Hand preference and local asymmetry in cerebral cortex, basal ganglia, and cerebellar white matter

Skin temperature changes in response to body ownership modulation vary according to the side of stimulation

A growing body of research has shown that a unilateral alteration in the sense of limb ownership is associated with the cooling of a limb's temperature. However, the recent emergence of contradictory results calls into question the existence of a relationship between this physiological reaction and the sense of body ownership. In the light of evidence that the malleability of the sense of hand ownership differs based on the preferential motor use of the hand to which the illusion is applied, one might observe the same lateralised pattern in the skin temperature cooling. In particular, if skin temperature change is a signature of body ownership, we expected a stronger illusion and reduction in skin temperature when altering ownership alteration of the left hand compared to the right hand in dextral individuals. To test this hypothesis, we selectively perturbated body ownership of the left or right hand in 24 healthy participants in different experimental sessions using the Mirror-Box Illusion (MBI) paradigm. Participants were asked to tap synchronously or asynchronously at a constant rhythm with their left and right index fingers against two parallel mirrors while looking at their reflected right/left hand. Skin temperature was measured before and after each MBI application, and explicit judgments of ownership and proprioceptive drift were collected. The results showed a consistent cooling of the hand's temperature only when the illusion was performed on the left hand. Proprioceptive drift exhibited the same pattern. In contrast, the explicit judgment of ownership of the reflected hand was similar across the two hands. These data provide evidence in favor of a specific laterality effect of the physiological response to an induced alteration of body part ownership. Moreover, they highlight the possibility of a direct link between proprioception and skin temperature.

Does the Degree and/or Direction of Handedness in Children With Developmental Coordination Disorder Influence Motor and Cognitive Performance? A Pilot Study

Research has shown that nonright-handedness in children with developmental coordination disorder (DCD) is associated with poorer motor and cognitive performance. This study investigated the influence of degree and direction of handedness on performance using the Home Handedness Questionnaire, the Hit-the-Dot test, the Movement Assessment Battery for Children, and the digital Trail-Making Test. Eighteen children with DCD and 21 typically developing children aged 8–12 years participated in this study. The distribution of degree and direction of handedness in the group of DCD children were not different from that found in the typically developing group. In the Hit-the-Dot test, typically developing children significantly performed better than children with DCD, no matter which hand was dominant or to which degree. A significant inconsistent-handed advantage in the subdomain balance was found for children with DCD. Inconsistent handedness also seems to be an advantage for children with DCD on the digital Trail-Making Test performance. The relationship between the subcategories of the Movement Assessment Battery for Children and the digital Trail-Making Test part B is stronger for consistent than for inconsistent handedness. Our findings suggest that children with DCD and inconsistent handedness might benefit from greater crosstalk across hemispheres. In addition, these predispositions can be reinforced or discouraged throughout development and via occupational therapy.

Machine learning of large-scale multimodal brain imaging data reveals neural correlates of hand preference

Lateralization is a fundamental characteristic of many behaviors and the organization of the brain, and atypical lateralization has been suggested to be linked to various brain-related disorders such as autism and schizophrenia. Right-handedness is one of the most prominent markers of human behavioural lateralization, yet its neurobiological basis remains to be determined. Here, we present a large-scale analysis of handedness, as measured by self-reported direction of hand preference, and its variability related to brain structural and functional organization in the UK Biobank (N = 36,024). A multivariate machine learning approach with multi-modalities of brain imaging data was adopted, to reveal how well brain imaging features could predict individual's handedness (i.e., right-handedness vs. non-right-handedness) and further identify the top brain signatures that contributed to the prediction. Overall, the results showed a good prediction performance, with an area under the receiver operating characteristic curve (AUROC) score of up to 0.72, driven largely by resting-state functional measures. Virtual lesion analysis and large-scale decoding analysis suggested that the brain networks with the highest importance in the prediction showed functional relevance to hand movement and several higher-level cognitive functions including language, arithmetic, and social interaction. Genetic analyses of contributions of common DNA polymorphisms to the imaging-derived handedness prediction score showed a significant heritability (h²=7.55%, p <0.001) that was similar to and slightly higher than that for the behavioural measure itself (h²=6.74%, p <0.001). The genetic correlation between the two was high (r_g=0.71), suggesting that the imaging-derived score could be used as a surrogate in genetic studies where the behavioural measure is not available. This large-scale study using multimodal brain imaging and multivariate machine learning has shed new light on the neural correlates of human handedness.

Contribution of the sensorimotor beta oscillations and the cortico-basal ganglia-thalamic circuitry during value-based decision making: A simultaneous EEG-fMRI investigation

In decision neuroscience, the motor system has primarily been considered to be involved in executing choice actions. However, a competing perspective suggests its engagement in the evaluation of options, traditionally considered to be performed by the brain's valuation system. Here, we investigate the role of the motor system in value-based decision making by determining the neural circuitries associated with the sensorimotor beta oscillations previously identified to encode decision options. In a simultaneous EEG-fMRI study, participants evaluated reward and risk associated with a forthcoming action. A significant sensorimotor beta desynchronization was identified prior to and independent of response. The level of beta desynchronization showed evidence of encoding the reward levels. This beta desynchronization covaried, on a trial-by-trial level, with BOLD activity in the cortico-basal ganglia-thalamic circuitry. In contrast, there was only a weak covariation within the valuation network, despite significant modulation of its BOLD activity by reward levels. These results suggest that the way in which decision variables are processed differs in the valuation network and in the cortico-basal ganglia-thalamic circuitry. We propose that sensorimotor beta oscillations indicate incentive motivational drive towards a choice action computed from the decision variables even prior to making a response, and it arises from the cortico-basal ganglia-thalamic circuitry.

Broca's area and the search for anatomical asymmetry: commentary and perspectives

We present a brief commentary on the field's search for an anatomical asymmetry between Broca's area and its homologue in the non-dominant hemisphere, focusing on a selection of studies, including research from the last decade. We demonstrate that, several years after the influential review of Keller and colleagues from 2009, and despite recent advances in neuroimaging, the existence of a structural asymmetry of Broca's area is still controversial. This is especially the case for studies of the macroanatomy of this region. We point out the inconsistencies in methodology across studies that could account for the discrepancy in results. Investigations of the microstructure of Broca's area show a trend of a leftward asymmetry, but it is still unclear how these results relate to language dominance. We suggest that it may be necessary to combine multiple metrics in a systematic manner to find robust asymmetries and to expand the regional scope of structural investigations. Finally, based on the current state of the literature, we should not rule out the possibility that language dominance may simply not be reflected in local anatomical differences in the brain.

Exploring the Interaction Between Handedness and Body Parts Ownership by Means of the Implicit Association Test

The experience of owning a body is built upon the integration of exteroceptive, interoceptive, and proprioceptive signals. Recently, it has been suggested that motor signals could be particularly important in producing the feeling of body part ownership. One thus may hypothesize that the strength of this feeling may not be spatially uniform; rather, it could vary as a function of the degree by which different body parts are involved in motor behavior. Given that our dominant hand plays a leading role in our motor behavior, we hypothesized that it could be more strongly associated with one’s self compared to its non-dominant counterpart. To explore whether this possible asymmetry manifests as a stronger implicit association of the right hand (vs left hand) with the self, we administered the Implicit Association Test to a group of 70 healthy individuals. To control whether this asymmetric association is human-body specific, we further tested whether a similar asymmetry characterizes the association between a right (vs left) animal body part with the concept of self, in an independent sample of subjects (N = 70, 140 subjects total). Our results revealed a linear relationship between the magnitude of the implicit association between the right hand with the self and the subject’s handedness. In detail, the strength of this association increased as a function of hand preference. Critically, the handedness score did not predict the association of the right-animal body part with the self. These findings suggest that, in healthy individuals, the dominant and non-dominant hands are differently perceived at an implicit level as belonging to the self. We argue that such asymmetry may stem from the different roles that the two hands play in our adaptive motor behavior.

A novel virtual reality approach for functional lateralization in healthy adults

Functional lateralization relates to a natural asymmetry in the dominance right or left body side, and is a fundamental principle of the brain. The hemispheres of the brain control the contralateral body side, and show subtle, yet striking, anatomical asymmetries and functional lateralization. Innovative technologies, including Virtual Reality (VR), are entering the areas of experimental research, modeling and simulation related to the study of lateralization, with new perspectives of different applications in modern medical practice. Researchers/clinicians note that there are fewer VR studies with healthy participants, and which are important in evaluating/interpreting clinical outcomes, and testing the usefulness, limitations, and sensitivity of VR. The presented influence of the domination of upper/lower limbs on the performance of VR exercises was studied in healthy right-handed adults. Virtual testing sessions were performed independently with both/ dominant/ non-dominant hands, and the similar VR sessions were conduced on a Wii Balance Board (WBB) with the choice of body side, at different levels of the difficulty. The obtained results are consistent with other studies which show that cognitive-motor training in VR with the WBB platform is a very sensitive and promising tool for recognizing/assessing functional asymmetries of the right-left body side not only in disturbed lateralization, but also in the test training of healthy subjects.

Morphological and functional variability in central and subcentral motor cortex of the human brain

There is a long-established link between anatomy and function in the somatomotor system in the mammalian cerebral cortex. The morphology of the central sulcus is predictive of the location of functional activation peaks relating to movement of different effectors in individuals. By contrast, morphological variation in the subcentral region and its relationship to function is, as yet, unknown. Investigating the subcentral region is particularly important in the context of speech, since control of the larynx during human speech production is related to activity in this region. Here, we examined the relationship between morphology in the central and subcentral region and the location of functional activity during movement of the hand, lips, tongue, and larynx at the individual participant level. We provide a systematic description of the sulcal patterns of the subcentral and adjacent opercular cortex, including the inter-individual variability in sulcal morphology. We show that, in the majority of participants, the anterior subcentral sulcus is not continuous, but consists of two distinct segments. A robust relationship between morphology of the central and subcentral sulcal segments and movement of different effectors is demonstrated. Inter-individual variability of underlying anatomy might thus explain previous inconsistent findings, in particular regarding the ventral larynx area in subcentral cortex. A surface registration based on sulcal labels indicated that such anatomical information can improve the alignment of functional data for group studies.

Handedness and White Matter Networks

The development and persistence of laterality is a key feature of human motor behavior, with the asymmetry of hand use being the most prominent. The idea that asymmetrical functions of the hands reflect asymmetries in terms of structural and functional brain organization has been tested many times. However, despite advances in laterality research and increased understanding of this population-level bias, the neural basis of handedness remains elusive. Recent developments in diffusion magnetic resonance imaging enabled the exploration of lateralized motor behavior also in terms of white matter and connectional neuroanatomy. Despite incomplete and partly inconsistent evidence, structural connectivity of both intrahemispheric and interhemispheric white matter seems to differ between left and right-handers. Handedness was related to asymmetry of intrahemispheric pathways important for visuomotor and visuospatial processing (superior longitudinal fasciculus), but not to projection tracts supporting motor execution (corticospinal tract). Moreover, the interindividual variability of the main commissural pathway corpus callosum seems to be associated with handedness. The review highlights the importance of exploring new avenues for the study of handedness and presents the latest state of knowledge that can be used to guide future neuroscientific and genetic research.