Yeungnam University, 317-1, Daemyung dong, Namku, Daegu 705-717, Republic of Korea.
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Bolognini N, Convento S, Fusaro M, Vallar G. The sound-induced phosphene illusion. Exp Brain Res 2013; 231:469-78. [DOI: 10.1007/s00221-013-3711-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 09/16/2013] [Indexed: 11/30/2022]
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Salminen-Vaparanta N, Vanni S, Noreika V, Valiulis V, Móró L, Revonsuo A. Subjective Characteristics of TMS-Induced Phosphenes Originating in Human V1 and V2. Cereb Cortex 2013; 24:2751-60. [DOI: 10.1093/cercor/bht131] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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The second face of blindness: processing speed deficits in the intact visual field after pre- and post-chiasmatic lesions. PLoS One 2013; 8:e63700. [PMID: 23667657 PMCID: PMC3648511 DOI: 10.1371/journal.pone.0063700] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Accepted: 04/09/2013] [Indexed: 01/25/2023] Open
Abstract
Purpose Damage along the visual pathway results in a visual field defect (scotoma), which retinotopically corresponds to the damaged neural tissue. Other parts of the visual field, processed by the uninjured tissue, are considered to be intact. However, perceptual deficits have been observed in the “intact” visual field, but these functional impairments are poorly understood. We now studied temporal processing deficits in the intact visual field of patients with either pre- or post-chiasmatic lesions to better understand the functional consequences of partial blindness. Methods Patients with pre- (n = 53) or post- chiasmatic lesions (n = 98) were tested with high resolution perimetry – a method used to map visual fields with supra-threshold light stimuli. Reaction time of detections in the intact visual field was then analyzed as an indicator of processing speed and correlated with features of the visual field defect. Results Patients from both groups exhibited processing speed deficits in their presumably “intact” field as indicated by comparison to a normative sample. Further, in both groups processing speed was found to be a function of two factors. Firstly, a spatially restricted (retinotopic) influence of the scotoma was seen in longer reaction times when stimuli were presented in intact field sectors close to the defect. Secondly, patients with larger scotomata had on average longer reaction times in their intact field indicating a more general (non-retinotopic) influence of the scotoma. Conclusions Processing speed deficits in the “intact” visual field of patients with visual system damage demonstrate that visual system lesions have more widespread consequences on perception than previously thought. Because dysfunctions of the seeing field are expected to contribute to subjective vision, including visual tests of the presumed “intact” field may help to better understand vision loss and to improve methods of vision restoration and rehabilitation.
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Cowey A, Alexander I, Ellison A. Modulation of cortical excitability can speed up blindsight but not improve it. Exp Brain Res 2012; 224:469-75. [PMID: 23229773 DOI: 10.1007/s00221-012-3327-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 10/26/2012] [Indexed: 11/28/2022]
Abstract
Blindsight has been widely investigated and its properties documented. One property still debated and contested is the puzzling absence of phenomenal visual percepts of visual stimuli that can be detected with perfect accuracy. We investigated the possibility that phenomenal visual percepts of exogenous visual stimuli in patient GY might be induced by using transcranial direct current stimulation. High contrast and low contrast stimuli were presented as a moving grating in his blind hemifield. When left area MT/V5 was anodally stimulated during the presentation of high-contrast gratings, he never reported a phenomenal percept of a moving grating but showed perfect blindsight performance. When applied along with low contrast gratings, for which accuracy was titrated to 60-70 %, performance did not improve but responses were significantly faster. Cathodal stimulation had no effect. Results are explained in the framework of GY's reorganized cortical connexions and oscillatory patterns known to be involved in awareness in GY. The apparent presence of phenomenal visual percepts in earlier studies is shown to be a semantic confusion about what he means when he says that he sees in his blind field.
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Affiliation(s)
- Alan Cowey
- Department of Experimental Psychology, Oxford University, South Parks Road, Oxford OX1 3UD, UK
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Perez C, Peyrin C, Cavézian C, Coubard O, Caetta F, Raz N, Levin N, Doucet G, Andersson F, Obadia M, Gout O, Héran F, Savatovsky J, Chokron S. An FMRI investigation of the cortical network underlying detection and categorization abilities in hemianopic patients. Brain Topogr 2012; 26:264-77. [PMID: 22878845 DOI: 10.1007/s10548-012-0244-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2011] [Accepted: 07/21/2012] [Indexed: 10/28/2022]
Abstract
The current study aims to investigate visual scene perception and its neuro-anatomical correlates for stimuli presented in the central visual field of patients with homonymous hemianopia, and thereby to assess the effect of a right or a left occipital lesion on brain reorganization. Fourteen healthy participants, three left brain damaged (LBD) patients with right homonymous hemianopia and five right brain damaged (RBD) patients with left homonymous hemianopia performed a visual detection task (i.e. "Is there an image on the screen?") and a categorization task (i.e. "Is it an image of a highway or a city?") during a block-designed functional magnetic resonance imaging recording session. Cerebral activity analyses of the posterior areas-the occipital lobe in particular-highlighted bi-hemispheric activation during the detection task but more lateralized, left occipital lobe activation during the categorization task in healthy participants. Conversely, in patients, the same network of activity was observed in both tasks. However, LBD patients showed a predominant activation in their right hemisphere (occipital lobe and posterior temporal areas) whereas RBD patients showed a more bilateral activation (in the occipital lobes). Overall, our preliminary findings suggest a specific pattern of cerebral activation depending on the task instruction in healthy participants and cerebral reorganization of the posterior areas following brain injury in hemianopic patients which could depend upon the side of the occipital lesion.
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Affiliation(s)
- Céline Perez
- Laboratoire de Psychologie et NeuroCognition, UMR 5105 CNRS- UPMF, Grenoble, France
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Manipulation of pre-target activity on the right frontal eye field enhances conscious visual perception in humans. PLoS One 2012; 7:e36232. [PMID: 22615759 PMCID: PMC3352916 DOI: 10.1371/journal.pone.0036232] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2012] [Accepted: 03/28/2012] [Indexed: 11/28/2022] Open
Abstract
The right Frontal Eye Field (FEF) is a region of the human brain, which has been consistently involved in visuo-spatial attention and access to consciousness. Nonetheless, the extent of this cortical site’s ability to influence specific aspects of visual performance remains debated. We hereby manipulated pre-target activity on the right FEF and explored its influence on the detection and categorization of low-contrast near-threshold visual stimuli. Our data show that pre-target frontal neurostimulation has the potential when used alone to induce enhancements of conscious visual detection. More interestingly, when FEF stimulation was combined with visuo-spatial cues, improvements remained present only for trials in which the cue correctly predicted the location of the subsequent target. Our data provide evidence for the causal role of the right FEF pre-target activity in the modulation of human conscious vision and reveal the dependence of such neurostimulatory effects on the state of activity set up by cue validity in the dorsal attentional orienting network.
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Characterization of visual percepts evoked by noninvasive stimulation of the human posterior parietal cortex. PLoS One 2011; 6:e27204. [PMID: 22087266 PMCID: PMC3210763 DOI: 10.1371/journal.pone.0027204] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Accepted: 10/12/2011] [Indexed: 12/03/2022] Open
Abstract
Phosphenes are commonly evoked by transcranial magnetic stimulation (TMS) to study the functional organization, connectivity, and excitability of the human visual brain. For years, phosphenes have been documented only from stimulating early visual areas (V1–V3) and a handful of specialized visual regions (V4, V5/MT+) in occipital cortex. Recently, phosphenes were reported after applying TMS to a region of posterior parietal cortex involved in the top-down modulation of visuo-spatial processing. In the present study, we systematically characterized parietal phosphenes to determine if they are generated directly by local mechanisms or emerge through indirect activation of other visual areas. Using technology developed in-house to record the subjective features of phosphenes, we found no systematic differences in the size, shape, location, or frame-of-reference of parietal phosphenes when compared to their occipital counterparts. In a second experiment, discrete deactivation by 1 Hz repetitive TMS yielded a double dissociation: phosphene thresholds increased at the deactivated site without producing a corresponding change at the non-deactivated location. Overall, the commonalities of parietal and occipital phosphenes, and our ability to independently modulate their excitability thresholds, lead us to conclude that they share a common neural basis that is separate from either of the stimulated regions.
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Conscious perception and the frontal lobes: comment on Lau and Rosenthal. Trends Cogn Sci 2011; 15:507; author reply 508-9. [DOI: 10.1016/j.tics.2011.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Accepted: 09/13/2011] [Indexed: 10/17/2022]
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Elkin-Frankston S, Fried P, Rushmore RJ, Valero-Cabré A. From qualia to quantia: A system to document and quantify phosphene percepts elicited by non-invasive neurostimulation of the human occipital cortex. J Neurosci Methods 2011; 198:149-57. [DOI: 10.1016/j.jneumeth.2011.02.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2010] [Revised: 02/11/2011] [Accepted: 02/16/2011] [Indexed: 10/18/2022]
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Silvanto J, Rees G. What does Neural Plasticity Tell us about Role of Primary Visual Cortex (V1) in Visual Awareness? Front Psychol 2011; 2:6. [PMID: 21713187 PMCID: PMC3111426 DOI: 10.3389/fpsyg.2011.00006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2010] [Accepted: 01/04/2011] [Indexed: 11/21/2022] Open
Abstract
The complete loss of visual awareness resulting from a lesion to the primary visual cortex (V1) suggests that this region is indispensable for conscious visual perception. There are however a number cases of conscious perception in the absence of V1 which appear to challenge this conclusion. These include reports of patients with bilateral V1 lesions sustained at an early age whose conscious vision has spontaneously recovered, as well as stroke patients who have recovered some conscious vision with the help of rehabilitation programs. In addition, the phenomenon of hemianopic completion and percepts induced by brain stimulation suggest that V1 may not be necessary for conscious perception in all circumstances. Furthermore, that the visual abilities in the cat are associated with the recovery of normal extrastriate tuning properties rather than emulation of V1 functions suggests that there is nothing unique about the functional properties of this region in visual awareness. Rather, the dramatic effect of a V1 lesion on visual awareness may be due to its role in providing the majority of extrastriate visual input, the loss of which abolishes normal neural responsiveness throughout the visual cortex.
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Affiliation(s)
- Juha Silvanto
- Brain Research Unit, Low Temperature Laboratory and Advanced Magnetic Imaging Centre, School of Science and Technology, Aalto University Espoo, Finland
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Unique contributions of brain stimulation to the study of consciousness: where neuroscience meets philosophy. CNS Spectr 2010; 15:154-6. [PMID: 20414164 DOI: 10.1017/s1092852900027425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
True progress in understanding how experience arises from the brain has been relatively slow when viewed from a historical perspective. Recently, several technologies to study and stimulate the brain have been applied to this field of inquiry. Such progress was made only 2,500 years after the ancient Greek philosopher Parmenides first adopted a technical procedure involving the application of formal logic instruments to explore the perception of experiences.At the phenomenological level, consciousness has been referred to as “what vanishes every night when we fall into dreamless sleep and reappears when we wake up or when we dream. It is also all we are and all we have: lose consciousness and, as far as you are concerned, your own self, and the entire world dissolves into nothingness”. According to the integrated information theory, consciousness is integrated information.The term “consciousness” therefore has two key senses: wakefulness and awareness. Wakefulness is a state of consciousness distinguished from coma or sleep. Having one's eyes open is generally an indication of wakefulness and we usually assume that anyone who is awake will also be aware. Awareness implies not merely being conscious but also being conscious of something. The broad definition of consciousness includes a large range of processes that we normally regard as unconscious (eg, blindsight or priming by neglected or masked stimuli).Both sleep and anesthesia are reversible states of eyes-closed unresponsiveness to environmental stimuli in which the individual lacks both wakefulness and awareness. In contrast to sleep, where sufficient stimulation will return the individual to wakefulness, even the most vigorous exogenous stimulation cannot produce awakening in a patient under an adequate level of general anesthesia.
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Bandpass characteristics of high-frequency sensitivity and visual experience in blindsight. Conscious Cogn 2010; 19:144-51. [PMID: 20129798 DOI: 10.1016/j.concog.2010.01.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2009] [Revised: 01/08/2010] [Accepted: 01/11/2010] [Indexed: 11/22/2022]
Abstract
Patient RP suffers a unilateral right homonymous quadrant anopia but demonstrates better than chance discrimination for stimuli presented in the blind field at temporal frequencies between 33 and 47Hz (all significant at p<.05, binomial). Examination of her reports of visual experience during blind-field discrimination suggests a more complex picture in which experiences particular to correct discrimination are not found at low-mid-gamma frequencies, but are significantly more likely than average (76%, p<.001) at a lower frequency (22Hz) at which blindsight is not observed. We believe that visual experience may serve to support blindsight if discrimination tasks are generally impaired at frequencies outside of the low-mid-gamma band. If this is so, although generally experienced as non-specific and unstructured light, the visual experience that accompanies discrimination performance must be based upon a neural representation which includes information on the visual features present in the stimulus.
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Das A, Huxlin KR. New approaches to visual rehabilitation for cortical blindness: outcomes and putative mechanisms. Neuroscientist 2010; 16:374-87. [PMID: 20103505 DOI: 10.1177/1073858409356112] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Cortical blindness is a chronic loss of vision following damage to the primary visual cortex (V1) or its postchiasmal afferents. Such damage is followed by a brief period of spontaneous plasticity that rarely lasts beyond 6 months. Following this initial phase, the visual deficit is thought to be stable, intractable, and permanent. Cortically blind subjects demonstrate spontaneous oculomotor adaptations to their deficits that can be further improved by saccadic localization training. However, saccadic training does not improve visual sensitivity in the blind field. In contrast, recent studies by a number of independent groups suggest that localized, repetitive perceptual training can improve visual sensitivity in the blind field, although mechanisms underlying the observed recovery remain unclear. This review discusses the current literature on rehabilitative strategies used for cortical blindness with emphasis on the use of perceptual training methods. The putative mechanisms that underlie the resulting, training-induced visual improvements are then outlined, along with the special challenges posed to their elucidation by the great variability in the extent and sometimes nature of the V1 damage sustained in different individuals.
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Affiliation(s)
- Anasuya Das
- University of Rochester Flaum Eye Institute, Rochester, New York 14642, USA
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Ro T. What can TMS tell us about visual awareness? Cortex 2010; 46:110-3. [DOI: 10.1016/j.cortex.2009.03.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2008] [Revised: 10/15/2008] [Accepted: 10/23/2008] [Indexed: 10/21/2022]
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