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Zhang H, Feng Y, Li W, Liang X, Huang G, Qi S. Topological arrangement of coronal segments in human callosal fibers in vivo tractography. Front Neuroanat 2023; 17:1097247. [PMID: 37325424 PMCID: PMC10264571 DOI: 10.3389/fnana.2023.1097247] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Accepted: 04/27/2023] [Indexed: 06/17/2023] Open
Abstract
The topography of human callosal fibers in the midsagittal corpus callosum (mid-CC), in terms of cortical termination, is inconsistent in the literature. Despite being a high-profile and controversial topic, heterotopic callosal bundles (HeCBs) have not been studied from a whole-brain perspective. Here, we used multi-modal magnetic resonance imaging data from Human Connectome Project Development to explore these two topographic aspects by combining whole-brain tractography based on multi-shell multi-tissue constrained spherical deconvolution, the post-tractography reducing-false-positive-streamline algorithm of Convex Optimization Modeling for Microstructure Informed Tractography 2, and the new cortex parcellation atlas of Human Connectome Project multi-modal parcellation, version 1.0. We proposed that the callosal streamlines would demonstrate a topological arrangement of coronal segments arranged from anterior to posterior, with each perpendicular to the long axis of the mid-CC following its natural curvature, and the adjacent segments overlapping one another owing to the existence of HeCBs. We found that the cortices connected by the coronal segments, from anterior to posterior, corresponded exactly to the cortices from anterior to posterior in the flattened cortical surfaces of this atlas, indicating the original relative positions of the neocortex before curling and flipping during brain evolution. For each cortical area defined by this atlas, the sum strength of the HeCBs was far greater than that of the homotopic callosal bundle. Our findings on the topography of the whole CC would help in further understanding the network between the bilateral hemispheres and preventing disconnection syndromes in clinical settings.
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Affiliation(s)
- Hui Zhang
- Department of Neurosurgery, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Yuan Feng
- Sleep Medicine Center, Department of Psychiatric, Nanfang Hospital, Southern Medical University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Proteomics, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China
| | - Weiguang Li
- Department of Neurosurgery, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Xili Liang
- Department of Neurology, The First Clinical Medical School, Southern Medical University, Guangzhou, China
| | - Guanglong Huang
- Department of Neurosurgery, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Songtao Qi
- Department of Neurosurgery, Nanfang Hospital, Southern Medical University, Guangzhou, China
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2
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Szczupak D, Lent R, Tovar-Moll F, Silva AC. Heterotopic connectivity of callosal dysgenesis in mice and humans. Front Neurosci 2023; 17:1191859. [PMID: 37274193 PMCID: PMC10232863 DOI: 10.3389/fnins.2023.1191859] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Accepted: 05/02/2023] [Indexed: 06/06/2023] Open
Abstract
The corpus callosum (CC), the largest brain commissure and the primary white matter pathway for interhemispheric cortical connectivity, was traditionally viewed as a predominantly homotopic structure, connecting mirror areas of the cortex. However, new studies verified that most callosal commissural fibers are heterotopic. Recently, we reported that ~75% of the callosal connections in the brains of mice, marmosets, and humans are heterotopic, having an essential role in determining the global properties of brain networks. In the present study, we leveraged high-resolution diffusion-weighted imaging and graph network modeling to investigate the relationship between heterotopic and homotopic callosal fibers in human subjects and in a spontaneous mouse model of Corpus Callosum Dysgenesis (CCD), a congenital developmental CC malformation that leads to widespread whole-brain reorganization. Our results show that the CCD brain is more heterotopic than the normotypical brain, with both mouse and human CCD subjects displaying highly variable heterotopicity maps. CCD mice have a clear heterotopicity cluster in the anterior CC, while hypoplasic humans have strongly variable patterns. Graph network-based connectivity profile showed a direct impact of heterotopic connections on CCD brains altering several network-based statistics. Our collective results show that CCD directly alters heterotopic connections and brain connectivity.
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Affiliation(s)
- Diego Szczupak
- Department of Neurobiology, University of Pittsburgh Brain Institute, University of Pittsburgh, Pittsburgh, PA, United States
| | - Roberto Lent
- Institute of Biomedical Sciences, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
- D’Or Institute Research and Education (IDOR), Rio de Janeiro, Brazil
| | | | - Afonso C. Silva
- Department of Neurobiology, University of Pittsburgh Brain Institute, University of Pittsburgh, Pittsburgh, PA, United States
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3
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Szczupak D, Iack PM, Rayêe D, Liu C, Lent R, Tovar-Moll F, Silva AC. The relevance of heterotopic callosal fibers to interhemispheric connectivity of the mammalian brain. Cereb Cortex 2023; 33:4752-4760. [PMID: 36178137 PMCID: PMC10110439 DOI: 10.1093/cercor/bhac377] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 08/29/2022] [Accepted: 08/30/2022] [Indexed: 11/14/2022] Open
Abstract
The corpus callosum (CC) is the largest white matter structure and the primary pathway for interhemispheric brain communication. Investigating callosal connectivity is crucial to unraveling the brain's anatomical and functional organization in health and disease. Classical anatomical studies have characterized the bulk of callosal axonal fibers as connecting primarily homotopic cortical areas. Whenever detected, heterotopic callosal fibers were ascribed to altered sprouting and pruning mechanisms in neurodevelopmental diseases such as CC dysgenesis (CCD). We hypothesized that these heterotopic connections had been grossly underestimated due to their complex nature and methodological limitations. We used the Allen Mouse Brain Connectivity Atlas and high-resolution diffusion-weighted imaging to identify and quantify homotopic and heterotopic callosal connections in mice, marmosets, and humans. In all 3 species, we show that ~75% of interhemispheric callosal connections are heterotopic and comprise the central core of the CC, whereas the homotopic fibers lay along its periphery. We also demonstrate that heterotopic connections have an essential role in determining the global properties of brain networks. These findings reshape our view of the corpus callosum's role as the primary hub for interhemispheric brain communication, directly impacting multiple neuroscience fields investigating cortical connectivity, neurodevelopment, and neurodevelopmental disorders.
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Affiliation(s)
- Diego Szczupak
- Department of Neurobiology, University of Pittsburgh Brain Institute, University of Pittsburgh, Pittsburgh, PA 15261, United States
| | - Pamela Meneses Iack
- Institute of Biomedical Sciences, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro 21941-590, Brazil
| | - Danielle Rayêe
- Institute of Ophtalmology and Visual Sciences, Albert Einstein College of Medicine, NY 10461, United States
| | - Cirong Liu
- Institute of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai 200031, China
| | - Roberto Lent
- Institute of Biomedical Sciences, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro 21941-590, Brazil
- D’Or Institute Research and Education (IDOR), Rio de Janeiro 22281-100, Brazil
| | - Fernanda Tovar-Moll
- D’Or Institute Research and Education (IDOR), Rio de Janeiro 22281-100, Brazil
| | - Afonso C Silva
- Department of Neurobiology, University of Pittsburgh Brain Institute, University of Pittsburgh, Pittsburgh, PA 15261, United States
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4
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Bencivenga F, Tullo MG, Sulpizio V, Galati G. Interhemispheric interplay between the left and right premotor cortex during grasping as assessed by dynamic causal modelling. Sci Rep 2023; 13:4958. [PMID: 36973324 PMCID: PMC10042845 DOI: 10.1038/s41598-023-31602-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Accepted: 03/14/2023] [Indexed: 03/29/2023] Open
Abstract
Research on the contribution of the ipsilateral hemisphere to unilateral movements, and how it is mediated by transcallosal connections, has so far provided contradictory findings. By using dynamic causal modelling (DCM) and Parametric Empirical Bayes analyses applied to fMRI data, we sought to describe effective connectivity during pantomimed and imagined right-hand grasping within the grasping network, namely the anterior intraparietal sulcus, ventral and dorsal (PMd) premotor cortex, supplementary motor area and primary motor cortex (M1). The two-fold aim of the present work was to explore a) whether right and left parieto-frontal areas show similar connectivity couplings, and b) the interhemispheric dynamics between these regions across the two hemispheres. We detected a network architecture comparable across hemispheres during executed but not imagined grasping movements. Furthermore, during pantomimed grasping the interhemispheric crosstalk was mainly driven by premotor areas: we found an inhibitory influence from the right PMd toward the left premotor and motor areas and excitatory couplings between homologous ventral premotor and supplementary motor regions. Overall, our results support the view that dissociable components of unilateral grasping execution are encoded by a non-lateralized set of brain areas complexly intertwined by interhemispheric dynamics, whereas motor imagery obeys different principles.
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Affiliation(s)
- Federica Bencivenga
- PhD Program in Behavioral Neuroscience, Department of Psychology, "Sapienza" University of Rome, Rome, Italy.
- Brain Imaging Laboratory, Department of Psychology, "Sapienza" University of Rome, Via Dei Marsi, 78, 00185, Rome, Italy.
- Cognitive and Motor Rehabilitation and Neuroimaging Unit, Santa Lucia Foundation (IRCCS Fondazione Santa Lucia), Rome, Italy.
| | - Maria Giulia Tullo
- Department of Translational and Precision Medicine, "Sapienza" University of Rome, Rome, Italy
| | - Valentina Sulpizio
- Brain Imaging Laboratory, Department of Psychology, "Sapienza" University of Rome, Via Dei Marsi, 78, 00185, Rome, Italy
- Cognitive and Motor Rehabilitation and Neuroimaging Unit, Santa Lucia Foundation (IRCCS Fondazione Santa Lucia), Rome, Italy
| | - Gaspare Galati
- Brain Imaging Laboratory, Department of Psychology, "Sapienza" University of Rome, Via Dei Marsi, 78, 00185, Rome, Italy
- Cognitive and Motor Rehabilitation and Neuroimaging Unit, Santa Lucia Foundation (IRCCS Fondazione Santa Lucia), Rome, Italy
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5
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A macroscopic link between interhemispheric tract myelination and cortico-cortical interactions during action reprogramming. Nat Commun 2022; 13:4253. [PMID: 35869067 PMCID: PMC9307658 DOI: 10.1038/s41467-022-31687-5] [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: 03/15/2021] [Accepted: 06/16/2022] [Indexed: 11/15/2022] Open
Abstract
Myelination has been increasingly implicated in the function and dysfunction of the adult human brain. Although it is known that axon myelination shapes axon physiology in animal models, it is unclear whether a similar principle applies in the living human brain, and at the level of whole axon bundles in white matter tracts. Here, we hypothesised that in humans, cortico-cortical interactions between two brain areas may be shaped by the amount of myelin in the white matter tract connecting them. As a test bed for this hypothesis, we use a well-defined interhemispheric premotor-to-motor circuit. We combined TMS-derived physiological measures of cortico-cortical interactions during action reprogramming with multimodal myelin markers (MT, R1, R2* and FA), in a large cohort of healthy subjects. We found that physiological metrics of premotor-to-motor interaction are broadly associated with multiple myelin markers, suggesting interindividual differences in tract myelination may play a role in motor network physiology. Moreover, we also demonstrate that myelination metrics link indirectly to action switching by influencing local primary motor cortex dynamics. These findings suggest that myelination levels in white matter tracts may influence millisecond-level cortico-cortical interactions during tasks. They also unveil a link between the physiology of the motor network and the myelination of tracts connecting its components, and provide a putative mechanism mediating the relationship between brain myelination and human behaviour. Myelination is a key regulator of brain function. Here the authors use MR-based myelin measures to examine if cortico-cortical interactions, as assessed by paired pulse transcranial magnetic stimulation, are affected by variations in myelin in the human brain.
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Chiou-Tan F, Ughwanogho U, Taber K. Special anatomy series: Updates in structural, functional, and clinical relevance of the corpus callosum: What new imaging techniques have revealed. THE JOURNAL OF THE INTERNATIONAL SOCIETY OF PHYSICAL AND REHABILITATION MEDICINE 2022. [DOI: 10.4103/jisprm.jisprm-000159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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Kagan I, Gibson L, Spanou E, Wilke M. Effective connectivity and spatial selectivity-dependent fMRI changes elicited by microstimulation of pulvinar and LIP. Neuroimage 2021; 240:118283. [PMID: 34147628 DOI: 10.1016/j.neuroimage.2021.118283] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2020] [Revised: 05/04/2021] [Accepted: 06/16/2021] [Indexed: 11/30/2022] Open
Abstract
The thalamic pulvinar and the lateral intraparietal area (LIP) share reciprocal anatomical connections and are part of an extensive cortical and subcortical network involved in spatial attention and oculomotor processing. The goal of this study was to compare the effective connectivity of dorsal pulvinar (dPul) and LIP and to probe the dependency of microstimulation effects on task demands and spatial tuning properties of a given brain region. To this end, we applied unilateral electrical microstimulation in the dPul (mainly medial pulvinar) and LIP in combination with event-related BOLD fMRI in monkeys performing fixation and memory-guided saccade tasks. Microstimulation in both dPul and LIP enhanced task-related activity in monosynaptically-connected fronto-parietal cortex and along the superior temporal sulcus (STS) including putative face patch locations, as well as in extrastriate cortex. LIP microstimulation elicited strong activity in the opposite homotopic LIP while no homotopic activation was found with dPul stimulation. Both dPul and LIP stimulation also elicited activity in several heterotopic cortical areas in the opposite hemisphere, implying polysynaptic propagation of excitation. Despite extensive activation along the intraparietal sulcus evoked by LIP stimulation, there was a difference in frontal and occipital connectivity elicited by posterior and anterior LIP stimulation sites. Comparison of dPul stimulation with the adjacent but functionally dissimilar ventral pulvinar also showed distinct connectivity. On the level of single trial timecourses within each region of interest (ROI), most ROIs did not show task-dependence of stimulation-elicited response modulation. Across ROIs, however, there was an interaction between task and stimulation, and task-specific correlations between the initial spatial selectivity and the magnitude of stimulation effect were observed. Consequently, stimulation-elicited modulation of task-related activity was best fitted by an additive model scaled down by the initial response amplitude. In summary, we identified overlapping and distinct patterns of thalamocortical and corticocortical connectivity of pulvinar and LIP, highlighting the dorsal bank and fundus of STS as a prominent node of shared circuitry. Spatial task-specific and partly polysynaptic modulations of cue and saccade planning delay period activity in both hemispheres exerted by unilateral pulvinar and parietal stimulation provide insight into the distributed interhemispheric processing underlying spatial behavior.
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Affiliation(s)
- Igor Kagan
- Decision and Awareness Group, Cognitive Neuroscience Laboratory, German Primate Center, Leibniz Institute for Primate Research, Kellnerweg 4, Goettingen 37077, Germany; Department of Cognitive Neurology, University of Goettingen, Robert-Koch-Str. 40, Goettingen 37075, Germany; Leibniz ScienceCampus Primate Cognition, Kellnerweg 4, Goettingen 37077, Germany.
| | - Lydia Gibson
- Decision and Awareness Group, Cognitive Neuroscience Laboratory, German Primate Center, Leibniz Institute for Primate Research, Kellnerweg 4, Goettingen 37077, Germany; Department of Cognitive Neurology, University of Goettingen, Robert-Koch-Str. 40, Goettingen 37075, Germany
| | - Elena Spanou
- Decision and Awareness Group, Cognitive Neuroscience Laboratory, German Primate Center, Leibniz Institute for Primate Research, Kellnerweg 4, Goettingen 37077, Germany
| | - Melanie Wilke
- Decision and Awareness Group, Cognitive Neuroscience Laboratory, German Primate Center, Leibniz Institute for Primate Research, Kellnerweg 4, Goettingen 37077, Germany; Department of Cognitive Neurology, University of Goettingen, Robert-Koch-Str. 40, Goettingen 37075, Germany; Leibniz ScienceCampus Primate Cognition, Kellnerweg 4, Goettingen 37077, Germany
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8
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Unno S, Shinoda M, Soma K, Kubo A, Sessle BJ, Matsui T, Ando M, Asaka J, Otsuki K, Yonemoto H, Onose H, Sakanashi K, Iwata K. Properties of heat-sensitive neurons in the premotor cortex of conscious monkeys. J Oral Sci 2020; 62:382-386. [PMID: 32741851 DOI: 10.2334/josnusd.19-0512] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Abstract
To investigate neuronal activity involved in responses to noxious stimuli in conscious monkeys, the animals were subjected to a task that required them to detect a small change in facial skin temperature or light (second temperature: T2, second light: V2) relative to an initial condition (T1 or V1), and to detect changes in V2 along with a heat task. Recordings were obtained from 57 neurons in the ventral premotor cortex (PMv) during the heat or light detection task. T1 neurons and T2 neurons showed increased activity only during T1 or T2, and T1/T2 neurons were activated by both T1 and T2 stimuli. T1/T2 neurons showed an increase in firing at higher T1 temperatures, whereas T1 neurons did not. About half of the non-light/heat-sensitive T1/T2 neurons showed increased firing at higher T2 temperatures, whereas T2 neurons showed no such increase. The heat responses of heat-sensitive PMv neurons were significantly suppressed when monkeys shifted their attention from heat to light. The present findings suggest that heat-sensitive PMv neurons may be involved in motor responses to noxious heat, whereas light/heat-PMv neurons may be involved in emotional and motivational aspects of pain and inappropriate motor responses to allow escape from noxious stimuli.
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Affiliation(s)
- Shumpei Unno
- Department of Oral Physiology, School of Dentistry, Matsumoto Dental University
| | | | - Kumi Soma
- Department of Pediatric Dentistry, Nihon University School of Dentistry
| | - Asako Kubo
- Department of Physiology, Nihon University School of Dentistry
| | - Barry J Sessle
- Faculty of Dentistry and Department of Physiology, Faculty of Medicine, University of Toronto
| | - Tomoyuki Matsui
- Department of Pediatric Dentistry, Nihon University School of Dentistry
| | - Masatoshi Ando
- Department of Oral and Maxillofacial Surgery, Nihon University School of Dentistry
| | - Junichi Asaka
- Department of Physiology, Nihon University School of Dentistry
| | | | | | - Hiroki Onose
- Department of Physiology, Nihon University School of Dentistry
| | | | - Koichi Iwata
- Department of Physiology, Nihon University School of Dentistry
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Suárez R, Paolino A, Fenlon LR, Morcom LR, Kozulin P, Kurniawan ND, Richards LJ. A pan-mammalian map of interhemispheric brain connections predates the evolution of the corpus callosum. Proc Natl Acad Sci U S A 2018; 115:9622-9627. [PMID: 30181276 PMCID: PMC6156618 DOI: 10.1073/pnas.1808262115] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The brain of mammals differs from that of all other vertebrates, in having a six-layered neocortex that is extensively interconnected within and between hemispheres. Interhemispheric connections are conveyed through the anterior commissure in egg-laying monotremes and marsupials, whereas eutherians evolved a separate commissural tract, the corpus callosum. Although the pattern of interhemispheric connectivity via the corpus callosum is broadly shared across eutherian species, it is not known whether this pattern arose as a consequence of callosal evolution or instead corresponds to a more ancient feature of mammalian brain organization. Here we show that, despite cortical axons using an ancestral commissural route, monotremes and marsupials share features of interhemispheric connectivity with eutherians that likely predate the origin of the corpus callosum. Based on ex vivo magnetic resonance imaging and tractography, we found that connections through the anterior commissure in both fat-tailed dunnarts (Marsupialia) and duck-billed platypus (Monotremata) are spatially segregated according to cortical area topography. Moreover, cell-resolution retrograde and anterograde interhemispheric circuit mapping in dunnarts revealed several features shared with callosal circuits of eutherians. These include the layered organization of commissural neurons and terminals, a broad map of connections between similar (homotopic) regions of each hemisphere, and regions connected to different areas (heterotopic), including hyperconnected hubs along the medial and lateral borders of the cortex, such as the cingulate/motor cortex and claustrum/insula. We therefore propose that an interhemispheric connectome originated in early mammalian ancestors, predating the evolution of the corpus callosum. Because these features have been conserved throughout mammalian evolution, they likely represent key aspects of neocortical organization.
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Affiliation(s)
- Rodrigo Suárez
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4070, Australia;
| | - Annalisa Paolino
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4070, Australia
| | - Laura R Fenlon
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4070, Australia
| | - Laura R Morcom
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4070, Australia
| | - Peter Kozulin
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4070, Australia
| | - Nyoman D Kurniawan
- Centre for Advanced Imaging, The University of Queensland, Brisbane, QLD 4070, Australia
| | - Linda J Richards
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD 4070, Australia;
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4070, Australia
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10
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Chu R, Meltzer JA, Bitan T. Interhemispheric interactions during sentence comprehension in patients with aphasia. Cortex 2018; 109:74-91. [PMID: 30312780 DOI: 10.1016/j.cortex.2018.08.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Revised: 05/03/2018] [Accepted: 08/28/2018] [Indexed: 02/06/2023]
Abstract
Right-hemisphere involvement in language processing following left-hemisphere damage may reflect either compensatory processes, or a release from homotopic transcallosal inhibition, resulting in excessive right-to-left suppression that is maladaptive for language performance. Using fMRI, we assessed inter-hemispheric effective connectivity in fifteen patients with post-stroke aphasia, along with age-matched and younger controls during a sentence comprehension task. Dynamic Causal Modeling was used with four bilateral regions including inferior frontal gyri (IFG) and primary auditory cortices (A1). Despite the presence of lesions, satisfactory model fit was obtained in 9/15 patients. In young controls, the only significant homotopic connection (RA1-LA1), was excitatory, while inhibitory connections emanated from LIFG to both left and right A1's. Interestingly, these connections were also correlated with language comprehension scores in patients. The results for homotopic connections show that excitatory connectivity from RA1-to-LA1 and inhibitory connectivity from LA1-to-RA1 are associated with general auditory verbal comprehension. Moreover, negative correlations were found between sentence comprehension and top-down coupling for both heterotopic (LIFG-to-RA1) and intra-hemispheric (LIFG-to-LA1) connections. These results do not show an emergence of a new compensatory right to left excitation in patients nor do they support the existence of left to right transcallosal suppression in controls. Nevertheless, the correlations with performance in patients are consistent with some aspects of both the compensation model, and the transcallosal suppression account for the role of the RH. Altogether our results suggest that changes to both excitatory and inhibitory homotopic and heterotopic connections due to LH damage may be maladaptive, as they disrupt the normal inter-hemispheric coordination and communication.
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Affiliation(s)
- Ronald Chu
- Baycrest Health Sciences, Rotman Research Institute, Toronto, ON, Canada; University of Toronto, Department of Psychology, Toronto, ON, Canada.
| | - Jed A Meltzer
- Baycrest Health Sciences, Rotman Research Institute, Toronto, ON, Canada; University of Toronto, Department of Psychology, Toronto, ON, Canada; University of Toronto, Department of Speech-Language Pathology, Toronto, ON, Canada; Canadian Partnership for Stroke Recovery, Ottawa, ON, Canada
| | - Tali Bitan
- University of Toronto, Department of Speech-Language Pathology, Toronto, ON, Canada; University of Haifa, Department of Psychology and IIPDM, Haifa, Israel
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