Lateral frontoparietal functional connectivity based on individual sulcal morphology

A salient neuroanatomical feature of the human brain is its pronounced cortical folding, and there is mounting evidence that sulcal morphology is relevant to functional brain architecture and cognition. Recent studies have emphasized putative tertiary sulci (pTS): small, shallow, late-developing, and evolutionarily new sulci that have been posited to serve as functional landmarks in association cortices. A fruitful approach to characterizing brain architecture has been to delineate regions based on transitions in fMRI-based functional connectivity profiles; however, exact regional boundaries can change depending on the data used to generate the parcellation. As sulci are fixed neuroanatomical structures, here, we propose to anchor functional connectivity to individual-level sulcal anatomy. We characterized fine-grained patterns of functional connectivity across 42 sulci in lateral prefrontal (LPFC) and lateral parietal cortices (LPC) in a pediatric sample (N = 43; 20 female; ages 7-18). Further, we test for relationships between pTS morphology and functional network architecture, focusing on depth as a defining characteristic of these shallow sulci, and one that has been linked to variability in cognition. We find that 1) individual sulci have distinct patterns of connectivity, but nonetheless cluster together into groups with similar patterns - in some cases with distant rather than neighboring sulci, 2) there is moderate agreement in cluster assignments at the group and individual levels, underscoring the need for individual-level analyses, and 3) across individuals, greater depth was associated with higher network centrality for several pTS. These results highlight the importance of considering individual sulcal morphology for understanding functional brain organization.

Significance Statement

A salient, and functionally relevant, feature of the human brain is its pronounced cortical folding. However, the links between sulcal anatomy and brain function are still poorly understood - particularly for small, shallow, individually variable sulci in association cortices. Here, we explore functional connectivity among individually defined sulci in lateral prefrontal and parietal regions. We find that individual sulci have distinct patterns of connectivity but nonetheless cluster together into groups with similar connectivity - in some cases spanning lateral prefrontal and parietal sulci. We further show that the network centrality of specific sulci is positively associated with their depth, thereby helping to bridge the gap between individual differences in brain anatomy and functional networks leveraging the sulcal anatomy of the individual.

Semi-Automatic GUI Platform to Characterize Brain Development in Preterm Children Using Ultrasound Images

The third trimester of pregnancy is the most critical period for human brain development, during which significant changes occur in the morphology of the brain. The development of sulci and gyri allows for a considerable increase in the brain surface. In preterm newborns, these changes occur in an extrauterine environment that may cause a disruption of the normal brain maturation process. We hypothesize that a normalized atlas of brain maturation with cerebral ultrasound images from birth to term equivalent age will help clinicians assess these changes. This work proposes a semi-automatic Graphical User Interface (GUI) platform for segmenting the main cerebral sulci in the clinical setting from ultrasound images. This platform has been obtained from images of a cerebral ultrasound neonatal database images provided by two clinical researchers from the Hospital Sant Joan de Déu in Barcelona, Spain. The primary objective is to provide a user-friendly design platform for clinicians for running and visualizing an atlas of images validated by medical experts. This GUI offers different segmentation approaches and pre-processing tools and is user-friendly and designed for running, visualizing images, and segmenting the principal sulci. The presented results are discussed in detail in this paper, providing an exhaustive analysis of the proposed approach's effectiveness.

Optimal blocking of the cerebral cortex for cytoarchitectonic examination: a neuronavigation-based approach

Certain sulci of the human cerebral cortex hold consistent relationships to cytoarchitectonic areas (e.g. the primary motor cortical area 4 and the somatosensory cortical area 3 occupy the anterior and posterior banks of the central sulcus, respectively). Recent research has improved knowledge of the cortical sulci and their variability across individuals. However, other than the so-called primary sulci, understanding of the precise relationships cortical folds hold with many cytoarchitectonic areas remains elusive. To examine these relationships, the cortex must be blocked, sectioned, and histologically processed in a manner that allows the cytoarchitectonic layers to be clearly observed. The optimal strategy to view the cytoarchitecture is to block and section the cortex perpendicular to the sulcal orientation. Most cytoarchitectonic investigations of the cortex, however, have been conducted on specimens cut along a single axis (e.g. the coronal plane), which distorts the appearance of the cytoarchitectonic layers within parts of the cortical ribbon not sectioned optimally. Thus, to understand further the relationships between sulci and cytoarchitectonic areas, the cortex should be sectioned optimally to the sulci of interest. A novel approach for blocking the cortex optimally using structural magnetic resonance imaging (MRI) and surgical neuronavigation tools is presented here.

Sulcal depth in prefrontal cortex: a novel predictor of working memory performance

The neuroanatomical changes that underpin cognitive development are of major interest in neuroscience. Of the many aspects of neuroanatomy to consider, tertiary sulci are particularly attractive as they emerge last in gestation, show a protracted development after birth, and are either human- or hominoid-specific. Thus, they are ideal targets for exploring morphological-cognitive relationships with cognitive skills that also show protracted development such as working memory (WM). Yet, the relationship between sulcal morphology and WM is unknown-either in development or more generally. To fill this gap, we adopted a data-driven approach with cross-validation to examine the relationship between sulcal depth in lateral prefrontal cortex (LPFC) and verbal WM in 60 children and adolescents between ages 6 and 18. These analyses identified 9 left, and no right, LPFC sulci (of which 7 were tertiary) whose depth predicted verbal WM performance above and beyond the effect of age. Most of these sulci are located within and around contours of previously proposed functional parcellations of LPFC. This sulcal depth model outperformed models with age or cortical thickness. Together, these findings build empirical support for a classic theory that tertiary sulci serve as landmarks in association cortices that contribute to late-maturing human cognitive abilities.

Adult neurogenesis in the telencephalon of the lizard Podarcis liolepis

In adult lizards, new neurons are generated from neural stem cells in the ventricular zone of the lateral ventricles. These new neurons migrate and integrate into the main telencephalic subdivisions. In this work we have studied adult neurogenesis in the lizard Podarcis liolepis (formerly Podarcis hispanica) by administering [³H]-thymidine and bromodeoxyuridine as proliferation markers and euthanizing the animals at different survival times to determine the identity of progenitor cells and to study their lineage derivatives. After short survival times, only type B cells are labeled, suggesting that they are neural stem cells. Three days after administration, some type A cells are labeled, corresponding to recently formed neuroblasts. Type A cells migrate to their final destinations, where they differentiate into mature neurons and integrate into functional circuits. Our results after long survival periods suggest that, in addition to actively dividing type B cells, there is also a type B subpopulation with low proliferative activity. We also found that new neurons incorporated into the olfactory bulb are generated both in situ, in the walls of the anterior extension of the lateral ventricle of the olfactory bulbs, but also at more caudal levels, most likely in anterior levels of the sulcus ventralis/terminalis. These cells follow a tangential migration toward the olfactory bulbs where they integrate. We hypothesized that at least part of the newly generated neurons would undergo a specialization process over time. In support of this prediction, we found two neuronal populations in the cellular layer of the medial cortex, which we named type I and II neurons. At intermediate survival times (1 month) only type II neurons were labeled with [³H]-thymidine, while at longer survival times (3, 6, or 12 months) both type I and type II neurons were labeled. This study sheds light on the ultrastructural characteristics of the ventricular zone of P. liolepis as a neurogenic niche, and adds to our knowledge of the processes whereby newly generated neurons in the adult brain migrate and integrate into their final destinations.

A mesoscale finite element modeling approach for understanding brain morphology and material heterogeneity effects in chronic traumatic encephalopathy

Chronic Traumatic Encephalopathy (CTE) affects a significant portion of athletes in contact sports but is difficult to quantify using clinical examinations and modeling approaches. We use an in silico approach to quantify CTE biomechanics using mesoscale Finite Element (FE) analysis that bridges with macroscale whole head FE analysis. The sulci geometry produces complex stress waves that interact with one another to create increased shear stresses at the sulci depth that are significantly larger than in analyses without sulci (from 0.5 to 18.0 kPa). Sulci peak stress concentration regions coincide with experimentally observed CTE sites documented in the literature. HighlightsSulci introduce stress localizations at their depth in the gray matterSulci stress fields interact to produce stress concentration sites in white matterDifferentiating brain tissue properties did not significantly affect peak stresses.

Are endocasts reliable proxies for brains? A 3D quantitative comparison of the extant human brain and endocast

Endocasts (i.e., replicas of the inner surface of the bony braincase) constitute a critical proxy for qualifying and quantifying variations in brain shape and organization in extinct taxa. In the absence of brain tissues preserved in the fossil record, endocasts provide the only direct evidence of brain evolution. However, debates on whether or not information inferred from the study of endocasts reflects brain shape and organization have polarized discussions in paleoneurology since the earliest descriptions of cerebral imprints in fossil hominin crania. By means of imaging techniques (i.e., MRIs and CT scans) and 3D modelling methods (i.e., surface-based comparisons), we collected consistent morphological (i.e., shape) and structural (i.e., sulci) information on the variation patterns between the brain and the endocast based on a sample of extant human individuals (N = 5) from the 3D clinical image database of the Steve Biko Academic Hospital in Pretoria (South Africa) and the Hôpitaux Universitaires Pitié Salpêtrière in Paris (France). Surfaces of the brain and endocast of the same individual were segmented from the 3D MRIs and CT images, respectively. Sulcal imprints were automatically detected. We performed a deformation-based shape analysis to compare both the shape and the sulcal pattern of the brain and the endocast. We demonstrated that there is close correspondence in terms of morphology and organization between the brain and the corresponding endocast with the exception of the superior region. By comparatively quantifying the shape and organization of the brain and endocast, this work represents an important reference for paleoneurological studies.

The Subplate: A Potential Driver of Cortical Folding?

In many species of Mammalia, the surface of the brain develops from a smooth structure to one with many fissures and folds, allowing for vast expansion of the surface area of the cortex. The importance of understanding what drives cortical folding extends beyond mere curiosity, as conditions such as preterm birth, intrauterine growth restriction, and fetal alcohol syndrome are associated with impaired folding in the infant and child. Despite being a key feature of brain development, the mechanisms driving cortical folding remain largely unknown. In this review we discuss the possible role of the subplate, a developmentally transient compartment, in directing region-dependent development leading to sulcal and gyral formation. We discuss the development of the subplate in species with lissencephalic and gyrencephalic cortices, the characteristics of the cells found in the subplate, and the possible presence of molecular cues that guide axons into, and out of, the overlying and multilayered cortex before the appearance of definitive cortical folds. An understanding of what drives cortical folding is likely to help in understanding the origins of abnormal folding patterns in clinical pathologies.

The Cerebral Cortex is Bisectionally Segregated into Two Fundamentally Different Functional Units of Gyri and Sulci

The human cerebral cortex is highly folded into diverse gyri and sulci. Accumulating evidences suggest that gyri and sulci exhibit anatomical, morphological, and connectional differences. Inspired by these evidences, we performed a series of experiments to explore the frequency-specific differences between gyral and sulcal neural activities from resting-state and task-based functional magnetic resonance imaging (fMRI) data. Specifically, we designed a convolutional neural network (CNN) based classifier, which can differentiate gyral and sulcal fMRI signals with reasonable accuracies. Further investigations of learned CNN models imply that sulcal fMRI signals are more diverse and more high frequency than gyral signals, suggesting that gyri and sulci truly play different functional roles. These differences are significantly associated with axonal fiber wiring and cortical thickness patterns, suggesting that these differences might be deeply rooted in their structural and cellular underpinnings. Further wavelet entropy analyses demonstrated the validity of CNN-based findings. In general, our collective observations support a new concept that the cerebral cortex is bisectionally segregated into 2 functionally different units of gyri and sulci.

Toward a Common Terminology for the Gyri and Sulci of the Human Cerebral Cortex

The gyri and sulci of the human brain were defined by pioneers such as Louis-Pierre Gratiolet and Alexander Ecker, and extensified by, among others, Dejerine (1895) and von Economo and Koskinas (1925). Extensive discussions of the cerebral sulci and their variations were presented by Ono et al. (1990), Duvernoy (1992), Tamraz and Comair (2000), and Rhoton (2007). An anatomical parcellation of the spatially normalized single high resolution T1 volume provided by the Montreal Neurological Institute (MNI; Collins, 1994; Collins et al., 1998) was used for the macroscopical labeling of functional studies (Tzourio-Mazoyer et al., 2002; Rolls et al., 2015). In the standard atlas of the human brain by Mai et al. (2016), the terminology from Mai and Paxinos (2012) is used. It contains an extensively analyzed individual brain hemisphere in the MNI-space. A recent revision of the terminology on the central nervous system in the Terminologia Anatomica (TA, 1998) was made by the Working Group Neuroanatomy of the Federative International Programme for Anatomical Terminology (FIPAT) of the International Federation of Associations of Anatomists (IFAA), and posted online as the Terminologia Neuroanatomica (TNA, 2017: http://FIPAT.library.dal.ca) as the official FIPAT terminology. This review deals with the various terminologies for the cerebral gyri and sulci, aiming for a common terminology.

Relationship Between Sulcal Characteristics and Brain Aging

This study aimed to determine whether sulcal morphology differs between middle age (MA) and older healthy individuals. Furthermore, we sought to determine whether age-related differences in sulcal characteristics were more strongly associated with differences in local or global cortical volumes. Participants (age 44–50, N = 403; age 64–70, N = 390) from the Personality and Total Health Through Life (PATH) study were included. Sulci were 17.3% wider, on average, in old age (OA) compared to MA participants, with the largest difference in the left superior frontal sulcus. Differences in sulcal width were generally higher in males than females. Differences in the width of the superior frontal and central sulci were significantly associated with differences in the volume of adjacent local gyri, while age-related differences in the width of lateral and superior temporal sulci were associated with differences in whole brain cortical volume. These findings suggest that sulcal characteristics provide unique information about changes in local and global brain structure in aging.

Influences of Brain Size, Sex, and Sex Chromosome Complement on the Architecture of Human Cortical Folding

Gyrification is a fundamental property of the human cortex that is increasingly studied by basic and clinical neuroscience. However, it remains unclear if and how the global architecture of cortical folding varies with 3 interwoven sources of anatomical variation: brain size, sex, and sex chromosome dosage (SCD). Here, for 375 individuals spanning 7 karyotype groups (XX, XY, XXX, XYY, XXY, XXYY, XXXXY), we use structural neuroimaging to measure a global sulcation index (SI, total sulcal/cortical hull area) and both determinants of sulcal area: total sulcal length and mean sulcal depth. We detail large and patterned effects of sex and SCD across all folding metrics, but show that these effects are in fact largely consistent with the normative scaling of cortical folding in health: larger human brains have disproportionately high SI due to a relative expansion of sulcal area versus hull area, which arises because disproportionate sulcal lengthening overcomes a lack of proportionate sulcal deepening. Accounting for these normative allometries reveals 1) brain size-independent sulcal lengthening in males versus females, and 2) insensitivity of overall folding architecture to SCD. Our methodology and findings provide a novel context for future studies of human cortical folding in health and disease.

A gradient in cortical pathology in multiple sclerosis by in vivo quantitative 7 T imaging

We used a surface-based analysis of T2* relaxation rates at 7 T magnetic resonance imaging, which allows sampling quantitative T2* throughout the cortical width, to map in vivo the spatial distribution of intracortical pathology in multiple sclerosis. Ultra-high resolution quantitative T2* maps were obtained in 10 subjects with clinically isolated syndrome/early multiple sclerosis (≤ 3 years disease duration), 18 subjects with relapsing-remitting multiple sclerosis (≥ 4 years disease duration), 13 subjects with secondary progressive multiple sclerosis, and in 17 age-matched healthy controls. Quantitative T2* maps were registered to anatomical cortical surfaces for sampling T2* at 25%, 50% and 75% depth from the pial surface. Differences in laminar quantitative T2* between each patient group and controls were assessed using general linear model (P < 0.05 corrected for multiple comparisons). In all 41 multiple sclerosis cases, we tested for associations between laminar quantitative T2*, neurological disability, Multiple Sclerosis Severity Score, cortical thickness, and white matter lesions. In patients, we measured, T2* in intracortical lesions and in the intracortical portion of leukocortical lesions visually detected on 7 T scans. Cortical lesional T2* was compared with patients' normal-appearing cortical grey matter T2* (paired t-test) and with mean cortical T2* in controls (linear regression using age as nuisance factor). Subjects with multiple sclerosis exhibited relative to controls, independent from cortical thickness, significantly increased T2*, consistent with cortical myelin and iron loss. In early disease, T2* changes were focal and mainly confined at 25% depth, and in cortical sulci. In later disease stages T2* changes involved deeper cortical laminae, multiple cortical areas and gyri. In patients, T2* in intracortical and leukocortical lesions was increased compared with normal-appearing cortical grey matter (P < 10(-10) and P < 10(-7)), and mean cortical T2* in controls (P < 10(-5) and P < 10(-6)). In secondary progressive multiple sclerosis, T2* in normal-appearing cortical grey matter was significantly increased relative to controls (P < 0.001). Laminar T2* changes may, thus, result from cortical pathology within and outside focal cortical lesions. Neurological disability and Multiple Sclerosis Severity Score correlated each with the degree of laminar quantitative T2* changes, independently from white matter lesions, the greatest association being at 25% depth, while they did not correlate with cortical thickness and volume. These findings demonstrate a gradient in the expression of cortical pathology throughout stages of multiple sclerosis, which was associated with worse disability and provides in vivo evidence for the existence of a cortical pathological process driven from the pial surface.

Quantifying sulcal and gyral topography in relation to deep seated and ventricular lesions: cadaveric study for basing surgical approaches and review of literature

OBJECTIVE

Numerical implication of sulcal and gyral topography for surgical approaches has not been studied.

METHODS

Percentage gain of distance using sulci as compared to that of gyri was calculated by measuring distances toward the ventricles in 15 hemispheres.

RESULTS

Superior frontal sulcus was closest proving greater than 50% gain in distance compared to superior frontal gyrus; inferior temporal sulcus provided greater gain in the temporal lobe.

CONCLUSION

Sulci provide upto 58% distance gain. For trans-gyral approaches, MFG and ITG were found closer to the respective ventricular area.

Atypical sulcal anatomy in young children with autism spectrum disorder

Autism spectrum disorder is associated with an altered early brain development. However, the specific cortical structure abnormalities underlying this disorder remain largely unknown. Nonetheless, atypical cortical folding provides lingering evidence of early disruptions in neurodevelopmental processes and identifying changes in the geometry of cortical sulci is of primary interest for characterizing these structural abnormalities in autism and their evolution over the first stages of brain development. Here, we applied state-of-the-art sulcus-based morphometry methods to a large highly-selective cohort of 73 young male children of age spanning from 18 to 108 months. Moreover, such large cohort was selected through extensive behavioral assessments and stringent inclusion criteria for the group of 59 children with autism. After manual labeling of 59 different sulci in each hemisphere, we computed multiple shape descriptors for each single sulcus element, hereby separating the folding measurement into distinct factors such as the length and depth of the sulcus. We demonstrated that the central, intraparietal and frontal medial sulci showed a significant and consistent pattern of abnormalities across our different geometrical indices. We also found that autistic and control children exhibited strikingly different relationships between age and structural changes in brain morphology. Lastly, the different measures of sulcus shapes were correlated with the CARS and ADOS scores that are specific to the autistic pathology and indices of symptom severity. Inherently, these structural abnormalities are confined to regions that are functionally relevant with respect to cognitive disorders in ASD. In contrast to those previously reported in adults, it is very unlikely that these abnormalities originate from general compensatory mechanisms unrelated to the primary pathology. Rather, they most probably reflect an early disruption on developmental trajectory that could be part of the primary pathology.

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A new single-site cohort of 73 young children (1.5–11 years) with autism and controls

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State-of-the-art methodology used to compare geometrical attributes of sulci

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Combination of automatic extraction of descriptors with manual identification of sulci

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Clearly evidence localized sulcal shape abnormalities in the autism group

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Different relationships between age and structural changes in brain morphology

A system for the generation of curves on 3D brain images

In this study, a computational optimal system for the generation of curves on triangulated surfaces representing 3D brains is described. The algorithm is based on optimally computing geodesics on the triangulated surfaces following Kimmel and Sethian ([1998]: Proc Natl Acad Sci 95:15). The system can be used to compute geodesic curves for accurate distance measurements as well as to detect sulci and gyri. These curves are defined based on local surface curvatures that are computed following a novel approach presented in this study. The corresponding software is available to the research community.