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      Abnormal Asymmetry of Brain Connectivity in Schizophrenia

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          Recently, a growing body of data has revealed that beyond a dysfunction of connectivity among different brain areas in schizophrenia patients (SCZ), there is also an abnormal asymmetry of functional connectivity compared with healthy subjects. The loss of the cerebral torque and the abnormalities of gyrification, with an increased or more complex cortical folding in the right hemisphere may provide an anatomical basis for such aberrant connectivity in SCZ. Furthermore, diffusion tensor imaging studies have shown a significant reduction of leftward asymmetry in some key white-matter tracts in SCZ. In this paper, we review the studies that investigated both structural brain asymmetry and asymmetry of functional connectivity in healthy subjects and SCZ. From an analysis of the existing literature on this topic, we can hypothesize an overall generally attenuated asymmetry of functional connectivity in SCZ compared to healthy controls. Such attenuated asymmetry increases with the duration of the disease and correlates with psychotic symptoms. Finally, we hypothesize that structural deficits across the corpus callosum may contribute to the abnormal asymmetry of intra-hemispheric connectivity in schizophrenia.

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          Most cited references 115

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          Hemispheric asymmetry reduction in older adults: the HAROLD model.

          A model of the effects of aging on brain activity during cognitive performance is introduced. The model is called HAROLD (hemispheric asymmetry reduction in older adults), and it states that, under similar circumstances, prefrontal activity during cognitive performances tends to be less lateralized in older adults than in younger adults. The model is supported by functional neuroimaging and other evidence in the domains of episodic memory, semantic memory, working memory, perception, and inhibitory control. Age-related hemispheric asymmetry reductions may have a compensatory function or they may reflect a dedifferentiation process. They may have a cognitive or neural origin, and they may reflect regional or network mechanisms. The HAROLD model is a cognitive neuroscience model that integrates ideas and findings from psychology and neuroscience of aging.
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            Meta-analysis of diffusion tensor imaging studies in schizophrenia.

            The objective of the study was to identify whether there are consistent regional white matter changes in schizophrenia. A systematic search was conducted for voxel-based diffusion tensor imaging fractional anisotropy studies of patients with schizophrenia (or related disorders) in relation to comparison groups. The authors carried out meta-analysis of the co-ordinates of fractional anisotropy differences. For the meta-analysis they used the Activation Likelihood Estimation (ALE) method hybridized with the rank approach used in Genome Scan Meta-Analysis (GSMA). This system detects three-dimensional conjunctions of co-ordinates from multiple studies and permits the weighting of studies in relation to sample size. Fifteen articles were identified for inclusion in the meta-analysis, including a total of 407 patients with schizophrenia and 383 comparison subjects. The studies reported fractional anisotropy reductions at 112 co-ordinates in schizophrenia and no fractional anisotropy increases. Over all studies, significant reductions were present in two regions: the left frontal deep white matter and the left temporal deep white matter. The first region, in the left frontal lobe, is traversed by white matter tracts interconnecting the frontal lobe, thalamus and cingulate gyrus. The second region, in the temporal lobe, is traversed by white matter tracts interconnecting the frontal lobe, insula, hippocampus-amygdala, temporal and occipital lobe. This suggests that two networks of white matter tracts may be affected in schizophrenia, with the potential for 'disconnection' of the gray matter regions which they link.
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              Human brain: left-right asymmetries in temporal speech region.

              We have found marked anatomical asymmetries between tile upper surfaces of the human right and left temporal lobes. The planum temporale (the area behind Hesch's gyrus) is larger on the left in 65 percent of brains; on the right it is larger in only 11 percent. The left planum is on the average one-third longer than the planum. This area makes up part of the temporal speech cortex, whose importance is well established on the basis of both anatomical findings in aphasic patients ans cortical stimulation at operation.

                Author and article information

                URI : http://frontiersin.org/people/u/75783
                URI : http://frontiersin.org/people/u/13399
                Front Hum Neurosci
                Front Hum Neurosci
                Front. Hum. Neurosci.
                Frontiers in Human Neuroscience
                Frontiers Media S.A.
                22 December 2014
                : 8
                1Dipartimento di Medicina dei Sistemi, Clinica Psichiatrica, Università di Roma Tor Vergata , Rome, Italy
                2Laboratorio di Neurologia Clinica e Comportamentale, Fondazione Santa Lucia IRCCS , Rome, Italy
                3Temerty Centre for Therapeutic Brain Intervention, Centre for Addiction and Mental Health, University of Toronto , Toronto, ON, Canada
                Author notes

                Edited by: Silvio Ionta, Centre Hospitalier Universitaire Vaudois and University of Lausanne Switzerland

                Reviewed by: Wi Hoon Jung, University of Pennsylvania, USA; Thilo Kellermann, RWTH Aachen University, Germany; Branislava Curcic-Blake, University Medical Center Groningen, Netherlands

                *Correspondence: Michele Ribolsi, Dipartimento di Medicina dei Sistemi, Clinica Psichiatrica, Università Tor Vergata, Via Nomentana 1362, Rome 00137, Italy e-mail: michele.81@ 123456live.it

                This article was submitted to the journal Frontiers in Human Neuroscience.

                Copyright © 2014 Ribolsi, Daskalakis, Siracusano and Koch.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                Page count
                Figures: 0, Tables: 2, Equations: 0, References: 131, Pages: 11, Words: 9560
                Review Article


                schizophrenia, connectivity, asymmetry, interhemispheric, diffusion tensor imaging, fmri


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