Anatomical step-by-step dissection of common approaches to the third ventricle for trainees: surgical anatomy of the anterior transcortical and interhemispheric transcallosal approaches, surgical principles, and illustrative pediatric cases.

PURPOSE: To create a high-quality, cadaver-based, operatively oriented resource documenting the anterior transcortical and interhemispheric transcallosal approaches as corridors to the third ventricle targeted towards neurosurgical trainees at all levels. METHODS: Two formalin-fixed, latex-injected specimens were dissected under microscopic magnification and endoscopic-assisted visualization. Dissections of the transcortical and transcallosal craniotomies with transforaminal, transchoroidal, and interforniceal transventricular approaches were performed. The dissections were documented in a stepwise fashion using three-dimensional photographic image acquisition techniques and supplemented with representative cases to highlight pertinent surgical principles. RESULTS: The anterior transcortical and interhemispheric corridors afford excellent access to the anterior two-thirds of the third ventricle with varying risks associated with frontal lobe versus corpus callosum disruption, respectively. The transcortical approach offers a more direct, oblique view of the ipsilateral lateral ventricle, whereas the transcallosal approach readily establishes biventricular access through a paramedian corridor. Once inside the lateral ventricle, intraventricular angled endoscopy further enhances access to the extreme poles of the third ventricle from either open transcranial approach. Subsequent selection of either the transforaminal, transchoroidal, or interforniceal routes can be performed through either craniotomy and is ultimately dependent on individual deep venous anatomy, the epicenter of ventricular pathology, and the concomitant presence of hydrocephalus or embryologic cava. Key steps described include positioning and skin incision; scalp dissection; craniotomy flap elevation; durotomy; transcortical versus interhemispheric dissection with callosotomy; the aforementioned transventricular routes; and their relevant intraventricular landmarks. CONCLUSIONS: Approaches to the ventricular system for maximal safe resection of pediatric brain tumors are challenging to master yet represent foundational cranial surgical techniques. We present a comprehensive operatively oriented guide for neurosurgery residents that combines stepwise open and endoscopic cadaveric dissections with representative case studies to optimize familiarity with third ventricle approaches, mastery of relevant microsurgical anatomy, and preparation for operating room participation.

Single-subject electroencephalography measurement of interhemispheric transfer time for the in-vivo estimation of axonal morphology.

Assessing axonal morphology in vivo opens new avenues for the combined study of brain structure and function. A novel approach has recently been introduced to estimate the morphology of axonal fibers from the combination of magnetic resonance imaging (MRI) data and electroencephalography (EEG) measures of the interhemispheric transfer time (IHTT). In the original study, the IHTT measures were computed from EEG data averaged across a group, leading to bias of the axonal morphology estimates. Here, we seek to estimate axonal morphology from individual measures of IHTT, obtained from EEG data acquired in a visual evoked potential experiment. Subject-specific IHTTs are computed in a data-driven framework with minimal a priori constraints, based on the maximal peak of neural responses to visual stimuli within periods of statistically significant evoked activity in the inverse solution space. The subject-specific IHTT estimates ranged from 8 to 29 ms except for one participant and the between-session variability was comparable to between-subject variability. The mean radius of the axonal radius distribution, computed from the IHTT estimates and the MRI data, ranged from 0 to 1.09 µm across subjects. The change in axonal g-ratio with axonal radius ranged from 0.62 to 0.81 µm-α . The single-subject measurement of the IHTT yields estimates of axonal morphology that are consistent with histological values. However, improvement of the repeatability of the IHTT estimates is required to improve the specificity of the single-subject axonal morphology estimates.

Corpus callosum structural characteristics in very preterm children and adolescents: Developmental trajectory and relationship to cognitive functioning.

Previous studies suggest that structural alteration of the corpus callosum, i.e., the largest white matter commissural pathway, occurs after a preterm birth in the neonatal period and lasts across development. The present study aims to unravel corpus callosum structural characteristics across childhood and adolescence in very preterm (VPT) individuals, and their associations with general intellectual, executive and socio-emotional functioning. Neuropsychological assessments, T1-weighted and multi-shell diffusion MRI were collected in 79 VPT and 46 full term controls aged 6-14 years. Volumetric, diffusion tensor and neurite orientation dispersion and density imaging (NODDI) measures were extracted on 7 callosal portions using TractSeg. A multivariate data-driven approach (partial least squares correlation) and a cohort-based age normative modelling approach were used to explore associations between callosal characteristics and neuropsychological outcomes. The VPT and a full-term control groups showed similar trends of white-matter maturation over time, i.e., increase FA and reduced ODI, in all callosal segments, that was associated with increase in general intellectual functioning. However, using a cohort-based age-related normative modelling, findings show atypical pattern of callosal development in the VPT group, with reduced callosal maturation over time that was associated with poorer general intellectual and working memory functioning, as well as with lower gestational age.

Structural integrity of corpus callosum in patients with migraine: a diffusion tensor imaging study.

The aim of this study was to compare structural changes of corpus callosum (CC), which is the largest collection of white matter in the brain, among migraineurs and healthy controls (HC). Diffusion tensor imaging (DTI) method which provides information about microscopic organization of the cell, especially white matter was used for this purpose. Fifty-one patients who were diagnosed with migraine and 44 age- and sex-matched HC were included in the study. Socio-demographic and clinical characteristics of the patients were noted. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) measurements of CC genu, splenium, and body were performed for all participants. A significant difference was determined between migraine patients and HC regarding the FA values in the genu of CC (p < 0.001). When the clinical data of migraine patients and FA values in the genu of CC were analyzed via linear regression analysis, no significant finding was detected (p > 0.05). In conclusion, it can be suggested that there are microstructural changes in the CC of migraneurs; however, the clinical variable associated with this structural deterioration could not be determined.

Three dimensional development and asymmetry of the corpus callosum in the 0-18 age group: A retrospective magnetic resonance imaging study.

Most of the corpus callosum (CC) developmental studies are concerned with its two-dimensional structure. Linear and area measurements do not directly assess the CC size but estimate the overall structure from the cross-sectional image. This study investigated age- and sex-related changes in volumetric development and asymmetry of CC from birth to 18. For this retrospective study, we selected 696 patients (329 [47.27%] females) with both 3D-T1-weighted sequence and normal radiological anatomy from patients 0-18 years of age who had brain magnetic resonance imaging (MRI) between 2012 and 2020. The genu, body, splenium, and total volume of CC were calculated using MRICloud. The measurement results of 23 age groups were analyzed with SPSS (ver.28). Total CC volume was 18740.76 ± 4314.06 mm3 between 0 and 18 years of age, and its ratio to total brain volume (TBV) was 1.70% ± 0.23%. We observed that the total CC volume has six developmental periods 0 years, 1, 2-4, 5-9, 10-16, and 17-18 years. Genu and body grew in five developmental periods, while splenium in seven. There was intermittent sexual dimorphism in the CC volume in the first 4 years of life (p < 0.05). However, sex factor was insignificant in CC ratio to TBV. Total CC was right lateralized on average 1.81% (ranging -0.59% to 4.52%). Genu was 8.70% lateralized to the right, the body was 2.99% to the left, and the splenium was 1.41% to the right. The three-dimensional development of CC agreed with the two-dimensional developmental data of CC except for some differences.

Endoscopic Anatomy of Transcallosal Hemispherotomy: Laboratory Study with Advanced Three-Dimensional Modeling.

BACKGROUND: Epilepsy surgery has an important role in the treatment of patients with medically intractable seizures. Various authors have proposed an endoscopic technique to perform disconnective procedures. A detailed description of intracerebral anatomy seen through an endoscopic transcallosal corridor has not been reported. The aim of this study was to present a cadaveric step-by-step anatomical demonstration of endoscopic transcallosal hemispherotomy using a dedicated three-dimensional model. METHODS: Anatomical dissections were performed on 6 cadaveric heads (12 hemispheres), and the disconnective procedure was performed using an endoscopic transcallosal approach. A dedicated three-dimensional model was used to better illustrate each step. A simulation of the disconnective procedure was performed by recreating the surgical steps on a subject from the Human Connectome Project dataset, and a calculation of the fiber tracts intersected was performed. RESULTS: Analyzing data extracted from the three-dimensional model and tractography simulation, 100% of the fibers (streamlines) of corpus callosum, corticopontine tracts, corticospinal tract, and inferior fronto-occipital fascicle were transected. Moreover, a satisfactory number of fibers (>95%) of the thalamocortical tracts, corticostriatal tracts, corona radiata, fornix, and uncinate fascicle were disconnected. CONCLUSIONS: This anatomical study described the relevant neurovascular structures to enable prediction of feasibility and control of the surgical procedure using the endoscopic transcallosal approach. The quantitative analysis permitted estimation of the theoretical efficacy of the procedure, confirming its relevant role in disconnective surgery.

Generalisation of continuous time random walk to anomalous diffusion MRI models with an age-related evaluation of human corpus callosum.

Diffusion MRI measures of the human brain provide key insight into microstructural variations across individuals and into the impact of central nervous system diseases and disorders. One approach to extract information from diffusion signals has been to use biologically relevant analytical models to link millimetre scale diffusion MRI measures with microscale influences. The other approach has been to represent diffusion as an anomalous transport process and infer microstructural information from the different anomalous diffusion equation parameters. In this study, we investigated how parameters of various anomalous diffusion models vary with age in the human brain white matter, particularly focusing on the corpus callosum. We first unified several established anomalous diffusion models (the super-diffusion, sub-diffusion, quasi-diffusion and fractional Bloch-Torrey models) under the continuous time random walk modelling framework. This unification allows a consistent parameter fitting strategy to be applied from which meaningful model parameter comparisons can be made. We then provided a novel way to derive the diffusional kurtosis imaging (DKI) model, which is shown to be a degree two approximation of the sub-diffusion model. This link between the DKI and sub-diffusion models led to a new robust technique for generating maps of kurtosis and diffusivity using the sub-diffusion parameters ßSUB and DSUB. Superior tissue contrast is achieved in kurtosis maps based on the sub-diffusion model. 7T diffusion weighted MRI data for 65 healthy participants in the age range 19-78 years was used in this study. Results revealed that anomalous diffusion model parameters α and ß have shown consistent positive correlation with age in the corpus callosum, indicating α and ß are sensitive to tissue microstructural changes in ageing.

Heritability in corpus callosum morphology and its association with tool use skill in chimpanzees (Pan troglodytes): Reproducibility in two genetically isolated populations.

The corpus callosum (CC) is the major white matter tract connecting the left and right cerebral hemispheres. It has been hypothesized that individual variation in CC morphology is negatively associated with forebrain volume (FBV) and this accounts for variation in behavioral and brain asymmetries as well as sex differences. To test this hypothesis, CC surface area and thickness as well as FBV was quantified in 221 chimpanzees with known pedigrees. CC surface area, thickness and FBV were significantly heritable and phenotypically associated with each other; however, no significant genetic association was found between FBV, CC surface area and thickness. The CC surface area and thickness measures were also found to be significantly heritable in both chimpanzee cohorts as were phenotypic associations with variation in asymmetries in tool use skill, suggesting that these findings are reproducible. Finally, significant phenotypic and genetic associations were found between hand use skill and region-specific variation in CC surface area and thickness. These findings suggest that common genes may underlie individual differences in chimpanzee tool use skill and interhemispheric connectivity as manifest by variation in surface area and thickness within the anterior region of the CC.

Anatomía del cuerpo calloso en ratas sometidas a estrés prenatal crónico / Anatomy of corpus callosum in rats submitted to chronic prenatal stress

RESUMEN: El cuerpo calloso (CC), es la mayor comisura de sustancia blanca del encéfalo de los mamíferos placentados, constituida por numerosos haces de fibras transversales que conectan áreas corticales de ambos hemisferios cerebrales. Por otro lado, el estrés se define como una respuesta general del organismo ante demandas externas o internas, inicialmente amenazantes, que consiste en movilizar recursos fisiológicos y psicológicos para poderlas afrontar. Dada la importancia del cuerpo calloso en las conexiones cortico-corticales, el objetivo del presente estudio, fue evaluar el efecto en ratas, de un estrés prenatal crónico por inmovilización, sobre la anatomía macroscópica del CC. Se utilizaron seis ratas preñadas de la cepa Wistar de 250 g, de las cuales tres fueron sometidas, a partir del octavo día postconcepción, a una restricción de movimiento por diez días (2h/día). Posteriormente, las madres prosiguieron su gestación, parto y lactancia. Al nacimiento, las camadas fueron ajustadas a seis crías machos por madre (n=36), destetadas a los 21 días y sacrificadas a los 45-52 días de edad. Los encéfalos fueron seccionados a través de la cisura interhemisférica y ambos hemisferios fotografiados por su cara medial. Las imágenes fueron digitalizadas y analizadas mediante el programa Scion Image®, para la medición del área total, parciales (tercio anterior, medio, posterior y quinto posterior) y perímetro callosal. Es así como, el estrés prenatal por inmovilización, afectó significativamente (p<0,01), la morfología macroscópica del cuerpo calloso. Evidenciándose una disminución del área total, áreas parciales y perímetro callosal, en los animales sometidos a restricción prenatal. Estableciendo una relación directa entre número de axones y área callosal e inversa entre diámetro y densidad axonal; lo observado podría tener incidencia en la transferencia interhemisférica.

SUMMARY: The Corpus Callosum (CC) is the largest white matter commissure in the brain of placental mammals, consisting of numerous transverse fiber bundles that connect cortical areas of both cerebral hemispheres. On the other hand, stress is defined as a general response of the organism to external or internal demands, initially threatening, which consists of mobilizing physiological and psychological resources to be able to face them. Given the importance of CC in cortico-cortical connections, the aim of the present study, was to evaluate the effect of chronic pre-natal immobilization stress on the macroscopic anatomy of CC in rats. Six 250g pregnant rats of the Wistar strain were used, of which three were subjected, starting on the eighth post-conception day, to movement restriction for ten days (2h/day). Subsequently, the mothers continued their gestation, delivery and lactation. At birth, litters were adjusted to six male offspring per mother (n=36), which were weaned at 21 days and slaughtered at 45-52 days of age. The brains were fixed, and later sectioned through the interhemispheric fissure and both hemispheres photographed by their medial aspect. The images were digitized and analyzed using the Scion Image® program, for the measurement of the total area, partial area (ante- rior, middle and posterior thirds, as well as posterior fifth) and callosal perimeter. Thus, prenatal stress due to immobilization significantly affected (p<0.01), the macroscopic morphology of the CC. Evidence shows a decrease in the total area, partial areas and callosal perimeter in the animals subjected to prenatal restraint, as compared to normal animals. Establishing a direct relationship between number of axons and callosal area and an inverse relationship between diameter and axonal density, what was observed may have an impact on interhemispheric transfer.

Regional White Matter Scaling in the Human Brain.

Anatomical organization of the primate cortex varies as a function of total brain size, where possession of a larger brain is accompanied by disproportionate expansion of associative cortices alongside a relative contraction of sensorimotor systems. However, equivalent scaling maps are not yet available for regional white matter anatomy. Here, we use three large-scale neuroimaging datasets to examine how regional white matter volume (WMV) scales with interindividual variation in brain volume among typically developing humans (combined N = 2391: 1247 females, 1144 males). We show that WMV scaling is regionally heterogeneous: larger brains have relatively greater WMV in anterior and posterior regions of cortical white matter, as well as the genu and splenium of the corpus callosum, but relatively less WMV in most subcortical regions. Furthermore, regions of positive WMV scaling tend to connect previously-defined regions of positive gray matter scaling in the cortex, revealing a coordinated coupling of regional gray and white matter organization with naturally occurring variations in human brain size. However, we also show that two commonly studied measures of white matter microstructure, fractional anisotropy (FA) and magnetization transfer (MT), scale negatively with brain size, and do so in a manner that is spatially unlike WMV scaling. Collectively, these findings provide a more complete view of anatomic scaling in the human brain, and offer new contexts for the interpretation of regional white matter variation in health and disease.SIGNIFICANCE STATEMENT Recent work has shown that, in humans, regional cortical and subcortical anatomy show systematic changes as a function of brain size variation. Here, we show that regional white matter structures also show brain-size related changes in humans. Specifically, white matter regions connecting higher-order cortical systems are relatively expanded in larger human brains, while subcortical and cerebellar white matter tracts responsible for unimodal sensory or motor functions are relatively contracted. This regional scaling of white matter volume (WMV) is coordinated with regional scaling of cortical anatomy, but is distinct from scaling of white matter microstructure. These findings provide a more complete view of anatomic scaling of the human brain, with relevance for evolutionary, basic, and clinical neuroscience.

Corpus Callosum and Its Connections: A Fiber Dissection Study.

OBJECTIVE: We performed a fine white fiber dissection to demonstrate the extensive connections of the corpus callosum. MATERIAL AND METHODS: Three formalin-fixed frozen cadaveric human brain specimens were dissected using Klingler's technique. On one half of each hemisphere, the superior connections of the corpus callosum were dissected and in the other half the inferior connections of the corpus callosum were dissected. RESULTS: The mean length of the corpus callosum from the rostrum to the splenium was 7.8 cm. The fibers of the corpus callosum were classified as superior/dorsal radiations, inferior/ventral radiations, anterior radiations, and posterior radiations. The entire transverse length of the dorsal callosal radiation from one hemisphere to the other was 8.1 cm. For anterior interhemispheric approaches, an incision in the anterior part of the body not extending beyond 3.5 cm from the genu was found to be safe with regards to crossing motor fibers. CONCLUSIONS: The corpus callosum was found to have intricate connections with all the lobes of the cerebral hemispheres, including the insular region and the limbic and paralimbic areas. Based on the course and traverse of the callosal fibers, a transverse incision in the corpus callosum should be preferred when performing a callosotomy to access intraventricular lesions as this splits the callosal fibers instead of transecting them. The analysis of the course of the callosal radiations enhances understanding of the growth pattern of primary corpus callosal gliomas and helps to design a safe surgical strategy.

Development of human white matter pathways in utero over the second and third trimester.

During the second and third trimesters of human gestation, rapid neurodevelopment is underpinned by fundamental processes including neuronal migration, cellular organization, cortical layering, and myelination. In this time, white matter growth and maturation lay the foundation for an efficient network of structural connections. Detailed knowledge about this developmental trajectory in the healthy human fetal brain is limited, in part, due to the inherent challenges of acquiring high-quality MRI data from this population. Here, we use state-of-the-art high-resolution multishell motion-corrected diffusion-weighted MRI (dMRI), collected as part of the developing Human Connectome Project (dHCP), to characterize the in utero maturation of white matter microstructure in 113 fetuses aged 22 to 37 wk gestation. We define five major white matter bundles and characterize their microstructural features using both traditional diffusion tensor and multishell multitissue models. We found unique maturational trends in thalamocortical fibers compared with association tracts and identified different maturational trends within specific sections of the corpus callosum. While linear maturational increases in fractional anisotropy were seen in the splenium of the corpus callosum, complex nonlinear trends were seen in the majority of other white matter tracts, with an initial decrease in fractional anisotropy in early gestation followed by a later increase. The latter is of particular interest as it differs markedly from the trends previously described in ex utero preterm infants, suggesting that this normative fetal data can provide significant insights into the abnormalities in connectivity which underlie the neurodevelopmental impairments associated with preterm birth.

Redundancy circuits of the commissural pathways in human and rhesus macaque brains.

It has been hypothesized that the human brain has less redundancy than animals, but the structural evidence has not been identified to confirm this claim. Here, we report three redundancy circuits of the commissural pathways in primate brains, namely the orbitofrontal, temporal, and occipital redundancy circuits of the anterior commissure and corpus callosum. Each redundancy circuit has two distinctly separated routes connecting a common pair of cortical regions. We mapped their trajectories in human and rhesus macaque brains using individual and population-averaged tractography. The dissection results confirmed the existence of these redundancy circuits connecting the orbitofrontal lobe, amygdala, and visual cortex. The volume analysis showed a significant reduction in the orbitofrontal and occipital redundancy circuits of the human brain, whereas the temporal redundancy circuit had a substantial organizational difference between the human and rhesus macaque. Our results support the hypothesis that the human brain has less redundancy in the commissural pathways than that of the rhesus macaque brain. Further studies are needed to explore its neuropathological implications.

Variability of white matter anatomy in the subcallosal cingulate area.

The subcallosal cingulate (SCC) area is a putative hub in the brain network underlying depression. Deep brain stimulation (DBS) targeting a particular subregion of SCC, identified as the intersection of forceps minor (FM), uncinate fasciculus (UCF), cingulum and fronto-striatal fiber bundles, may be critical to a therapeutic response in patients with severe, treatment-resistant forms of major depressive disorder (MDD). The pattern and variability of the white matter anatomy and organization within SCC has not been extensively characterized across individuals. The goal of this study is to investigate the variability of white matter bundles within the SCC that structurally connect this region with critical nodes in the depression network. Structural and diffusion data from 100 healthy subjects from the Human Connectome Project database were analyzed. Anatomically defined SCC regions were used as seeds to perform probabilistic tractography and to estimate the connectivity from the SCC to subject-specific target areas believed to be involved in the pathology of MDD including ventral striatum (VS), UCF, anterior cingulate cortex (ACC), and medial prefrontal cortex (mPFC). Four distinct areas of connectivity were identified within SCC across subjects: (a) postero-lateral SCC connectivity to medial temporal regions via UCF, (b) postero-medial connectivity to VS, (c) superior-medial connectivity to ACC via cingulum bundle, and (d) antero-lateral connectivity to mPFC regions via forceps minor. Assuming white matter connectivity is critical to therapeutic response, the improved anatomic understanding of SCC as well as an appreciation of the intersubject variability are critical to developing optimized therapeutic targeting for SCC DBS.

Examining the effect of online advertisement cues on human responses using eye-tracking, EEG, and MRI.

This study sought to emphasize how disciplines such as neuroscience and marketing can be applied in advertising and consumer behavior. The application of neuroscience methods in analyzing and understanding human behavior related to the Elaboration Likelihood Model (ELM) and brain activity has recently garnered attention. This study examines brain processes while participants attempted to elicit preferences for a product, and demonstrates factors that influence consumer behavior using eye-tracking, electroencephalography (EEG), and magnetic resonance imaging (MRI) from a neuroscience approach. We planned two conditions of online advertising, namely, peripheral cues without argument and central cues with argument strength. Thirty respondents participated in the experiment, consisting of eye-tracking, EEG, and MRI instruments to explore brain activity in central cue conditions. We investigated whether diffusion tensor imaging (DTI) analysis could detect regional brain changes. Using eye-tracking, we found that the responses were mainly in the mean fixation duration, number of fixations, mean saccade duration, and number of saccade durations for the central cue condition. Moreover, the findings show that the fusiform gyrus and frontal cortex are significantly associated with building a relationship by inferring central cues in the EEG assay. The MRI images show that the fusiform gyrus and frontal cortex are significantly active in the central cue condition. DTI analysis indicates that the corpus callosum has changed in the central cue condition. We used eye-tracking, EEG, MRI, and DTI to understand that these connections may apprehend responses when viewing advertisements, especially in the fusiform gyrus, frontal cortex, and corpus callosum.

Structural and functional connectivity mapping of the human corpus callosum organization with white-matter functional networks.

The corpus callosum serves as a crucial organization for understanding the information integration between the two hemispheres. Our previous study explored the functional connectivity between the corpus callosum and white-matter functional networks (WM-FNs), but the corresponding physical connectivity remains unknown. The current study uses the resting-state fMRI of Human Connectome Project data to identify ten WM-FNs in 108 healthy subjects, and then independently maps the structural and functional connectivity between the corpus callosum and above WM-FNs using the diffusion tensor images (DTI) tractography and resting-state functional connectivity (RSFC). Our results demonstrated that the structural and functional connectivity between the human corpus callosum and WM-FNs have the following high overall correspondence: orbitofrontal WM-FN, DTI map = 89% and RSFC map = 92%; sensorimotor middle WM-FN, DTI map = 47% and RSFC map = 77%; deep WM-FN, DTI map = 50% and RSFC map = 79%; posterior corona radiata WM-FN, DTI map = 82% and RSFC map = 73%. These findings reinforce the notion that the corpus callosum has unique spatial distribution patterns connecting to distinct WM-FNs. However, important differences between the structural and functional connectivity mapping results were also observed, which demonstrated a synergy between DTI tractography and RSFC toward better understanding the information integration of primary and higher-order functional systems in the human brain.

Handedness and White Matter Networks.

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

Comparative morphology of the corpus callosum across the adult lifespan in chimpanzees (Pan troglodytes) and humans.

The human corpus callosum exhibits substantial atrophy in old age, which is stronger than what would be predicted from parallel changes in overall brain anatomy. To date, however, it has not been conclusively established whether this accentuated decline represents a common feature of brain aging across species, or whether it is a specific characteristic of the aging human brain. In the present cross-sectional study, we address this question by comparing age-related difference in corpus callosum morphology of chimpanzees and humans. For this purpose, we measured total midsagittal area and regional thickness of the corpus callosum from T1-weighted MRI data from 213 chimpanzees, aged between 9 and 54 years. The results were compared with data drawn from a large-scale human sample which was age-range matched using two strategies: (a) matching by chronological age (human sample size: n = 562), or (b) matching by accounting for differences in longevity and various maturational events between the species (i.e., adjusted human age range: 13.6 to 80.9 years; n = 664). Using generalized additive modeling to fit and compare aging trajectories, we found significant differences between the two species. The chimpanzee aging trajectory compared with the human trajectory was characterized by a slower increase from adolescence to middle adulthood, and by a lack of substantial decline from middle to old adulthood, which, however, was present in humans. Thus, the accentuated decline of the corpus callosum found in aging humans is not a universal characteristic of the aging brain, and appears to be human-specific.

The Anatomy of the Convergence of Major Deep Cerebral Veins in the Pineal Region: A Computed Tomography Angiography Study.

BACKGROUND: The anatomy of the veins in the pineal region is one of the most complex areas in the brain because all major deep cerebral veins converge there: the internal cerebral veins (ICVs), the great cerebral vein of Galen (GV), the basal veins (BVs), and the internal occipital veins (IOVs). The aim of this study was to comprehensively describe the anatomy of the veins in the pineal region using computed tomography angiography. METHODS: Head computed tomography angiography scans of 250 adult Polish patients were evaluated. We assessed the location of the junction of 2 ICVs and the presence of a narrowing of the GV and arachnoid granulation at the GV-straight sinus junction. We evaluated the presence, appearance, and termination of the BV, and the presence and termination of the IOV. RESULTS: The study showed that 2 ICVs usually converged posterior to the splenium of the corpus callosum (62.4%). Narrowing of the BV was observed in 51.2% of patients, and the arachnoid granulation was found in 25.2%. The 3 segments of the BV were well visualized in 66% of the studied hemispheres. The BV flowed into the GV in 34.8% of the hemispheres. The IOV was present in 90.2% of the hemispheres and terminated medially in 84.5%. CONCLUSIONS: Because an injury to major deep cerebral veins may result in severe postoperative neurologic deficits, it is essential for neurosurgeons to be familiar with both normal and variant patterns of veins in the pineal region.

Microstructural white matter connectivity underlying the attentional networks system.

Nowadays, there is considerable controversy regarding the structural connectivity underlying the attentional networks system (i.e., alerting and vigilance, orienting, and executive control). The present study aimed at further examining and dissociating the white matter connectivity underlying attentional and vigilance functioning by overcoming some critical limitations in previous research. To this end, we performed virtual in vivo dissections of attention-related white matter tracts from thirty healthy adults. Participants completed two sessions of the Attentional Networks Test for Interactions and Vigilance, a suitable task to assess simultaneously phasic alertness, orienting, executive control, and the executive component of vigilance (i.e., the ability to detect infrequent critical signals). Whereas we found a consistent correlation between phasic alertness and both the right dorsolateral prefrontal caudate tract and the splenium of the corpus callosum, evidence obtained for white matter connectivity underlying orienting, executive control, and executive vigilance, was either weak at the best, inconsistent, or null. White matter connectivity seemed to support nevertheless the most reliable performance: overall reaction time for attentional functioning was significantly associated with the left cingulate fasciculus and overall reaction time for executive vigilance was significantly linked to the bilateral superior longitudinal fasciculus I. The present outcomes provide interesting, consistent, and reliable evidence concerning the structural connectivity underlying the alerting network. We still consider that further evidence is necessary to better understand the controversial relationship between attentional/vigilance processes and microstructural white matter connectivity though.