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Physiological Reviews Jul 2020Comparative studies on brain asymmetry date back to the 19th century but then largely disappeared due to the assumption that lateralization is uniquely human. Since the... (Review)
Review
Comparative studies on brain asymmetry date back to the 19th century but then largely disappeared due to the assumption that lateralization is uniquely human. Since the reemergence of this field in the 1970s, we learned that left-right differences of brain and behavior exist throughout the animal kingdom and pay off in terms of sensory, cognitive, and motor efficiency. Ontogenetically, lateralization starts in many species with asymmetrical expression patterns of genes within the Nodal cascade that set up the scene for later complex interactions of genetic, environmental, and epigenetic factors. These take effect during different time points of ontogeny and create asymmetries of neural networks in diverse species. As a result, depending on task demands, left- or right-hemispheric loops of feedforward or feedback projections are then activated and can temporarily dominate a neural process. In addition, asymmetries of commissural transfer can shape lateralized processes in each hemisphere. It is still unclear if interhemispheric interactions depend on an inhibition/excitation dichotomy or instead adjust the contralateral temporal neural structure to delay the other hemisphere or synchronize with it during joint action. As outlined in our review, novel animal models and approaches could be established in the last decades, and they already produced a substantial increase of knowledge. Since there is practically no realm of human perception, cognition, emotion, or action that is not affected by our lateralized neural organization, insights from these comparative studies are crucial to understand the functions and pathologies of our asymmetric brain.
Topics: Animals; Biological Evolution; Brain; Functional Laterality; History, 19th Century; History, 20th Century; History, 21st Century; Humans; Research
PubMed: 32233912
DOI: 10.1152/physrev.00006.2019 -
Neuron Apr 2017The brains of humans and other animals are asymmetrically organized, but we still know little about the ontogenetic and neural fundaments of lateralizations. Here, we... (Review)
Review
The brains of humans and other animals are asymmetrically organized, but we still know little about the ontogenetic and neural fundaments of lateralizations. Here, we review the current state of understanding about the role of genetic and non-genetic factors for the development of neural and behavioral asymmetries in vertebrates. At the genetic level, the Nodal signaling cascade is of central importance, but several other genetic pathways have been discovered to also shape the lateralized embryonic brain. Studies in humans identified several relevant genes with mostly small effect sizes but also highlight the extreme importance of non-genetic factors for asymmetry development. This is also visible in visual asymmetry in birds, in which genes only affect embryonic body position, while the resulting left-right difference of visual stimulation shapes visual pathways in a lateralized way. These and further studies in zebrafish and humans highlight that the many routes from genes to asymmetries of function run through left-right differences of neural pathways. They constitute the lateralized blueprints of our perception, cognition, and action.
Topics: Animals; Functional Laterality; Habenula; Humans; Neural Pathways; Photic Stimulation; Visual Pathways; Visual Perception
PubMed: 28426959
DOI: 10.1016/j.neuron.2017.02.045 -
Deutsches Arzteblatt International Dec 2011The human cerebrum is asymmetrical, consisting of two hemispheres with differing functions. Recent epidemiological and neurobiological research has shed new light on the... (Review)
Review
BACKGROUND
The human cerebrum is asymmetrical, consisting of two hemispheres with differing functions. Recent epidemiological and neurobiological research has shed new light on the development of the cerebral lateralization of motor processes, including handedness. In this article, we present these findings from a medical perspective.
METHOD
We selectively searched the PubMed online database for articles including the terms "handedness," "left handedness," "right handedness," and "cerebral lateralization." Highly ranked and commonly cited articles were included in our analysis.
RESULTS
The emergence of handedness has been explained by physiological and pathological models. Handedness arose early in evolution and has probably been constitutive for the development of higher cognitive functions. For instance, handedness may have provided the basis for the development of speech and fine motor skills, both of which have played a critical role in the evolution of mankind. The disadvantages of certain types of handedness are discussed, as some cases seem to be associated with disease.
CONCLUSION
The consideration of handedness from the epidemiological, neurobiological, and medical points of view provides insight into cerebral lateralization.
Topics: Brain; Brain Diseases; Functional Laterality; Humans; Models, Neurological
PubMed: 22259638
DOI: 10.3238/arztebl.2011.0849 -
Annual Review of Psychology Jan 2018This article reviews the effects of lesions to the frontal cortex on the ability to carry out active thought, namely, to reason, think flexibly, produce strategies, and... (Review)
Review
This article reviews the effects of lesions to the frontal cortex on the ability to carry out active thought, namely, to reason, think flexibly, produce strategies, and formulate and realize plans. We discuss how and why relevant neuropsychological studies should be carried out. The relationships between active thought and both intelligence and language are considered. The following basic processes necessary for effective active thought are reviewed: concentration, set switching, inhibiting potentiated responses, and monitoring and checking. Different forms of active thought are then addressed: abstraction, deduction, reasoning in well-structured and ill-structured problem spaces, novel strategy generation, and planning. We conclude that neuropsychological findings are valuable for providing information on systems rather than networks, especially information concerning prefrontal lateralization of function. We present a synthesis of the respective roles of the left and right lateral prefrontal cortex in active thought.
Topics: Attention; Functional Laterality; Humans; Intelligence; Prefrontal Cortex; Thinking
PubMed: 28813204
DOI: 10.1146/annurev-psych-010416-044123 -
Cerebral Cortex (New York, N.Y. : 1991) Jul 2022Striatal loci are connected to both the ipsilateral and contralateral frontal cortex. Normative quantitation of the dissimilarity between striatal loci's hemispheric...
Striatal loci are connected to both the ipsilateral and contralateral frontal cortex. Normative quantitation of the dissimilarity between striatal loci's hemispheric connection profiles and its spatial variance across the striatum, and assessment of how interindividual differences relate to function, stands to further the understanding of the role of corticostriatal circuits in lateralized functions and the role of abnormal corticostriatal laterality in neurodevelopmental and other neuropsychiatric disorders. A resting-state functional connectivity fingerprinting approach (n = 261) identified "laterality hotspots"-loci whose profiles of connectivity with ipsilateral and contralateral frontal cortex were disproportionately dissimilar-in the right rostral ventral putamen, left rostral central caudate, and bilateral caudal ventral caudate. Findings were replicated in an independent sample and were robust to both preprocessing choices and the choice of cortical atlas used for parcellation definitions. Across subjects, greater rightward connectional laterality at the right ventral putamen hotspot and greater leftward connectional laterality at the left rostral caudate hotspot were associated with higher performance on tasks engaging lateralized functions (i.e., response inhibition and language, respectively). In sum, we find robust and reproducible evidence for striatal loci with disproportionately lateralized connectivity profiles where interindividual differences in laterality magnitude are associated with behavioral capacities on lateralized functions.
Topics: Brain Mapping; Corpus Striatum; Functional Laterality; Humans; Magnetic Resonance Imaging; Neural Pathways; Putamen
PubMed: 34727171
DOI: 10.1093/cercor/bhab392 -
Seizure Apr 2020Epileptic seizure semiology adds important information to the formulation of the hypothesis of the epileptogenic zone. Seizure semiology in infants and children are... (Review)
Review
Epileptic seizure semiology adds important information to the formulation of the hypothesis of the epileptogenic zone. Seizure semiology in infants and children are simple and elementary, becoming more complex with maturation of brain. Also in this age group, seizure semiology may be generalized in a setting of a focal lesion or may show focal signs with misleading localization values. We review seizure semiology of patients aged one month to ten years with respect to lateralization and localization of the epileptogenic zone.
Topics: Child; Child, Preschool; Epilepsies, Partial; Epilepsy, Generalized; Functional Laterality; Humans; Infant; Seizures
PubMed: 31708348
DOI: 10.1016/j.seizure.2019.10.015 -
Brain Structure & Function Mar 2022Emotions are valenced mental responses and associated physiological reactions that occur spontaneously and automatically in response to internal or external stimuli, and... (Review)
Review
Emotions are valenced mental responses and associated physiological reactions that occur spontaneously and automatically in response to internal or external stimuli, and can influence our behavior, and can themselves be modulated to a certain degree voluntarily or by external stimuli. They are subserved by large-scale integrated neuronal networks with epicenters in the amygdala and the hippocampus, and which overlap in the anterior cingulate cortex. Although emotion processing is accepted as being lateralized, the specific role of each hemisphere remains an issue of controversy, and two major hypotheses have been proposed. In the right-hemispheric dominance hypothesis, all emotions are thought to be processed in the right hemisphere, independent of their valence or of the emotional feeling being processed. In the valence lateralization hypothesis, the left is thought to be dominant for the processing of positively valenced stimuli, or of stimuli inducing approach behaviors, whereas negatively valenced stimuli, or stimuli inducing withdrawal behaviors, would be processed in the right hemisphere. More recent research points at the existence of multiple interrelated networks, each associated with the processing of a specific component of emotion generation, i.e., its generation, perception, and regulation. It has thus been proposed to move from hypotheses supporting an overall hemispheric specialization for emotion processing toward dynamic models incorporating multiple interrelated networks which do not necessarily share the same lateralization patterns.
Topics: Amygdala; Emotions; Functional Laterality; Neurons
PubMed: 34216271
DOI: 10.1007/s00429-021-02331-7 -
Neuron Mar 2021Visual working memory (WM) storage is largely independent between the left and right visual hemifields/cerebral hemispheres, yet somehow WM feels seamless. We studied...
Visual working memory (WM) storage is largely independent between the left and right visual hemifields/cerebral hemispheres, yet somehow WM feels seamless. We studied how WM is integrated across hemifields by recording neural activity bilaterally from lateral prefrontal cortex. An instructed saccade during the WM delay shifted the remembered location from one hemifield to the other. Before the shift, spike rates and oscillatory power showed clear signatures of memory laterality. After the shift, the lateralization inverted, consistent with transfer of the memory trace from one hemisphere to the other. Transferred traces initially used different neural ensembles from feedforward-induced ones, but they converged at the end of the delay. Around the time of transfer, synchrony between the two prefrontal hemispheres peaked in theta and beta frequencies, with a directionality consistent with memory trace transfer. This illustrates how dynamics between the two cortical hemispheres can stitch together WM traces across visual hemifields.
Topics: Animals; Female; Functional Laterality; Macaca mulatta; Male; Memory, Short-Term; Prefrontal Cortex; Visual Perception
PubMed: 33561399
DOI: 10.1016/j.neuron.2021.01.016 -
Trends in Cognitive Sciences Feb 2013Hemispheric specialization (HS) is a hemisphere-dependent relationship between a cognitive, sensory, or motor function and a set of brain structures. It includes both... (Review)
Review
Hemispheric specialization (HS) is a hemisphere-dependent relationship between a cognitive, sensory, or motor function and a set of brain structures. It includes both the hosting by a given hemisphere of specialized networks that have unique functional properties and mechanisms that enable the inter-hemispheric coordination necessary for efficient processing. Long derived from neuropsychological and behavioral observations, knowledge of HS is currently being profoundly modified by cutting-edge neuroimaging research that focuses both on the neural implementation of HS for language, visuospatial functions, and motor control/handedness across development and on the analysis of interactions between brain regions within and across hemispheres. New findings reveal the fundamental role of lateralization in the large-scale architecture of the human brain, whose ontogenesis has begun to be investigated with genetic-heritability brain mapping.
Topics: Brain; Brain Mapping; Cognition; Functional Laterality; Humans; Movement; Neuroimaging; Sensation
PubMed: 23317751
DOI: 10.1016/j.tics.2012.12.004 -
Science (New York, N.Y.) Jun 2013In most people, language is processed predominantly by the left hemisphere of the brain, but we do not know how or why. A popular view is that developmental language... (Review)
Review
In most people, language is processed predominantly by the left hemisphere of the brain, but we do not know how or why. A popular view is that developmental language disorders result from a poorly lateralized brain, but until recently, evidence has been weak and indirect. Modern neuroimaging methods have made it possible to study normal and abnormal development of lateralized function in the developing brain and have confirmed links with language and literacy impairments. However, there is little evidence that weak cerebral lateralization has common genetic origins with language and literacy impairments. Our understanding of the association between atypical language lateralization and developmental disorders may benefit if we reconceptualize the nature of cerebral asymmetry to recognize its multidimensionality and consider variation in lateralization over developmental time. Contrary to popular belief, cerebral lateralization may not be a highly heritable, stable characteristic of individuals; rather, weak lateralization may be a consequence of impaired language learning.
Topics: Animals; Cerebral Cortex; Cognition Disorders; Dyslexia; Forkhead Transcription Factors; Functional Laterality; Genetic Predisposition to Disease; Humans; Language Development; Language Development Disorders; Mitochondrial Proteins; Nerve Tissue Proteins; Neuronal Plasticity; Polymorphism, Single Nucleotide; Repressor Proteins; Ribosomal Proteins; Ultrasonography, Doppler, Transcranial
PubMed: 23766329
DOI: 10.1126/science.1230531