Somatosensory system in two types of motor reorganization in congenital hemiparesis: topography and function

This study investigates the (re-)organization of somatosensory functions following early brain lesions. Using functional magnetic resonance imaging (fMRI), passive hand movement was studied. Transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG) were used as complementary methods. fMRI data was analyzed on the first level with regard to topographical variability; second-level group effects as well as the overall integrity of the somatosensory circuitry were also assessed. Subjects with unilateral brain lesions occurring in the third trimester of pregnancy or perinatally with different types of motor reorganization were included: patients with regular, contralateral motor organization following middle cerebral artery strokes (CONTRA(MCA), n = 6) and patients with reorganized, ipsilateral motor functions due to periventricular lesions (IPSI(PL), n = 8). Motor impairment was similar, but sensory impairment was more pronounced in the CONTRA(MCA) group. Using fMRI and MEG, both groups showed a normal pattern with a contralateral somatosensory representation, despite the transhemispherically reorganized primary motor cortex in the IPSI(PL) group, as verified by TMS. Activation topography for the paretic hands was more variable than for the nonparetic hand in both groups. The cortico-cerebellar circuitry was well-preserved in almost all subjects. We conclude that in both models of motor reorganization, no interhemispheric reorganization of somatosensory functions occurred. Also, no relevant intrahemispheric reorganization was observed apart from a higher topographical variability of fMRI activations. This preserved pattern of somatosensory organization argues in favor of a differential lesion effect on motor and somatosensory functions and demonstrates a limited compensatory potential for the latter.

Strengthening of laterality of verbal and visuospatial functions during childhood and adolescence

Cognitive functions in the child's brain develop in the context of complex adaptive processes, determined by genetic and environmental factors. Little is known about the cerebral representation of cognitive functions during development. In particular, knowledge about the development of right hemispheric (RH) functions is scarce. Considering the dynamics of brain development, localization and lateralization of cognitive functions must be expected to change with age. Twenty healthy subjects (8.6-20.5 years) were examined with fMRI and neuropsychological tests. All participants completed two fMRI tasks known to activate left hemispheric (LH) regions (language tasks) and two tasks known to involve predominantly RH areas (visual search tasks). A laterality index (LI) was computed to determine the asymmetry of activation. Group analysis revealed unilateral activation of the LH language circuitry during language tasks while visual search tasks induced a more widespread RH activation pattern in frontal, superior temporal, and occipital areas. Laterality of language increased between the ages of 8-20 in frontal (r = 0.392, P = 0.049) and temporal (r = 0.387, P = 0.051) areas. The asymmetry of visual search functions increased in frontal (r = -0.525, P = 0.009) and parietal (r = -0.439, P = 0.027) regions. A positive correlation was found between Verbal-IQ and the LI during a language task (r = 0.585, P = 0.028), while visuospatial skills correlated with LIs of visual search (r = -0.621, P = 0.018). To summarize, cognitive development is accompanied by changes in the functional representation of neuronal circuitries, with a strengthening of lateralization not only for LH but also for RH functions. Our data show that age and performance, independently, account for the increases of laterality with age.

Visual adaptation to convexity in macaque area V4

Aftereffects are perceptual illusions caused by visual adaptation to one or more stimulus attribute, such as orientation, motion, or shape. Neurophysiological studies seeking to understand the basis of visual adaptation have observed firing rate reduction and changes in tuning of stimulus-selective neurons following periods of prolonged visual stimulation. In the domain of shape, recent psychophysical work has shown that adaptation to a convex pattern induces a subsequently seen rectangle to appear slightly concave. In the present study, we investigate the possible contribution of V4 neurons of rhesus monkeys, which are thought to be involved in the coding of convexity, to shape-specific adaptation. Visually responsive neurons were monitored during the brief presentation of simple shapes varying in their convexity level. Each test presentation was preceded by either a blank period or several seconds of adaptation to a convex or concave stimulus, presented in two different sizes. Adaptation consistently shifted the tuning of neurons away from the convex or concave adapter, including shifting response to the neutral rectangle in the direction of the opposite convexity. This repulsive shift resembled the known perceptual distortion associated with adaptation to such stimuli. In addition, adaptation caused a nonspecific response decrease, as well as a specific decrease for repeated stimuli. The latter effects were observed whether or not the adapting and test stimuli matched closely in their size. Taken together, these results provide evidence for shape-specific adaptation of neurons in area V4, which may contribute to the perception of the convexity aftereffect.

Combined functional and causal connectivity analyses of language networks in children: a feasibility study

Instead of assessing activation in distinct brain regions, approaches to investigating the networks underlying distinct brain functions have come into the focus of neuroscience research. Here, we provide a completely data-driven framework for assessing functional and causal connectivity in functional magnetic resonance imaging (fMRI) data, employing Granger's causality. We investigate the networks underlying story processing in 17 healthy children (8f, 9m, 10.4+/-2.8 years, 6.5-15.4 years). Extensive functional connectivity exists between brain regions, including some not detected in standard random effects analyses. Causal connectivity analyses demonstrate a clear dominance of left-sided language regions for both forward and backward interactions with other network nodes. We believe our approach to be useful in helping to assess language networks in the normal or pathological setting; it may also aid in providing better starting estimates for the more hypothesis-driven approaches like structural equation or dynamic causal modeling.

Increases in language lateralization in normal children as observed using magnetoencephalography

Previous functional magnetic resonance imaging (fMRI) studies investigating hemispheric dominance for language have shown that hemispheric specialization increases with age. We employed magnetoencephalography (MEG) to investigate these effects as a function of normal development. In sum, 22 healthy children aged 7-16 years were investigated using two language tasks: a verb-generation (VG) task and a vowel-identification (VI) task. Significant hemispheric differences were found for both tasks in cerebral language areas using oscillatory MEG spectral analyses, confirming the MEG's ability to detect hemispheric specialization for language in children. Additionally, a significant increase of this lateralization as a function of age was observed for both tasks. As performance in the VI task showed no correlation with age, this increase seems to be unrelated to performance. These results confirm an increase in hemispheric specialization as a function of normal brain maturation.

Reorganization of the cerebro-cerebellar network of language production in patients with congenital left-hemispheric brain lesions

Patients with congenital lesions of the left cerebral hemisphere may reorganize language functions into the right hemisphere. In these patients, language production is represented homotopically to the left-hemispheric language areas. We studied cerebellar activation in five patients with congenital lesions of the left cerebral hemisphere to assess if the language network is reorganized completely in these patients, i.e. including also cerebellar language functions. As compared to a group of controls matched for age, sex, and verbal IQ, the patients recruited an area not in the right but in the left cerebellar hemisphere. The extent of laterality of the cerebellar activation correlated significantly with the laterality of the frontal activation. We suggest that the developing brain reacts to early focal lesions in the left hemisphere with a mirror-image organization of the entire cerebro-cerebellar network engaged in speech production.

Infant brain probability templates for MRI segmentation and normalization

Spatial normalization and segmentation of infant brain MRI data based on adult or pediatric reference data may not be appropriate due to the developmental differences between the infant input data and the reference data. In this study we have constructed infant templates and a priori brain tissue probability maps based on the MR brain image data from 76 infants ranging in age from 9 to 15 months. We employed two processing strategies to construct the infant template and a priori data: one processed with and one without using a priori data in the segmentation step. Using the templates we constructed, comparisons between the adult templates and the new infant templates are presented. Tissue distribution differences are apparent between the infant and adult template, particularly in the gray matter (GM) maps. The infant a priori information classifies brain tissue as GM with higher probability than adult data, at the cost of white matter (WM), which presents with lower probability when compared to adult data. The differences are more pronounced in the frontal regions and in the cingulate gyrus. Similar differences are also observed when the infant data is compared to a pediatric (age 5 to 18) template. The two-pass segmentation approach taken here for infant T1W brain images has provided high quality tissue probability maps for GM, WM, and CSF, in infant brain images. These templates may be used as prior probability distributions for segmentation and normalization; a key to improving the accuracy of these procedures in special populations.

Prefrontal-thalamic-cerebellar gray matter networks and executive functioning in schizophrenia

OBJECTIVE

Poor executive functioning is a core deficit in schizophrenia and has been linked to frontal lobe alterations. We aimed to identify (1) prefrontal cerebral areas in which decreased volume is linked to executive dysfunction in schizophrenia; and (2) areas throughout the brain that are volumetrically related to the prefrontal area identified in the first analysis, thus detecting more extended volumetric networks associated with executive functioning.

METHOD

Fifty-three outpatients with schizophrenia and 62 healthy controls, matched for age, gender and handedness, were recruited. High-resolution images were acquired on a 1.5 tesla scanner and regional gray and white matter volumes were analyzed by voxel-based morphometry within SPM5 (statistical parametric mapping, University College London, UK). Executive functioning was assessed using the Wisconsin Card Sorting Test (WCST).

RESULTS

Twenty-one patients with poor executive functioning showed reduced dorsolateral prefrontal and anterior cingulate gray matter volume as compared to 30 patients with high WCST performance, with a maximum effect in the left dorsolateral prefrontal cortex. Left dorsolateral prefrontal gray matter volume predicted WCST performance after controlling for possible confounding effects of global cognitive functioning, verbal attention span, negative symptoms, illness duration and education. In this area, both patient groups had less gray matter than healthy controls. Left dorsolateral prefrontal gray matter volume was positively related to dorsal prefrontal, anterior cingulate and parietal gray matter volume; and negatively related to thalamic, cerebellar, pontine and right parahippocampal gray matter volume.

CONCLUSIONS

Volumetric alterations in prefrontal-thalamic-cerebellar gray matter networks may lead to executive dysfunction in schizophrenia.

LI-tool: A new toolbox to assess lateralization in functional MR-data

A lateralization index (LI) is commonly computed to describe the asymmetry of activation as detectable by various functional imaging techniques, particularly functional magnetic resonance imaging (fMRI). In this article, we examine and compare different approaches that have been used in the past. For illustration purposes, 100 synthetic datasets and real fMRI-data from 12 subjects were evaluated. As shown before, the calculation of a lateralization index suffers from a number of drawbacks, namely vulnerability to statistical outliers, data sparsity, thresholding effects and lack of taking into account regional variability of activation. Optional processing steps investigated here seem to increase reliability of the such-calculated indices. To allow a more standardized, reproducible and accessible evaluation of laterality effects, current and new approaches have been implemented in a versatile toolbox running within the spm2 or spm5 software environment.

Brain representation of active and passive hand movements in children

Several functional neuroimaging studies have been performed exploring the sensorimotor function in children with neurologic disorders. However, little is known about normal activation patterns of the sensorimotor system at a young age. We explored brain representation of active and passive hand movements in school-age children and young adults. Nine healthy children (7-15 y) and six adults were studied. Functional magnetic resonance imaging (fMRI) data were acquired on a 1.5-T scanner in block designs. Active movement consisted of repetitive opening and closing of the hand; passive movement consisted of the same movement performed by the examiner. Both hands were assessed separately. The pattern of brain activation (contralateral primary sensorimotor cortex (SMC), ipsilateral cerebellum, supplementary motor area (SMA), and lateral premotor cortex (PMC) was generally more widespread in the adult group, suggesting a developmental course in the organization of both motor and sensory cortex. Surprisingly, no difference was generally detected when contrasting active versus passive tasks. Our results suggest that active and passive hand movements can be used for the exploration of the sensorimotor system in children. Passive and active tasks confirmed to be tightly coupled, thus supporting the idea of the former as a helpful performance-independent paradigm in the study of brain reorganization and presurgical assessment.

[Comparative in vitro analysis of vacuum plasma-sprayed titanium implants--evaluation of OPG, Osteokalzin and AP expression]

INTRODUCTION

The purpose of this study was to evaluate the influence of different surface topographies on the expression of bone cell-associated proteins, such as osteoprotegerin (OPG), osteocalcin and alkaline phosphatase (AP), and the production of the extracellular matrix (ECM) in vitro. Another aspect was the question as to whether a hydroxyapatite (HA) coating offers additional advantages. Vacuum plasma-sprayed (VPS) pure titanium was used to generate different surface topographies.

MATERIALS AND METHODS

The in vitro response of human bone marrow cells to VPS implants (porosity ranging from 25 to 50%, pore size ranging from 50 to 200 microm and roughness ranging from 0.191 to 0.547 mm) and cancellous structured titanium (cs-Ti) as a reference material (55% porosity, pore size of 500 microm, roughness 0.836 mm) were compared. The expression of bone cell-associated proteins, such as OPG, osteocalcin and alkaline phosphatase (AP), was evaluated. Scanning electron microscopy (SEM) was used to judge the production of ECM.

RESULTS

All implant materials induced the release of OPG, osteocalcin and AP. Significant differences were evident between the cs-Ti and the different VPS-Ti surface structures. There was no difference in the response between the VPS-Ti surfaces. SEM showed a dense and increased production of ECM on the VPS-Ti surfaces. An additional HA coating caused a faster production of ECM and higher levels of OPG.

CONCLUSIONS

The in vitro data presented here demonstrate the superiority of VPS-Ti surfaces over cs-Ti, which is already in clinical use. Differences between the VPS-Ti surfaces were not evident. Presumably, VPS-Ti surfaces offer good prerequisites for a successful integration of the implant in the surrounding tissue. An additional HA coating could influence these events positively.

Diffusion-weighted magnetic resonance imaging of treatment-associated changes in recurrent and residual medulloblastoma: preliminary observations in three children

PURPOSE

To emphasize a possible role of magnetic resonance (MR) diffusion-weighted imaging (DWI) for lesion conspicuity and detection of treatment effects in children with medulloblastoma.

MATERIAL AND METHODS

Three children with medulloblastoma (two residual and one recurrent) were examined repetitively by MR diffusion-weighted imaging. Regional assessment of the apparent diffusion coefficient (ADC) was done for tumorous lesions and periventricular white matter appearing normal on standard MR images.

RESULTS

All lesions were clearly visible on DWI. In the case of recurrent tumor, on one scan, DWI showed lesions that were not seen on contrast-enhanced MRI. Increase (41%) of ADC was seen in one lesion, which subsequently responded completely to treatment over 27 months' follow-up. Intermediate increases (23-26%) of ADC were found with partial therapy response in three lesions. In contrast, a decrease (-11%) of ADC in two lesions was seen with tumor progression.

CONCLUSION

These observations may suggest a role for DWI in early detection of metastatic disease and treatment monitoring of medulloblastoma, warranting a formal study.

A combined bootstrap/histogram analysis approach for computing a lateralization index from neuroimaging data

Cerebral hemispheric specialization has traditionally been described using a lateralization index (LI). Such an index, however, shows a very severe threshold dependency and is prone to be influenced by statistical outliers. Reliability of this index thus has been inherently weak, and the assessment of this reliability is as yet not possible as methods to detect such outliers are not available. Here, we propose a new approach to calculating a lateralization index on functional magnetic resonance imaging data by combining a bootstrap procedure with a histogram analysis approach. Synthetic and real functional magnetic resonance imaging data was used to assess performance of our approach. Using a bootstrap algorithm, 10,000 indices are iteratively calculated at different thresholds, yielding a robust mean, maximum and minimum LI and thus allowing to attach a confidence interval to a given index. Taking thresholds into account, an overall weighted bootstrapped lateralization index is calculated. Additional histogram analyses of these bootstrapped values allow to judge reliability and the influence of outliers within the data. We conclude that the proposed methods yield a robust and specific lateralization index, sensitively detect outliers and allow to assess the underlying data quality.

Global and local development of gray and white matter volume in normal children and adolescents

Over the last decade, non-invasive, high-resolution magnetic resonance imaging has allowed investigating normal brain development. However, much is still not known in this context, especially with regard to regional differences in brain morphology between genders. We conducted a large-scale study utilizing fully automated analysis-approaches, using high-resolution MR-imaging data from 200 normal children and aimed at providing reference data for future neuroimaging studies. Global and local aspects of normal development of gray and white matter volume were investigated as a function of age and gender while covarying for known nuisance variables. Global developmental patterns were apparent in both gray and white matter, with gray matter decreasing and white matter increasing significantly with age. Gray matter loss was most pronounced in the parietal lobes and least in the cingulate and in posterior temporal regions. White matter volume gains with age were almost uniform, with an accentuation of the pyramidal tract. Gender influences were detectable for both gray and white matter. Voxel-based analyses confirmed significant differences in brain morphology between genders, like a larger amygdala in boys or a larger caudate in girls. We could demonstrate profound influences of both age and gender on normal brain morphology, confirming and extending earlier studies. The knowledge of such influence allows for the consideration of age- and gender-effects in future pediatric neuroimaging studies and advances our understanding of normal and abnormal brain development.

Language lateralization in magnetoencephalography: two tasks to investigate hemispheric dominance

Hemispheric specialization for language has been the focus of many studies, mainly using functional magnetic resonance imaging. Here, we used magnetoencephalography to investigate hemispheric dominance and time-dependent aspects of cortical language processing. We implemented a verb generation task and a newly designed vowel identification task. Eleven healthy adults were investigated. By using oscillatory magnetoencephalography spectral analysis, significant hemispheric differences were found for both tasks in cerebral language areas. Robust left-lateralization in frontal brain regions was observed with the verb generation task, confirming previous functional magnetic resonance imaging and magnetoencephalography studies. Our new vowel identification task yields significant left-lateralization in posterior language regions, making this silent and child-friendly task a valuable alternative for non-invasive language assessment in difficult populations.

The diallelic locus encoding the minor histocompatibility antigen HA-1 is evolutionarily conserved

The polymorphic minor histocompatibility antigen HA-1 induces powerful T-cell alloreactivities with important consequences for graft-vs-tumor activity and development of graft-vs-host disease in patients after human leukocyte antigen-matched stem-cell transplantation (SCT). In view of possible translational animal studies, we analyzed the evolutionary conservation of the diallelic HA-1 locus in four mammalian species. Our results show that rodents do not encode the HA-1(H) allele, neither show polymorphism in this position on the HA-1 gene. Contrariwise, the HA-1(H) allele is present in non-human primate species and dogs. Interestingly, both the HA-1(H) T-cell epitope and its non-immunogenic counterpart HA-1(R) are present in the latter species. Thus, the HA-1 allelic polymorphism is conserved in evolution in primates and dogs.

Lesion-induced right-hemispheric language and organization of nonverbal functions

Early left-hemispheric brain lesions may lead to a reorganization of language into the right hemisphere. Language functions are consecutively spared, but visuospatial functions show slight deficits. Cortical 'crowding' of the right hemisphere has been suggested as an explanation for this effect, but no direct evidence has as yet been put forward. We examined six patients with early left-hemispheric brain lesions and subsequent right-hemispheric language organization with functional magnetic resonance imaging and compared their activation patterns in a verbal and two nonverbal tasks with the patterns of six controls. In the patient group, nonverbal functions were reorganized neither interhemispherically nor intrahemispherically. Instead, verbal and nonverbal functions were mediated by a common right-hemispheric network. This argues in favour of the 'crowding hypothesis'.

An fMRI task battery for assessing hemispheric language dominance in children

Hemispheric dominance for language is an important issue in functional neuroimaging, particularly driven by efforts to overcome the need for the invasive Wada test, which is all the more pressing in children. Here, we aimed at developing new paradigms for functional magnetic resonance imaging (fMRI) for assessment of language dominance that can be used in younger children and allow for performance monitoring. Two new tasks (letter and animal task) were developed and compared to two reference tasks (synonyms and verb generation task) from the literature. Overall, 23 healthy children participated (13 boys, 10 girls, 10.2 +/- 2.5 years, range 6.1-15.3 years). Analysis was done using statistical nonparametrical mapping (SnPM2) on SPM2. Both reference tasks show activation in a number of left-frontal brain regions. The letter task induced a very localized activation in the left hemisphere's Broca's region, while not activating other frontal brain regions. Lateralization (as assessed in different anatomically and functionally defined regions) was consistent and strong. The animal task failed to activate frontal brain regions and was not suitable for assessing language dominance in children in this form. We conclude that while both reference tasks are useful for determining language dominance, they coactivate a number of task-related frontal areas not directly involved in language processing. Additionally, one task is not applicable in young children while the other does not allow performance monitoring. The letter task allows to selectively activate language areas in the dominant hemisphere and is applicable even in the very lowest age group amenable to fMRI investigations while still allowing performance monitoring. It may thus be a useful tool in assessing normal and pathological language organization.