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Concept: Popular psychology

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Hemispheric lateralization for language production and its relationships with manual preference and manual preference strength were studied in a sample of 297 subjects, including 153 left-handers (LH). A hemispheric functional lateralization index (HFLI) for language was derived from fMRI acquired during a covert sentence generation task as compared with a covert word list recitation. The multimodal HFLI distribution was optimally modeled using a mixture of 3 and 4 Gaussian functions in right-handers (RH) and LH, respectively. Gaussian function parameters helped to define 3 types of language hemispheric lateralization, namely “Typical” (left hemisphere dominance with clear positive HFLI values, 88% of RH, 78% of LH), “Ambilateral” (no dominant hemisphere with HFLI values close to 0, 12% of RH, 15% of LH) and “Strongly-atypical” (right-hemisphere dominance with clear negative HFLI values, 7% of LH). Concordance between dominant hemispheres for hand and for language did not exceed chance level, and most of the association between handedness and language lateralization was explained by the fact that all Strongly-atypical individuals were left-handed. Similarly, most of the relationship between language lateralization and manual preference strength was explained by the fact that Strongly-atypical individuals exhibited a strong preference for their left hand. These results indicate that concordance of hemispheric dominance for hand and for language occurs barely above the chance level, except in a group of rare individuals (less than 1% in the general population) who exhibit strong right hemisphere dominance for both language and their preferred hand. They call for a revisit of models hypothesizing common determinants for handedness and for language dominance.

Concepts: Left-handedness, Handedness, Ambidexterity, Michael Gazzaniga, Roger Wolcott Sperry, Right-handedness, Lateralization of brain function, Popular psychology

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Understanding the neurobiological mechanisms underlying inhibitory control is crucial given its role in various disease states and substance abuse/misuse. Neuroimaging research examining inhibitory control has yielded conflicting results on the relative importance of the left and right hemisphere during successful inhibition of a motor response. In the current study, a split-brain patient was examined in order to assess the independent inhibitory capabilities of each hemisphere. The patient’s right hemisphere exhibited superior inhibitory ability compared to his left hemisphere on three inhibitory control tasks. Although inferior to the right, the left hemisphere inhibited motor responses on inhibitory trials in all three tasks. The results from this study support the dominance of the right hemisphere in inhibitory control.

Concepts: Left-wing politics, Neuroscience, Right-wing politics, Split-brain, Michael Gazzaniga, Roger Wolcott Sperry, Lateralization of brain function, Popular psychology

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The objective of this study was to validate a line bisection judgement (LBJ) task for use in investigating the lateralized cerebral bases of spatial attention in a sample of 51 right-handed healthy participants. Using functional magnetic resonance imaging (fMRI), the participants performed a LBJ task that was compared to a visuomotor control task during which the participants made similar saccadic and motoric responses. Cerebral lateralization was determined using a voxel-based functional asymmetry analysis and a hemispheric functional lateralization index (HFLI) computed from fMRI contrast images. Behavioural attentional deviation biases were assessed during the LBJ task and a “paper and pencil” symbol cancellation task (SCT). Individual visuospatial skills were also evaluated. The results showed that both the LBJ and SCT tasks elicited leftward spatial biases in healthy subjects, although the biases were not correlated, which indicated their independence. Neuroimaging results showed that the LBJ task elicited a right hemispheric lateralization, with rightward asymmetries found in a large posterior occipito-parietal area, the posterior calcarine sulcus (V1p) and the temporo-occipital junction (TOJ) and in the inferior frontal gyrus, the anterior insula and the superior medial frontal gyrus. The comparison of the LBJ asymmetry map to the lesion map of neglect patients who suffer line bisection deviation demonstrated maximum overlap in a network that included the middle occipital gyrus (MOG), the TOJ, the anterior insula and the inferior frontal region, likely subtending spatial LBJ bias. Finally, the LBJ task-related cerebral lateralization was specifically correlated with the LBJ spatial bias but not with the SCT bias or with the visuospatial skills of the participants. Taken together, these results demonstrated that the LBJ task is adequate for investigating spatial lateralization in healthy subjects and is suitable for determining the factors underlying the variability of spatial cerebral lateralization.

Concepts: Human brain, Magnetic resonance imaging, Cerebrum, Inferior frontal gyrus, Lateralization of brain function, Popular psychology

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While the right-hemispheric lateralization of the face perception network is well established, recent evidence suggests that handedness affects the cerebral lateralization of face processing at the hierarchical level of the fusiform face area (FFA). However, the neural mechanisms underlying differential hemispheric lateralization of face perception in right- and left-handers are largely unknown. Using dynamic causal modeling (DCM) for fMRI, we aimed to unravel the putative processes that mediate handedness-related differences by investigating the effective connectivity in the bilateral core face perception network. Our results reveal an enhanced recruitment of the left FFA in left-handers compared to right-handers, as evidenced by more pronounced face-specific modulatory influences on both intra- and interhemispheric connections. As structural and physiological correlates of handedness-related differences in face processing, right- and left-handers varied with regard to their gray matter volume in the left fusiform gyrus and their pupil responses to face stimuli. Overall, these results describe how handedness is related to the lateralization of the core face perception network, and point to different neural mechanisms underlying face processing in right- and left-handers. In a wider context, this demonstrates the entanglement of structurally and functionally remote brain networks, suggesting a broader underlying process regulating brain lateralization.

Concepts: Human brain, Cerebrum, Fusiform face area, Fusiform gyrus, Ambidexterity, Lateralization of brain function, Popular psychology

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In Chinese orthography, the most common character structure consists of a semantic radical on the left and a phonetic radical on the right (SP characters); the minority, opposite arrangement also exists (PS characters). Recent studies showed that SP character processing is more left hemisphere (LH) lateralized than PS character processing. Nevertheless, it remains unclear whether this is due to phonetic radical position or character type frequency. Through computational modeling with artificial lexicons, in which we implement a theory of hemispheric asymmetry in perception but do not assume phonological processing being LH lateralized, we show that the difference in character type frequency alone is sufficient to exhibit the effect that the dominant type has a stronger LH lateralization than the minority type. This effect is due to higher visual similarity among characters in the dominant type than the minority type, demonstrating the modulation of visual similarity of words on hemispheric lateralization.

Concepts: Chinese language, French Revolution, Michael Gazzaniga, Roger Wolcott Sperry, Lateralization of brain function, Unicode, Popular psychology

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The present study reappraised the relationship between hemispheric specialization strength and cognitive skills in a sample of 297 individuals including 153 left-handers. It additionally assessed the interaction with manual laterality factors, such as handedness, asymmetry of hand motor skills, and familial sinistrality. A Hemispheric Functional Lateralization Index (HFLI) for language was derived from fMRI. Through mixture Gaussian modeling, three types of language hemispheric lateralization were defined: typical (left hemisphere dominance with clear positive HFLI), ambilateral (no dominant hemisphere with HFLI values close to 0), and strongly-atypical (right-hemisphere dominance with clear negative HFLI values). Three cognitive scores were derived from 12 tests covering various aspects of verbal and spatial cognition. Compared to both typical and strongly-atypical participants, those ambilateral for language production had lower performances in verbal and non-verbal domains, indicating that hemispheric specialization and cognitive skills are related in adults. Furthermore, this relationship was independent from handedness and asymmetry for motor skills, as no interaction was observed between these factors. On the other hand, the relationship between familial sinistrality and cognitive skills tended to differ according to language lateralization type. In contrast to previous reports in children, in the present adult population, we found no linear correlation between HFLI and cognitive skills, regardless of lateralization type.

Concepts: Cognition, Left-handedness, Handedness, Ambidexterity, Michael Gazzaniga, Roger Wolcott Sperry, Lateralization of brain function, Popular psychology

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The scaling of our finger forces according to the properties of manipulated objects is an elementary prerequisite of skilled motor behavior. Lesions of the motor-dominant left brain may impair several aspects of motor planning. For example, limb-apraxia, a tool-use disorder after left brain damage is thought to be caused by deficient recall or integration of tool-use knowledge into an action plan. The aim of the present study was to investigate whether left brain damage affects anticipatory force scaling when lifting everyday objects. We examined 26 stroke patients with unilateral brain damage (16 with left brain damage, ten with right brain damage) and 21 healthy control subjects. Limb apraxia was assessed by testing pantomime of familiar tool-use and imitation of meaningless hand postures. Participants grasped and lifted twelve randomly presented everyday objects. Grip force was measured with help of sensors fixed on thumb, index and middle-finger. The maximum rate of grip force was determined to quantify the precision of anticipation of object properties. Regression analysis yielded clear deficits of anticipation in the group of patients with left brain damage, while the comparison of patient with right brain damage with their respective control group did not reveal comparable deficits. Lesion-analyses indicate that brain structures typically associated with a tool-use network in the left hemisphere play an essential role for anticipatory grip force scaling, especially the left inferior frontal gyrus (IFG) and the premotor cortex (PMC). Furthermore, significant correlations of impaired anticipation with limb apraxia scores suggest shared representations. However, the presence of dissociations, implicates also independent processes. Overall, our findings suggest that the left hemisphere is engaged in anticipatory grip force scaling for lifting everyday objects. The underlying neural substrate is not restricted to a single region or stream; instead it may rely on the intact functioning of a left hemisphere network that may overlap with the left hemisphere dominant tool-use network.

Concepts: Brain, Human brain, Cerebral cortex, Cerebrum, Michael Gazzaniga, Roger Wolcott Sperry, Lateralization of brain function, Popular psychology

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Consistent with long-standing findings from behavioral studies, neuroimaging investigations have identified a region of the inferior temporal cortex that, in adults, shows greater face selectivity in the right than left hemisphere and, conversely, a region that shows greater word selectivity in the left than right hemisphere. What has not been determined is how this pattern of mature hemispheric specialization emerges over the course of development. The present study examines the hemispheric superiority for faces and words in children, young adolescents and adults in a discrimination task in which stimuli are presented briefly in either hemifield. Whereas adults showed the expected left and right visual field superiority for face and word discrimination, respectively, the young adolescents demonstrated only the right-field superiority for words and no field superiority for faces. Although the children’s overall accuracy was lower than that of the older groups, like the young adolescents, they exhibited a right visual field superiority for words but no field superiority for faces. Interestingly, the emergence of face lateralization was correlated with reading competence, measured on an independent standardized test, after regressing out age, quantitative reasoning scores, and face discrimination accuracy. Taken together, these findings suggest that the hemispheric organization of face and word recognition do not develop independently and that word lateralization, which emerges earlier, may drive later face lateralization. A theoretical account in which competition for visual representations unfolds over the course of development is proposed to account for the findings. (PsycINFO Database Record © 2013 APA, all rights reserved).

Concepts: Left-wing politics, Human brain, Cerebral cortex, Cerebrum, Michael Gazzaniga, Roger Wolcott Sperry, Lateralization of brain function, Popular psychology

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Studying the characteristics of movements performed under different action conditions may foster the understanding of disturbed tool use in apraxia and may enhance the knowledge about the links between states of action representations. We registered hand and arm movements during a hammering action executed under three task conditions: pantomime, demonstration with the hammer only, and actual execution with hammer and nail. Various movement parameters were calculated to characterize the kinematic aspects of the hammering movements. An apraxia score that reflects conceptual errors was derived from video-evaluation of pantomiming. Twenty-three patients with left brain damage (LBD), 10 patients with right brain damage (RBD), and 19 control subjects were tested. Patients performed with the non-paretic ipsilesional hand. Four apraxic LBD patients failed to perform the task due to severe conceptual errors. The remaining LBD patients frequently produced movements that were slower, shorter, and less vertical than those of control subjects in all task conditions. Lesion analyses for the LBD patients suggested that inferior frontal areas were particularly responsible for impaired performance. RBD patients performed normally in most kinematic task aspects. Although the conditions differed characteristically in geometry and kinematics, correlations of performance measures indicated that individual patterns in patients as well as in control subjects were stable across the conditions. Performance stability across conditions and the overlapping neural network both support the concept of a general action prototype that is adapted flexibly to environmental constraints. Findings in patients show that LBD can affect the execution of an actual hammering action also in the absence of conceptual errors. It remains to be shown however whether conceptual errors and abnormalities of movement kinematics have a common cause or are two independent manifestations of damage to the motor-dominant brain.

Concepts: Human brain, Performance, Classical mechanics, Kinematics, Nail, Lateralization of brain function, Hammer, Popular psychology