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Some functional e ects of sectioning the cerebral commis-sures in man
... Following the seminal work of Gazzaniga et al. (1962) indicating how cognitive function differed in the two hemispheres following sectioning of the commissures, hemispheric asymmetries in cognition have alternately been characterized as a dichotomy between local and global (van Kleeck, 1989), categorical and coordinate (Kosslyn, 1987;van der Ham et al., 2014), or serial and parallel (e.g., Cohen, 1973) processes (for review, see Bradshaw and Nettleton, 1981). In the present study, we did not set out to evaluate these competing accounts of hemispheric specialization; rather, we sought to characterize the contribution of each hemisphere to performance of a relational reasoning task adapted from one used in a prior fMRI study from our group (Wendelken and Bunge, 2010). ...
... We designed the current study to test the role of each hemisphere in relational encoding through the use of a visual half-field stimulus presentation procedure. This paradigm was originally developed for use in split-brain patients, who have either minimal or no connection between the two hemispheres (e.g., Gazzaniga et al., 1962). Here, our participants were healthy adults whose hemispheres are presumed to interact closely in the coordination of task performance (Weissman and Banich, 2000). ...
... As such, we were surprised by the magnitude of the behavioral difference elicited by visual half-field presentation in this study, with an average difference in accuracy of 11% between left-lateralized and right-lateralized ordered trials. Although claims of inter-hemispheric differences in cognition have been made for many years (Gazzaniga et al., 1962;Cohen, 1973), our study is the first to demonstrate hemispheric differences in relational encoding in neurologically intact participants. ...
Relational reasoning, or the ability to integrate multiple mental relations to arrive at a logical conclusion, is a critical component of higher cognition. A bilateral brain network involving lateral prefrontal and parietal cortices has been consistently implicated in relational reasoning. Some data suggest a preferential role for the left hemisphere in this form of reasoning, whereas others suggest that the two hemispheres make important contributions. To test for a hemispheric asymmetry in relational reasoning, we made use of an old technique known as visual half-field stimulus presentation to manipulate whether stimuli were presented briefly to one hemisphere or the other. Across two experiments, 54 neurologically healthy young adults performed a visuospatial transitive inference task. Pairs of colored shapes were presented rapidly in either the left or right visual hemifield as participants maintained central fixation, thereby isolating initial encoding to the contralateral hemisphere. We observed a left-hemisphere advantage for encoding a series of ordered visuospatial relations, but both hemispheres contributed equally to task performance when the relations were presented out of order. To our knowledge, this is the first study to reveal hemispheric differences in relational encoding in the intact brain. We discuss these findings in the context of a rich literature on hemispheric asymmetries in cognition.
... This led to the concept of disconnection syndromes, caused by the destruction of either the centers of convergence where crucial associations were formed or the conduction pathways transmitting information between these centers (Wernicke, 1874;Dejerine, 1892). The concept of disconnection syndromes was further developed in the 1960s: the studies of split-brain patients revealed the topographic organization and functional specificity of the corpus callosum ( Gazzaniga et al., 1962), and neo-associationism reinterpreted apraxia, amnesia, agnosia and hemispatial neglect (Geschwind, 1965a,b). However, the phenomenon of ''diaschisis'' questioned localization of brain functions: the destruction of a cortical area could produce transient symptoms in other distant areas, which showed that immediate symptoms were not a reliable guide to the function of a destroyed cortical area (von Monakow, 1914). ...
Our knowledge of the brain has evolved over millennia in philosophical, experimental and theoretical phases. We suggest that the next phase is simulation neuroscience. The main drivers of simulation neuroscience are big data generated at multiple levels of brain organization and the need to integrate these data to trace the causal chain of interactions within and across all these levels. Simulation neuroscience is currently the only methodology for systematically approaching the multiscale brain. In this review, we attempt to reconstruct the deep historical paths leading to simulation neuroscience, from the first observations of the nerve cell to modern efforts to digitally reconstruct and simulate the brain. Neuroscience began with the identification of the neuron as the fundamental unit of brain structure and function and has evolved towards understanding the role of each cell type in the brain, how brain cells are connected to each other, and how the seemingly infinite networks they form give rise to the vast diversity of brain functions. Neuronal mapping is evolving from subjective descriptions of cell types towards objective classes, subclasses and types. Connectivity mapping is evolving from loose topographic maps between brain regions towards dense anatomical and physiological maps of connections between individual genetically distinct neurons. Functional mapping is evolving from psychological and behavioral stereotypes towards a map of behaviors emerging from structural and functional connectomes. We show how industrialization of neuroscience and the resulting large disconnected datasets are generating demand for integrative neuroscience, how the scale of neuronal and connectivity maps is driving digital atlasing and digital reconstruction to piece together the multiple levels of brain organization, and how the complexity of the interactions between molecules, neurons, microcircuits and brain regions is driving brain simulation to understand the interactions in the multiscale brain.
... En fait, c'est à partir de ces observations que s'est développé le concept d'hémisphère dominant à propos de l'hémisphère gauche et du langage. Des études chez les patients ayant subit une callosectomie (le plus souvent à cause d'une épilepsie résistante) ont mis en évidence que l'hémisphère gauche était prédominant pour les fonctions langagières alors que l'hémisphère droit était prédominant pour les fonctions visuo-spatiales (e.g., Gazzaniga et al., 1962). Par la suite les études chez des patients atteints de lésion cérébrale de l'hémisphère droit ont permis de mieux caractériser les rôles de cet hémisphère notamment dans la reconnaissance des visages ou des objets, le jugement d'orientation de lignes, et d'une manière plus large le traitement des informations visuo-spatiales de l'hémi-espace gauche. ...
Lateralized anomalies in visuo-spatial processing in schizophrenia were assessed according to a double viewpoint: 1/ compared to Unilateral Spatial Neglect syndrome, an asymmetric disorder of visuo-spatial cognition; 2/ compared to healthy individuals, and the normal asymmetry. Our studies showed that in schizophrenia there is a lateralized deficit such as patients placed their mark to the left of healthy individuals in a manual line bisection task; this bias did not seem related to a simple perceptual defect; yet, it may rely on attentional mechanisms (such as the bisection mark deviated only in presence of a cue at the right end of the line), and/or representational mechanisms (such as a left bias was also observed in the visuo-spatial representation of numbers). Overall, these results are similar to performances of neglect patients in the very same tasks. On the other hand, direction and magnitude of the bias are closer to those observed in healthy individuals which in turn suggest that the asymmetry observed in schizophrenia may be an accentuation of the normal asymmetry. In the end, parietal cortex implication, as the main structure responsible of visuo-spatial processing and as the main lesion site in neglect, was consider in schizophrenia.
... As mentioned above, despite a severe lengthening of the CUD, following total callosotomy, IT of visuomotor information is still possible. This is in contrast to cognitive tasks in which the critical information cannot be shared by the two hemispheres as witnessed by the classic symptoms presented by split-brain patients, namely, tactile anomia and dyspraxia for the left hand (Gazzaniga, Bogen, & Sperry, 1967); visual alexia for stimuli presented to the left hemifield (Gazzaniga, Bogen, & Sperry, 1962) and left ear suppression in a dichotic listening task (Milner, Taylor, & Sperry, 1968). One important question concerns the pathways ensuring IT of simple visuomotor information following total callosal section. ...
It is now common knowledge that the total surgical section of the corpus callosum (CC) and of the other forebrain commissures prevents interhemispheric transfer (IT) of a host of mental functions. By contrast, IT of simple sensorimotor functions, although severely delayed, is not abolished, and an important question concerns the pathways subserving this residual IT. To answer this question we assessed visuomotor IT in split-brain patients using the Poffenberger paradigm (PP), that is, a behavioral paradigm in which simple reaction time (RT) to visual stimuli presented to the hemifield ipsilateral to the responding hand is compared to stimuli presented to the contralateral hemifield, a condition requiring an IT. We tested the possibility that the residual IT is mediated by the collicular commissure interconnecting the two sides of the superior colliculus (SC). To this purpose, we used short-wavelength visual stimuli, which in neurophysiological studies in non-human primates have been shown to be undetectable by collicular neurons. We found that, in both totally and partially callosotomised patients, IT was considerably longer with S-cone input than with L-cone input or with achromatic stimuli. This was not the case in healthy participants in whom IT was not affected by color. These data clearly show that the SC plays an important role in IT of sensorimotor information in the absence of the corpus callosum.
Our recent target article on the allocation of attention to action (herein called the AAA model; Franz, 2012) considered implicated subcortical processes and networks in people with intact corpus callosum (CC) and people without a CC due to commissurotomy or callosotomy. However, a small error in print—namely that the term “commissurotomy” was printed in place of “callosotomy” in some instances—led us to further explore whether any key functional roles have been attributed to the two primary cortical commissures (the anterior and posterior commissures) which remain intact in people with callosotomy, and if so, whether those would be relevant to our current AAA framework. Although existing evidence is sparse, here we consider the hypothesis that the anterior commissure (AC) is a remnant fiber tract which has been largely replaced with evolution of the CC (and we do not herein discuss the posterior commissure further). Indeed, a dearth of studies is available on the AC, calling the need for further research. Herein, we briefly review literature on the AC in humans and then propose a method that might be worthwhile to pursue in future studies.
Disconnection syndromes following corpus callosotomy represent complex and variably expressed groupings of signs and symptoms affecting motor control, spatial orientation, vision, hearing, and language. Little is known, however, about the functional topography of callosal fiber pathways. In addition, most published case reports and case series of corpus callosotomy seldom report neurological deficits. We sought to categorize these deficits based on surgical anatomy.
We comprehensively reviewed the literature and described, compiled, and tabulated the most common disconnection syndromes complicating corpus callosotomy. We depict the topography of the cerebral cortex and associated commissural fibers of the corpus callosum through illustrations and diffusion tensor imaging tractography.
Anatomical classification of disconnection syndromes will provide great value to neurosurgeons embarking on callosotomy, whether partial or complete. Such information will apply to procedures performed for epilepsy and to procedures where the corpus callosum is sectioned for access to lesions within the ventricular system.
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