Automated measurement of latent morphological features in the human corpus callosum

Assessment of the corpus callosum size in male individuals with high intelligence quotient (members of Mensa International)

OBJECTIVES

The aim of this study was to assess the size of the corpus callosum in members of Mensa International, which is the world's largest and oldest high-intelligence quotient (IQ) society.

METHODS

We performed T2-weighted magnetic resonance imaging (Repetition Time, TR = 3200 ms, Time of Echo, TE = 409 ms) to examine the brain of members of Mensa International (Polish national group) in order to assess the size of the corpus callosum. Results from 113 male MENSA members and 96 controls in the age range of 21-40 years were analyzed.

RESULTS

The comparative analysis showed that the mean length of the corpus callosum and the thickness of the isthmus were significantly greater in the Mensa members compared to the control groups. A statistically significant difference was also identified in the largest linear dimension of the brain from the frontal lobe to the occipital lobe. The mean corpus callosum cross-sectional area and its ratio to the brain area were significantly greater in the Mensa members.

CONCLUSIONS

The results show that the dimensions (linear measures and midsagittal cross-sectional surface area) of the corpus callosum were significantly greater in the group of Mensa members than in the controls.

Ethnicity Influences Corpus Callosum Dimensions

Background and Objective

Corpus callosum (CC), the main white matter cable which connects two hemispheres of brain, is important in special procedures such as stereotaxic surgeries vary in size, in different populations. Determination of possible size differences in ethnical groups has special values.

Patients and Methods

The size of the CC on midsagittal view was determined in 76 normal male subjects using MRI of brain hemispheres in northern Iran. The size of rostrum, body, splenium, length, and height of CC was measured for each subject. The width of the body of the corpus callosum (B), the anterior to posterior length (L) and the maximum height (H) of the corpus callosum, and ratios B/L and B/H were also calculated.

Results

The longitudinal dimensions of the CC were 70.21 mm and 74.05 mm in native Fars and Turkmens, respectively (P < 0.05). The heights were 25 mm and 25.75 mm in native Fars and Turkmen subjects, respectively. The width of CC in Turkmen people was significantly higher than native Fars people (P < 0.05). The Evans index in Turkmen group (0.314) was significantly higher than in native Fars (0.3). The B/L and B/H ratios were nonsignificantly different between two groups.

Conclusion

The CC parameters vary in different ethnical groups in northern Iran.

Callosotomy affects performance IQ: A meta-analysis of individual participant data

Morphometric neuroimaging studies on healthy adult individuals regularly report a positive association between intelligence test performance (IQ) and structural properties of the corpus callosum (CC). At the same time, studies examining the effect of callosotomy on epilepsy patients report only negligible changes in IQ as result of the surgery, partially contradicting the findings of the morphometry studies. Objective of the present meta-analysis of individual participant data (IPD) of 87 cases from 16 reports was to re-investigate the effect of callosotomy on full scale IQ as well as on the verbal and performance subscale under special consideration of two possible moderating factors: pre-surgical IQ levels and the extent of the surgery (complete vs. anterior transsection). The main finding was that callosotomy selectively affects performance IQ, whereby the effect is modulated by the pre-surgical level of performance. Patients with an above-median pre-surgery performance IQ level show a significant average decrease of -5.44 (CI_95%: - 8.33 to - 2.56) IQ points following the surgery, while the below-median group does not reveal a significant change in IQ (mean change: 1.01 IQ points; CI_95%: -1.83 to 3.86). Thus, the present analyses support the notion that callosotomy has a negative effect on the patients' performance IQ, but only in those patients, who at least have an average performance levels before the surgery. This observation also lends support to the findings of previous morphometry studies, indicating that the frequently observed CC-IQ correlation might indeed reflect a functional contribution of callosal interhemispheric connectivity to intelligence-test performance.

The corpus callosum as anatomical marker of intelligence? A critical examination in a large-scale developmental study

Intellectual abilities are supported by a large-scale fronto-parietal brain network distributed across both cerebral hemispheres. This bihemispheric network suggests a functional relevance of inter-hemispheric coordination, a notion which is supported by a series of recent structural magnetic resonance imaging (MRI) studies demonstrating correlations between intelligence scores (IQ) and corpus-callosum anatomy. However, these studies also reveal an age-related dissociation: mostly positive associations are reported in adult samples, while negative associations are found in developing samples. In the present study, we re-examine the association between corpus callosum and intelligence measures in a large (734 datasets from 495 participants) developmental mixed cross-sectional and longitudinal sample (6.4–21.9 years) using raw test scores rather than deviation IQ measures to account for the ongoing cognitive development in this age period. Analyzing mid-sagittal measures of regional callosal thickness, a positive association in the splenium of the corpus callosum was found for both verbal and performance raw test scores. This association was not present when the participants’ age was considered in the analysis. Thus, we did not reveal any association that cannot be explained by a temporal co-occurrence of overall developmental trends in intellectual abilities and corpus callosum maturation in the present developing sample.

Annual research review: progress in using brain morphometry as a clinical tool for diagnosing psychiatric disorders

Brain morphometry in recent decades has increased our understanding of the neural bases of psychiatric disorders by localizing anatomical disturbances to specific nuclei and subnuclei of the brain. At least some of these disturbances precede the overt expression of clinical symptoms and possibly are endophenotypes that could be used to diagnose an individual accurately as having a specific psychiatric disorder. More accurate diagnoses could significantly reduce the emotional and financial burden of disease by aiding clinicians in implementing appropriate treatments earlier and in tailoring treatment to the individual needs. Several methods, especially those based on machine learning, have been proposed that use anatomical brain measures and gold-standard diagnoses of participants to learn decision rules that classify a person automatically as having one disorder rather than another. We review the general principles and procedures for machine learning, particularly as applied to diagnostic classification, and then review the procedures that have thus far attempted to diagnose psychiatric illnesses automatically using anatomical measures of the brain. We discuss the strengths and limitations of extant procedures and note that the sensitivity and specificity of these procedures in their most successful implementations have approximated 90%. Although these methods have not yet been applied within clinical settings, they provide strong evidence that individual patients can be diagnosed accurately using the spatial pattern of disturbances across the brain.

Focal thinning of the posterior corpus callosum: normal variant or post-traumatic?

AIM

The corpus callosum (CC) can be affected by childhood traumatic brain injury (TBI), through focal lesions, reductions in size and arrested development. Little is known, however, about what constitutes normal CC shape and appearance and how it may be affected in the long-term after early TBI.

METHODS

In this study, the appearance of the CC was investigated in individuals with TBI assessed 10 years post-injury (n = 52, mean age = 16.82 years, SD = 3.55 years, 24 male) and compared to age-matched healthy controls (n = 44, mean age = 15.77 years, SD = 1.21 years, 18 male). A simple visual analysis technique was used to code the appearance of the CC according to location of focal thinning and severity of thinning and results between groups were compared using Chi-square analysis.

RESULTS

A significantly higher proportion of patients with childhood TBI had focal posterior thinning of the CC than age-matched controls (p = 0.001).

CONCLUSIONS

The findings call into question previous conclusions that focal posterior thinning is a normal variant of development. Instead, attenuations of the posterior portion of the CC in the long-term may reflect altered cortical and callosal development as a result of early brain injury, although the functional significance of this remains to be determined.

Negative associations between corpus callosum midsagittal area and IQ in a representative sample of healthy children and adolescents

Documented associations between corpus callosum size and cognitive ability have heretofore been inconsistent potentially owing to differences in sample characteristics, differing methodologies in measuring CC size, or the use of absolute versus relative measures. We investigated the relationship between CC size and intelligence quotient (IQ) in the NIH MRI Study of Normal Brain Development sample, a large cohort of healthy children and adolescents (aged six to 18, n = 198) recruited to be representative of the US population. CC midsagittal area was measured using an automated system that partitioned the CC into 25 subregions. IQ was measured using the Wechsler Abbreviated Scale of Intelligence (WASI). After correcting for total brain volume and age, a significant negative correlation was found between total CC midsagittal area and IQ (r = −0.147; p = 0.040). Post hoc analyses revealed a significant negative correlation in children (age<12) (r = −0.279; p = 0.004) but not in adolescents (age≥12) (r = −0.005; p = 0.962). Partitioning the subjects by gender revealed a negative correlation in males (r = −0.231; p = 0.034) but not in females (r = 0.083; p = 0.389). Results suggest that the association between CC and intelligence is mostly driven by male children. In children, a significant gender difference was observed for FSIQ and PIQ, and in males, a significant age-group difference was observed for FSIQ and PIQ. These findings suggest that the correlation between CC midsagittal area and IQ may be related to age and gender.

Relationship between intelligence and the size and composition of the corpus callosum

We investigated the relationship between the morphology of the corpus callosum (CC) and IQ in a healthy sample of individuals in their late teens and early twenties. The relationship between the area of the CC, measured at the midline, and IQ showed regional differences. We observed that a higher estimated performance IQ was associated with smaller area in the posterior regions of the CC, a finding that differs from a positive association previously observed in a somewhat older adult sample. In contrast, higher estimated verbal IQ was associated with decreased fractional anisotropy of the genu, an anterior portion of the CC. Age effects were also observed such that older age was associated with larger CC area. Our results suggest that CC morphology is related to cognitive performance, which may have implications for clinical populations in whom CC morphology is atypical.

Sparse decomposition and modeling of anatomical shape variation

Recent advances in statistics have spawned powerful methods for regression and data decomposition that promote sparsity, a property that facilitates interpretation of the results. Sparse models use a small subset of the available variables and may perform as well or better than their full counterparts if constructed carefully. In most medical applications, models are required to have both good statistical performance and a relevant clinical interpretation to be of value. Morphometry of the corpus callosum is one illustrative example. This paper presents a method for relating spatial features to clinical outcome data. A set of parsimonious variables is extracted using sparse principal component analysis, producing simple yet characteristic features. The relation of these variables with clinical data is then established using a regression model. The result may be visualized as patterns of anatomical variation related to clinical outcome. In the present application, landmark-based shape data of the corpus callosum is analyzed in relation to age, gender, and clinical tests of walking speed and verbal fluency. To put the data-driven sparse principal component method into perspective, we consider two alternative techniques, one where features are derived using a model-based wavelet approach, and one where the original variables are regressed directly on the outcome.

Age- and sex-related effects on the neuroanatomy of healthy elderly

Effects of age and sex, and their interaction on the structural brain anatomy of healthy elderly were assessed thanks to a cross-sectional study of a cohort of 662 subjects aged from 63 to 75 years. T1- and T2-weighted MRI scans were acquired in each subject and further processed using a voxel-based approach that was optimized for the identification of the cerebrospinal fluid (CSF) compartment. Analysis of covariance revealed a classical neuroanatomy sexual dimorphism, men exhibiting larger gray matter (GM), white matter (WM), and CSF compartment volumes, together with larger WM and CSF fractions, whereas women showed larger GM fraction. GM and WM were found to significantly decrease with age, while CSF volume significantly increased. Tissue probability map analysis showed that the highest rates of GM atrophy in this age range were localized in primary cortices, the angular and superior parietal gyri, the orbital part of the prefrontal cortex, and in the hippocampal region. There was no significant interaction between "Sex" and "Age" for any of the tissue volumes, as well as for any of the tissue probability maps. These findings indicate that brain atrophy during the seventh and eighth decades of life is ubiquitous and proceeds at a rate that is not modulated by "Sex".

Bilingual corpus callosum variability

Magnetic resonance imaging was used to produce midsagittal images of the corpus callosum of 19 right-handed adult male and female subjects. The preliminary findings of this study indicate that significant adaptation in the anterior midbody of the corpus callosum has occurred to accommodate multiple language capacity in bilingual individuals compared to monolingual individuals. The main interpretation of this finding is that the precentral gyrus is involved in bilingual faculty adaptation assuming a role consistent with the somatotopical input to areas dedicated to the mouth, and input to association tracts connecting the premotor and supplementary motor cortices. This paper discusses possible implications to neuroscientists, second language educators, and their students.

Morphological changes in aging brain structures are differentially affected by time-linked environmental influences despite strong genetic stability

This longitudinal study used the full twin model to estimate change and stability of genetic contributions to morphology of two brain structures, the corpus callosum and lateral ventricles. The 142 subjects were 34 monozygotic (MZ) and 37 dizygotic (DZ) elderly male twin pairs from the National Heart, Lung, and Blood Institute (NHLBI) Twin Study who underwent brain magnetic resonance imaging twice, separated by a 4-year interval. Genetic factors accounted for a substantial portion of individual differences in the size of the corpus callosum and its substructures and of lateral ventricular size. Longitudinal genetic analyses revealed no significant change in the heritability of these structures and no evidence for new genetic variance at Time 2 not present at Time 1. However, both the callosal and ventricular measures showed evidence for new environmental variance at Time 2 not present at Time 1. Confirming a previously posed hypothesis, the phenotypic correlation between absolute change in height of the corpus callosum and absolute change in ventricular volume was significant. Bivariate genetic analysis estimated a significant genetic correlation between the changes in these two structures and the genetic variance in the change of callosal height was entirely due to genes involved in the expansion of ventricles. Genetic stability was present even in old age when brain and other morphological changes can be rapid and highly variable across individuals, inconsistent with an hypothesis that random DNA damage is the cause of aging.

Brain Imaging Studies of the Anatomical and Functional Consequences of Preterm Birth for Human Brain Development

Premature birth can have devastating effects on brain development and long-term functional outcome. Rates of psychiatric illness and learning difficulties are high, and intelligence on average is lower than population means. Brain imaging studies of infants born prematurely have demonstrated reduced volumes of parietal and sensorimotor cortical gray matter regions. Studies of school-aged children have demonstrated reduced volumes of these same regions, as well as in temporal and premotor regions, in both gray and white matter. The degrees of these anatomical abnormalities have been shown to correlate with cognitive outcome and with the degree of fetal immaturity at birth. Functional imaging studies have shown that these anatomical abnormalities are associated with severe disturbances in the organization and use of neural systems subserving language, particularly for school-aged children who have low verbal IQs. Animal models suggest that hypoxia-ischemia may be responsible at least in part for some of the anatomical and functional abnormalities. Increasing evidence suggests that a host of mediators for hypoxic-ischemic insults likely contribute to the disturbances in brain development in preterm infants, including increased apoptosis, free-radical formation, glutamatergic excitotoxicity, and alterations in the expression of a large number of genes that regulate brain maturation, particularly those involved in the development of postsynaptic neurons and the stabilization of synapses. The collaboration of both basic neuroscientists and clinical researchers is needed to understand how normal brain development is derailed by preterm birth and to develop effective prevention and early interventions for these often devastating conditions.

Computer-assisted enhanced volumetric segmentation magnetic resonance imaging data using a mixture of artificial neural networks

An accurate computer-assisted method able to perform regional segmentation on 3D single modality images and measure its volume is designed using a mixture of unsupervised and supervised artificial neural networks. Firstly, an unsupervised artificial neural network is used to estimate representative textures that appear in the images. The region of interest of the resultant images is selected by means of a multi-layer perceptron after a training using a single sample slice, which contains a central portion of the 3D region of interest. The method was applied to magnetic resonance imaging data collected from an experimental acute inflammatory model (T(2) weighted) and from a clinical study of human Alzheimer's disease (T(1) weighted) to evaluate the proposed method. In the first case, a high correlation and parallelism was registered between the volumetric measurements, of the injured and healthy tissue, by the proposed method with respect to the manual measurements (r = 0.82 and p < 0.05) and to the histopathological studies (r = 0.87 and p < 0.05). The method was also applied to the clinical studies, and similar results were derived of the manual and semi-automatic volumetric measurement of both hippocampus and the corpus callosum (0.95 and 0.88).

Deformation-based surface morphometry applied to gray matter deformation

We present a unified statistical approach to deformation-based morphometry applied to the cortical surface. The cerebral cortex has the topology of a 2D highly convoluted sheet. As the brain develops over time, the cortical surface area, thickness, curvature, and total gray matter volume change. It is highly likely that such age-related surface changes are not uniform. By measuring how such surface metrics change over time, the regions of the most rapid structural changes can be localized. We avoided using surface flattening, which distorts the inherent geometry of the cortex in our analysis and it is only used in visualization. To increase the signal to noise ratio, diffusion smoothing, which generalizes Gaussian kernel smoothing to an arbitrary curved cortical surface, has been developed and applied to surface data. Afterward, statistical inference on the cortical surface will be performed via random fields theory. As an illustration, we demonstrate how this new surface-based morphometry can be applied in localizing the cortical regions of the gray matter tissue growth and loss in the brain images longitudinally collected in the group of children and adolescents.