Human cerebral cortex: a system for the integration of volume- and surface-based representations

Joint source based morphometry identifies linked gray and white matter group differences

We present a multivariate approach called joint source based morphometry (jSBM), to identify linked gray and white matter regions which differ between groups. In jSBM, joint independent component analysis (jICA) is used to decompose preprocessed gray and white matter images into joint sources and statistical analysis is used to determine the significant joint sources showing group differences and their relationship to other variables of interest (e.g. age or sex). The identified joint sources are groupings of linked gray and white matter regions with common covariation among subjects. In this study, we first provide a simulation to validate the jSBM approach. To illustrate our method on real data, jSBM is then applied to structural magnetic resonance imaging (sMRI) data obtained from 120 chronic schizophrenia patients and 120 healthy controls to identify group differences. JSBM identified four joint sources as significantly associated with schizophrenia. Linked gray-white matter regions identified in each of the joint sources included: 1) temporal--corpus callosum, 2) occipital/frontal--inferior fronto-occipital fasciculus, 3) frontal/parietal/occipital/temporal--superior longitudinal fasciculus and 4) parietal/frontal--thalamus. Age effects on all four joint sources were significant, but sex effects were significant only for the third joint source. Our findings demonstrate that jSBM can exploit the natural linkage between gray and white matter by incorporating them into a unified framework. This approach is applicable to a wide variety of problems to study linked gray and white matter group differences.

Cross-validation of brain segmentation by SPM5 and SIENAX

Volumes of cerebral grey (GM) or white matter (WM) are often used as clinical observations or statistical covariates. Several automated segmentation tools can be used for this purpose, but they have not been validated against each other. We used the most common ones, SPM5 and SIENAX 2.4, to derive volumes of grey and white matter in 56 healthy subjects (mean age 49+/-13, range 22-80) and compared the two methods. Both methods yielded significant correlations with age in the expected directions, and estimates of parenchymal volumes were highly correlated. However, without use of prior probability maps, or priors, in SIENAX, GM was significantly underestimated in comparison to SPM (0.52+/-.06 vs 0.66+/-.07 L) and WM was significantly overestimated (0.48+/-.07 vs 0.46+/-.07 L). This error was associated with misclassification of GM as cerebrospinal fluid, especially in deep grey matter. Invoking prior probabilities in SIENAX resulted in excellent agreement with SPM: GM and WM volumes were found to be 0.64+/-0.07 L and 0.47+/-0.07 L, respectively. We conclude that SIENAX requires priors for accurate volumetric estimates, and then provides close agreement with SPM5.

Cortical thickness abnormalities in cocaine addiction--a reflection of both drug use and a pre-existing disposition to drug abuse?

The structural effects of cocaine on neural systems mediating cognition and motivation are not well known. By comparing the thickness of neocortical and paralimbic brain regions between cocaine-dependent and matched control subjects, we found that four of 18 a priori regions involved with executive regulation of reward and attention were significantly thinner in addicts. Correlations were significant between thinner prefrontal cortex and reduced keypresses during judgment and decision making of relative preference in addicts, suggesting one basis for restricted behavioral repertoires in drug dependence. Reduced effortful attention performance in addicts also correlated with thinner paralimbic cortices. Some thickness differences in addicts were correlated with cocaine use independent of nicotine and alcohol, but addicts also showed diminished thickness heterogeneity and altered hemispheric thickness asymmetry. These observations suggest that brain structure abnormalities in addicts are related in part to drug use and in part to predisposition toward addiction.

Evidence for abnormalities of cortical development in adolescent-onset schizophrenia

Voxel-Based Morphometry (VBM) identifies differences in grey matter brain structure in patients with schizophrenia relative to healthy controls, with particularly prominent differences found in patients with the more severe, adolescent-onset form of the disease. However, as VBM is sensitive to a combination of changes in grey matter thickness, intensity and folding, specific neuropathological interpretations are not possible. Here, we attempt to more precisely define cortical changes in 25 adolescent-onset schizophrenic patients and 25 age- and sex-matched healthy volunteers using Surface-Based Morphometry (SBM) to disambiguate the relative contributions of cortical thickness and surface area differences to changes in regional grey matter (GM) density measured with VBM. Cortical changes in schizophrenia were widespread, including particularly the prefrontal cortex and superior temporal gyrus. Nine regions of apparent reduction in GM density in patients relative to healthy matched controls were found using VBM that were not found with SBM-derived cortical thickness measures. In Regions of Interest (ROIs) derived from the VBM group results, we confirmed that local surface area differences accounted for these VBM changes. Our results emphasize widespread, but focally distinct cortical pathology in adolescent-onset schizophrenia. Evidence for changes in local surface area (as opposed to simply cortical thinning) is consistent with a neurodevelopmental contribution to the underlying neuropathology of the disease.

Towards further understanding of the co-morbidity between attention deficit hyperactivity disorder and bipolar disorder: a MRI study of brain volumes

BACKGROUND

Although attention deficit hyperactivity disorder (ADHD) and bipolar disorder (BPD) co-occur frequently and represent a particularly morbid clinical form of both disorders, neuroimaging research addressing this co-morbidity is scarce. Our aim was to evaluate the morphometric magnetic resonance imaging (MRI) underpinnings of the co-morbidity of ADHD with BPD, testing the hypothesis that subjects with this co-morbidity would have neuroanatomical correlates of both disorders.

METHOD

Morphometric MRI findings were compared between 31 adults with ADHD and BPD and with those of 18 with BPD, 26 with ADHD, and 23 healthy controls. The volumes (cm(3)) of our regions of interest (ROIs) were estimated as a function of ADHD status, BPD status, age, sex, and omnibus brain volume using linear regression models.

RESULTS

When BPD was associated with a significantly smaller orbital prefrontal cortex and larger right thalamus, this pattern was found in co-morbid subjects with ADHD plus BPD. Likewise, when ADHD was associated with significantly less neocortical gray matter, less overall frontal lobe and superior prefrontal cortex volumes, a smaller right anterior cingulate cortex and less cerebellar gray matter, so did co-morbid ADHD plus BPD subjects.

CONCLUSIONS

Our results support the hypothesis that ADHD and BPD independently contribute to volumetric alterations of selective and distinct brain structures. In the co-morbid state of ADHD plus BPD, the profile of brain volumetric abnormalities consists of structures that are altered in both disorders individually. Attention to co-morbidity is necessary to help clarify the heterogeneous neuroanatomy of both BPD and ADHD.

Improving the resolution of functional brain imaging: analyzing functional data in anatomical space

The accurate mapping of functional magnetic resonance imaging (fMRI) activations to anatomical structures is critical for fMRI studies of brain organization. In the commonly used functional space analysis method, functional images are realigned to a functional reference image and processed in low-resolution functional space. The average functional activations are then projected into high-resolution anatomical space for visualization. Here, we describe a new technique, anatomical space analysis (ASA), whereby low-resolution functional images are first coregistered and resampled directly into high-resolution anatomical space with all subsequent data processing performed in high-resolution space. A major advantage of ASA is that minor scanner sampling instabilities and small head movements can increase spatial resolution by providing multiple samples of the relationship between functional and anatomical space. Both simulations and analyses of real fMRI data show that ASA improves the precision, objectivity and reproducibility of functional brain mapping.

Displacement of brain regions in preterm infants with non-synostotic dolichocephaly investigated by MRI

Regional investigations of newborn MRI are important to understand the appearance and consequences of early brain injury. Previously, regionalization in neonates has been achieved with a Talairach parcellation, using internal landmarks of the brain. Non-synostotic dolichocephaly defines a bi-temporal narrowing of the preterm infant's head caused by pressure on the immature skull. The impact of dolichocephaly on brain shape and regional brain shift, which may compromise the validity of the parcellation scheme, has not yet been investigated. Twenty-four preterm and 20 fullterm infants were scanned at term equivalent. Skull shapes were investigated by cephalometric measurements and population registration. Brain tissue volumes were calculated to rule out brain injury underlying skull shape differences. The position of Talairach landmarks was evaluated. Cortical structures were segmented to determine a positional shift between both groups. The preterm group displayed dolichocephalic head shapes and had similar brain volumes compared to the mesocephalic fullterm group. In preterm infants, Talairach landmarks were consistently positioned relative to each other and to the skull base, but were displaced with regard to the calvarium. The frontal and superior region was enlarged; central and temporal gyri and sulci were shifted comparing preterm and fullterm infants. We found that, in healthy preterm infants, dolichocephaly led to a shift of cortical structures, but did not influence deep brain structures. We concluded that the validity of a Talairach parcellation scheme is compromised and may lead to a miscalculation of regional brain volumes and inconsistent parcel contents when comparing infant populations with divergent head shapes.