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Corballis MC, Corballis PM. Can the mind be split? A historical introduction. Neuropsychologia 2021; 163:108041. [PMID: 34582823 DOI: 10.1016/j.neuropsychologia.2021.108041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2020] [Revised: 08/20/2021] [Accepted: 09/12/2021] [Indexed: 11/28/2022]
Abstract
The idea that the mind might be composed of distinct conscious entities goes back at least to the mid-19th century, and was at first based on the bilateral symmetry of the brain, with each side seemingly a mirror-image replica of the other. This led to early speculation as to whether section of the forebrain commissures might lead to separate, independent consciousnesses. This was not put to the test until the 1960s, first in commissurotomized cats and monkeys, and then in humans who had undergone commissurotomy for the relief of intractable epilepsy. Initial results did indeed suggest independent consciousness in each separated hemisphere, but later findings have also revealed a degree of mental unity, especially in some perceptual functions and in motor control. Some of these findings might be interpreted in terms of subcortical connections or external cross-cuing, and also address questions about the nature of consciousness in a more concrete way.
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Affiliation(s)
- Michael C Corballis
- School of Psychology, University of Auckland, Science Centre, 23 Symonds Street, Auckland Central, New Zealand.
| | - Paul M Corballis
- School of Psychology, University of Auckland, Science Centre, 23 Symonds Street, Auckland Central, New Zealand.
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Hausmann M, Corballis MC, Fabri M. Revisiting the attentional bias in the split brain. Neuropsychologia 2021; 162:108042. [PMID: 34582822 DOI: 10.1016/j.neuropsychologia.2021.108042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2020] [Revised: 09/10/2021] [Accepted: 09/12/2021] [Indexed: 10/20/2022]
Abstract
Previous research has revealed a strong right bias in allocation of attention in split brain subjects, suggesting that a pathological attention bias occurs not only after unilateral (usually right-hemispheric) damage but also after functional disconnection of intact right-hemispheric areas involved in allocation of attention from those in the left hemisphere. Here, we investigated the laterality bias in spatial attention, as measured with the greyscales task, in two split-brain subjects (D.D.C. and D.D.V.) who had undergone complete callosotomy. The greyscales task requires participants to judge the darker (or brighter) of two left-right mirror-reversed luminance gradients under conditions of free viewing, and offers an efficient means of quantifying pathological attentional biases in patients with unilateral lesions. As predicted, the results of the two split-brain subjects revealed a pathological rightward bias in allocation of attention, suggesting strong dependence on a single hemisphere (the left) in spatial attention, which is opposite to what one expects from people with intact commissures, and is remarkable in that it occurs in free viewing. In that sense both split-brain patients are behaving as though the brain is indeed split, especially in D.D.C. who had undergone partial resection of the anterior commissure in addition to complete callosotomy, whereas the anterior commissure is still intact in D.D.V. The findings support the view that the commissural pathways play a significant role in integration of attentional processes across cerebral hemispheres.
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Affiliation(s)
- Markus Hausmann
- Department of Psychology, Durham University, United Kingdom.
| | | | - Mara Fabri
- Department of Experimental and Clinical Medicine, Politechnic University of Marche, Ancona, Italy
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Affiliation(s)
- Armin Saysani
- School of Psychology and Centre for Brain Research, the University of Auckland, Auckland, New Zealand
| | - Michael C. Corballis
- School of Psychology and Centre for Brain Research, the University of Auckland, Auckland, New Zealand
- Centre for Brain Research, the University of Auckland, Auckland, New Zealand
| | - Paul M. Corballis
- School of Psychology and Centre for Brain Research, the University of Auckland, Auckland, New Zealand
- Centre for Brain Research, the University of Auckland, Auckland, New Zealand
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Abstract
It is commonly assumed that cerebral asymmetry is unidimensional, but evidence increasingly suggests that different brain circuits are independently lateralized. This might explain why the search for a laterality gene has provided multiple candidates, each with weak linkage. An alternative possibility is that there is a single genetically invariant source of lateralization, perhaps cytoplasmic, and subject to many influences, some genetic, some epigenetic, and some random. This could further explain why laterality is associated with a variety of disorders, such as dyslexia, schizophrenia, stress disorders, and depression.
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Abstract
Until fairly late in the nineteenth century, it was held that the brain was bilaterally symmetrical. With the discovery of left-brain dominance for language, the so-called "laws of symmetry" were revoked, and asymmetry was then seen as critical to the human condition, with the left hemisphere, in particular, assuming superordinate properties. I trace this idea from the early discoveries of the late nineteenth century through the split-brain studies of the 1960s, and beyond. Although the idea has persisted, the evidence has revealed widespread cerebral asymmetries in nonhuman animals, and even language and its asymmetries are increasingly understood to have evolved gradually, rather than in a single speciation event. The left hemisphere nevertheless seemed to take over a role previously taken by other structures, such as the pineal gland and the hippocampus minor, in a determined effort to place humans on a pedestal above all other species.
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Abstract
Euan Macphail's work and ideas captured a pivotal time in the late 20th century when behavioral laws were considered to apply equally across vertebrates, implying equal intelligence, but it was also a time when behaviorism was challenged by the view that language was unique to humans, and bestowed a superior mental status. Subsequent work suggests greater continuity between humans and their forebears, challenging the Chomskyan assumption that language evolved in a single step ("the great leap forward") in humans. Language is now understood to be based on an amalgam of cognitive functions, including mental time travel, theory of mind, and what may be more broadly defined as imagination. These functions probably evolved gradually in hominin evolution and are present in varying degrees in non-human species. The blending of language into cognition provides for both interspecies differences in mental function, and continuity between humans and other species. What does seem to be special to humans is the ability to communicate the contents of imagination, although even this is not absolute, and is perhaps less adaptive than we like to think.
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Affiliation(s)
- Michael C. Corballis
- Faculty of Science, School of Psychology, The University of Auckland, Auckland, New Zealand
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Moreau D, Corballis MC. When averaging goes wrong: The case for mixture model estimation in psychological science. ACTA ACUST UNITED AC 2019; 148:1615-1627. [DOI: 10.1037/xge0000504] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
Language could not exist without memory, in all its forms: working memory for sequential production and understanding, implicit memory for grammatical rules, semantic memory for knowledge, and episodic memory for communicating personal experience. Episodic memory is part of a more general capacity for mental travel both forward and backward in time, and extending even into fantasy and stories. I argue that the generativity of mental time travel underlies the generativity of language itself, and could be the basis of what Chomsky calls I-language, or universal grammar (UG), a capacity for recursive thought independent of communicative language itself. Whereas Chomsky proposed that I-language evolved in a single step well after the emergence of Homo sapiens, I suggest that generative imagination, extended in space and time, has a long evolutionary history, and that it was the capacity to share internal thoughts, rather than the nature of the thoughts themselves, that more clearly distinguishes humans from other species.
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Affiliation(s)
- Michael C Corballis
- School of Psychology, Faculty of Science, University of Auckland, Auckland, New Zealand
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Abstract
The human brain is often characterized in terms of a duality, with the left and right brains serving complementary functions, and even individuals are sometimes classified as either "left-brained" or "right-brained." Recent evidence from brain imaging shows that hemispheric asymmetry is multidimensional, comprised of independent lateralized circuits. Cerebral asymmetries, which include handedness, probably arise in phylogenesis through the fissioning of ancestral systems that divided and lateralized with increasing demand for specialization. They also vary between individuals, with some showing absent or reversed asymmetries. It is unlikely that this variation is controlled by a single gene, as sometimes assumed, but depends rather on complex interplay among several, perhaps many, genes. Hemispheric asymmetry has often been regarded as a unique mark of being human, but it has also become evident that behavioral and cerebral asymmetries are not confined to humans, and are widespread among animal species. They nevertheless exist against a fundamental background of bilateral symmetry, suggesting a tradeoff between the two. Individual differences in asymmetry, moreover, are themselves adaptive, contributing to the cognitive and behavioral specializations necessary for societies to operate efficiently.
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Abstract
Cognition is heavily grounded in space. As animals that move in space, we travel both physically and mentally in space and time, reliving past events, imagining future ones, and even constructing imaginary scenarios that play out in stories. Mental exploration of space is extraordinarily flexible, allowing us to zoom, adopt different vantage points, mentally rotate, and attach objects and sense impressions to create events, whether remembered, planned, or simply invented. The properties of spatiotemporal cognition depend on a hippocampal–entorhinal circuit of place cells, grid cells and border cells, with combinations of grid-cell modules generating a vast number of potential spatial remappings. The generativity of language, often considered one of its defining properties, may therefore derive not from the nature of language itself, but rather from the generativity of spatiotemporal scenarios, with language having evolved as a means of sharing them. Much our understanding of the hippocampal–entorhinal circuit is derived from neurophysiological recording in the rat brain, implying that the spatiotemporal cognition underpinning language has a long evolutionary history.
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Affiliation(s)
- Armin Saysani
- School of Psychology and Centre for Brain Research, The University of Auckland, Auckland, New Zealand
| | - Michael C. Corballis
- School of Psychology and Centre for Brain Research, The University of Auckland, Auckland, New Zealand
| | - Paul M. Corballis
- School of Psychology and Centre for Brain Research, The University of Auckland, Auckland, New Zealand
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Corballis MC. Space, time, and language: Comment on "Rethinking foundations of language from a multidisciplinary perspective" by Tao Gong, Lan Shuai and Yicheng Wu. Phys Life Rev 2018; 26-27:144-145. [PMID: 30005973 DOI: 10.1016/j.plrev.2018.06.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 06/27/2018] [Indexed: 11/18/2022]
Affiliation(s)
- Michael C Corballis
- School of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
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Corballis MC. Fearful asymmetry: Bouillaud, Dax, Broca, and the localization of language, Paris, 1825-1879. Laterality 2018; 23:501-503. [DOI: 10.1080/1357650x.2017.1394320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Affiliation(s)
- Armin Saysani
- School of Psychology and Centre for Brain Research, The University of Auckland, Auckland, New Zealand
| | - Michael C. Corballis
- School of Psychology and Centre for Brain Research, The University of Auckland, Auckland, New Zealand
| | - Paul M. Corballis
- School of Psychology and Centre for Brain Research, The University of Auckland, Auckland, New Zealand
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Abstract
Mirror-image confusions are common, especially in children and in some cases of neurological impairment. They can be a special impediment in activities such as reading and writing directional scripts, where mirror-image patterns (such as b and d) must be distinguished. Treating mirror images as equivalent, though, can also be adaptive in the natural world, which carries no systematic left-right bias and where the same object or event can appear in opposite viewpoints. Mirror-image equivalence and confusion are natural consequences of a bilaterally symmetrical brain. In the course of learning, mirror-image equivalence may be established through a process of symmetrization, achieved through homotopic interhemispheric exchange in the formation of memory circuits. Such circuits would not distinguish between mirror images. Learning to discriminate mirror-image discriminations may depend either on existing brain asymmetries, or on extensive learning overriding the symmetrization process. The balance between mirror-image equivalence and mirror-image discrimination may nevertheless be precarious, with spontaneous confusions or reversals, such as mirror writing, sometimes appearing naturally or as a manifestation of conditions like dyslexia.
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Affiliation(s)
- Michael C Corballis
- School of Psychology, University of Auckland, University of Auckland, Auckland, New Zealand
| | - Paul M Corballis
- School of Psychology, University of Auckland, University of Auckland, Auckland, New Zealand
| | - Giovanni Berlucchi
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Italy
- National Institute of Neuroscience, Italy
| | - Carlo A Marzi
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Italy
- National Institute of Neuroscience, Italy
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Scarf D, Corballis MC, Güntürkün O, Colombo M. Do 'literate' pigeons (Columba livia) show mirror-word generalization? Anim Cogn 2017; 20:999-1002. [PMID: 28707141 DOI: 10.1007/s10071-017-1116-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2017] [Revised: 07/04/2017] [Accepted: 07/08/2017] [Indexed: 11/29/2022]
Abstract
Many children pass through a mirror stage in reading, where they write individual letters or digits in mirror and find it difficult to correctly utilize letters that are mirror images of one another (e.g., b and d). This phenomenon is thought to reflect the fact that the brain does not naturally discriminate left from right. Indeed, it has been argued that reading acquisition involves the inhibition of this default process. In the current study, we tested the ability of literate pigeons, which had learned to discriminate between 30 and 62 words from 7832 nonwords, to discriminate between words and their mirror counterparts. Subjects were sensitive to the left-right orientation of the individual letters, but not the order of letters within a word. This finding may reflect the fact that, in the absence of human-unique top-down processes, the inhibition of mirror generalization may be limited.
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Affiliation(s)
- Damian Scarf
- Department of Psychology, University of Otago, Dunedin, New Zealand.
| | | | - Onur Güntürkün
- Department of Psychology, Institute of Cognitive Neuroscience, Biopsychology, Ruhr-University Bochum, 44780, Bochum, Germany
| | - Michael Colombo
- Department of Psychology, University of Otago, Dunedin, New Zealand.
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Abstract
In the vast clade of animals known as the bilateria, cerebral and behavioral asymmetries emerge against the backdrop of bilateral symmetry, with a functional trade-off between the two. Asymmetries can lead to more efficient processing and packaging of internal structures, but at the expense of efficient adaptation to a natural world without systematic left-right bias. Asymmetries may arise through the fissioning of ancestral structures that are largely symmetrical, creating new circuits. In humans these may include asymmetrical adaptations to language and manufacture, and as one or other hemisphere gains dominance for functions that were previously represented bilaterally. This is best illustrated in the evolution of such functions as language and tool manufacture in humans, which may derive from the mirror-neuron system in primates, but similar principles probably apply to the many other asymmetries now evident in a wide range of animals. Asymmetries arise in largely independent manner with multi-genetic sources, rather than as a single over-riding principle.
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Häberling IS, Corballis PM, Corballis MC. Language, gesture, and handedness: Evidence for independent lateralized networks. Cortex 2016; 82:72-85. [DOI: 10.1016/j.cortex.2016.06.003] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 02/25/2016] [Accepted: 06/06/2016] [Indexed: 12/16/2022]
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Affiliation(s)
- Lucy L M Patston
- Department of Psychology, University of Auckland, Auckland, New Zealand.
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Abstract
Information regarding anatomical connectivity in the human brain can be gathered using diffusion tensor imaging (DTI). Fractional anisotropy (FA) is the most commonly derived value, and reflects how strongly directional are the underlying tracts. Differences in FA are thus associated with differences in the underlying microstructure of the brain. The relationships between these differences in microstructure and functional differences in corresponding regions have also been examined. Previous studies have found an effect of handedness on functional lateralization in the brain and corresponding microstructural differences. Here, using tract-based spatial statistics to analyse DTI-derived FA values, we further investigated the structural white matter architecture in the brains of right- and left-handed males. We found significantly higher FA values for left-handed, relatively to right-handed, individuals, in all major lobes, and in the corpus callosum. In support of previous suggestions, we find that there is a difference in the microstructure of white matter in left- and right-handed males that could underpin reduced lateralization of function in left-handed individuals.
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Affiliation(s)
- Nicole S McKay
- a School of Psychology , University of Auckland , Auckland , New Zealand
| | - Sarina J Iwabuchi
- b Division of Psychiatry and Applied Psychology, Centre for Translational Neuroimaging in Mental Health, Institute of Mental Health , University of Nottingham , Nottingham , UK
| | | | | | - Ian J Kirk
- a School of Psychology , University of Auckland , Auckland , New Zealand
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Abstract
Phil Bryden was a seminal figure in the development of the field of cerebral lateralization in the last half of the twentieth century, and a founding editor of this journal. Here his founding co-editors reminisce about their friend and colleague, and reflect on his wide-ranging influence in the field and in their own careers.
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Affiliation(s)
| | | | - M Barbara Bulman-Fleming
- c Department of Psychology , University of Waterloo (UW) , Waterloo , Ontario, Victoria BC , Canada
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Abstract
In 46 right-handers and 46 left-handers, we used functional magnetic resonance imaging to record activity in the frontal lobes while they generated words, the temporal lobe while they made synonym judgments, and the parietal lobe while they watched videos of manual actions. In each case we also recorded activity in the cerebellum. Laterality indices showed a significant left-hemispheric bias in each cortical lobe and a right-hemispheric bias in the cerebellum for the 2 language tasks, but not during action observation. Cerebellar asymmetry also correlated negatively with frontal and temporal asymmetry, reflecting contralateral connections, but not with parietal asymmetry. A factor analysis of the inter-correlations among laterality indices revealed 2 factors, implying independent lateralized networks, with cerebellar asymmetry strongly linked to a language network in frontal and temporal cortices, and handedness strongly linked to an action-observation network in the parietal lobe.
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Häberling IS, Steinemann A, Corballis MC. Cerebral asymmetry for language: Comparing production with comprehension. Neuropsychologia 2015; 80:17-23. [PMID: 26548403 DOI: 10.1016/j.neuropsychologia.2015.11.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2015] [Revised: 10/12/2015] [Accepted: 11/04/2015] [Indexed: 10/22/2022]
Abstract
Although left-hemispheric damage can impair both the production and comprehension of language, it has been claimed that comprehension is more bilaterally represented than is production. A variant of this theme is based on the theory that different aspects of language are processed by a dorsal stream, responsible for mapping words to articulation, and a ventral stream for processing input for meaning. Some have claimed that the dorsal stream is left-hemispheric, while the ventral stream is bilaterally organized. We used fMRI to record activation while left- and right-handed participants performed covert word-generation task and judged whether word pairs were synonyms. Regions of interest were Broca's area as part of the dorsal stream and the superior and middle temporal gyri as part of the ventral stream. Laterality indices showed equal left-hemispheric lateralization in Broca's area for word generation and both Broca's area and temporal lobe for the synonym judgments. Handedness influenced laterality equally in each area and task, with right-handers showing stronger left-hemispheric dominance than left-handers. Although our findings provide no evidence that asymmetry is more pronounced for production than for comprehension, correlations between the tasks and regions of interest support the view that lateralization in the temporal lobe depends on feedback influences from frontal regions.
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Affiliation(s)
- Isabelle S Häberling
- School of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
| | - Anita Steinemann
- School of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
| | - Michael C Corballis
- School of Psychology, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.
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van Mulukom V, Schacter DL, Corballis MC, Addis DR. The degree of disparateness of event details modulates future simulation construction, plausibility, and recall. Q J Exp Psychol (Hove) 2015; 69:234-42. [PMID: 26052883 DOI: 10.1080/17470218.2015.1051559] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Several episodic simulation studies have suggested that the plausibility of future events may be influenced by the disparateness of the details comprising the event. However, no study had directly investigated this idea. In the current study, we designed a novel episodic combination paradigm that varied the disparateness of details through a social sphere manipulation. Participants recalled memory details from three different social spheres. Details were recombined either within spheres or across spheres to create detail sets for which participants imagined future events in a second session. Across-sphere events were rated as significantly less plausible than within-sphere events and were remembered less often. The presented paradigm, which increases control over the disparateness of details in future event simulations, may be useful for future studies concerned with the similarity of the simulations to previous events and its plausibility.
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Affiliation(s)
- Valerie van Mulukom
- a School of Psychology , The University of Auckland , Auckland , New Zealand.,b Centre for Brain Research , The University of Auckland , Auckland , New Zealand
| | - Daniel L Schacter
- c Department of Psychology , Harvard University , Cambridge , MA , USA
| | - Michael C Corballis
- a School of Psychology , The University of Auckland , Auckland , New Zealand.,b Centre for Brain Research , The University of Auckland , Auckland , New Zealand
| | - Donna Rose Addis
- a School of Psychology , The University of Auckland , Auckland , New Zealand.,b Centre for Brain Research , The University of Auckland , Auckland , New Zealand
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Abstract
Until recently it was widely held that language, and its left-hemispheric representation in the brain, were uniquely human, emerging abruptly after the emergence of Homo sapiens. Changing views of language suggest that it was not a recent and sudden development in human evolution, but was adapted from dual-stream circuity long predating hominins, including a system in nonhuman primates specialized for intentional grasping. This system was gradually tailored for skilled manual operations (praxis) and communication. As processing requirements grew more demanding, the neural circuits were increasingly lateralized, with the left hemisphere assuming dominance, at least in the majority of individuals. The trend toward complexity and lateralization was probably accelerated in hominins when bipedalism freed the hands for more complex manufacture and tool use, and more expressive communication. The incorporation of facial and vocal gestures led to the emergence of speech as the dominant mode of language, although gestural communication may have led to generative language before speech became dominant. This scenario provides a more Darwinian perspective on language and its lateralization than has been commonly assumed.
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Abstract
Handedness and brain asymmetry are widely regarded as unique to humans, and associated with complementary functions such as a left-brain specialization for language and logic and a right-brain specialization for creativity and intuition. In fact, asymmetries are widespread among animals, and support the gradual evolution of asymmetrical functions such as language and tool use. Handedness and brain asymmetry are inborn and under partial genetic control, although the gene or genes responsible are not well established. Cognitive and emotional difficulties are sometimes associated with departures from the "norm" of right-handedness and left-brain language dominance, more often with the absence of these asymmetries than their reversal.
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Colbert-White EN, Corballis MC, Fragaszy DM. Where Apes and Songbirds are Left Behind: A Comparative Assessment of the Requisites for Speech. CCBR 2014. [DOI: 10.3819/ccbr.2014.90004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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Abstract
A central component of mind wandering is mental time travel, the calling to mind of remembered past events and of imagined future ones. Mental time travel may also be critical to the evolution of language, which enables us to communicate about the non-present, sharing memories, plans, and ideas. Mental time travel is indexed in humans by hippocampal activity, and studies also suggest that the hippocampus in rats is active when the animals replay or pre play activity in a spatial environment, such as a maze. Mental time travel may have ancient origins, contrary to the view that it is unique to humans. Since mental time travel is also thought to underlie language, these findings suggest that language evolved gradually from pre-existing cognitive capacities, contrary to the view of Chomsky and others that language and symbolic thought emerged abruptly, in a single step, within the past 100,000 years.
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van Mulukom V, Schacter DL, Corballis MC, Addis DR. Re-imagining the future: repetition decreases hippocampal involvement in future simulation. PLoS One 2013; 8:e69596. [PMID: 23936055 PMCID: PMC3720617 DOI: 10.1371/journal.pone.0069596] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Accepted: 06/10/2013] [Indexed: 12/05/2022] Open
Abstract
Imagining or simulating future events has been shown to activate the anterior right hippocampus (RHC) more than remembering past events does. One fundamental difference between simulation and memory is that imagining future scenarios requires a more extensive constructive process than remembering past experiences does. Indeed, studies in which this constructive element is reduced or eliminated by “pre-imagining” events in a prior session do not report differential RHC activity during simulation. In this fMRI study, we examined the effects of repeatedly simulating an event on neural activity. During scanning, participants imagined 60 future events; each event was simulated three times. Activation in the RHC showed a significant linear decrease across repetitions, as did other neural regions typically associated with simulation. Importantly, such decreases in activation could not be explained by non-specific linear time-dependent effects, with no reductions in activity evident for the control task across similar time intervals. Moreover, the anterior RHC exhibited significant functional connectivity with the whole-brain network during the first, but not second and third simulations of future events. There was also evidence of a linear increase in activity across repetitions in right ventral precuneus, right posterior cingulate and left anterior prefrontal cortex, which may reflect source recognition and retrieval of internally generated contextual details. Overall, our findings demonstrate that repeatedly imagining future events has a decremental effect on activation of the hippocampus and many other regions engaged by the initial construction of the simulation, possibly reflecting the decreasing novelty of simulations across repetitions, and therefore is an important consideration in the design of future studies examining simulation.
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Affiliation(s)
- Valerie van Mulukom
- School of Psychology, The University of Auckland, Auckland, New Zealand
- Centre for Brain Research, The University of Auckland, Auckland, New Zealand
| | - Daniel L. Schacter
- Department of Psychology, Harvard University, Cambridge, Massachusetts, United States of America
| | - Michael C. Corballis
- School of Psychology, The University of Auckland, Auckland, New Zealand
- Centre for Brain Research, The University of Auckland, Auckland, New Zealand
| | - Donna Rose Addis
- School of Psychology, The University of Auckland, Auckland, New Zealand
- Centre for Brain Research, The University of Auckland, Auckland, New Zealand
- * E-mail:
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Häberling IS, Badzakova-Trajkov G, Corballis MC. Asymmetries of the arcuate fasciculus in monozygotic twins: genetic and nongenetic influences. PLoS One 2013; 8:e52315. [PMID: 23300971 PMCID: PMC3534675 DOI: 10.1371/journal.pone.0052315] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Accepted: 11/16/2012] [Indexed: 12/02/2022] Open
Abstract
We assessed cerebral asymmetry for language in 35 monozygotic twin pairs. Using DTI, we reconstructed the arcuate fasciculus in each twin. Among the male twins, right-handed pairs showed greater left-sided asymmetry of connectivity in the arcuate fasciculus than did those with discordant handedness, and within the discordant group the right-handers had greater left-sided volume asymmetry of the arcuate fasciculus than did their left-handed co-twins. There were no such effects in the female twins. Cerebral asymmetry for language showed more consistent results, with the more left-cerebrally dominant twins also showing more leftward asymmetry of high anisotropic fibers in the arcuate fasciculus, a result applying equally to female as to male twins. Reversals of arcuate fasciculus asymmetry were restricted to pairs discordant for language dominance, with the left-cerebrally dominant twins showing leftward and the right-cerebrally dominant twins rightward asymmetry of anisotropic diffusion in the arcuate fasciculus. Because monozygotic twin pairs share the same genotype, our results indicate a strong nongenetic component in arcuate fasciculus asymmetry, particularly in those discordant for cerebral asymmetry.
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Affiliation(s)
- Isabelle S Häberling
- Research Centre for Cognitive Neuroscience and Department of Psychology, The University of Auckland, Auckland, New Zealand.
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Abstract
In humans, hippocampal activity responds to the imagining of past or future events. In rats, hippocampal activity is tied to particular locations in a maze, occurs after the animal has been in the maze, and sometimes corresponds to locations the animal did not actually visit. This suggests that mental time travel has neurophysiological underpinnings that go far back in evolution, and may not be, as some (including myself) have claimed, unique to humans.
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Affiliation(s)
- Michael C Corballis
- School of Psychology, University of Auckland, Private Bag 92019, Auckland, New Zealand.
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Abstract
The authors' aim was to compare interhemispheric transfer time between 2 groups: highly skilled sportsmen and control subjects. Left- and right-handed individuals were included in the study. The Poffenberger paradigm was used to measure the crossed-uncrossed difference, representing the time to transfer information from one hemisphere to the other. No difference in laterality was found, but the results revealed a greater crossed-uncrossed difference in the skilled sportsmen than in the controls. The authors suggest that this may be due to more highly developed within-hemisphere integration of inputs and outputs, at the expense of cross-hemisphere integration.
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Affiliation(s)
- Gabriele Semprini
- Department of Histology, Embryology, and Applied Biology, University of Bologna, Italy.
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Häberling IS, Badzakova-Trajkov G, Corballis MC. The Corpus Callosum in Monozygotic Twins Concordant and Discordant for Handedness and Language Dominance. J Cogn Neurosci 2012; 24:1971-82. [DOI: 10.1162/jocn_a_00267] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Abstract
We used diffusion tensor imaging to assess callosal morphology in 35 pairs of monozygotic twins, of which 17 pairs were concordant for handedness and 18 pairs were discordant for handedness. Functional hemispheric language dominance was established for each twin member using fMRI, resulting in 26 twin pairs concordant and 9 twin pairs discordant for language dominance. On the basis of genetic models of handedness and language dominance, which assume one “right shift” (RS) gene with two alleles, an RS+ allele biasing toward right-handedness and left cerebral language dominance and an RS− allele leaving both asymmetries to chance, all twins were classified according to their putative genotypes, and the possible effects of the gene on callosal morphology was assessed. Whereas callosal size was under a high genetic control that was independent of handedness and language dominance, twin pairs with a high probability of carrying the putative RS+ allele showed a connectivity pattern characterized by a genetically controlled, low anisotropic diffusion over the whole corpus callosum. In contrast, the high connectivity pattern exhibited by twin pairs more likely to lack the RS+ allele was under significantly less genetic influence. The data suggest that handedness and hemispheric dominance for speech production might be at least partly dependent on genetically controlled processes of axonal pruning in the corpus callosum.
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Roser ME, Corballis MC, Jansari A, Fulford J, Benattayallah A, Adams WM. Bilateral redundancy gain and callosal integrity in a man with callosal lipoma: a diffusion-tensor imaging study. Neurocase 2012; 18:185-98. [PMID: 21787244 DOI: 10.1080/13554794.2011.568505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
We investigated whether abnormalities in the structural organization of the corpus callosum in the presence of curvilinear lipoma are associated with increased facilitation of response time to bilateral stimuli, an effect known as the redundancy gain (RG). A patient (A.J.) with a curvilinear lipoma of the corpus callosum, his genetically-identical twin, and age-matched control participants made speeded responses to luminant stimuli. Structural organization of callosal regions was assessed with diffusion-tensor imaging. A.J. was found to have reduced structural integrity in the splenium of the corpus callosum and produced a large RG suggestive of neural summation.
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Affiliation(s)
- Matthew E Roser
- School of Psychology, University of Plymouth, Plymouth, Devon PL4 8AA, UK.
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Corballis MC. Who's in charge? Free will and the science of the brain. Laterality 2012. [DOI: 10.1080/1357650x.2012.690416] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Corballis MC, Badzakova-Trajkov G, Häberling IS. Right hand, left brain: genetic and evolutionary bases of cerebral asymmetries for language and manual action. Wiley Interdiscip Rev Cogn Sci 2011; 3:1-17. [PMID: 26302469 DOI: 10.1002/wcs.158] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Most people are right-handed and left-cerebrally dominant for language. This pattern of asymmetry, as well as departures from it, have been reasonably accommodated in terms of a postulated gene with two alleles, one disposing to this common pattern and the other leaving the direction of handedness and language asymmetry to chance. There are some leads as to the location of the gene or genes concerned, but no clear resolution; one possibility is that the chance factor is achieved by epigenetic cancelling of the lateralizing gene rather than through a chance allele. Neurological evidence suggests that the neural basis of manual praxis, including pantomime and tool use, is more closely associated with cerebral asymmetry for language than with handedness, and is homologous with the so-called "mirror system" in the primate brain, which is specialized for manual grasping. The evidence reviewed supports the theory that language itself evolved within the praxic system, and became lateralized in humans, and perhaps to a lesser extent in our common ancestry with the great apes. WIREs Cogn Sci 2012, 3:1-17. doi: 10.1002/wcs.158 For further resources related to this article, please visit the WIREs website.
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Iwabuchi SJ, Häberling IS, Badzakova-Trajkov G, Patston LLM, Waldie KE, Tippett LJ, Corballis MC, Kirk IJ. Regional differences in cerebral asymmetries of human cortical white matter. Neuropsychologia 2011; 49:3599-604. [PMID: 21939675 DOI: 10.1016/j.neuropsychologia.2011.09.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2010] [Revised: 07/08/2011] [Accepted: 09/08/2011] [Indexed: 11/20/2022]
Abstract
The form of the structural asymmetries across the cerebral hemispheres, that support well-established functional asymmetries, are not well understood. Although, many previous studies have investigated structural differences in areas associated with strong functional asymmetries, such as language processes, regions of the brain with less well established functional laterality have received less attention. The current study aims to address this by exploring global white matter asymmetries of the healthy human brain using diffusion tensor imaging (DTI) and tractography. DTI was conducted on twenty-nine healthy right-handed males, and pathways from the four major lobes were reconstructed using probabilistic tractography. Mean FA, parallel and perpendicular diffusion values were calculated and compared across hemispheres for each pathway generated. Significant asymmetries in the parietal (rightward asymmetry) and occipital (leftward asymmetry) pathways were found in FA measures. However, asymmetric patterns in parallel and/or perpendicular diffusion were observed in all four lobes, even in pathways with symmetrical FA. For instance, significant rightward asymmetry in parallel diffusion was found in the parietal and frontal lobes, whereas significant leftward asymmetry was found in the temporal and occipital lobes. We suggest that these different patterns of diffusion asymmetry reflect differences in microanatomy that support the known patterns of differential functional asymmetry. The different directions of anatomical asymmetry support the notion that there may be a number of different lateralising influences operating in the brain.
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Affiliation(s)
- Sarina J Iwabuchi
- Research Centre for Cognitive Neuroscience, Department of Psychology, University of Auckland, Auckland, New Zealand.
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Badzakova-Trajkov G, Häberling IS, Corballis MC. Magical ideation, creativity, handedness, and cerebral asymmetries: A combined behavioural and fMRI study. Neuropsychologia 2011; 49:2896-903. [DOI: 10.1016/j.neuropsychologia.2011.06.016] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2010] [Revised: 06/07/2011] [Accepted: 06/14/2011] [Indexed: 10/18/2022]
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Häberling IS, Badzakova-Trajkov G, Corballis MC. Callosal tracts and patterns of hemispheric dominance: a combined fMRI and DTI study. Neuroimage 2010; 54:779-86. [PMID: 20920586 DOI: 10.1016/j.neuroimage.2010.09.072] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 09/14/2010] [Accepted: 09/26/2010] [Indexed: 10/19/2022] Open
Abstract
Left-hemispheric dominance for language and right-hemispheric dominance for spatial processing are distinctive characteristics of the human brain. However, variations of these hemispheric asymmetries have been observed, with a minority showing crowding of both functions to the same hemisphere or even a mirror reversal of the typical lateralization pattern. Here, we used diffusion tensor imaging and functional magnetic imaging to investigate the role of the corpus callosum in participants with atypical hemispheric dominance. The corpus callosum was segmented according to the projection site of the underlying fibre tracts. Analyses of the microstructure of the identified callosal segments revealed that atypical hemispheric dominance for language was associated with high anisotropic diffusion through the corpus callosum as a whole. This effect was most evident in participants with crowding of both functions to the right. The enhanced anisotropic diffusion in atypical hemispheric dominance implies that in these individuals the two hemispheres are more heavily interconnected.
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Affiliation(s)
- Isabelle S Häberling
- Research Centre for Cognitive Neuroscience, Department of Psychology, The University of Auckland, Auckland, New Zealand.
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Markwick A, Corballis MC. Corrigendum to: Perceived motion induced by a neglected stimulus [48 (4) 1041–1046]. Neuropsychologia 2010. [DOI: 10.1016/j.neuropsychologia.2010.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Corballis MC, Birse K, Paggi A, Manzoni T, Pierpaoli C, Fabri M. Mirror-image discrimination and reversal in the disconnected hemispheres. Neuropsychologia 2010; 48:1664-9. [PMID: 20167229 DOI: 10.1016/j.neuropsychologia.2010.02.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 12/30/2009] [Accepted: 02/09/2010] [Indexed: 01/18/2023]
Abstract
Two callosotomized patients and 24 neurologically normal subjects performed simple binary discriminations between upright letters flashed in one or other visual field. Where discrimination of the letters F and R by name either showed a left-hemisphere advantage or no hemispheric effect, discrimination of whether the same letters were normal or backward showed a right-hemisphere advantage. These results suggest that discrimination of mirror-image letters depends on matching to an exemplar, for which the right-hemisphere is dominant, while letter naming depends on abstract category recognition. One commissurotomized patient, DDV, showed systematic left-right reversal of the letters in the left visual field, classifying the normal letters as reversed and reversed ones as normal, and persisted with this reversal when the letters were shown in free vision. This suggests that reversed exemplars of the letters may be laid down the right cerebral hemisphere. There was no such reversal in the other patient (DDC).
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Affiliation(s)
- Michael C Corballis
- Department of Psychology, University of Auckland, Private Bag 92019, Auckland 1164, New Zealand.
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Abstract
The mirror system provided a natural platform for the subsequent evolution of language. In nonhuman primates, the system provides for the understanding of biological action, and possibly for imitation, both prerequisites for language. I argue that language evolved from manual gestures, initially as a system of pantomime, but with gestures gradually "conventionalizing" to assume more symbolic form. The evolution of episodic memory and mental time travel, probably beginning with the genus Homo during the Pleistocene, created pressure for the system to "grammaticalize," involving the increased vocabulary necessary to refer to episodes separated in time and place from the present, constructions such as tense to refer to time itself, and the generativity to construct future (and fictional) episodes. In parallel with grammaticalization, the language medium gradually incorporated facial and then vocal elements, culminating in autonomous speech (albeit accompanied still by manual gesture) in our own species, Homo sapiens.
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