Pars triangularis asymmetry and language dominance

A speech fluency brain network derived from gliomas

The brain network of speech fluency has not yet been investigated via a study with a large and homogenous sample. This study analysed multimodal imaging data from 115 patients with low-grade glioma to explore the brain network of speech fluency. We applied voxel-based lesion-symptom mapping to identify domain-specific regions and white matter pathways associated with speech fluency. Direct cortical stimulation validated the domain-specific regions intra-operatively. We then performed connectivity-behaviour analysis with the aim of identifying connections that significantly correlated with speech fluency. Voxel-based lesion-symptom mapping analysis showed that damage to domain-specific regions (the middle frontal gyrus, the precentral gyrus, the orbital part of inferior frontal gyrus and the insula) and white matter pathways (corticospinal fasciculus, internal capsule, arcuate fasciculus, uncinate fasciculus, frontal aslant tract) are associated with reduced speech fluency. Furthermore, we identified connections emanating from these domain-specific regions that exhibited significant correlations with speech fluency. These findings illuminate the interaction between domain-specific regions and 17 domain-general regions-encompassing the superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus and rolandic operculum, superior temporal gyrus, temporal pole, inferior temporal pole, middle cingulate gyrus, supramarginal gyrus, fusiform gyrus, inferior parietal lobe, as well as subcortical structures such as thalamus-implicating their collective role in supporting fluent speech. Our detailed mapping of the speech fluency network offers a strategic foundation for clinicians to safeguard language function during the surgical intervention for brain tumours.

An MRI Study of Morphology, Asymmetry, and Sex Differences of Inferior Precentral Sulcus

Numerous studies utilizing magnetic resonance imaging (MRI) have observed sex and interhemispheric disparities in sulcal morphology, which could potentially underpin certain functional disparities in the human brain. Most of the existing research examines the precentral sulcus comprehensively, with a rare focus on its subsections. To explore the morphology, asymmetry, and sex disparities within the inferior precentral sulcus (IPCS), we acquired 3.0T magnetic resonance images from 92 right-handed Chinese adolescents. Brainvisa was used to reconstruct the IPCS structure and calculate its mean depth (MD). Based on the morphological patterns of IPCS, it was categorized into five distinct types. Additionally, we analyzed four different types of spatial relationships between IPCS and inferior frontal sulcus (IFS). There was a statistically significant sex disparity in the MD of IPCS, primarily observed in the right hemisphere. Females exhibited significantly greater asymmetry in the MD of IPCS compared to males. No statistically significant sex or hemispheric variations were identified in sulcal patterns. Our findings expand the comprehension of inconsistencies in sulcal structure, while also delivering an anatomical foundation for the study of related regions' function.

Delta-alpha cross-frequency coupling for different brain regions

Neural interactions occur on different levels and scales. It is of particular importance to understand how they are distributed among different neuroanatomical and physiological relevant brain regions. We investigated neural cross-frequency couplings between different brain regions according to the Desikan-Killiany brain parcellation. The adaptive dynamic Bayesian inference method was applied to EEG measurements of healthy resting subjects in order to reconstruct the coupling functions. It was found that even after averaging over all subjects, the mean coupling function showed a characteristic waveform, confirming the direct influence of the delta-phase on the alpha-phase dynamics in certain brain regions and that the shape of the coupling function changes for different regions. While the averaged coupling function within a region was of similar form, the region-averaged coupling function was averaged out, which implies that there is a common dependence within separate regions across the subjects. It was also found that for certain regions the influence of delta on alpha oscillations is more pronounced and that oscillations that influence other are more evenly distributed across brain regions than the influenced oscillations. When presenting the information on brain lobes, it was shown that the influence of delta emanating from the brain as a whole is greatest on the alpha oscillations of the cingulate frontal lobe, and at the same time the influence of delta from the cingulate parietal brain lobe is greatest on the alpha oscillations of the whole brain.

Texture-based brain networks for characterization of healthy subjects from MRI

Brain networks have been widely used to study the relationships between brain regions based on their dynamics using, e.g. fMRI or EEG, and to characterize their real physical connections using DTI. However, few studies have investigated brain networks derived from structural properties; and those have been based on cortical thickness or gray matter volume. The main objective of this work was to investigate the feasibility of obtaining useful information from brain networks derived from structural MRI, using texture features. We also wanted to verify if texture brain networks had any relation with established functional networks. T1-MR images were segmented using AAL and texture parameters from the gray-level co-occurrence matrix were computed for each region, for 760 subjects. Individual texture networks were used to evaluate the structural connections between regions of well-established functional networks; assess possible gender differences; investigate the dependence of texture network measures with age; and single out brain regions with different texture-network characteristics. Although around 70% of texture connections between regions belonging to the default mode, attention, and visual network were greater than the mean connection value, this effect was small (only between 7 and 15% of these connections were larger than one standard deviation), implying that texture-based morphology does not seem to subside function. This differs from cortical thickness-based morphology, which has been shown to relate to functional networks. Seventy-five out of 86 evaluated regions showed significant (ANCOVA, p < 0.05) differences between genders. Forty-four out of 86 regions showed significant (ANCOVA, p < 0.05) dependence with age; however, the R2 indicates that this is not a linear relation. Thalamus and putamen showed a very unique texture-wise structure compared to other analyzed regions. Texture networks were able to provide useful information regarding gender and age-related differences, as well as for singling out specific brain regions. We did not find a morphological texture-based subsidy for the evaluated functional brain networks. In the future, this approach will be extended to neurological patients to investigate the possibility of extracting biomarkers to help monitor disease evolution or treatment effectiveness.

Gut microbiome association with brain imaging markers, APOE genotype, calcium and vegetable intakes, and obesity in healthy aging adults

Introduction

Advanced age is a significant factor in changes to brain physiology and cognitive functions. Recent research has highlighted the critical role of the gut microbiome in modulating brain functions during aging, which can be influenced by various factors such as apolipoprotein E (APOE) genetic variance, body mass index (BMI), diabetes, and dietary intake. However, the associations between the gut microbiome and these factors, as well as brain structural, vascular, and metabolic imaging markers, have not been well explored.

Methods

We recruited 30 community dwelling older adults between age 55-85 in Kentucky. We collected the medical history from the electronic health record as well as the Dietary Screener Questionnaire. We performed APOE genotyping with an oral swab, gut microbiome analysis using metagenomics sequencing, and brain structural, vascular, and metabolic imaging using MRI.

Results

Individuals with APOE e2 and APOE e4 genotypes had distinct microbiota composition, and higher level of pro-inflammatory microbiota were associated higher BMI and diabetes. In contrast, calcium- and vegetable-rich diets were associated with microbiota that produced short chain fatty acids leading to an anti-inflammatory state. We also found that important gut microbial butyrate producers were correlated with the volume of the thalamus and corpus callosum, which are regions of the brain responsible for relaying and processing information. Additionally, putative proinflammatory species were negatively correlated with GABA production, an inhibitory neurotransmitter. Furthermore, we observed that the relative abundance of bacteria from the family Eggerthellaceae, equol producers, was correlated with white matter integrity in tracts connecting the brain regions related to language, memory, and learning.

Discussion

These findings highlight the importance of gut microbiome association with brain health in aging population and could have important implications aimed at optimizing healthy brain aging through precision prebiotic, probiotic or dietary interventions.

Grey Matter Reshaping of Language-Related Regions Depends on Tumor Lateralization

A brain tumor in the left hemisphere can decrease language laterality as assessed through fMRI. However, it remains unclear whether or not this decreased language laterality is associated with a structural reshaping of the grey matter, particularly within the language network. Here, we examine if the disruption of the language hubs exclusively affects the macrostructural properties of the contralateral homologues or whether it affects both hemispheres. This study uses voxel-based morphometry applied to high-resolution MR T1-weighted MPRAGE images from 31 adult patients' left hemisphere, which is dominant for language. Eighteen patients had brain tumors in the left hemisphere, and thirteen had tumors in the right hemisphere. A cohort of 71 healthy individuals matched with respect to age and sex was used as a baseline. We defined 10 ROIs per hemisphere involved in language function. Two separate repeated-measure ANOVAs were conducted with the volume per region as the dependent variable. For the patients, tumor lateralization (right versus left) served as a between-subject factor. The current study demonstrated that the presence of a brain tumor generates global volumetric changes affecting the left language regions and their contralateral homologues. These changes are mediated by the lateralization of the lesion. Our findings suggest that functional mechanisms are supported by the rearrangement of the grey matter.

How can graph theory inform the dual-stream model of speech processing? a resting-state fMRI study of post-stroke aphasia

The dual-stream model of speech processing has been proposed to represent the cortical networks involved in speech comprehension and production. Although it is arguably the prominent neuroanatomical model of speech processing, it is not yet known if the dual-stream model represents actual intrinsic functional brain networks. Furthermore, it is unclear how disruptions after a stroke to the functional connectivity of the dual-stream model's regions are related to specific types of speech production and comprehension impairments seen in aphasia. To address these questions, in the present study, we examined two independent resting-state fMRI datasets: (1) 28 neurotypical matched controls and (2) 28 chronic left-hemisphere stroke survivors with aphasia collected at another site. Structural MRI, as well as language and cognitive behavioral assessments, were collected. Using standard functional connectivity measures, we successfully identified an intrinsic resting-state network amongst the dual-stream model's regions in the control group. We then used both standard functional connectivity analyses and graph theory approaches to determine how the functional connectivity of the dual-stream network differs in individuals with post-stroke aphasia, and how this connectivity may predict performance on clinical aphasia assessments. Our findings provide strong evidence that the dual-stream model is an intrinsic network as measured via resting-state MRI, and that weaker functional connectivity of the hub nodes of the dual-stream network defined by graph theory methods, but not overall average network connectivity, is weaker in the stroke group than in the control participants. Also, the functional connectivity of the hub nodes predicted specific types of impairments on clinical assessments. In particular, the relative strength of connectivity of the right hemisphere's homologues of the left dorsal stream hubs to the left dorsal hubs versus right ventral stream hubs is a particularly strong predictor of post-stroke aphasia severity and symptomology.

Response assignment influences visual recognition

This study investigated whether two different neural systems influenced performance in an immediate visual recognition, i.e. visual same/different task. An observer had to respond rapidly whether a test consonant had just appeared in the study string by pressing one of two response keys, labeled same and different. When the same response was assigned to the response key on the right, there was no effect of study-string position on target response time (RT), indicating that the test item was not compared with the study string. When the different response was assigned to the response key on the right, same RT was an increasing function of the left-to-right position of a target in the study string and different RT was slower than same RT, indicating that during test the study string was compared with the test item. Functional magnetic resonance imaging confirmed that the caudate and left hippocampus were more active when the different response was assigned to the right key but the right hippocampus was more active when the same response was assigned to the right key. Therefore, two different computational processes are performed by two different brain systems depending on whether the same or different response is assigned to the right response key.

Grey matter reshaping of language-related regions depends on tumor lateralization

A brain tumor in the left hemisphere can decrease language laterality as assessed with fMRI. However, it remains unclear whether or not this decreased language laterality is associated with a structural reshaping of the grey matter, particularly within the language network. Here, we examine if the disruption of language hubs exclusively affects macrostructural properties of contralateral homologues (as suggested by previous research), or whether it affects both hemispheres. This study uses voxel-based morphometry applied to high-resolution MR T1-weighted MPRAGE images from 31 adult patients left-dominant for language. Eighteen patients had brain tumors in the left hemisphere, and 13 had tumors in the right hemisphere. A cohort of 71 healthy individuals matched on age and sex was used as a baseline. We defined 10 ROIs per hemisphere known to subserve language function. Two separate repeated-measures ANOVAs were conducted with the volume per region as the dependent variables. For the patients, tumor lateralization (right versus left) served as a between-subject factor. The current study demonstrated that the presence of a brain tumor generates a global volumetric change affecting left language regions and their contralateral homologues. These changes are mediated by the lateralization of the lesion. Our findings suggest that compensatory functional mechanisms are supported by the rearrangement of the grey matter, although future longitudinal research should determine the temporal course of such changes.

Microsurgical anatomy and insular connectivity of the cerebral opercula

OBJECTIVE

Radiological, anatomical, and electrophysiological studies have shown the insula and cerebral opercula to have extremely high functionality. Because of this complexity, interventions in this region cause higher morbidity compared to those in other areas of the brain. In most early studies of the insula and white matter pathways, insular dissection was begun after the opercula were removed. In this study, the authors examined the insula and deep white matter pathways to evaluate the insula as a whole with the surrounding opercula.

METHODS

Twenty formalin-fixed adult cerebral hemispheres were studied using fiber microdissection techniques and examination of sectional anatomy. Dissections were performed from lateral to medial, medial to lateral, inferior to superior, and superior to inferior. A silicone brain model was used to show the normal gyral anatomy. Sections and fibers found at every stage of dissection were photographed with a professional camera. MRI tractography studies were used to aid understanding of the dissections.

RESULTS

The relationships between the insula and cerebral opercula were investigated in detail through multiple dissections and sections. The relationship of the extreme and external capsules with the surrounding opercula and the fronto-occipital fasciculus with the fronto-orbital operculum was demonstrated. These findings were correlated with the tractography studies. Fibers of the extreme capsule connect the medial aspect of the opercula with the insula through the peri-insular sulcus. Medial to lateral dissections were followed with the removal of the central core structures, and in the last step, the medial surface of the cerebral opercula was evaluated in detail.

CONCLUSIONS

This anatomical study clarifies our understanding of the insula and cerebral opercula, which have complex anatomical and functional networks. This study also brings a new perspective to the connection of the insula and cerebral opercula via the extreme and external capsules.

Using neuroimaging genomics to investigate the evolution of human brain structure

Alterations in brain size and organization represent some of the most distinctive changes in the emergence of our species. Yet, there is limited understanding of how genetic factors contributed to altered neuroanatomy during human evolution. Here, we analyze neuroimaging and genetic data from up to 30,000 people in the UK Biobank and integrate with genomic annotations for different aspects of human evolution, including those based on ancient DNA and comparative genomics. We show that previously reported signals of recent polygenic selection for cortical anatomy are not replicable in a more ancestrally homogeneous sample. We then investigate relationships between evolutionary annotations and common genetic variants shaping cortical surface area and white-matter connectivity for each hemisphere. Our analyses identify single-nucleotide polymorphism heritability enrichment in human-gained regulatory elements that are active in early brain development, affecting surface areas of several parts of the cortex, including left-hemispheric speech-associated regions. We also detect heritability depletion in genomic regions with Neanderthal ancestry for connectivity of the uncinate fasciculus; this is a white-matter tract involved in memory, language, and socioemotional processing with relevance to neuropsychiatric disorders. Finally, we show that common genetic loci associated with left-hemispheric pars triangularis surface area overlap with a human-gained enhancer and affect regulation of ZIC4, a gene implicated in neurogenesis. This work demonstrates how genomic investigations of present-day neuroanatomical variation can help shed light on the complexities of our evolutionary past.

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.

Structural perisylvian asymmetry in naturally occurring atypical language dominance

Functional and anatomical hemispheric asymmetries abound in the neural language system, yet the relationship between them remains elusive. One attractive proposal is that structural interhemispheric differences reflect or even drive functional language laterality. However, studies on structure-function couplings either find that left and right language dominant individuals display similar leftward structural asymmetry or yield inconsistent results. The current study aimed to replicate and extend prior work by comparing structural asymmetries between neurologically healthy left-handers with right hemispheric language dominance (N = 24) and typically lateralized left-handed controls (N = 39). Based on structural MRI data, anatomical measures of six 'language-related' perisylvian structures were derived, including the surface area of five gray matter regions with known language functions and the FDC (combined fiber density and fiber-bundle cross-sectional area) of the arcuate fasciculus. Only the surface area of the pars triangularis and the anterior insula differed significantly between participant groups, being on average leftward asymmetric in those with typical dominance, but right lateralized in volunteers with atypical language specialization. However, these findings did not survive multiple testing correction and the asymmetry of these structures demonstrated much inter-individual variability in either subgroup. By integrating our findings with those reported previously we conclude that while some perisylvian anatomical asymmetries may differ subtly between typical and atypical speech dominants at the group level, they serve as poor participant-specific predictors of hemispheric language specialization.

Interactions Between Aging and Alzheimer's Disease on Structural Brain Networks

Normative aging and Alzheimer's disease (AD) propagation alter anatomical connections among brain parcels. However, the interaction between the trajectories of age- and AD-linked alterations in the topology of the structural brain network is not well understood. In this study, diffusion-weighted magnetic resonance imaging (MRI) datasets of 139 subjects from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database were used to document their structural brain networks. The 139 participants consist of 45 normal controls (NCs), 37 with early mild cognitive impairment (EMCI), 27 with late mild cognitive impairment (LMCI), and 30 AD patients. All subjects were further divided into three subgroups based on their age (56-65, 66-75, and 71-85 years). After the structural connectivity networks were built using anatomically-constrained deterministic tractography, their global and nodal topological properties were estimated, including network efficiency, characteristic path length, transitivity, modularity coefficient, clustering coefficient, and betweenness. Statistical analyses were then performed on these metrics using linear regression, and one- and two-way ANOVA testing to examine group differences and interactions between aging and AD propagation. No significant interactions were found between aging and AD propagation in the global topological metrics (network efficiency, characteristic path length, transitivity, and modularity coefficient). However, nodal metrics (clustering coefficient and betweenness centrality) of some cortical parcels exhibited significant interactions between aging and AD propagation, with affected parcels including left superior temporal, right pars triangularis, and right precentral. The results collectively confirm the age-related deterioration of structural networks in MCI and AD patients, providing novel insight into the cross effects of aging and AD disorder on brain structural networks. Some early symptoms of AD may also be due to age-associated anatomic vulnerability interacting with early anatomic changes associated with AD.

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.

Asymmetry in the Cytoarchitecture of the Area 44 Homolog of the Brain of the Chimpanzee Pan troglodytes

The evolution of the brain in apes and man followed a joint pathway stemming from common ancestors 5-10 million years ago. However, although apparently sharing similar organization and neurochemical properties, association areas of the isocortex remain one of the cornerstones of what sets humans aside from other primates. Brodmann's area 44, the area of Broca, is known for its implication in speech, and thus indirectly is a key mark of human uniqueness. This latero-caudal part of the frontal lobe shows a marked functional asymmetry in humans, and takes part in other complex functions, including learning and imitation, tool use, music and contains the mirror neuron system (MNS). Since the main features in the cytoarchitecture of Broca's area remains relatively constant in hominids, including in our closest relative, the chimpanzee Pan troglodytes, investigations on the finer structure, cellular organization, connectivity and eventual asymmetry of area 44 have a direct bearing on the understanding of the neural mechanisms at the base of our language. The semi-automated image analysis technology that we employed in the current study showed that the structure of the cortical layers of the chimpanzee contains elements of asymmetry that are discussed in relation to the corresponding human areas and the putative resulting disparity of function.

Left-handed musicians show a higher probability of atypical cerebral dominance for language

Music processing and right hemispheric language lateralization share a common network in the right auditory cortex and its frontal connections. Given that the development of hemispheric language dominance takes place over several years, this study tested whether musicianship could increase the probability of observing right language dominance in left-handers. Using a classic fMRI language paradigm, results showed that atypical lateralization was more predominant in musicians (40%) than in nonmusicians (5%). Comparison of left-handers with typical left and atypical right lateralization revealed that: (a) atypical cases presented a thicker right pars triangularis and more gyrified left Heschl's gyrus; and (b) the right pars triangularis of atypical cases showed a stronger intra-hemispheric functional connectivity with the right angular gyrus, but a weaker interhemispheric functional connectivity with part of the left Broca's area. Thus, musicianship is the first known factor related to a higher prevalence of atypical language dominance in healthy left-handed individuals. We suggest that differences in the frontal and temporal cortex might act as shared predisposing factors to both musicianship and atypical language lateralization.

Bilaterally Symmetrical: To Be or Not to Be?

We belong to a clade of species known as the bilateria, with a body plan that is essentially symmetrical with respect to left and right, an adaptation to the indifference of the natural world to mirror-reflection. Limbs and sense organs are in bilaterally symmetrical pairs, dictating a high degree of symmetry in the brain itself. Bilateral symmetry can be maladaptive, though, especially in the human world where it is important to distinguish between left and right sides, and between left-right mirror images, as in reading directional scripts. The brains of many animals have evolved asymmetries, often but not exclusively in functions not dependent on sensory input or immediate reaction to the environment. Brain asymmetries in humans have led to exaggerate notions of a duality between the sides of the brain. The tradeoff between symmetry and asymmetry results in individual differences in brain asymmetries and handedness, contributing to a diversity of aptitude and divisions of labor. Asymmetries may have their origin in fundamental molecular asymmetries going far back in biological evolution.

Evolution of cerebral asymmetry

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.

A pilot investigation of neuroimaging predictors for the benefits from pivotal response treatment for children with autism

Children with autism spectrum disorder (ASD) frequently exhibit language delays and functional communication deficits. Pivotal response treatment (PRT) is an effective intervention for targeting these skills; however, similar to other behavioral interventions, response to PRT is variable across individuals. Thus, objective markers capable of predicting treatment response are critically-needed to identify which children are most likely to benefit from this intervention. In this pilot study, we investigated whether structural neuroimaging measures from language regions in the brain are associated with response to PRT. Children with ASD (n = 18) who were receiving PRT to target their language deficits were assessed with MRI at baseline. T1-weighted images were segmented with FreeSurfer and morphometric measures of the primary language regions (inferior frontal (IFG) and superior temporal (STG) gyri) were evaluated. Children with ASD and language deficits did not exhibit the anticipated relationships between baseline structural measures of language regions and baseline language abilities, as assessed by the number of utterances displayed during a structured laboratory observation (SLO). Interestingly, the level of improvement on the SLO was correlated with baseline asymmetry of the IFG, and the size of the left STG at baseline was correlated with the level of improvement on standardized parental questionnaires. Although very preliminary, the observed associations between baseline structural properties of language regions and improvement in language abilities following PRT suggest that neuroimaging measures may be able to help identify which children are most likely to benefit from specific language treatments, which could help improve precision medicine for children with ASD.

The homotopic connectivity of the functional brain: a meta-analytic approach

Homotopic connectivity (HC) is the connectivity between mirror areas of the brain hemispheres. It can exhibit a marked and functionally relevant spatial variability, and can be perturbed by several pathological conditions. The voxel-mirrored homotopic connectivity (VMHC) is a technique devised to enquire this pattern of brain organization, based on resting state functional connectivity. Since functional connectivity can be revealed also in a meta-analytical fashion using co-activations, here we propose to calculate the meta-analytic homotopic connectivity (MHC) as the meta-analytic counterpart of the VMHC. The comparison between the two techniques reveals their general similarity, but also highlights regional differences associated with how HC varies from task to rest. Two main differences were found from rest to task: (i) regions known to be characterized by global hubness are more similar than regions displaying local hubness; and (ii) medial areas are characterized by a higher degree of homotopic connectivity, while lateral areas appear to decrease their degree of homotopic connectivity during task performance. These findings show that MHC can be an insightful tool to study how the hemispheres functionally interact during task and rest conditions.

Impact of connectivity between the pars triangularis and orbitalis on identifying the frontal language area in patients with dominant frontal gliomas

We have previously revealed that identification of the frontal language area (FLA) can be difficult in patients with dominant frontal glioma involving the pars triangularis (PT). The present study added new cases and performed additional analyses. We noticed a new finding that the presence of extension to the pars orbitalis (POr) was associated with negative response to the FLA. The aim of the present study was to evaluate the impact of PT involvement with extension to the POr on the failure to identify the FLA. From 2000 to 2017, awake craniotomy was performed on 470 patients. Of these patients, the present study included 148 consecutive patients with frontal glioma on the dominant side. We evaluated whether tumors involved the PT or extended to the POr. Thirty one of 148 patients showed involvement of the PT, and we examined the detailed characteristics of these 31 patients. The rate of negative response for the FLA was 61% in patients with involvement of the PT. In 31 patients with frontal glioma involving the PT, univariate analyses showed significant correlation between extension to the POr and failure to identify the FLA (P = 0.0070). Similarly, multivariate analysis showed only extension to the POr correlated significantly with failure to identify the FLA (P = 0.0129). We found new evidence that extension to the POr which impacts connectivity between the PT and POr correlated significantly with negative response to the FLA of patients with dominant frontal glioma.

Morphological patterns and spatial probability maps of two defining sulci of the posterior ventrolateral frontal cortex of the human brain: the sulcus diagonalis and the anterior ascending ramus of the lateral fissure

The sulcus diagonalis (ds) and the anterior ascending ramus of the lateral fissure (aalf) are two defining sulci of the posterior ventrolateral frontal cortex, which is also known as the anterior language region in the language dominant hemisphere. The aalf extends dorsally from the lateral fissure, separating the pars opercularis from the pars triangularis of the inferior frontal gyrus. The ds, which is a relatively vertical sulcus, is found within the pars opercularis. Given the proximity and similar orientation of these two sulci, it can be difficult to identify them properly. The present study provides a means of differentiating these two sulci accurately using magnetic resonance imaging (MRI). Voxels within the ds and the aalf were labeled in 40 in vivo MRI volumes (1.5 T) that had been linearly registered to the Montreal Neurological Institute stereotaxic space to examine the morphological patterns of these two sulci and classify these patterns based on relations with neighboring sulci. The morphological variability and spatial extent of each sulcus was then quantified in the form of volumetric and surface spatial probability maps. The ds, a rather superficial sulcus, could be identified in 51.25% of hemispheres. The aalf, on the other hand, could be identified in 96.25% of hemispheres and was observed to extend medially, deep below the surface of the hemisphere, to reach the circular sulcus of the insula. Understanding the details of the sulcal morphology of this region, which, in the language dominant left hemisphere, constitutes Broca's area, is crucial to functional and structural neuroimaging studies investigating language.

A voxel-based asymmetry study of the relationship between hemispheric asymmetry and language dominance in Wada tested patients

Determining the anatomical basis of hemispheric language dominance (HLD) remains an important scientific endeavor. The Wada test remains the gold standard test for HLD and provides a unique opportunity to determine the relationship between HLD and hemispheric structural asymmetries on MRI. In this study, we applied a whole‐brain voxel‐based asymmetry (VBA) approach to determine the relationship between interhemispheric structural asymmetries and HLD in a large consecutive sample of Wada tested patients. Of 135 patients, 114 (84.4%) had left HLD, 10 (7.4%) right HLD, and 11 (8.2%) bilateral language representation. Fifty‐four controls were also studied. Right‐handed controls and right‐handed patients with left HLD had comparable structural brain asymmetries in cortical, subcortical, and cerebellar regions that have previously been documented in healthy people. However, these patients and controls differed in structural asymmetry of the mesial temporal lobe and a circumscribed region in the superior temporal gyrus, suggesting that only asymmetries of these regions were due to brain alterations caused by epilepsy. Additional comparisons between patients with left and right HLD, matched for type and location of epilepsy, revealed that structural asymmetries of insula, pars triangularis, inferior temporal gyrus, orbitofrontal cortex, ventral temporo‐occipital cortex, mesial somatosensory cortex, and mesial cerebellum were significantly associated with the side of HLD. Patients with right HLD and bilateral language representation were significantly less right‐handed. These results suggest that structural asymmetries of an insular‐fronto‐temporal network may be related to HLD.

Bayesian Multiresolution Variable Selection for Ultra-High Dimensional Neuroimaging Data

Ultra-high dimensional variable selection has become increasingly important in analysis of neuroimaging data. For example, in the Autism Brain Imaging Data Exchange (ABIDE) study, neuroscientists are interested in identifying important biomarkers for early detection of the autism spectrum disorder (ASD) using high resolution brain images that include hundreds of thousands voxels. However, most existing methods are not feasible for solving this problem due to their extensive computational costs. In this work, we propose a novel multiresolution variable selection procedure under a Bayesian probit regression framework. It recursively uses posterior samples for coarser-scale variable selection to guide the posterior inference on finer-scale variable selection, leading to very efficient Markov chain Monte Carlo (MCMC) algorithms. The proposed algorithms are computationally feasible for ultra-high dimensional data. Also, our model incorporates two levels of structural information into variable selection using Ising priors: the spatial dependence between voxels and the functional connectivity between anatomical brain regions. Applied to the resting state functional magnetic resonance imaging (R-fMRI) data in the ABIDE study, our methods identify voxel-level imaging biomarkers highly predictive of the ASD, which are biologically meaningful and interpretable. Extensive simulations also show that our methods achieve better performance in variable selection compared to existing methods.

Individual variability in verbal fluency correlates with γ-aminobutyric acid concentration in the left inferior frontal gyrus

A particular feature of the inferior frontal gyrus (IFG), which is considered a central region for language processing, is leftward functional/anatomical asymmetry. However, previous studies have not clearly shown lateralization of neurotransmitters in the cortical regions. Using proton magnetic resonance spectroscopy, we measured γ-aminobutyric acid (GABA) concentrations in the bilateral IFG. To evaluate individual variability in linguistic performance, we further used a verbal fluency test. Although GABA+/creatine (Cr) values were not different between the left and the right IFG, we found a significant correlation between category fluency scores and GABA+/Cr values in the left IFG. No correlation was found between letter fluency scores and GABA+/Cr values. We also confirmed that the result was independent of the references used (Cr and H2O). Our results show a new physiological basis of linguistic performance as well as leftward asymmetry of the IFG.

Investigation of topographical anatomy of Broca's area: an anatomic cadaveric study

PURPOSE

The sulci constituting the structure of the pars triangularis and opercularis, considered as 'Broca's area', present wide anatomical and morphological variations between different hemispheres. The boundaries are described differently from one another in various studies. The aim of this study was to explore the topographical anatomy, confirm the morphological asymmetry and highlight anatomical variations in Broca's area.

METHODS

This study was performed with 100 hemispheres to investigate the presence, continuity, patterns and connections of the sulcal structures that constitute the morphological asymmetry of Broca's area.

RESULTS

Considerable individual anatomical and morphological variations between the inferior frontal gyrus and related sulcal structures were detected. Rare bilateralism findings supported the morphological asymmetry. The inferior frontal sulcus was identified as a single segment in 54 % of the right and two separate segments in 52 % of the left hemispheres, which was the most common pattern. The diagonal sulcus was present in 48 % of the right and 54 % of the left hemispheres. It was most frequently connected to the ascending ramus on both sides. A 'V' shape was observed in 42.5 % of the right hemispheres and a 'Y' shape in 38.3 % of the left hemispheres, which was the most common shape of the pars triangularis. Moreover, the full results are specified in detail.

CONCLUSIONS

Knowledge of the anatomical variations in this region is indispensable for understanding the functional structure and performing safe surgery. However, most previously published studies have aimed to determine the anatomical asymmetry of the motor speech area without illuminating the topographical anatomy encountered during surgery.

Structural Asymmetry of Dorsolateral Prefrontal Cortex Correlates with Depressive Symptoms: Evidence from Healthy Individuals and Patients with Major Depressive Disorder

In this study, we investigated the role of structural asymmetry of the dorsolateral prefrontal cortex (DLPFC) in the continuum of depression from healthy individuals to patients. Structural magnetic resonance imaging was performed in 70 patients with major depressive disorder (MDD), 49 matched controls, and 349 healthy university students to calculate structural asymmetry indexes of the DLPFC. First-episode, treatment-naive MDD patients showed a relatively lower asymmetry index than healthy controls, and their asymmetry index was negatively correlated with the depressive symptoms. This abnormality was normalized by antidepressants in medicated MDD patients. Furthermore, the asymmetry index was negatively correlated with the depressive symptoms in university students; this was replicated at two time points in a subgroup of students, suggesting good test-retest reliability. Our findings are consistent with previous studies that support the imbalance hypothesis of MDD and suggest a potential structural basis underlying the functional asymmetry of the DLPFC in depression. In future, the structural index of the DLPFC may become a potential biomarker to evaluate individuals' risk for the onset of MDD.

Difficulty in identification of the frontal language area in patients with dominant frontal gliomas that involve the pars triangularis

OBJECTIVE Identification of language areas using functional brain mapping is sometimes impossible using current methods but essential to preserve language function in patients with gliomas located within or near the frontal language area (FLA). However, the factors that influence the failure to detect language areas have not been elucidated. The present study evaluated the difficulty in identifying the FLA in dominant-side frontal gliomas that involve the pars triangularis (PT) to determine the factors that influenced failed positive language mapping. METHODS Awake craniotomy was performed on 301 patients from April 2000 to October 2013 at Tokyo Women's Medical University. Recurrent cases were excluded, and patients were also excluded if motor mapping indicated their glioma was in or around the motor area on the dominant or nondominant side. Eighty-two consecutive cases of primary frontal glioma on the dominant side were analyzed for the present study. MRI was used for all patients to evaluate whether tumors involved the PT and to perform language functional mapping with a bipolar electrical stimulator. Eighteen of 82 patients (mean age 39 ± 13 years) had tumors that showed involvement of the PT, and the detailed characteristics of these 18 patients were examined. RESULTS The FLA could not be identified with intraoperative brain mapping in 14 (17%) of 82 patients; 11 (79%) of these 14 patients had a tumor involving the PT. The negative response rate in language mapping was only 5% in patients without involvement of the PT, whereas this rate was 61% in patients with involvement of the PT. Univariate analyses showed no significant correlation between identification of the FLA and sex, age, histology, or WHO grade. However, failure to identify the FLA was significantly correlated with involvement of the PT (p < 0.0001). Similarly, multivariate analyses with the logistic regression model showed that only involvement of the PT was significantly correlated with failure to identify the FLA (p < 0.0001). In 18 patients whose tumors involved the PT, only 1 patient had mild preoperative dysphasia. One week after surgery, language function worsened in 4 (22%) of 18 patients. Six months after surgery, 1 (5.6%) of 18 patients had a persistent mild speech deficit. The mean extent of resection was 90% ± 7.1%. Conclusions Identification of the FLA can be difficult in patients with frontal gliomas on the dominant side that involve the PT, but the positive mapping rate of the FLA was 95% in patients without involvement of the PT. These findings are useful for establishing a positive mapping strategy for patients undergoing awake craniotomy for the treatment of frontal gliomas on the dominant side. Thoroughly positive language mapping with subcortical electrical stimulation should be performed in patients without involvement of the PT. More careful continuous neurological monitoring combined with subcortical electrical stimulation is needed when removing dominant-side frontal gliomas that involve the PT.

Choosing words: left hemisphere, right hemisphere, or both? Perspective on the lateralization of word retrieval

Language is considered to be one of the most lateralized human brain functions. Left hemisphere dominance for language has been consistently confirmed in clinical and experimental settings and constitutes one of the main axioms of neurology and neuroscience. However, functional neuroimaging studies are finding that the right hemisphere also plays a role in diverse language functions. Critically, the right hemisphere may also compensate for the loss or degradation of language functions following extensive stroke-induced damage to the left hemisphere. Here, we review studies that focus on our ability to choose words as we speak. Although fluidly performed in individuals with intact language, this process is routinely compromised in aphasic patients. We suggest that parceling word retrieval into its subprocesses-lexical activation and lexical selection-and examining which of these can be compensated for after left hemisphere stroke can advance the understanding of the lateralization of word retrieval in speech production. In particular, the domain-general nature of the brain regions associated with each process may be a helpful indicator of the right hemisphere's propensity for compensation.

Structural asymmetry of the insula is linked to the lateralization of gesture and language

The control of gesture is one of the most left-lateralized functions, and the insular cortex is one of the most left-biased structures in the human brain. Therefore, we investigated whether structural asymmetries of the insula are linked to the organization of functional activity during gesture planning. We reconstructed and parcellated the insular cortex of 27 participants. First, we tested 15 strongly left-handed individuals because of a higher incidence of atypical organization of functions such as gesture and language in such a population. The inter-hemispheric structural asymmetries were compared with the lateralization of activity for gesture in the supramarginal gyrus (the hotspot of signal increase regardless of the gesturing hand) and Broca’s area (the hotspot of signal increase for language production). The more pronounced leftward structural asymmetries were accompanied by greater left-hemisphere dominance for both of the studied functions. Conversely, an atypical, bilateral or rightward functional shift of gesture and language was accompanied by an attenuated leftward asymmetry of the insula. These significant relationships were driven primarily by differences in surface area. Subsequently, by adding 12 right-handed individuals to these analyses we demonstrated that the observed significant associations are generalizable to the population. These results provide the first demonstration of the relationships between structural inter-hemispheric differences of the insula and the cerebral specialization for gesture. They also corroborate the link between insular asymmetries and language lateralization. As such, these outcomes are relevant to the common cerebral specialization for gesture and language.

An automatic framework for quantitative validation of voxel based morphometry measures of anatomical brain asymmetry

The study of anatomical brain asymmetries has been a topic of great interest in the neuroimaging community in the past decades. However, the accuracy of brain asymmetry measurements has been rarely investigated. In this study, we propose a fully automatic methodology for the quantitative validation of brain tissue asymmetries as measured by Voxel Based Morphometry (VBM) from structural magnetic resonance (MR) images. Starting from a real MR image, the methodology generates simulated 3D MR images with a known and realistic pattern of inter-hemispheric asymmetry that models the left-occipital right-frontal petalia of a normal brain and the related rightward bending of the inter-hemispheric fissure. As an example, we generated a dataset of 64 simulated MR images and applied this dataset for the quantitative validation of optimized VBM measures of asymmetries in brain tissue composition. Our results suggested that VBM analysis strongly depended on the spatial normalization of the individual brain images, the selected template space, and the amount of spatial smoothing applied. The most accurate asymmetry detections were achieved by 9-degrees of freedom registration to the symmetrical template space with 4 to 8mm spatial smoothing.

Research updates in neuroimaging studies of children who stutter

In the past two decades, neuroimaging investigations of stuttering have led to important discoveries of structural and functional brain differences in people who stutter, providing significant clues to the neurological basis of stuttering. One major limitation, however, has been that most studies so far have only examined adults who stutter, whose brain and behavior likely would have adopted compensatory reactions to their stuttering; these confounding factors have made interpretations of the findings difficult. Developmental stuttering is a neurodevelopmental condition, and like many other neurodevelopmental disorders, stuttering is associated with an early childhood onset of symptoms and greater incidence in males relative to females. More recent studies have begun to examine children who stutter using various neuroimaging techniques that allow examination of functional neuroanatomy and interaction of major brain areas that differentiate children who stutter compared with age-matched controls. In this article, I review these more recent neuroimaging investigations of children who stutter, in the context of what we know about typical brain development, neuroplasticity, and sex differences relevant to speech and language development. Although the picture is still far from complete, these studies have potential to provide information that can be used as early objective markers, or prognostic indicators, for persistent stuttering in the future. Furthermore, these studies are the first steps in finding potential neural targets for novel therapies that may involve modulating neuroplastic growth conducive to developing and maintaining fluent speech, which can be applied to treatment of young children who stutter.

Grey matter correlates of three language tests in non-demented older adults

Language has been extensively investigated by functional neuroimaging studies. However, only a limited number of structural neuroimaging studies have examined the relationship between language performance and brain structure in healthy adults, and the number is even less in older adults. The present study sought to investigate correlations between grey matter volumes and three standardized language tests in late life. The participants were 344 non-demented, community-dwelling adults aged 70-90 years, who were drawn from the population-based Sydney Memory and Ageing Study. The three language tests included the Controlled Oral Word Association Task (COWAT), Category Fluency (CF), and Boston Naming Test (BNT). Correlation analyses between voxel-wise GM volumes and language tests showed distinctive GM correlation patterns for each language test. The GM correlates were located in the right frontal and left temporal lobes for COWAT, in the left frontal and temporal lobes for CF, and in bilateral temporal lobes for BNT. Our findings largely corresponded to the neural substrates of language tasks revealed in fMRI studies, and we also observed a less hemispheric asymmetry in the GM correlates of the language tests. Furthermore, we divided the participants into two age groups (70-79 and 80-90 years old), and then examined the correlations between structural laterality indices and language performance for each group. A trend toward significant difference in the correlations was found between the two age groups, with stronger correlations in the group of 70-79 years old than those in the group of 80-90 years old. This difference might suggest a further decline of language lateralization in different stages of late life.

Using IQ discrepancy scores to examine the neural correlates of specific cognitive abilities

The underlying neural determinants of general intelligence have been studied intensively, and seem to derive from the anatomical and functional characteristics of a frontoparietal network. Little is known, however, about the underlying neural correlates of domain-specific cognitive abilities, the other factors hypothesized to explain individual performance on intelligence tests. Previous preliminary studies have suggested that spatially distinct neural structures do not support domain-specific cognitive abilities. To test whether differences between abilities that affect performance on verbal and performance tasks derive instead from the morphological features of a single anatomical network, we assessed in two independent samples of healthy human participants (N=83 and N=58; age range, 5-57 years) the correlation of cortical thickness with the magnitude of the verbal intelligence quotient (VIQ)-performance intelligence quotient (PIQ) discrepancy. We operationalized the VIQ-PIQ discrepancy by regressing VIQ onto PIQ (VIQ-regressed-on-PIQ score), and by regressing PIQ onto VIQ (PIQ-regressed-on-VIQ score). In both samples, a progressively thinner cortical mantle in anterior and posterior regions bilaterally was associated with progressively greater (more positive) VIQ-regressed-on-PIQ scores. A progressively thicker cortical mantle in anterior and posterior regions bilaterally was associated with progressively greater (more positive) PIQ-regressed-on-VIQ scores. Variation in cortical thickness in these regions accounted for a large portion of the overall variance in magnitude of the VIQ-PIQ discrepancy. The degree of hemispheric asymmetry in cortical thickness accounted for a much smaller but statistically significant portion of variance in VIQ-PIQ discrepancy.

Main effect and interactions of brain regions and gender in the calculation of volumetric asymmetry indices in healthy human brains: ANCOVA analyses of in vivo 3T MRI data

INTRODUCTION

Macroanatomical right-left hemispheric differences in the brain are termed asymmetries, although there is no clear information on the global influence of gender and brain-regions. The aim of this study was to evaluate the main effects and interactions of these variables on the measurement of volumetric asymmetry indices (VAIs).

MATERIALS AND METHODS

Forty-seven healthy young-adult volunteers (23 males, 24 females) agreed to undergo brain magnetic resonance imaging in a 3T scanner. Image post processing using voxel-based volumetry allowed the calculation of 54 VAIs from the frontal, temporal, parietal and occipital lobes, limbic system, basal ganglia, and cerebellum for each cerebral hemisphere. Multivariate ANCOVA analysis calculated the main effects and interactions on VAIs of gender and brain regions controlling the effect of age.

RESULTS

The only significant finding was the main effect of brain regions (F (6, 9373.605) 44.369, P < .001; partial η2 = .101, and power of 1.0), with no significant interaction between gender and brain regions (F (6, 50.517) .239, P = .964).

CONCLUSION

Volumetric asymmetries are present across all brain regions, with larger values found in the limbic system and parietal lobe. The absence of a significant influence of gender and age in the evaluation of the numerous measurements generated by multivariate analyses in this study should not discourage researchers to report and interpret similar results, as this topic still deserves further assessment.

Network structure underlying resolution of conflicting non-verbal and verbal social information

Social judgments often require resolution of incongruity in communication contents. Although previous studies revealed that such conflict resolution recruits brain regions including the medial prefrontal cortex (mPFC) and posterior inferior frontal gyrus (pIFG), functional relationships and networks among these regions remain unclear. In this functional magnetic resonance imaging study, we investigated the functional dissociation and networks by measuring human brain activity during resolving incongruity between verbal and non-verbal emotional contents. First, we found that the conflict resolutions biased by the non-verbal contents activated the posterior dorsal mPFC (post-dmPFC), bilateral anterior insula (AI) and right dorsal pIFG, whereas the resolutions biased by the verbal contents activated the bilateral ventral pIFG. In contrast, the anterior dmPFC (ant-dmPFC), bilateral superior temporal sulcus and fusiform gyrus were commonly involved in both of the resolutions. Second, we found that the post-dmPFC and right ventral pIFG were hub regions in networks underlying the non-verbal- and verbal-content-biased resolutions, respectively. Finally, we revealed that these resolution-type-specific networks were bridged by the ant-dmPFC, which was recruited for the conflict resolutions earlier than the two hub regions. These findings suggest that, in social conflict resolutions, the ant-dmPFC selectively recruits one of the resolution-type-specific networks through its interaction with resolution-type-specific hub regions.

Sex differences in structural brain asymmetry predict overt aggression in early adolescents

The devastating social, emotional and economic consequences of human aggression are laid bare nightly on newscasts around the world. Aggression is principally mediated by neural circuitry comprising multiple areas of the prefrontal cortex and limbic system, including the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), amygdala and hippocampus. A striking characteristic of these regions is their structural asymmetry about the midline (i.e. left vs right hemisphere). Variations in these asymmetries have been linked to clinical disorders characterized by aggression and the rate of aggressive behavior in psychiatric patients. Here, we show for the first time that structural asymmetries in prefrontal cortical areas are also linked to aggression in a normal population of early adolescents. Our findings indicate a relationship between parent reports of aggressive behavior in adolescents and structural asymmetries in the limbic and paralimbic ACC and OFC, and moreover, that this relationship varies by sex. Furthermore, while there was no relationship between aggression and structural asymmetries in the amygdala or hippocampus, hippocampal volumes did predict aggression in females. Taken together, the results suggest that structural asymmetries in the prefrontal cortex may influence human aggression, and that the anatomical basis of aggression varies substantially by sex.

Variability and asymmetry of the sulcal contours defining Broca's area homologue in the chimpanzee brain

There has been recent motivation to search for neuroanatomical asymmetries in nonhuman primates in order to provide comparative information on how the human brain is structurally organized to support specific cognitive capabilities, such as language functions. We took the opportunity to study Broca's area homologue in a novel sample of 80 preserved postmortem chimpanzee (Pan troglodytes) cerebral hemispheres. Consistent with the only prior study documenting the morphology of Broca's area homologue in the chimpanzee (Sherwood et al. [2003] Anat Rec 271:276–285), we report great interindividual variation in the structure and connections of the sulci investigated, most notably a left-sided bias in the bifurcation of the inferior precentral sulcus, an anatomical feature that occurs much more frequently in chimpanzees relative to humans. Consistent with our recent neuroimaging report (Keller et al. [2009b] J Neurosci 29:14607–14616), no population-based interhemispheric asymmetries of sulcal length existed that could be considered markers of the size of Broca's area homologue. With strict anatomical guidelines, we report that the diagonal sulcus was present in 25% left and 20% right chimpanzee hemispheres studied, which is substantially less that the general prevalence in humans. Through the presentation of schematic drawings, photographs, morphological recordings and sulcal length metrics, our data illustrate the interindividual variability of Broca's area homologue in the chimpanzee and support the notion of no macroscopic asymmetry of this important homologous language brain region in one of the closest evolutionary ancestor to modern humans.

Alterations in brain structures underlying language function in young adults at high familial risk for schizophrenia

INTRODUCTION

Neuroanatomical and cognitive alterations typical of schizophrenia (SZ) patients are observed to a lesser extent in their adolescent and adult first-degree relatives, likely reflecting neurodevelopmental abnormalities associated with genetic risk for the illness. The anatomical pathways for language are hypothesized to be abnormal and to underlie the positive symptoms of schizophrenia. Examining non-psychotic relatives at high familial risk (FHR) for schizophrenia may clarify if these deficits represent trait markers associated with genetic vulnerability, rather than specific markers resulting from the pathological process underlying schizophrenia.

METHODS

T1 MRI scans from a 3T Siemens scanner of young adult FHR subjects (N=46) and controls with no family history of illness (i.e. at low genetic risk LRC; N=31) were processed using FreeSurfer 5.0. We explored volumetric and lateralization alterations in regions associated with language processing. An extensive neuropsychological battery of language measures was administered.

RESULTS

No significant differences were observed between groups on any language measures. Controlling intracranial volume, significantly smaller left pars triangularis (PT) (p<0.01) and right pars orbitalis (PO) (p<0.01) volumes and reversal of the L>R pars orbitalis (p<0.001) lateralization were observed in FHR subjects. In addition, the L pars triangularis and R pars orbitalis correlated with performance on tests of linguistic function in the FHR group.

CONCLUSIONS

Reduced volume and reversed structural asymmetry in language-related regions hypothesized to be altered in SZ are also found in first degree relatives at FHR, despite normal language performance. To clarify if these findings are endophenotypes for Sz, future studies would need to be performed of ill and well family members no longer within the age range of risk for illness to show these deficits segregate with schizophrenia within families. Moreover, measures of complex language need to be studied to determine if FHR individuals manifest impairments in some aspects of language function.

Sulcal morphology and volume of Broca's area linked to handedness and sex

We investigated the effect of handedness and sex on: (i) sulcal contours defining PO and PTR and (ii) volume estimates of PO and PTR subfields in 40 left- and 42 right-handers. Results show an effect of handedness on discontinuity of the inferior frontal sulcus (IFS: P<0.01). Discontinuity of IFS was observed in: 43% left- and 62% right hemispheres in right-handers and in 65% left- and 48% right-hemispheres in left-handers. PO volume asymmetry was rightward in left-handed males (P=0.007) and females (P=0.02), showed a leftward trend in right-handed males (P=0.06), and was non-asymmetrical in right-handed females (P=0.96, i.e. left- and right-hemisphere PO volumes did not differ significantly). PO volume asymmetry in males differed significantly between handedness groups (P=0.001). Findings indicate a high degree of variability in the sulcal contours of PO and PTR and volume asymmetry of PO: the factors sex and handedness can explain some of this variability.

VBM-DTI correlates of verbal intelligence: a potential link to Broca's area

Human brain lesion studies first investigated the biological roots of cognitive functions including language in the late 1800s. Neuroimaging studies have reported correlation findings with general intelligence predominantly in fronto-parietal cortical areas. However, there is still little evidence about the relationship between verbal intelligence and structural properties of the brain. We predicted that verbal performance is related to language regions of Broca's and Wernicke's areas. Verbal intelligence quotient (vIQ) was assessed in 30 healthy young subjects. T1-weighted MRI and diffusion tensor imaging data sets were acquired. Voxel-wise regression analyses were used to correlate fractional anisotropy (FA) and mean diffusivity values with vIQ. Moreover, regression analyses of regional brain volume with vIQ were performed adopting voxel-based morphometry (VBM) and ROI methodology. Our analyses revealed a significant negative correlation between vIQ and FA and a significant positive correlation between vIQ and mean diffusivity in the left-hemispheric Broca's area. VBM regression analyses did not show significant results, whereas a subsequent ROI analysis of Broca's area FA peak cluster demonstrated a positive correlation of gray matter volume and vIQ. These findings suggest that cortical thickness in Broca's area contributes to verbal intelligence. Diffusion parameters predicted gray matter ratio in Broca's area more sensitive than VBM methodology.