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Pedersini CA, Guàrdia-Olmos J, Montalà-Flaquer M, Cardobi N, Sanchez-Lopez J, Parisi G, Savazzi S, Marzi CA. Functional interactions in patients with hemianopia: A graph theory-based connectivity study of resting fMRI signal. PLoS One 2020; 15:e0226816. [PMID: 31905211 PMCID: PMC6944357 DOI: 10.1371/journal.pone.0226816] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Accepted: 12/05/2019] [Indexed: 12/12/2022] Open
Abstract
The assessment of task-independent functional connectivity (FC) after a lesion causing hemianopia remains an uncovered topic and represents a crucial point to better understand the neural basis of blindsight (i.e. unconscious visually triggered behavior) and visual awareness. In this light, we evaluated functional connectivity (FC) in 10 hemianopic patients and 10 healthy controls in a resting state paradigm. The main aim of this study is twofold: first of all we focused on the description and assessment of density and intensity of functional connectivity and network topology with and without a lesion affecting the visual pathway, and then we extracted and statistically compared network metrics, focusing on functional segregation, integration and specialization. Moreover, a study of 3-cycle triangles with prominent connectivity was conducted to analyze functional segregation calculated as the area of each triangle created connecting three neighboring nodes. To achieve these purposes we applied a graph theory-based approach, starting from Pearson correlation coefficients extracted from pairs of regions of interest. In these analyses we focused on the FC extracted by the whole brain as well as by four resting state networks: The Visual (VN), Salience (SN), Attention (AN) and Default Mode Network (DMN), to assess brain functional reorganization following the injury. The results showed a general decrease in density and intensity of functional connections, that leads to a less compact structure characterized by decrease in functional integration, segregation and in the number of interconnected hubs in both the Visual Network and the whole brain, despite an increase in long-range inter-modules connections (occipito-frontal connections). Indeed, the VN was the most affected network, characterized by a decrease in intra- and inter-network connections and by a less compact topology, with less interconnected nodes. Surprisingly, we observed a higher functional integration in the DMN and in the AN regardless of the lesion extent, that may indicate a functional reorganization of the brain following the injury, trying to compensate for the general reduced connectivity. Finally we observed an increase in functional specialization (lower between-network connectivity) and in inter-networks functional segregation, which is reflected in a less compact network topology, highly organized in functional clusters. These descriptive findings provide new insight on the spontaneous brain activity in hemianopic patients by showing an alteration in the intrinsic architecture of a large-scale brain system that goes beyond the impairment of a single RSN.
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Affiliation(s)
- Caterina A. Pedersini
- Physiology and Psychology Section, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Joan Guàrdia-Olmos
- Department of Social Psychology and Quantitative Psychology, School of Psychology, Institute of Neuroscience, Institute of Complex Systems, University of Barcelona, Barcelona, Spain
| | - Marc Montalà-Flaquer
- Department of Social Psychology and Quantitative Psychology, School of Psychology, Institute of Complex Systems, University of Barcelona, Barcelona, Spain
| | - Nicolò Cardobi
- Physiology and Psychology Section, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Javier Sanchez-Lopez
- Physiology and Psychology Section, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Giorgia Parisi
- Physiology and Psychology Section, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Silvia Savazzi
- Physiology and Psychology Section, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
- Perception and Awareness (PandA) Laboratory, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
- National Institute of Neuroscience, Verona, Italy
| | - Carlo A. Marzi
- Physiology and Psychology Section, Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
- National Institute of Neuroscience, Verona, Italy
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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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Mazzi C, Tagliabue CF, Mazzeo G, Savazzi S. Reliability in reporting perceptual experience: Behaviour and electrophysiology in hemianopic patients. Neuropsychologia 2019; 128:119-126. [PMID: 29355647 PMCID: PMC6562273 DOI: 10.1016/j.neuropsychologia.2018.01.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 01/07/2018] [Accepted: 01/15/2018] [Indexed: 12/02/2022]
Abstract
Patients with hemianopia can present with the so called blindsight phenomenon: the ability to perform above chance in the absence of acknowledged awareness. Proper awareness reports are, thus, crucial to distinguish pure forms of blindsight from forms of conscious, yet degraded, vision. It has, in fact, been recently shown that 1) dichotomous and graded measures to assess awareness can lead to different behavioural results in patients with hemianopia and that 2) different grades of perceptual clarity show different electrophysiological correlates in healthy participants. Here, in hemianopic patients, we assessed awareness by means of the four-point Perceptual Awareness Scale (PAS) and investigated its neural correlates with Event Related Potentials (ERPs). Results showed that patients, in most of the cases, can rate the clarity of their perceptual experience in a graded manner. Moreover, graded perceptual experiences correlated with the amplitude of deflections in ERPs. These results call for the need to assess perceptual awareness with graded measures and for the importance to use electrophysiological data to correlate behaviour with neural processing.
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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
| | - Chiara Francesca Tagliabue
- 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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Sanchez-Lopez J, Pedersini CA, Di Russo F, Cardobi N, Fonte C, Varalta V, Prior M, Smania N, Savazzi S, Marzi CA. Visually evoked responses from the blind field of hemianopic patients. Neuropsychologia 2019; 128:127-139. [PMID: 28987906 PMCID: PMC5845440 DOI: 10.1016/j.neuropsychologia.2017.10.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 10/02/2017] [Accepted: 10/03/2017] [Indexed: 11/28/2022]
Abstract
Hemianopia is a visual field defect characterized by decreased vision or blindness in the contralesional visual field of both eyes. The presence of well documented above-chance unconscious behavioural responses to visual stimuli presented to the blind hemifield (blindsight) has stimulated a great deal of research on the neural basis of this important phenomenon. The present study is concerned with electrophysiological responses from the blind field. Since previous studies found that transient Visual Evoked Potentials (VEPs) are not entirely suitable for this purpose here we propose to use Steady-State VEPs (SSVEPs). A positive result would have important implications for the understanding of the neural bases of conscious vision. We carried out a passive SSVEP stimulation with healthy participants and hemianopic patients. Stimuli consisted of four black-and-white sinusoidal Gabor gratings presented one in each visual field quadrant and flickering one at a time at a 12Hz rate. To assess response reliability a Signal-to-Noise Ratio analysis was conducted together with further analyses in time and frequency domains to make comparisons between groups (healthy participants and patients), side of brain lesion (left and right) and visual fields (sighted and blind). The important overall result was that stimulus presentation to the blind hemifield yielded highly reliable responses with time and frequency features broadly similar to those found for cortical extrastriate areas in healthy controls. Moreover, in the intact hemifield of hemianopics and in healthy controls there was evidence of a role of prefrontal structures in perceptual awareness. Finally, the presence of different patterns of brain reorganization depended upon the side of lesion.
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Affiliation(s)
- Javier Sanchez-Lopez
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy.
| | - Caterina A Pedersini
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy
| | - Francesco Di Russo
- Department. of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy; IRCCS Santa Lucia Foundation, Rome, Italy
| | - Nicolò Cardobi
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy
| | - Cristina Fonte
- Neuromotor and Cognitive Rehabilitation Research Center, Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy
| | - Valentina Varalta
- Neuromotor and Cognitive Rehabilitation Research Center, Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy
| | | | - Nicola Smania
- Neuromotor and Cognitive Rehabilitation Research Center, Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy
| | - Silvia Savazzi
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy; Perception and Awareness (PandA) Laboratory, Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy; National Institute of Neuroscience, Verona, Italy
| | - Carlo A Marzi
- Department of Neuroscience, Biomedicine and Movement, University of Verona, Italy; National Institute of Neuroscience, Verona, Italy
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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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