Hemispheric Specialization Of Function Research Articles

Functional Brain Adaptations During Speech Processing in 4-Month-Old Bilingual Infants.

Language learning is influenced by both neural development and environmental experiences. This work investigates the influence of early bilingual experience on the neural mechanisms underlying speech processing in 4-month-old infants. We study how an early environmental factor such as bilingualism interacts with neural development by comparing monolingual and bilingual infants' brain responses to speech. We used functional near-infrared spectroscopy (fNIRS) to measure 4-month-old Spanish-Basque bilingual and Spanish monolingual infants' brain responses while they listened to forward (FW) and backward (BW) speech stimuli in Spanish. We reveal distinct neural signatures associated with bilingual adaptations, including increased engagement of bilateral inferior frontal and temporal regions during speech processing in bilingual infants, as opposed to left hemispheric functional specialization observed in monolingual infants. This study provides compelling evidence of bilingualism-induced brain adaptations during speech processing in infants as young as 4 months. These findings emphasize the role of early language experience in shaping neural plasticity during infancy suggesting that bilingual exposure at this young age profoundly influences the neural mechanisms underlying speech processing.

Using rare genetic mutations to revisit structural brain asymmetry

Asymmetry between the left and right hemisphere is a key feature of brain organization. Hemispheric functional specialization underlies some of the most advanced human-defining cognitive operations, such as articulated language, perspective taking, or rapid detection of facial cues. Yet, genetic investigations into brain asymmetry have mostly relied on common variants, which typically exert small effects on brain-related phenotypes. Here, we leverage rare genomic deletions and duplications to study how genetic alterations reverberate in human brain and behavior. We designed a pattern-learning approach to dissect the impact of eight high-effect-size copy number variations (CNVs) on brain asymmetry in a multi-site cohort of 552 CNV carriers and 290 non-carriers. Isolated multivariate brain asymmetry patterns spotlighted regions typically thought to subserve lateralized functions, including language, hearing, as well as visual, face and word recognition. Planum temporale asymmetry emerged as especially susceptible to deletions and duplications of specific gene sets. Targeted analysis of common variants through genome-wide association study (GWAS) consolidated partly diverging genetic influences on the right versus left planum temporale structure. In conclusion, our gene-brain-behavior data fusion highlights the consequences of genetically controlled brain lateralization on uniquely human cognitive capacities.

Handedness as a major determinant of lateral bias in human functional cradling.

Studies examining infant cradling have almost uniformly concluded with a general human left-side bias for cradling, indicating that people prefer to hold an infant to the left of their body. Explanations for the notion of the left-side cradling bias have traditionally been searched for in a variety of factors, for example, in terms of maternal heartbeat, genetic factors, in the form of an ear asymmetry where auditory information is perceived faster through the left ear, as a result of a right hemispheric functional specialization for perception of emotions and faces, and in identifying a motor bias of the infant, such as the tendency of newborn infants to lie with the face to the right when placed supine. Interestingly, handedness is generally considered an inadequate explanation for the lateralized cradling bias, despite it being an intuitively plausible one. In this brief review, I put forward the cradler's handedness as the most convincing and elegant determinant of the cradling bias. This explanation is consistent with a developmental cascades' framework where the cradling bias can be understood as the result of a multitude of factors across a range of levels and systems.

Lateralization of early orthographic processing during natural reading is impaired in developmental dyslexia

Skilled reading requires specialized visual cortical processing of orthographic information and its impairment has been proposed as a potential correlate of compromised reading in dyslexia. However, which stage of orthographic information processing during natural reading is disturbed in dyslexics remains unexplored. Here we addressed this question by simultaneously measuring the eye movements and EEG of dyslexic and control young adults during natural reading. Isolated meaningful sentences were presented at five inter-letter spacing levels spanning the range from minimal to extra-large spacing, and participants were instructed to read the text silently at their own pace. Control participants read faster, performed larger saccades and shorter fixations compared to dyslexics. While reading speed peaked around the default letter spacing, saccade amplitude increased and fixation duration decreased with the increase of letter spacing in both groups. Lateralization of occipito-temporal fixation-related EEG activity (FREA) was found in three consecutive time intervals corresponding to early orthographic processing in control readers. Importantly, the lateralization in the time range of the first negative left occipito-temporal FREA peak was specific for first fixations and exhibited an interaction effect between reading ability and letter spacing. The interaction originated in the significant decrease of FREA lateralization at extra-large compared to default letter spacing in control readers and the lack of lateralization in both letter spacing conditions in the case of dyslexics. These findings suggest that expertise-driven hemispheric functional specialization for early orthographic processing thought to be responsible for letter identity extraction during natural reading is compromised in dyslexia.

The Intricate Web of Asymmetric Processing of Social Stimuli in Humans

Although the population-level preference for the use of the right hand is the clearest example of behavioral lateralization, it represents only the best-known instance of a variety of functional asymmetries observable in humans. What is interesting is that many of such asymmetries emerge during the processing of social stimuli, as often occurs in the case of human bodies, faces and voices. In the present paper, after reviewing previous literature about human functional asymmetries for social and emotional stimuli, we suggest some possible links among them and stress the necessity of a comprehensive account (in both ontogenetic and phylogenetic terms) for these not yet fully explained phenomena. In particular, we propose that the advantages of lateralization for emotion processing should be considered in light of previous suggestions that (i) functional hemispheric specialization enhances cognitive capacity and efficiency, and (ii) the alignment (at the population level) of the direction of behavioral asymmetries emerges, under social pressures, as an evolutionary stable strategy.

«Шум» как ключ к семиозису: мозг и культура (40 лет спустя)

The article explores the context important for the analysis of Lotman’s talk at the seminar on the problem of semiogenesis and functional specialization of cerebral hemispheres as a model of intellectual processes, which was held in Tartu. Forty years later, the author anal­yses changes in the viewpoints on the proposed model, taking into account the data of experi­mental neuroscience. The article emphasizes the fundamental value and topicality of Yuri Lotman’s ideas on the production of meaning in individual and cross-cultural space.

Handedness Development: A Model for Investigating the Development of Hemispheric Specialization and Interhemispheric Coordination

The author presents his perspective on the character of science, development, and handedness and relates these to his investigations of the early development of handedness. After presenting some ideas on what hemispheric specialization of function might mean for neural processing and how handedness should be assessed, the neuroscience of control of the arms/hands and interhemispheric communication and coordination are examined for how developmental processes can affect these mechanisms. The author’s work on the development of early handedness is reviewed and placed within a context of cascading events in which different forms of handedness emerge from earlier forms but not in a deterministic manner. This approach supports a continuous rather than categorical distribution of handedness and accounts for the predominance of right-handedness while maintaining a minority of left-handedness. Finally, the relation of the development of handedness to the development of several language and cognitive skills is examined.

EEG Effective Source Projections Are More Bilaterally Symmetric in Infants Than in Adults

Although anatomical brain hemispheric asymmetries have been clearly documented in the infant brain, findings concerning functional hemispheric specialization have been inconsistent. The present report aims to assess whether bilaterally symmetric synchronous activity between the two hemispheres is a characteristic of the infant brain. To asses cortical bilateral synchronicity, we used decomposition by independent component analysis (ICA) of high-density electroencephalographic (EEG) data collected in an auditory passive oddball paradigm. Decompositions of concatenated 64-channel EEG data epochs from each of 34 typically developing 6-month-old infants and from 18 healthy young adults participating in the same passive auditory oddball protocol were compared to characterize differences in functional brain organization between early life and adulthood. Our results show that infant EEG decompositions comprised a larger number of independent component (IC) effective source processes compatible with a cortical origin and having bilaterally near-symmetric scalp projections (13.8% of the infant data ICs presented a bilateral pattern vs. 4.3% of the adult data ICs). These IC projections could be modeled as the sum of potentials volume-conducted to the scalp from synchronous locally coherent field activities in corresponding left and right cortical source areas. To conclude, in this paradigm, source-resolved infant brain EEG exhibited more bilateral synchronicity than EEG produced by the adult brain, supporting the hypothesis that more strongly unilateral and likely more functionally specialized unihemispheric cortical field activities are concomitants of brain maturation.

Laterality of Eye Use by Bottlenose (Tursiops truncatus) and Rough-Toothed (Steno bredanensis) Dolphins While Viewing Predictable and Unpredictable Stimuli

Laterality of eye use has been increasingly studied in cetaceans. Research supports that many cetacean species keep prey on the right side while feeding and preferentially view unfamiliar objects with the right eye. In contrast, the left eye has been used more by calves while in close proximity to their mothers. Despite some discrepancies across and within species, laterality of eye use generally indicates functional specialization of brain hemispheres in cetaceans. The present study aimed to examine laterality of eye use in bottlenose dolphins (Tursiops truncatus) and rough-toothed dolphins (Steno bredanensis) under managed care. Subjects were video-recorded through an underwater window while viewing two different stimuli, one predictable and static and the other unpredictable and moving. Bottlenose dolphins displayed an overall right-eye preference, especially while viewing the unpredictable, moving stimulus. Rough-toothed dolphins did not display eye preference while viewing stimuli. No significant correlations between degree of laterality and behavioral interest in the stimuli were found. Only for bottlenose dolphins were the degree of laterality and curiosity ratings correlated. This study extends research on cetacean lateralization to a species not extensively examined and to stimuli that varied in movement and degree of predictability. Further research is needed to make conclusions regarding lateralization in cetaceans.

Distinctive Patterns of Seizure-Related White Matter Alterations in Right and Left Temporal Lobe Epilepsy.

Background: We hypothesized that right and left temporal lobe epilepsy (RTLE and LTLE, respectively) have distinctive spatial patterns of white matter (WM) changes that can be differentiated and interpreted with the use of multiple diffusion parameters. We compared the global microstructure of fiber bundles with regard to WM alterations in both RTLE and LTLE, addressing some of the methodological issues of previous studies.Methods: Diffusion tensor imaging data from 17 patients with RTLE (age: 40.7 ± 10.4), 15 patients with LTLE (age: 37.3 ± 10.4), and 15 controls (age: 34.8 ± 11.2) were used in the study. WM integrity was quantified by fractional anisotropy (FA), mean diffusivity (MD), longitudinal diffusivity (LD), and radial diffusivity (RD). The diffusion parameters were compared between the groups in tracts representing the core of the fiber bundles. The volumes of hippocampi and amygdala were subsequently compared across the groups, while the data were adjusted for the effect of hippocampal sclerosis.Results: Significantly reduced FA and increased MD, LD, and RD were found bilaterally over widespread brain regions in RTLE. An increase in MD and RD values was observed in widespread WM fiber bundles ipsilaterally in LTLE, largely overlapping with regions where FA was lower, while no increase in LD was observed. We also found a difference between the LTLE and RTLE groups for the right hippocampal volume (with and without adjustment for HS), whereas no significant volume differences were found between patients and controls.Conclusions: It appears that patients with RTLE exhibit a more widespread pattern of WM alterations that extend far beyond the temporal lobe in both ipsilateral and contralateral hemisphere; furthermore, these changes seem to reflect more severe damage related to chronic degeneration. Conversely, more restrained changes in the LTLE may imply a pattern of less severe axonal damage, more restricted to ipsilateral hemisphere. Comprehensive finding of more prominent hippocampal atrophy in the RTLE raises an interesting issue of seizure-induced implications on gray matter and WM microstructure that may not necessarily mean a straightforward causal relationship. Further correlations of diffusion-derived metrics with neuropsychological and functional imaging measures may provide complementary information on underlying WM abnormalities with regard to functional hemispheric specialization.

Development of brain-wide connectivity architecture in awake rats

Childhood and adolescence are both critical developmental periods, evidenced by complex neurophysiological changes the brain undergoes and high occurrence rates of neuropsychiatric disorders during these periods. Despite substantial progress in elucidating the developmental trajectories of individual neural circuits, our knowledge of developmental changes of whole-brain connectivity architecture in animals is sparse. To fill this gap, here we longitudinally acquired rsfMRI data in awake rats during five developmental stages from juvenile to adulthood. We found that the maturation timelines of brain circuits were heterogeneous and system specific. Functional connectivity (FC) tended to decrease in subcortical circuits, but increase in cortical circuits during development. In addition, the developing brain exhibited hemispheric functional specialization, evidenced by reduced inter-hemispheric FC between homotopic regions, and lower similarity of region-to-region FC patterns between the two hemispheres. Finally, we showed that whole-brain network development was characterized by reduced clustering (i.e. local communication) but increased integration (distant communication). Taken together, the present study has systematically characterized the development of brain-wide connectivity architecture from juvenile to adulthood in awake rats. It also serves as a critical reference point for understanding circuit- and network-level changes in animal models of brain development-related disorders. Furthermore, FC data during brain development in awake rodents contain high translational value and can shed light onto comparative neuroanatomy.

Interhemispheric Differences Observed during the Performance of Cognitive Tasks Using Doppler Ultrasound

The article presents empirical data on the possible use of transcranial Doppler sonography as a method for the identification of functional specialization of hemispheres. We investigated intrahemispheric differences in the increase in blood flow velocity indicators during the performance of cognitive tasks with verbal and nonverbal stimuli in 20 healthy right-handed participants and 20 right-handed patients with local unilateral vascular brain lesions. We observed interhemispheric and intrahemispheric differences in blood flow velocity indicators between arteries during the performance of cognitive tasks with different variants of verbal stimuli in all participants. It has been found that one of the hemispheres plays a dominant role in verbal and nonverbal stimulus processing.

Sensorimotor lateralization scaffolds cognitive specialization.

In this chapter, we review hemispheric differences for sensorimotor function and cognitive abilities. Specifically, we examine the left-hemisphere specialization for visuomotor control and its interplay with language, executive function, and musical training. Similarly, we discuss right-hemisphere lateralization for haptic processing and its relationship to spatial and numerical processing. We propose that cerebral lateralization for sensorimotor functions served as a foundation for the development of higher cognitive abilities and their hemispheric functional specialization. We further suggest that sensorimotor and cognitive functions are inextricably linked. Based on the studies discussed in this chapter our view is that sensorimotor control serves as a loom upon which the fibers of language, executive function, spatial, and numerical processing are woven together to create the fabric of cognition.

Functional hemispheric specialization for verbal and visual perceptual processes in terms of blood flow velocity changes in unilateral brain lesions

Objective : to comparatively analyze the patterns of functional hemispheric specialization in patients with local brain tumor lesions and in healthy participants. Patients and methods . 40 patients (20 men and 20 women) with local unilateral brain tumor lesions (astrocytomas, gliomas, metastases) aged 19–60 years (mean age, 33±9.2 years) were examined for functional hemispheric specialization for verbal and visual perceptual functions when performing cognitive tasks by functional transcranial Doppler ultrasonography. The findings were compared with those in 57 healthy individuals (mean age, 28±5.1 years). All the participants were right-handed. Results. There was a more pronounced increase in blood flow velocity (BFV) while performing verbal cognitive tasks in the vessels of the left hemisphere (LH) and a more marked rise in that when fulfilling non-verbal cognitive tasks in the vessels of the right hemisphere (RH). The trends in the ratio of LH/RH BFV amplification when performing cognitive tasks were observed to be the same as previously observed in the healthy participants.

Functional Connectivity Architecture of the Human Brain

Imaging studies suggest that individual differences in cognition and behavior might relate to differences in brain connectivity, particularly in the higher order association regions. Understanding the extent to which two brains can differ is crucial in clinical and basic neuroscience research. Here we highlight two major sources of variance that contribute to intersubject variability in connectivity measurements but are often mixed: the spatial distribution variability and the connection strength variability. We then offer a hypothesis about how the cortical surface expansion during human evolution may have led to remarkable intersubject variability in brain connectivity. We propose that a series of changes in connectivity architecture occurred in response to the pressure for processing efficiency in the enlarged brain. These changes not only distinguish us from our evolutionary ancestors, but also enable each individual to develop more uniquely. This hypothesis may gain support from the significant spatial correlations among evolutionary cortical expansion, the density of long-range connections, hemispheric functional specialization, and intersubject variability in connectivity.

Is there a left hemispheric asymmetry for tool affordance processing?

The perception of tools vs. other objects has been shown to activate the left premotor and somatosensory cortex, which represents object affordance associated with tool manipulability (Proverbio, Adorni, & D'Aniello, 2011). The question of whether hemispheric asymmetry depends on right hand use or is linked to a hemispheric functional specialization for fine-grained precision movement is unclear. Thus, in this paper, ERPs were recorded from 128 sites in response to the visual presentation of bidimensional (2D) pictures depicting unimanual (e.g., a hammer) and bimanual (e.g., a handlebar) tools (Study 1). Central N2 and prefrontal N400 components were much larger for bimanual than unimanual tools (over the left hemisphere for N400). SwLORETAs performed for both components showed at first the activation of the left parietal cortex (BA39) and then of the right homologous (BA40) one, for both grips but stronger for the bimanual coordination. At all times and for both grips, the left premotor cortex (BA6) was involved in coding action affordance, while only unimanual tools activated the left postcentral gyrus (BA3).In Study 2, unimanual tools were presented with an orientation congruent (standard) or incongruent to their interaction with the right hand (rotated), to manipulate affordance's quality. Standard objects elicited much larger ERP responses (namely: N1, N2, N400) than rotated tools (over the left hemisphere for N400). At the earliest stage (190–270ms) the significant intracranial sources were of visual nature (mainly the contralateral precuneus). Regions representing motor information were not involved. Rotated tools induced a smaller activation in the STS and parahippocampal regions (possibly coding affordable biological motion and the spatial aspects of hand/object interaction), whereas rotated tools activated to a greater extent the dorsolateral prefrontal cortex (DLPF, BA9). In the later time window standard objects activated the left BA6 and the right BA40 more than rotated objects.Overall, these data suggest that viewing tools automatically activates mental representations associated with their manipulation. The left premotor cortex was found to be involved with any kind of object and grip, as early as 200ms post-stimulus, thus supporting the hypothesis of a LH asymmetry in the neural representation of grasping, within this region. The right supramarginal gyrus was also found to be crucially involved later in time.

Tonkean macaques communicate with their right hand

There are two conflicting hypotheses to explain the origins of language. Vocal origin theory states that language results from the gradual evolution of animals’ vocal communication, but gestural origin theory considers that language evolved from gestures, with the initial left-hemispheric control of manual gestures gradually encompassing vocalizations. To contribute to this debate, we investigated functional hemispheric specialization related to hand biases when grasping or showing an object through manual gesture in Tonkean macaques. The results of this study, the first quantitative study on Tonkean macaques’ handedness, showed a remarkable convergence of the Tonkean macaques’ handedness patterns with those of baboons and human infants, with hand preferences for manual communicative gestures significantly favoring the use of the right hand. Our findings support the hypothesis that left hemispheric lateralization for language is derived from a gestural communication system that was present in the common ancestor of macaques, baboons and humans.

The Effect of Handedness on Visual P300 Responses and Visual Scanning Pathways

AbstractIt is thought that hemispheric asymmetry is reflected to behavioral asymmetries. The most prominent behavioral asymmetry is hand preference. This study consisted of two groups (14 each) with different handedness. Event-Related Potentials (ERPs) to a visual oddball task were recorded from 19 sites, and another session with a “change detection paradigm” was applied, where the visual scanning pathways were recorded. Although the comparison of P300 grand averages of 19 sites showed no significant difference between the groups, the comparison of the central sites (Fz, Cz, Pz) showed significant differences of both, amplitude and latency, (p<0.05; p<0.04) respectively, where larger amplitudes and longer latencies were found in the right handed group. Both groups have showed larger P300 amplitudes of right hemispheric responses (p<0.01) in inter-hemispheric comparison. The results of “change detection paradigm” have shown no significant difference between the groups. The cognitive processing of visual information was found to be more dominant at the right hemisphere in both groups, and stronger at central sites in right handed subjects than their left handed counter partners. The study included both, right- and left handed subjects, which makes it more specific than the previous studies in the field. The present findings were related with the results of studies which examine the thickness of the skull, the size of corpus callosal area and the functional specialization of hemispheres.

How anatomical asymmetry of human auditory cortex can lead to a rightward bias in auditory evoked fields

Auditory evoked fields and potentials, such as the N1 or the 40-Hz steady state response, are often stronger in the right compared to the left auditory cortex. Here we investigated whether a greater degree of cortical folding in left auditory cortex could result in increased MEG signal cancelation and a subsequent bias in MEG auditory signals toward the right hemisphere. Signal cancelation, due to non-uniformity of the orientations of underlying neural currents, affects MEG and EEG signals generated by any neuronal activity of reasonable spatial extent. We simulated MEG signals in patches of auditory cortex in seventeen subjects, and measured the relationships between underlying activity distribution, cortical non-uniformity, signal cancelation and resulting (fitted) dipole strength and position. Our results suggest that the cancelation of MEG signals from auditory cortex is asymmetric, due to underlying anatomy, and this asymmetry may result in a rightward bias in measurable dipole amplitudes. The effect was significant across all auditory areas tested, with the exception of planum temporale. Importantly, we also show how the rightward bias could be partially or completely offset by increased cortical area, and therefore increased cortical activity, on the left side. We suggest that auditory researchers are aware of the impact of cancelation and its resulting rightward bias in signal strength from auditory cortex. These findings are important for studies seeking functional hemispheric specialization in the auditory cortex with MEG as well as for integration of MEG with other imaging modalities.

Functional Hemispheric Specialization in Processing Phonemic and Prosodic Auditory Changes in Neonates

This study focuses on the early cerebral base of speech perception by examining functional lateralization in neonates for processing segmental and suprasegmental features of speech. For this purpose, auditory evoked responses of full-term neonates to phonemic and prosodic contrasts were measured in their temporal area and part of the frontal and parietal areas using near-infrared spectroscopy (NIRS). Stimuli used here were phonemic contrast /itta/ and /itte/ and prosodic contrast of declarative and interrogative forms /itta/ and /itta?/. The results showed clear hemodynamic responses to both phonemic and prosodic changes in the temporal areas and part of the parietal and frontal regions. In particular, significantly higher hemoglobin (Hb) changes were observed for the prosodic change in the right temporal area than for that in the left one, whereas Hb responses to the vowel change were similarly elicited in bilateral temporal areas. However, Hb responses to the vowel contrast were asymmetrical in the parietal area (around supra marginal gyrus), with stronger activation in the left. These results suggest a specialized function of the right hemisphere in prosody processing, which is already present in neonates. The parietal activities during phonemic processing were discussed in relation to verbal-auditory short-term memory. On the basis of this study and previous studies on older infants, the developmental process of functional lateralization from birth to 2 years of age for vowel and prosody was summarized.