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Ocklenburg S, Mundorf A, Gerrits R, Karlsson EM, Papadatou-Pastou M, Vingerhoets G. Clinical implications of brain asymmetries. Nat Rev Neurol 2024; 20:383-394. [PMID: 38783057 DOI: 10.1038/s41582-024-00974-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/08/2024] [Indexed: 05/25/2024]
Abstract
No two human brains are alike, and with the rise of precision medicine in neurology, we are seeing an increased emphasis on understanding the individual variability in brain structure and function that renders every brain unique. Functional and structural brain asymmetries are a fundamental principle of brain organization, and recent research suggests substantial individual variability in these asymmetries that needs to be considered in clinical practice. In this Review, we provide an overview of brain asymmetries, variations in such asymmetries and their relevance in the clinical context. We review recent findings on brain asymmetries in neuropsychiatric and neurodevelopmental disorders, as well as in specific learning disabilities, with an emphasis on large-scale database studies and meta-analyses. We also highlight the relevance of asymmetries for disease symptom onset in neurodegenerative diseases and their implications for lateralized treatments, including brain stimulation. We conclude that alterations in brain asymmetry are not sufficiently specific to act as diagnostic biomarkers but can serve as meaningful symptom or treatment response biomarkers in certain contexts. On the basis of these insights, we provide several recommendations for neurological clinical practice.
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Affiliation(s)
- Sebastian Ocklenburg
- Department of Psychology, MSH Medical School Hamburg, Hamburg, Germany.
- ICAN Institute for Cognitive and Affective Neuroscience, MSH Medical School Hamburg, Hamburg, Germany.
- Biopsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany.
| | - Annakarina Mundorf
- ISM Institute for Systems Medicine and Department of Human Medicine, MSH Medical School Hamburg, Hamburg, Germany
- Division of Cognitive Neuroscience, Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Robin Gerrits
- Department of Experimental-Clinical and Health Psychology, Ghent University, Ghent, Belgium
- Ghent Institute for Functional and Metabolic Imaging (GIfMI), Ghent University, Ghent, Belgium
| | - Emma M Karlsson
- Department of Experimental-Clinical and Health Psychology, Ghent University, Ghent, Belgium
- Ghent Institute for Functional and Metabolic Imaging (GIfMI), Ghent University, Ghent, Belgium
| | - Marietta Papadatou-Pastou
- National and Kapodistrian University of Athens, Athens, Greece
- Biomedical Research Foundation, Academy of Athens, Athens, Greece
| | - Guy Vingerhoets
- Department of Experimental-Clinical and Health Psychology, Ghent University, Ghent, Belgium
- Ghent Institute for Functional and Metabolic Imaging (GIfMI), Ghent University, Ghent, Belgium
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2
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Gerrits R. Variability in Hemispheric Functional Segregation Phenotypes: A Review and General Mechanistic Model. Neuropsychol Rev 2024; 34:27-40. [PMID: 36576683 DOI: 10.1007/s11065-022-09575-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 07/15/2022] [Accepted: 11/16/2022] [Indexed: 12/29/2022]
Abstract
Many functions of the human brain are organized asymmetrically and are subject to strong population biases. Some tasks, like speaking and making complex hand movements, exhibit left hemispheric dominance, whereas others, such as spatial processing and recognizing faces, favor the right hemisphere. While pattern of preference implies the existence of a stereotypical way of distributing functions between the hemispheres, an ever-increasing body of evidence indicates that not everyone follows this pattern of hemispheric functional segregation. On the contrary, the review conducted in this article shows that departures from the standard hemispheric division of labor are routinely observed and assume many distinct forms, each having a different prevalence rate. One of the key challenges in human neuroscience is to model this variability. By integrating well-established and recently emerged ideas about the mechanisms that underlie functional lateralization, the current article proposes a general mechanistic model that explains the observed distribution of segregation phenotypes and generates new testable hypotheses.
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Affiliation(s)
- Robin Gerrits
- Department of Experimental Psychology, Ghent University, Ghent, Belgium.
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3
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Gerrits R, Vingerhoets G. Brain functional segregation, handedness and cognition in situs inversus totalis: A replication study. Neuropsychologia 2023; 191:108731. [PMID: 37949213 DOI: 10.1016/j.neuropsychologia.2023.108731] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 10/04/2023] [Accepted: 11/06/2023] [Indexed: 11/12/2023]
Abstract
Situs inversus totalis (SIT) is a rare congenital anomaly in which the arrangement of the visceral organs is completely left-right mirrored. A previous study by our lab suggests that SIT (N = 15) correlated with more heterogeneous asymmetrical brain organization and increased left-handedness. In addition, visceral reversal correlated with poorer cognitive performance, especially when hemisphere organization was atypical. The current study sought to replicate these findings in a larger sample. We scanned 23 volunteers with SIT as well as an equal number of controls with usual organ arrangement, and used fMRI to determine their hemisphere dominance for two left hemisphere functions (language and manual praxis) and two right hemisphere functions (spatial attention and face recognition). Effects of SIT etiology were explored by pooling data from the original cohort with the replication sample. Our results reveal that each of those four cognitive functions demonstrated the expected population dominance in SIT, albeit they were less pronounced - but not significantly so - compared to controls. Unusual patterns of hemispheric crowding and mirror-reversal of functional brain organization was observed more often in SIT (48%) than in the controls (30%), but this difference also did not reach statistical significance. However, left-handedness was found to be significantly more common in SIT (26%) than in the overall population (10.6%). Finally, cognitive ability, as assessed by a neuropsychological test battery, was not associated with organ situs or hemisphere organization. Taken together, our data adds to the growing evidence that the determinants of visceral and neural asymmetries are largely independent from one another and that complete situs inversus does not co-occur with an obligatory transposition of the brain's functional architecture. There nevertheless might be instances in which (genetic) mechanisms could simultaneously cause complete visceral reversal and atypical brain laterality.
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Affiliation(s)
- Robin Gerrits
- Department of Experimental Psychology, Ghent University, Ghent, Belgium
| | - Guy Vingerhoets
- Department of Experimental Psychology, Ghent University, Ghent, Belgium.
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4
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Dogaru BG, Munteanu C. The Role of Hydrogen Sulfide (H 2S) in Epigenetic Regulation of Neurodegenerative Diseases: A Systematic Review. Int J Mol Sci 2023; 24:12555. [PMID: 37628735 PMCID: PMC10454626 DOI: 10.3390/ijms241612555] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 08/04/2023] [Accepted: 08/07/2023] [Indexed: 08/27/2023] Open
Abstract
This review explores the emerging role of hydrogen sulfide (H2S) in modulating epigenetic mechanisms involved in neurodegenerative diseases. Accumulating evidence has begun to elucidate the multifaceted ways in which H2S influences the epigenetic landscape and, subsequently, the progression of various neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's disease. H2S can modulate key components of the epigenetic machinery, such as DNA methylation, histone modifications, and non-coding RNAs, impacting gene expression and cellular functions relevant to neuronal survival, inflammation, and synaptic plasticity. We synthesize recent research that positions H2S as an essential player within this intricate network, with the potential to open new therapeutic avenues for these currently incurable conditions. Despite significant progress, there remains a considerable gap in our understanding of the precise molecular mechanisms and the potential therapeutic implications of modulating H2S levels or its downstream targets. We conclude by identifying future directions for research aimed at exploiting the therapeutic potential of H2S in neurodegenerative diseases.
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Affiliation(s)
- Bombonica Gabriela Dogaru
- Faculty of Medicine, “Iuliu Hatieganu” University of Medicine and Pharmacy, 400012 Cluj-Napoca, Romania;
- Clinical Rehabilitation Hospital, 400437 Cluj-Napoca, Romania
| | - Constantin Munteanu
- Teaching Emergency Hospital “Bagdasar-Arseni” (TEHBA), 041915 Bucharest, Romania
- Faculty of Medical Bioengineering, University of Medicine and Pharmacy “Grigore T. Popa” Iași, 700454 Iași, Romania
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5
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Abbondanza F, Dale PS, Wang CA, Hayiou‐Thomas ME, Toseeb U, Koomar TS, Wigg KG, Feng Y, Price KM, Kerr EN, Guger SL, Lovett MW, Strug LJ, van Bergen E, Dolan CV, Tomblin JB, Moll K, Schulte‐Körne G, Neuhoff N, Warnke A, Fisher SE, Barr CL, Michaelson JJ, Boomsma DI, Snowling MJ, Hulme C, Whitehouse AJO, Pennell CE, Newbury DF, Stein J, Talcott JB, Bishop DVM, Paracchini S. Language and reading impairments are associated with increased prevalence of non-right-handedness. Child Dev 2023; 94:970-984. [PMID: 36780127 PMCID: PMC10330064 DOI: 10.1111/cdev.13914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Revised: 12/09/2022] [Accepted: 12/12/2022] [Indexed: 02/14/2023]
Abstract
Handedness has been studied for association with language-related disorders because of its link with language hemispheric dominance. No clear pattern has emerged, possibly because of small samples, publication bias, and heterogeneous criteria across studies. Non-right-handedness (NRH) frequency was assessed in N = 2503 cases with reading and/or language impairment and N = 4316 sex-matched controls identified from 10 distinct cohorts (age range 6-19 years old; European ethnicity) using a priori set criteria. A meta-analysis (Ncases = 1994) showed elevated NRH % in individuals with language/reading impairment compared with controls (OR = 1.21, CI = 1.06-1.39, p = .01). The association between reading/language impairments and NRH could result from shared pathways underlying brain lateralization, handedness, and cognitive functions.
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Affiliation(s)
| | - Philip S. Dale
- Department of Speech and Hearing SciencesUniversity of New MexicoAlbuquerqueNew MexicoUSA
| | - Carol A. Wang
- School of Medicine and Public HealthUniversity of NewcastleCallaghanNew South WalesAustralia
| | | | - Umar Toseeb
- Department of EducationUniversity of YorkYorkUK
| | | | - Karen G. Wigg
- Division of Experimental and Translational Neuroscience, Krembil Research InstituteUniversity Health NetworkTorontoOntarioCanada
| | - Yu Feng
- Division of Experimental and Translational Neuroscience, Krembil Research InstituteUniversity Health NetworkTorontoOntarioCanada
| | - Kaitlyn M. Price
- Division of Experimental and Translational Neuroscience, Krembil Research InstituteUniversity Health NetworkTorontoOntarioCanada
- Program in Neuroscience and Mental HealthHospital for Sick ChildrenTorontoOntarioCanada
- Department of PhysiologyUniversity of TorontoTorontoOntarioCanada
| | - Elizabeth N. Kerr
- Department of PaediatricsUniversity of TorontoTorontoOntarioCanada
- Department of PsychologyHospital for Sick ChildrenTorontoOntarioCanada
| | - Sharon L. Guger
- Department of PsychologyHospital for Sick ChildrenTorontoOntarioCanada
| | - Maureen W. Lovett
- Program in Neuroscience and Mental HealthHospital for Sick ChildrenTorontoOntarioCanada
- Department of PaediatricsUniversity of TorontoTorontoOntarioCanada
| | - Lisa J. Strug
- Genetics and Genome BiologyHospital for Sick ChildrenTorontoOntarioCanada
- Dalla Lana School of Public HealthUniversity of TorontoTorontoOntarioCanada
| | - Elsje van Bergen
- Department of Biological PsychologyVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - Conor V. Dolan
- Department of Biological PsychologyVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | | | - Kristina Moll
- Department of Child and Adolescent Psychiatry, Psychotherapy and PsychosomaticsLudwig‐Maximilians‐University Hospital MunichMunchenGermany
| | - Gerd Schulte‐Körne
- Department of Child and Adolescent Psychiatry, Psychotherapy and PsychosomaticsLudwig‐Maximilians‐University Hospital MunichMunchenGermany
| | - Nina Neuhoff
- Department of Child and Adolescent Psychiatry, Psychotherapy and PsychosomaticsLudwig‐Maximilians‐University Hospital MunichMunchenGermany
| | | | - Simon E. Fisher
- Language and Genetics DepartmentMax Planck Institute for PsycholinguisticsNijmegenThe Netherlands
- Donders Institute for Brain, Cognition and BehaviourRadboud UniversityNijmegenThe Netherlands
| | - Cathy L. Barr
- Division of Experimental and Translational Neuroscience, Krembil Research InstituteUniversity Health NetworkTorontoOntarioCanada
- Program in Neuroscience and Mental HealthHospital for Sick ChildrenTorontoOntarioCanada
- Department of PhysiologyUniversity of TorontoTorontoOntarioCanada
| | | | - Dorret I. Boomsma
- Department of Biological PsychologyVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | | | | | | | - Craig E. Pennell
- School of Medicine and Public HealthUniversity of NewcastleCallaghanNew South WalesAustralia
| | - Dianne F. Newbury
- Department of Biological and Medical SciencesOxford Brookes UniversityOxfordUK
| | - John Stein
- Department of PhysiologyUniversity of OxfordOxfordUK
| | - Joel B. Talcott
- Aston Brain Center, School of Life and Health SciencesAston UniversityBirminghamUK
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Labache L, Ge T, Yeo BTT, Holmes AJ. Language network lateralization is reflected throughout the macroscale functional organization of cortex. Nat Commun 2023; 14:3405. [PMID: 37296118 PMCID: PMC10256741 DOI: 10.1038/s41467-023-39131-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 05/30/2023] [Indexed: 06/12/2023] Open
Abstract
Hemispheric specialization is a fundamental feature of human brain organization. However, it is not yet clear to what extent the lateralization of specific cognitive processes may be evident throughout the broad functional architecture of cortex. While the majority of people exhibit left-hemispheric language dominance, a substantial minority of the population shows reverse lateralization. Using twin and family data from the Human Connectome Project, we provide evidence that atypical language dominance is associated with global shifts in cortical organization. Individuals with atypical language organization exhibit corresponding hemispheric differences in the macroscale functional gradients that situate discrete large-scale networks along a continuous spectrum, extending from unimodal through association territories. Analyses reveal that both language lateralization and gradient asymmetries are, in part, driven by genetic factors. These findings pave the way for a deeper understanding of the origins and relationships linking population-level variability in hemispheric specialization and global properties of cortical organization.
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Affiliation(s)
- Loïc Labache
- Department of Psychology, Yale University, New Haven, CT, 06520, US.
| | - Tian Ge
- Psychiatric and Neurodevelopmental Genetics Unit, Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, 02114, US
- Center for Precision Psychiatry, Department of Psychiatry, Massachusetts General Hospital, Boston, MA, 02114, US
- Stanley Center for Psychiatric Research, Broad Institute, Cambridge, MA, 02142, US
| | - B T Thomas Yeo
- Department of Electrical and Computer Engineering, Centre for Sleep and Cognition, National University of Singapore, Singapore, SG, 119077, Singapore
- Department of Electrical and Computer Engineering, Centre for Translational Magnetic Resonance Research, National University of Singapore, Singapore, SG, 119077, Singapore
- N.1 Institute for Health, National University of Singapore, Singapore, SG, 119077, Singapore
- Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, 02129, US
- National University of Singapore Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, SG, 119077, Singapore
| | - Avram J Holmes
- Department of Psychology, Yale University, New Haven, CT, 06520, US.
- Department of Psychiatry, Yale University, New Haven, CT, 06520, US.
- Wu Tsai Institute, Yale University, New Haven, CT, 06520, US.
- Department of Psychiatry, Brain Health Institute, Rutgers University, Piscataway, NJ, 08854, US.
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McManus IC. Compellingly negative: Bayesian analysis shows handedness and dementia are not associated. Brain Commun 2023; 5:fcad162. [PMID: 37265599 PMCID: PMC10231802 DOI: 10.1093/braincomms/fcad162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 04/18/2023] [Accepted: 05/17/2023] [Indexed: 06/03/2023] Open
Abstract
This scientific commentary refers to "The role of hand preference in cognition and neuropsychiatric symptoms in neurodegenerative diseases" by Saari & Vuoksimaa (https://doi.org/10.1093/braincomms/fcad137).
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Affiliation(s)
- I C McManus
- Correspondence to: I C McManus, Research Department of Clinical, Educational and Health Psychology, University College London Faculty of Brain Sciences, Gower Street London, London WC1E 6BT, UK E-mail:
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Stewart AG, Millard AR. The sinister story of a gauche deliverer and his corrie-fisted tribesmen: Ehud and the left-handed artillery. Laterality 2023:1-17. [PMID: 37139692 DOI: 10.1080/1357650x.2023.2199965] [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: 05/05/2023]
Abstract
Bias against left-handers is well-documented and seen in the etymology of "left" and "right" in most languages. The subject of this study, Ehud, lived between the exodus of the Hebrew slaves from Egypt and the establishment of the Israelite kingdom (c1200-1000 BC), at the transition between the Late Bronze Age and Iron Age 1. His left-handedness was crucial to his deliverance of the proto-nation from tyranny, recorded in Judges in the Hebrew Bible. The description of Ehud as left-handed ('iṭṭēr yaḏ-yεmînô) is used once more in the Hebrew Bible, also in Judges, to describe the artillery of Ehud's tribe. The words apparently mean "bound/restricted in the right hand", sometimes interpreted as "ambidextrous". This is unlikely: ambidexterity is uncommon. The artillery used the sling with either hand, but Ehud used his left (śεm'ōl) hand to draw his sword. śεm'ōl, used throughout the Hebrew Bible, means left, without bias or derogatory implications. We suggest that 'iṭṭēr yaḏ-yεmînô was a right-handed bias towards left-handed people, but Ehud's left-handed victory was recognized as significant. Significant enough that (a) the language changed and the biased description was dropped in favour of simple description, and (b) the army changed with the development of left-handed slingers (artillery).
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Affiliation(s)
- Alex G Stewart
- College of Life and Environmental Science, University of Exeter, Exeter, UK
- Health Protection, Public Health England, Liverpool, UK
| | - Alan R Millard
- Department of Archaeology, Classics and Egyptology, Liverpool University, Liverpool, UK
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Light-induced asymmetries in embryonic retinal gene expression are mediated by the vascular system and extracellular matrix. Sci Rep 2022; 12:12086. [PMID: 35840576 PMCID: PMC9287303 DOI: 10.1038/s41598-022-14963-8] [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: 11/28/2021] [Accepted: 06/15/2022] [Indexed: 11/29/2022] Open
Abstract
Left–right asymmetries in the nervous system (lateralisation) influence a broad range of behaviours, from social responses to navigation and language. The role and pathways of endogenous and environmental mechanisms in the ontogeny of lateralisation remains to be established. The domestic chick is a model of both endogenous and experience-induced lateralisation driven by light exposure. Following the endogenous rightward rotation of the embryo, the asymmetrical position in the egg results in a greater exposure of the right eye to environmental light. To identify the genetic pathways activated by asymmetric light stimulation, and their time course, we exposed embryos to different light regimes: darkness, 6 h of light and 24 h of light. We used RNA-seq to compare gene expression in the right and left retinas and telencephalon. We detected differential gene expression in right vs left retina after 6 h of light exposure. This difference was absent in the darkness condition and had already disappeared by 24 h of light exposure, suggesting that light-induced activation is a self-terminating phenomenon. This transient effect of light exposure was associated with a downregulation of the sensitive-period mediator gene DIO2 (iodothyronine deiodinase 2) in the right retina. No differences between genes expressed in the right vs. left telencephalon were detected. Gene networks associated with lateralisation were connected to vascularisation, cell motility, and the extracellular matrix. Interestingly, we know that the extracellular matrix—including the differentially expressed PDGFRB gene—is involved in morphogenesis, sensitive periods, and in the endogenous chiral mechanism of primary cilia, that drives lateralisation. Our data show a similarity between endogenous and experience-driven lateralisation, identifying functional gene networks that affect lateralisation in a specific time window.
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Cognitive and Neurophysiological Models of Brain Asymmetry. Symmetry (Basel) 2022. [DOI: 10.3390/sym14050971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Asymmetry is an inherent characteristic of brain organization in both humans and other vertebrate species, and is evident at the behavioral, neurophysiological, and structural levels. Brain asymmetry underlies the organization of several cognitive systems, such as emotion, communication, and spatial processing. Despite this ubiquity of asymmetries in the vertebrate brain, we are only beginning to understand the complex neuronal mechanisms underlying the interaction between hemispheric asymmetries and cognitive systems. Unfortunately, despite the vast number of empirical studies on brain asymmetries, theoretical models that aim to provide mechanistic explanations of hemispheric asymmetries are sparse in the field. Therefore, this Special Issue aims to highlight empirically based mechanistic models of brain asymmetry. Overall, six theoretical and four empirical articles were published in the Special Issue, covering a wide range of topics, from human handedness to auditory laterality in bats. Two key challenges for theoretical models of brain asymmetry are the integration of increasingly complex molecular data into testable models, and the creation of theoretical models that are robust and testable across different species.
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