Fiber tracking using magnetic resonance diffusion tensor imaging and its applications to human brain development

Genetic and Environmental Contributions to Subcortical Gray Matter Microstructure and Volume in the Developing Brain

Using baseline (ages 9-10) and two-year follow-up (ages 11-12) data from monozygotic and dizygotic twins enrolled in the longitudinal Adolescent Brain Cognitive Development^SM Study, we investigated the genetic and environmental contributions to microstructure and volume of nine subcortical gray matter regions. Microstructure was assessed using diffusion MRI data analyzed using restriction spectrum imaging (RSI) and diffusion tensor imaging (DTI) models. The highest heritability estimates (estimate [95% confidence interval]) for microstructure were found using the RSI model in the pallidum (baseline: 0.859 [0.818, 0.889], follow-up: 0.835 [0.787, 0.871]), putamen (baseline: 0.859 [0.819, 0.889], follow-up: 0.874 [0.838, 0.902]), and thalamus (baseline: 0.855 [0.814, 0.887], follow-up: 0.819 [0.769, 0.857]). For volumes the corresponding regions were the caudate (baseline: 0.831 [0.688, 0.992], follow-up: 0.848 [0.701, 1.011]) and putamen (baseline: 0.906 [0.875, 0.914], follow-up: 0.906 [0.885, 0.923]). The subcortical regions displayed high genetic stability (rA = 0.743-1.000) across time and exhibited unique environmental correlations (rE = 0.194-0.610). Individual differences in both gray matter microstructure and volumes can be largely explained by additive genetic effects in this sample.

Comparative study of preoperative functional imaging combined with tractography for prediction of iatrogenic motor deficits

OBJECTIVE

Robust preoperative imaging can improve the extent of resection in patients with brain tumors while minimizing postoperative neurological morbidity. Both structural and functional imaging techniques can provide helpful preoperative information. A recent study found that transcranial magnetic stimulation (TMS) tractography has significant predictive value for permanent deficits. The present study directly compares the predictive value of TMS tractography and task-based functional MRI (fMRI) tractography in the same cohort of glioma patients.

METHODS

Clinical outcome data were collected from charts of patients with motor eloquent glioma and preoperative fMRI and TMS studies. The primary outcome was a new or worsened motor deficit present at the 3-month postoperative follow-up, which was termed a "permanent deficit." Postoperative MR images were overlaid onto preoperative plans to determine which imaging features were resected. Multiple fractional anisotropic thresholds (FATs) were screened for both TMS and fMRI tractography. The predictive value of the various thresholds was modeled using receiver operating characteristic curve analysis.

RESULTS

Forty patients were included in this study. Six patients (15%) sustained permanent postoperative motor deficits. A significantly greater predictive value was found for TMS tractography than for fMRI tractography regardless of the FAT. Despite 35% of patients showing clinically relevant neuroplasticity captured by TMS, only 2.5% of patients showed a blood oxygen level–dependent signal displaced from the precentral gyrus. Comparing the best-performing FAT for both modalities, TMS seeded tractography showed superior predictive value across all metrics: sensitivity, specificity, positive predictive value, and negative predictive value.

CONCLUSIONS

The results from this study indicate that the prediction of permanent deficits with TMS tractography is superior to that with fMRI tractography, possibly because TMS tractography captures clinically relevant neuroplasticity. However, future large-scale prospective studies are needed to fully illuminate the proper role of each modality in comprehensive presurgical workups for patients with motor-eloquent tumors.

Imaging methods used in the assessment of environmental disease networks: a brief review for clinicians

Background

Across the globe, diseases secondary to environmental exposures have been described, and it was also found that existing diseases have been modified by exposure to environmental chemicals or an environmental factor that has been found in their pathogenesis. The Institute of Medicine has shared a permanent concern related to the nations environmental health capacity since 1988.

Main body

Contemporary imaging methods in the last 15 years started reporting alterations in different human systems such as the central nervous system, cardiovascular system and pulmonary system among others; evidence suggests the existence of a human environmental disease network. The primary anatomic regions, affected by environmental diseases, recently assessed with imaging methods include Brain (lead exposure, cerebral stroke, pesticide neurotoxicity), uses MRI, DTI, carotid ultrasonography and MRS; Lungs (smoke inhalation, organophosphates poisoning) are mainly assessed with radiography; Gastrointestinal system (chronic inflammatory bowel disease), recent studies have reported the use of aortic ultrasound; Heart (myocardial infarction), its link to environmental diseased has been proved with carotid ultrasound; and Arteries (artery hypertension), the impairment of aortic mechanical properties has been revealed with the use of aortic and brachial ultrasound.

Conclusions

Environmental epidemiology has revealed that several organs and systems in the human body are targets of air pollutants. Current imaging methods that can assess the deleterious effects of pollutants includes a whole spectrum: radiography, US, CT and MRI. Future studies will help to reveal additional links among environmental disease networks.

The Effects of Air Pollution on the Brain: a Review of Studies Interfacing Environmental Epidemiology and Neuroimaging

Purpose of Review

An emerging body of evidence has raised concern regarding the potentially harmful effects of inhaled pollutants on the central nervous system during the last decade. In the general population, traffic-related air pollution (TRAP) exposure has been associated with adverse effects on cognitive, behavior, and psychomotor development in children, and with cognitive decline and higher risk of dementia in the elderly. Recently, studies have interfaced environmental epidemiology with magnetic resonance imaging to investigate in vivo the effects of TRAP on the human brain. The aim of this systematic review was to describe and synthesize the findings from these studies. The bibliographic search was carried out in PubMed with ad hoc keywords.

Recent Findings

The selected studies revealed that cerebral white matter, cortical gray matter, and basal ganglia might be the targets of TRAP. The detected brain damages could be involved in cognition changes.

Summary

The effect of TRAP on cognition appears to be biologically plausible. Interfacing environmental epidemiology and neuroimaging is an emerging field with room for improvement. Future studies, together with inputs from experimental findings, should provide more relevant and detailed knowledge about the nature of the relationship between TRAP exposure and cognitive, behavior, and psychomotor disorders observed in the general population.

Brain Connectivity Exposed by Anisotropic X-ray Dark-field Tomography

To understand the interaction of different parts of the human brain it is essential to know how they are connected. Such connections are predominantly related to the brain's white matter, which forms the neuronal pathways, the axons. These axons, also referred to as nerve fibers, have a size on the micrometer scale and are therefore too small to be imaged by standard X-ray systems. In this paper, we use a grating interferometer and a method based on Anisotropic X-ray Dark-field Tomography (AXDT) with the goal to generate a three-dimensional tomographic reconstruction of these functional structures. A first preclinical survey shows that we successfully reconstruct the orientations of the brain fibers connectivity with our approach.

Structural and functional changes in the central nervous system in the course of anorexia nervosa

New achievements within structural and functional imaging of central nervous system offer a basis for better understanding of the mechanisms underlying many mental disorders. In everyday clinical practice, we encounter many difficulties in the therapy of eating disorders. They are caused by a complex psychopathological picture, varied grounds of the problems experienced by patients, often poor motivation for active participation in the treatment process, difficulties in communication between patients and therapeutic staff, and various biological conditions of eating disorders. In this paper, the latest reports on new concepts and methods of diagnosis and treatment of anorexia nervosa have been analyzed. The selection of the analyzed publications was based on the criteria taking into account the time of publication, the size of research cohorts, as well as the experience of research teams in the field of nutritional disorders, confirmed by the number of works and their citations. The work aims to spread current information on anorexia nervosa neurobiology that would allow for determining the brain regions involved in the regulation of food intake, and consequently that may be a potential place where neurobiochemical processes responsible for eating disorders occur. In addition, using modern methods of structural imaging, the authors want to show some of the morphometric variations, particularly within white matter, occurring in patients suffering from anorexia nervosa, as well as those evaluated with magnetoencephalography of processes associated with the neuronal processing of information related to food intake. For example as regards anorexia nervosa, it was possible to localize the areas associated with eating disorders and broaden our knowledge about the changes in these areas that cause and accompany the illness. The described in this paper research studies using diffusion MRI fiber tractography showed the presence of changes in the white matter pathways of the brain, especially in the corpus callosum, which indicate a reduced content of myelin. These changes probably reflect malnutrition, and directly represent the effect of lipid deficiency. This leads to a weakening of the structure, and even cell death. In addition, there are more and more reports that show the normal volume of brain cells in patients with long-term remission of anorexia. It was also shown that in patients in remission stage there are functional changes within the amygdala in response to a task not related symptomatologically with anorexia nervosa. The appearing in the scientific literature data stating that in patients with anorexia nervosa there is a reduced density of GFAP + cells of the hippocampus and increased expression of vimentin and nestin, is also worth noting.

Analysis of correlation between white matter changes and functional responses in thalamic stroke: a DTI & EEG study

Diffusion tensor imaging (DTI) allows in vivo structural brain mapping and detection of microstructural disruption of white matter (WM). One of the commonly used parameters for grading the anisotropic diffusivity in WM is fractional anisotropy (FA). FA value helps to quantify the directionality of the local tract bundle. Therefore, FA images are being used in voxelwise statistical analyses (VSA). The present study used Tract-Based Spatial Statistics (TBSS) of FA images across subjects, and computes the mean skeleton map to detect voxelwise knowledge of the tracts yielding to groupwise comparison. The skeleton image illustrates WM structure and shows any changes caused by brain damage. The microstructure of WM in thalamic stroke is investigated, and the VSA results of healthy control and thalamic stroke patients are reported. It has been shown that several skeleton regions were affected subject to the presence of thalamic stroke (FWE, p < 0.05). Furthermore the correlation of quantitative EEG (qEEG) scores and neurophysiological tests with the FA skeleton for the entire test group is also investigated. We compared measurements that are related to the same fibers across subjects, and discussed implications for VSA of WM in thalamic stroke cases, for the relationship between behavioral tests and FA skeletons, and for the correlation between the FA maps and qEEG scores.Results obtained through the regression analyses did not exceed the corrected statistical threshold values for multiple comparisons (uncorrected, p < 0.05). However, in the regression analysis of FA values and the theta band activity of EEG, cingulum bundle and corpus callosum were found to be related. These areas are parts of the Default Mode Network (DMN) where DMN is known to be involved in resting state EEG theta activity. The relation between the EEG alpha band power values and FA values of the skeleton was found to support the cortico-thalamocortical cycles for both subject groups. Further, the neurophysiological tests including Benton Face Recognition (BFR), Digit Span test (DST), Warrington Topographic Memory test (WTMT), California Verbal Learning test (CVLT) has been regressed with the FA skeleton maps for both subject groups. Our results corresponding to DST task were found to be similar with previously reported findings for working memory and episodic memory tasks. For the WTMT, FA values of the cingulum (right) that plays a role in memory process was found to be related with the behavioral responses. Splenium of corpus callosum was found to be correlated for both subject groups for the BFR.

Functional MRI vs. navigated TMS to optimize M1 seed volume delineation for DTI tractography. A prospective study in patients with brain tumours adjacent to the corticospinal tract

BACKGROUND

DTI-based tractography is an increasingly important tool for planning brain surgery in patients suffering from brain tumours. However, there is an ongoing debate which tracking approaches yield the most valid results. Especially the use of functional localizer data such as navigated transcranial magnetic stimulation (nTMS) or functional magnetic resonance imaging (fMRI) seem to improve fibre tracking data in conditions where anatomical landmarks are less informative due to tumour-induced distortions of the gyral anatomy. We here compared which of the two localizer techniques yields more plausible results with respect to mapping different functional portions of the corticospinal tract (CST) in brain tumour patients.

METHODS

The CSTs of 18 patients with intracranial tumours in the vicinity of the primary motor area (M1) were investigated by means of deterministic DTI. The core zone of the tumour-adjacent hand, foot and/or tongue M1 representation served as cortical regions of interest (ROIs). M1 core zones were defined by both the nTMS hot-spots and the fMRI local activation maxima. In addition, for all patients, a subcortical ROI at the level of the inferior anterior pons was implemented into the tracking algorithm in order to improve the anatomical specificity of CST reconstructions. As intra-individual control, we additionally tracked the CST of the hand motor region of the unaffected, i.e., non-lesional hemisphere, again comparing fMRI and nTMS M1 seeds. The plausibility of the fMRI-ROI- vs. nTMS-ROI-based fibre trajectories was assessed by a-priori defined anatomical criteria. Moreover, the anatomical relationship of different fibre courses was compared regarding their distribution in the anterior-posterior direction as well as their location within the posterior limb of the internal capsule (PLIC).

RESULTS

Overall, higher plausibility rates were observed for the use of nTMS- as compared to fMRI-defined cortical ROIs (p < 0.05) in tumour vicinity. On the non-lesional hemisphere, however, equally good plausibility rates (100%) were observed for both localizer techniques. fMRI-originated fibres generally followed a more posterior course relative to the nTMS-based tracts (p < 0.01) in both the lesional and non-lesional hemisphere.

CONCLUSION

NTMS achieved better tracking results than fMRI in conditions when the cortical tract origin (M1) was located in close vicinity to a brain tumour, probably influencing neurovascular coupling. Hence, especially in situations with altered BOLD signal physiology, nTMS seems to be the method of choice in order to identify seed regions for CST mapping in patients.

Research Review: Environmental exposures, neurodevelopment, and child mental health - new paradigms for the study of brain and behavioral effects

BACKGROUND

Environmental exposures play a critical role in the genesis of some child mental health problems.

METHODS

We open with a discussion of children's vulnerability to neurotoxic substances, changes in the distribution of toxic exposures, and cooccurrence of social and physical exposures. We address trends in prevalence of mental health disorders, and approaches to the definition of disorders that are sensitive to the subtle effects of toxic exposures. We suggest broadening outcomes to include dimensional measures of autism spectrum disorders, attention-deficit hyperactivity disorder, and child learning capacity, as well as direct assessment of brain function.

FINDINGS

We consider the impact of two important exposures on children's mental health: lead and pesticides. We argue that longitudinal research designs may capture the cascading effects of exposures across biological systems and the full-range of neuropsychological endpoints. Neuroimaging is a valuable tool for observing brain maturation under varying environmental conditions. A dimensional approach to measurement may be sensitive to subtle subclinical toxic effects, permitting the development of exposure-related profiles and testing of complex functional relationships between brain and behavior. Questions about the neurotoxic effects of chemicals become more pressing when viewed through the lens of environmental justice.

CONCLUSIONS

Reduction in the burden of child mental health disorders will require longitudinal study of neurotoxic exposures, incorporating dimensional approaches to outcome assessment, and measures of brain function. Research that seeks to identify links between toxic exposures and mental health outcomes has enormous public health and societal value.

Improved nTMS- and DTI-derived CST tractography through anatomical ROI seeding on anterior pontine level compared to internal capsule

Imaging of the course of the corticospinal tract (CST) by diffusion tensor imaging (DTI) is useful for function-preserving tumour surgery. The integration of functional localizer data into tracking algorithms offers to establish a direct structure–function relationship in DTI data. However, alterations of MRI signals in and adjacent to brain tumours often lead to spurious tracking results. We here compared the impact of subcortical seed regions placed at different positions and the influences of the somatotopic location of the cortical seed and clinical co-factors on fibre tracking plausibility in brain tumour patients.

The CST of 32 patients with intracranial tumours was investigated by means of deterministic DTI and neuronavigated transcranial magnetic stimulation (nTMS). The cortical seeds were defined by the nTMS hot spots of the primary motor area (M1) of the hand, the foot and the tongue representation. The CST originating from the contralesional M1 hand area was mapped as intra-individual reference. As subcortical region of interests (ROI), we used the posterior limb of the internal capsule (PLIC) and/or the anterior inferior pontine region (aiP). The plausibility of the fibre trajectories was assessed by a-priori defined anatomical criteria. The following potential co-factors were analysed: Karnofsky Performance Scale (KPS), resting motor threshold (RMT), T1-CE tumour volume, T2 oedema volume, presence of oedema within the PLIC, the fractional anisotropy threshold (FAT) to elicit a minimum amount of fibres and the minimal fibre length.

The results showed a higher proportion of plausible fibre tracts for the aiP-ROI compared to the PLIC-ROI. Low FAT values and the presence of peritumoural oedema within the PLIC led to less plausible fibre tracking results. Most plausible results were obtained when the FAT ranged above a cut-off of 0.105. In addition, there was a strong effect of somatotopic location of the seed ROI; best plausibility was obtained for the contralateral hand CST (100%), followed by the ipsilesional hand CST (>95%), the ipsilesional foot (>85%) and tongue (>75%) CST. In summary, we found that the aiP-ROI yielded better tracking results compared to the IC-ROI when using deterministic CST tractography in brain tumour patients, especially when the M1 hand area was tracked. In case of FAT values lower than 0.10, the result of the respective CST tractography should be interpreted with caution with respect to spurious tracking results. Moreover, the presence of oedema within the internal capsule should be considered a negative predictor for plausible CST tracking.

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Somatotopic CST tractography was done in 32 patients with eloquent brain tumours.

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Seeding ROIs were defined by navigated TMS of the M1 hot spot (hand, foot, tongue).

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Using the anterior pons as a second ROI yielded more plausible tracts than the PLIC.

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Low FAT and oedema of the internal capsule were negative predictors.

Neuroimaging is a novel tool to understand the impact of environmental chemicals on neurodevelopment

PURPOSE OF REVIEW

The prevalence of childhood neurodevelopmental disorders has been increasing over the last several decades. Prenatal and early childhood exposure to environmental toxicants is increasingly recognized as contributing to the growing rate of neurodevelopmental disorders. Very little information is known about the mechanistic processes by which environmental chemicals alter brain development. We review the recent advances in brain imaging modalities and discuss their application in epidemiologic studies of prenatal and early childhood exposure to environmental toxicants.

RECENT FINDINGS

Neuroimaging techniques (volumetric and functional MRI, diffusor tensor imaging, and magnetic resonance spectroscopy) have opened unprecedented access to study the developing human brain. These techniques are noninvasive and free of ionization radiation making them suitable for research applications in children. Using these techniques, we now understand much about structural and functional patterns in the typically developing brain. This knowledge allows us to investigate how prenatal exposure to environmental toxicants may alter the typical developmental trajectory.

SUMMARY

MRI is a powerful tool that allows in-vivo visualization of brain structure and function. Used in epidemiologic studies of environmental exposure, it offers the promise to causally link exposure with behavioral and cognitive manifestations and ultimately to inform programs to reduce exposure and mitigate adverse effects of exposure.

[Structural connectivity and diffusion tensor imaging in autism spectrum disorders]

Over the past years, diffusion tensor imaging (DTI) has become an important brain-imaging technique in neuropsychiatric research. DTI allows noninvasive visualization of white matter tracts. In addition, with DTI it is possible to quantify the structural integrity of the investigated fiber tracts. In child and adolescent psychiatry, DTI has become an increasingly important research tool, especially for conditions like autism spectrum disorders (ASD). Yet, correct interpretation of DTI findings can be challenging, especially for clinicians. Thus, the present review article explains the basic principles of this frequently used imaging technique as well as essential indices, like fractional anisotropy, radial, mean, and axial diffusivity and its two main applications, fibertracking and whole brain analysis. The strengths and weaknesses as well as future perspectives are discussed in light of DTI studies in children and adolescents with ASD.

Early registration of diffusion tensor images for group tractography of dystonia patients

PURPOSE

To make a group comparison of diffusion tensor imaging (DTI) results of dystonia patients and controls to reveal occult pathology. We propose using an early registration method that produces sharper group images and enables us to do group tractography.

MATERIALS AND METHODS

Twelve dystonia patients manifesting the disease, seven nonmanifesting dystonia mutation carriers (DYT1 and DYT6 gene mutations), and eight age-matched normal control subjects were imaged for a previous study. Early and late registration methods for DTI were compared. An early registration technique for a super set was proposed, in which the diffusion-weighted images were registered to a template, gradient vectors were reoriented for each subject, and they were combined into a super set before tensor calculation. The super set included images from all subjects and was useful for group comparisons. We used results obtained from the early registration of a super set for group analysis of tracts using the deterministic fiber-tracking technique.

RESULTS

In dystonia mutation carriers, we detected fewer fibers in the cerebello-thalamo-cortical pathways. This result agrees well with the findings of a previous study that utilized a probabilistic tractography method and demonstrated that gene carriers have less fiber tracts in the disease-involved pathway.

CONCLUSION

This analysis visualized group level white matter fractional anisotropy and tract differences between dystonia patients and controls, and can be useful in understanding the pathophysiology of other nonfocal white matter diseases.

A new approach for corticospinal tract reconstruction based on navigated transcranial stimulation and standardized fractional anisotropy values

PURPOSE

To establish a novel approach for fiber tracking based on navigated transcranial magnetic stimulation (nTMS) mapping of the primary motor cortex and to propose a new algorithm for determination of an individualized fractional anisotropy value for reliable and objective fiber tracking.

METHODS

50 patients (22 females, 28 males, median age 58 years (20-80)) with brain tumors compromising the primary motor cortex and the corticospinal tract underwent preoperative MR imaging and nTMS mapping. Stimulation spots evoking muscle potentials (MEP) closest to the tumor were imported into the fiber tracking software and set as seed points for tractography. Next the individual FA threshold, i.e. the highest FA value leading to visualization of tracts at a predefined minimum fiber length of 110 mm, was determined. Fiber tracking was then performed at a fractional anisotropy value of 75% and 50% of the individual FA threshold. In addition, fiber tracking according to the conventional knowledge-based approach was performed. Results of tractography of either method were presented to the surgeon for preoperative planning and integrated into the navigation system and its impact was rated using a questionnaire.

RESULTS

Mapping of the motor cortex was successful in all patients. A fractional anisotropy threshold for corticospinal tract reconstruction could be obtained in every case. TMS-based results changed or modified surgical strategy in 23 of 50 patients (46%), whereas knowledge-based results would have changed surgical strategy in 11 of 50 patients (22%). Tractography results facilitated intraoperative orientation and electrical stimulation in 28 of 50 (56%) patients. Tracking at 75% of the individual FA thresholds was considered most beneficial by the respective surgeons.

CONCLUSIONS

Fiber tracking based on nTMS by the proposed standardized algorithm represents an objective visualization method based on functional data and provides a valuable instrument for preoperative planning and intraoperative orientation and monitoring.

Mild traumatic brain injury: is diffusion imaging ready for primetime in forensic medicine?

Mild traumatic brain injury (MTBI) is difficult to accurately assess with conventional imaging because such approaches usually fail to detect any evidence of brain damage. Recent studies of MTBI patients using diffusion-weighted imaging and diffusion tensor imaging suggest that these techniques have the potential to help grade tissue damage severity, track its development, and provide prognostic markers for clinical outcome. Although these results are promising and indicate that the forensic diagnosis of MTBI might eventually benefit from the use of diffusion-weighted imaging and diffusion tensor imaging, healthy skepticism and caution should be exercised with regard to interpreting their meaning because there is no consensus about which methods of data analysis to use and very few investigations have been conducted, of which most have been small in sample size and examined patients at only one time point after injury.

Multi-tensor tractography of the motor pathway at 3T: a volunteer study

Conventional single-tensor tractography cannot depict the entire motor tract of the corticospinal tract because of fiber-crossing and other factors. Using a 3-tesla magnetic resonance (MR) unit, we compared single- and multi-tensor methods for the tract ratio of the 5 major components of the motor pathway, the lower extremity, trunk, hand, face, and tongue, in 5 healthy volunteers. Multi-tensor tractography is better than single-tensor tractography at 3T in depicting more fibers of non-trunk areas from the primary motor cortex.

Diffusion tractography: methods, validation and applications in patients with neurosurgical lesions

Diffusion tensor imaging (DTI) tractography is increasingly used in presurgical mapping in tumors located in eloquent areas since it is the only non invasive technique that permits in vivo dissection of white matter tracts. Concordance between the DTI tracts and subcortical electrical intraoperative mapping is high, and DTI tractography has proven useful to guide surgery. However, it presents limitations due to the technique and the tumor, which must be known before using the images in the operative room. This review focuses on the possibilities and limits of DTI imaging in intraoperative tumoral mapping and presents an overview of current knowledge.

Cerebellothalamocortical pathway abnormalities in torsinA DYT1 knock-in mice

The factors that determine symptom penetrance in inherited disease are poorly understood. Increasingly, magnetic resonance diffusion tensor imaging (DTI) and PET are used to separate alterations in brain structure and function that are linked to disease symptomatology from those linked to gene carrier status. One example is DYT1 dystonia, a dominantly inherited movement disorder characterized by sustained muscle contractions, postures, and/or involuntary movements. This form of dystonia is caused by a 3-bp deletion (i.e., ΔE) in the TOR1A gene that encodes torsinA. Carriers of the DYT1 dystonia mutation, even if clinically nonpenetrant, exhibit abnormalities in cerebellothalamocortical (CbTC) motor pathways. However, observations in human gene carriers may be confounded by variability in genetic background and age. To address this problem, we implemented a unique multimodal imaging strategy in a congenic line of DYT1 mutant mice that contain the ΔE mutation in the endogenous mouse torsinA allele (i.e., DYT1 knock-in). Heterozygous knock-in mice and littermate controls underwent microPET followed by ex vivo high-field DTI and tractographic analysis. Mutant mice, which do not display abnormal movements, exhibited significant CbTC tract changes as well as abnormalities in brainstem regions linking cerebellar and basal ganglia motor circuits highly similar to those identified in human nonmanifesting gene carriers. Moreover, metabolic activity in the sensorimotor cortex of these animals was closely correlated with individual measures of CbTC pathway integrity. These findings further link a selective brain circuit abnormality to gene carrier status and demonstrate that DYT1 mutant torsinA has similar effects in mice and humans.

Diffusion tensor imaging of mild traumatic brain injury

Mild traumatic brain injury (mTBI) remains a challenge to accurately assess with conventional neuroimaging. Recent research holds out the promise that diffusion tensor imaging (DTI) can be used to predict recovery in mTBI patients. Unlike computed tomography or conventional magnetic resonance imaging, DTI is sensitive to microstructural axonal injury, the neuropathology that is thought to be most responsible for the persistent cognitive and behavioral impairments that often occur after mTBI. Through the use of newer DTI analysis techniques such as automated region of interest analysis, tract-based voxel-wise analysis, and quantitative tractography, researchers have shown that frontal and temporal association white matter pathways are most frequently damaged in mTBI and that the microstructural integrity of these tracts correlates with behavioral and cognitive measures. Future longitudinal DTI studies are needed to elucidate how symptoms and the microstructural pathology evolve over time. Moving forward, large-scale investigations will ascertain whether DTI can serve as a predictive imaging biomarker for long-term neurocognitive deficits after mTBI that would be of value for triaging patients to clinical trials of experimental cognitive enhancement therapies and rehabilitation methods, as well as for monitoring their response to these interventions.

Tractography of developing white matter of the internal capsule and corpus callosum in very preterm infants

OBJECTIVES

To investigate in preterm infants associations between Diffusion Tensor Imaging (DTI) parameters of the posterior limb of the internal capsule (PLIC) and corpus callosum (CC) and age, white matter (WM) injury and clinical factors.

METHODS

In 84 preterm infants DTI was performed between 40-62 weeks postmenstrual age on 3 T MR. Fractional anisotropy (FA), apparent diffusion coefficient (ADC) values and fibre lengths through the PLIC and the genu and splenium were determined. WM injury was categorised as normal/mildly, moderately and severely abnormal. Associations between DTI parameters and age, WM injury and clinical factors were analysed.

RESULTS

A positive association existed between FA and age at imaging for fibres through the PLIC (r = 0.48 p < 0.001) and splenium (r = 0.24 p < 0.01). A negative association existed between ADC and age at imaging for fibres through the PLIC (r = -0.65 p < 0.001), splenium (r = -0.35 p < 0.001) and genu (r = -0.53 p < 0.001). No association was found between DTI parameters and gestational age, degree of WM injury or categorical clinical factors.

CONCLUSIONS

These results indicate that in our cohort of very preterm infants, at this young age, the development of the PLIC and CC is ongoing and independent of the degree of prematurity or WM injury.

Use of diffusion tensor imaging to examine subacute white matter injury progression in moderate to severe traumatic brain injury

OBJECTIVE

To demonstrate subacute progression of white matter (WM) injury (4.5mo-2.5y postinjury) in patients with traumatic brain injury using diffusion-tensor imaging.

DESIGN

Prospective, repeated-measures, within-subjects design.

SETTING

Inpatient neurorehabilitation program and teaching hospital MRI department.

PARTICIPANTS

Brain-injured adults (N=13) with a mean Glasgow Coma Scale score of 7.67+/-4.16.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Fractional anisotropy (FA) values were measured at 4.5 and 29 months postinjury in right and left frontal and temporal deep WM tracts and the anterior and posterior corpus callosum.

RESULTS

FA significantly decreased in frontal and temporal tracts: right frontal (.38+/-.06 to .30+/-.06; P<.005), left frontal (.37+/-.06 to .32+/-.06; P<.05), right temporal (.28+/-.05 to .22+/-.018; P<.005), and left temporal (.28+/-.05 to .24+/-.02; P<.05). No significant changes were in the corpus callosum.

CONCLUSIONS

Preliminary results demonstrate progression of WM damage as evidenced by interval changes in diffusion anisotropy. Future research should examine the relationship between decreased FA and long-term clinical outcome.

The corticospinal tract in Sturge-Weber syndrome: a diffusion tensor tractography study

OBJECTIVE

To utilize diffusion tensor tractography and evaluate the integrity of the corticospinal tract in children with unilateral Sturge-Weber syndrome (SWS).

METHODS

Sixteen children (age: 1.5-12.3 years) with SWS involving one hemisphere and varying degrees of motor deficit, underwent magnetic resonance imaging (MRI) as part of a prospective clinical research study. Diffusion tensor imaging (DTI) was obtained and fiber tracking of the corticospinal tract was performed yielding average FA and ADC values along the pathway. These values were compared between the two hemispheres (affected vs. unaffected) and also correlated with the degree of motor deficits, after correction for age.

RESULTS

Corticospinal tract FA values on the side of the affected hemisphere were lower (p=0.008) and ADC values were higher (p=0.011) compared to the normal side. Furthermore, FA and ADC values on the side of the angioma did not show the normal age-related variations, which the contralateral corticospinal pathway values did demonstrate. Although none of the patients had severe hemiparesis, those with moderate motor deficit had increased ADC values, as compared to those with mild (p=0.009) or no motor deficit (p=0.045).

CONCLUSION

MRI with DTI shows abnormalities of the corticospinal tract in children with SWS even before severe motor impairment develops. Thus, DTI can be a clinically useful method to evaluate the integrity of the corticospinal tract in young children who are at risk for progressive motor dysfunction.

Prefrontal cortex volumes in adolescents with alcohol use disorders: unique gender effects

BACKGROUND

Adolescents with alcohol use disorders (AUD) have shown smaller prefrontal cortex (PFC) volumes compared with healthy controls; however, differences may have been due to comorbid disorders. This study examined PFC volumes in male and female adolescents with AUD who did not meet criteria for comorbid mood or attention disorders.

METHODS

Participants were adolescents aged 15 to 17 who met criteria for AUD (n = 14), and demographically similar healthy controls (n = 17). Exclusions included any history of a psychiatric or neurologic disorder other than AUD or conduct disorder. Magnetic resonance imaging scans occurred after at least 5 days of abstinence from alcohol or drugs. Overall PFC volumes and white matter PFC volumes were compared between groups.

RESULTS

After controlling for conduct disorder, gender, and intracranial volume, AUD teens demonstrated marginally smaller anterior ventral PFC volumes (p = 0.09) than controls, and significant interactions between group and gender were observed (p < 0.001 to p < 0.03). Compared with same-gender controls, females with AUD demonstrated smaller PFC volumes, while males with AUD had larger PFC volumes. The same pattern was observed for PFC white matter volumes.

CONCLUSIONS

Consistent with adult literature, alcohol use during adolescence is associated with prefrontal volume abnormalities, including white matter differences. However, adolescents with AUD demonstrated gender-specific morphometric patterns. Thus, it is possible that gender may moderate the impact of adolescent alcohol use on prefrontal neurodevelopment, and the neurodevelopmental trajectories of heavy drinking boys and girls should be evaluated separately in longitudinal studies.

Extent of microstructural white matter injury in postconcussive syndrome correlates with impaired cognitive reaction time: a 3T diffusion tensor imaging study of mild traumatic brain injury

BACKGROUND AND PURPOSE

Diffusion tensor imaging (DTI) may be a useful index of microstructural changes implicated in diffuse axonal injury (DAI) linked to persistent postconcussive symptoms, especially in mild traumatic brain injury (TBI), for which conventional MR imaging techniques may lack sensitivity. We hypothesized that for mild TBI, DTI measures of DAI would correlate with impairments in reaction time, whereas the number of focal lesions on conventional 3T MR imaging would not.

MATERIALS AND METHODS

Thirty-four adult patients with mild TBI with persistent symptoms were assessed for DAI by quantifying traumatic microhemorrhages detected on a conventional set of T2*-weighted gradient-echo images and by DTI measures of fractional anisotropy (FA) within a set of a priori regions of interest. FA values 2.5 SDs below the region average, based on a group of 26 healthy control adults, were coded as exhibiting DAI.

RESULTS

DTI measures revealed several predominant regions of damage including the anterior corona radiata (41% of the patients), uncinate fasciculus (29%), genu of the corpus callosum (21%), inferior longitudinal fasciculus (21%), and cingulum bundle (18%). The number of damaged white matter structures as quantified by DTI was significantly correlated with mean reaction time on a simple cognitive task (r = 0.49, P = .012). In contradistinction, the number of traumatic microhemorrhages was uncorrelated with reaction time (r = -0.08, P = .71).

CONCLUSION

Microstructural white matter lesions detected by DTI correlate with persistent cognitive deficits in mild TBI, even in populations in which conventional measures do not. DTI measures may thus contribute additional diagnostic information related to DAI.

White matter fiber tracking method by vector interpolation with diffusion tensor imaging data in human brain

The directional diffusion information obtained by diffusion tensor magnetic resonance imaging (DT-MRI) can be used to noninvasively visualize white matter fibers in human brain. And it is the unique way to reconstruct those fibers in vivo. However, there are some obstacles for the reconstruction process, e.g., partial volume effect caused by low spatial resolution negatively affects the DT-MRI results, and continuous fibers are indicated by the discrete signal on the DT-MRI. A fiber tracking algorithm is proposed in this paper. Major eigenvectors and fractional anisotropy (FA) values of the correlative voxels are used for fiber tracking. As a result, this method shows stronger potential to depict the distribution of white matter fibers in human brain.

Diffusion tensor imaging segmentation of white matter structures using a Reproducible Objective Quantification Scheme (ROQS)

Reproducible Objective Quantification Scheme (ROQS) is a novel method for regional white matter measurements of diffusion tensor imaging (DTI) parameters that overcomes the limitations of previous approaches for analyzing large cohorts of subjects reliably. ROQS is a semi-automated technique that exploits the fiber orientation information from the diffusion tensor in conjunction with a binary masking and chain-linking algorithm to segment anatomically distinct white matter tracts for subsequent quantitative analysis of DTI parameters such as fractional anisotropy and apparent diffusion coefficient. When applied to 3-T whole-brain DTI of normal adult volunteers, ROQS is shown to segment the corpus callosum much faster than manual region of interest (ROI) delineation, and with better reproducibility and accuracy.

Reconstruction of the human visual system based on DTI fiber tracking

PURPOSE

To apply and to evaluate the newly developed advanced fast marching algorithm (aFM) in vivo by reconstructing the human visual pathway, which is characterized by areas of extensive fiber crossing and branching, i.e., the optic chiasm and the lateral geniculate nucleus (LGN).

MATERIALS AND METHODS

Diffusion tensor images were acquired in 10 healthy volunteers. Due to the proximity to bony structures and air-filled spaces of the optic chiasm, a high sensitivity encoding (SENSE) reduction factor was applied to reduce image distortions in this area. To reconstruct the visual system, three different seed areas were chosen separately. The results obtained by the aFM tracking algorithm were compared and validated with known anatomy.

RESULTS

The visual system could be reconstructed reproducibly in all subjects and the reconstructed fiber pathways are in good agreement with known anatomy.

CONCLUSION

The present work shows that the advanced aFM, which is especially designed for overcoming tracking limitations within areas of extensive fiber crossing, handles the fiber crossing and branching within the optic chiasm and the LGN correctly, thus allowing the reconstruction of the entire human visual fiber pathway, from the intraorbital segment of the optic nerves to the visual cortex.

Diffusion tensor imaging of brain development

Understanding early human brain development is of great clinical importance, as many neurological and neurobehavioral disorders have their origin in early structural and functional cerebral organization and maturation. Diffusion tensor imaging (DTI), a recent magnetic resonance (MR) modality which assesses water diffusion in biological tissues at a microstructural level, has revealed a powerful technique to explore the structural basis of normal brain development. In fact, the tissue organization can be probed non-invasively, and the age-related changes of diffusion parameters (mean diffusivity, anisotropy) reveal crucial maturational processes, such as white matter myelination. Nevertheless, the developing human brain presents several challenges for DTI applications compared with the adult brain. DTI may further be used to detect brain injury well before conventional MRI, as water diffusion changes are an early indicator of cellular injury. This is particularly critical in infants in the context of administration of neuroprotective therapies. Changes in diffusion characteristics further provide early evidence of both focal and diffuse white matter injury in association with periventricular leukomalacia in the preterm infant. Finally, with the development of 3D fiber tractography, the maturation of white matter connectivity can be followed throughout infant development into adulthood with the potential to study correlations between abnormalities on DTI and ultimate neurologic/cognitive outcome.

Diffusion changes in patients with systemic lupus erythematosus

BACKGROUND AND PURPOSE

Systemic lupus erythematosus (SLE) is an autoimmune disease in which almost all the organs are involved. Neuropsychiatric SLE is of one of the major concerns in the clinical evaluation of this disease. Routine magnetic resonance imaging (MRI) findings are often nonspecific or negative. In this study, we explored the use of diffusion tensor imaging in assisting with the diagnosis of SLE.

METHODS

Data from 34 SLE patients (age range, 18-73 years) and 29 age-matched volunteers (age range, 29-64 years) were analyzed. MRI was performed on a 1.5-T clinical MR scanner with a quadrature head coil. The average diffusion constant (D(av)) and diffusion anisotropy maps [fractional anisotropy (FA)] were determined on a pixel-by-pixel basis. Regional diffusion measurements were made by region of interest in the genu and splenium of the corpus callosum (CC), anterior and posterior limb of the internal capsule (IC) and frontal lobe and thalamus. The diffusion distribution was fitted to a triple-Gaussian model. The mean of the brain tissue distribution was determined as a mean diffusion constant for the whole brain (BD(av)). Student's t test was used to determine the diffusion difference between SLE patients and control subjects. The SLE patients were separated into two groups according to their MRI results. A P value lower than .05 was considered to be statistically significant.

RESULTS

Twenty of the 34 SLE patients with abnormal MRI results showed findings dominated by nonspecific white matter disease. The BD(av) and D(av) values of the frontal lobe, splenium CC and anterior IC were significantly higher in all SLE patients as compared with the control subjects. The SLE patients with normal MRI results also showed higher BD(av) and D(av) values in the frontal lobe, splenium and anterior and posterior limbs of the IC as compared with the control subjects. There was no significant difference in the D(av) values of the thalamus between the SLE patients and the control subjects. The BD(av) value in the SLE patient group was robustly correlated with the D(av) values of the frontal lobe, splenium and thalamus. These correlations were found to be similarly significant for the SLE patients with normal MRI findings. The diffusion anisotropy measurements showed that splenium CC had the highest FA value in both the control subjects and SLE patients. Overall, SLE patients had lower FA values in the genu and splenium CC as compared with the control subjects. In the group of patients with normal MRI findings, the FA values of the genu and splenium CC as well as the anterior IC were also lower than those in the control subjects. Pearson's correlation statistics revealed robust correlations between the measurements of D(av) and FA values in the SLE patient group.

CONCLUSION

Quantitative diffusion imaging and diffusion anisotropy showed early changes in the brains of the SLE patients. Increased BD(av) and D(av) values of the frontal lobe as well as decreased anisotropy in the genu CC and anterior IC may represent preclinical signs of central nervous system involvement of SLE even when the routine MRI findings are negative or nonspecific. Quantitative diffusion analysis may prove to be useful in detecting the initial brain involvement of SLE and may enable monitoring of early disease progression and treatment efficacy.

Diffusion tensor imaging of frontal white matter and executive functioning in cocaine-exposed children

BACKGROUND

Although animal studies have demonstrated frontal white matter and behavioral changes resulting from prenatal cocaine exposure, no human studies have associated neuropsychological deficits in attention and inhibition with brain structure. We used diffusion tensor imaging to investigate frontal white matter integrity and executive functioning in cocaine-exposed children.

METHODS

Six direction diffusion tensor images were acquired using a Siemens 3T scanner with a spin-echo echo-planar imaging pulse sequence on right-handed cocaine-exposed (n = 28) and sociodemographically similar non-exposed children (n = 25; mean age: 10.6 years) drawn from a prospective, longitudinal study. Average diffusion and fractional anisotropy were measured in the left and right frontal callosal and frontal projection fibers. Executive functioning was assessed using two well-validated neuropsychological tests (Stroop color-word test and Trail Making Test).

RESULTS

Cocaine-exposed children showed significantly higher average diffusion in the left frontal callosal and right frontal projection fibers. Cocaine-exposed children were also significantly slower on a visual-motor set-shifting task with a trend toward lower scores on a verbal inhibition task. Controlling for gender and intelligence, average diffusion in the left frontal callosal fibers was related to prenatal exposure to alcohol and marijuana and an interaction between cocaine and marijuana exposure. Performance on the visual-motor set-shifting task was related to prenatal cocaine exposure and an interaction between cocaine and tobacco exposure. Significant correlations were found between test performance and fractional anisotropy in areas of the frontal white matter.

CONCLUSIONS

Prenatal cocaine exposure, alone and in combination with exposure to other drugs, is associated with slightly poorer executive functioning and subtle microstructural changes suggesting less mature development of frontal white matter pathways. The relative contribution of postnatal environmental factors, including characteristics of the caregiving environment and stressors associated with poverty and out-of-home placement, on brain development and behavioral functioning in polydrug-exposed children awaits further research.

Surgical treatment of paraventricular cavernous angioma: fibre tracking for visualizing the corticospinal tract and determining surgical approach

Surgical treatment of deep-seated lesions involving the corticospinal tract is one of the most challenging areas of contemporary neurosurgery, even given the recent development of radiological methods including three-dimensional anisotropy contrast magnetic resonance imaging (MRI) axonography. Fibre tracking using diffusion tensor imaging is another MRI technique that can be used to visualize anisotropy and the orientation of white matter tracts in the brain. We report herein a patient with a paraventricular cavernous angioma manifesting as hemiparesis caused by haemorrhage. Preoperative conventional MRI failed to determine the anatomical relationship between the paraventricular lesion and the corticospinal tract, whereas fibre tracking using free software (dTV for MR-DTI analysis) indicated that the corticospinal tract was displaced anterolaterally from the medial side. The paraventricular lesion was completely removed without damaging the corticospinal tract using a transcortical transventricular approach. Preoperative fibre tracking is useful in surgical planning for procedures involving deep-seated lesions adjacent to the corticospinal tract, and may avoid postoperative morbidity due to corticospinal tract injury.

Possible axonal regrowth in late recovery from the minimally conscious state

We used diffusion tensor imaging (DTI) to study 2 patients with traumatic brain injury. The first patient recovered reliable expressive language after 19 years in a minimally conscious state (MCS); the second had remained in MCS for 6 years. Comparison of white matter integrity in the patients and 20 normal subjects using histograms of apparent diffusion constants and diffusion anisotropy identified widespread altered diffusivity and decreased anisotropy in the damaged white matter. These findings remained unchanged over an 18-month interval between 2 studies in the first patient. In addition, in this patient, we identified large, bilateral regions of posterior white matter with significantly increased anisotropy that reduced over 18 months. In contrast, notable increases in anisotropy within the midline cerebellar white matter in the second study correlated with marked clinical improvements in motor functions. This finding was further correlated with an increase in resting metabolism measured by PET in this subregion. Aberrant white matter structures were evident in the second patient's DTI images but were not clinically correlated. We propose that axonal regrowth may underlie these findings and provide a biological mechanism for late recovery. Our results are discussed in the context of recent experimental studies that support this inference.

Resolving fiber crossing using advanced fast marching tractography based on diffusion tensor imaging

Magnetic resonance diffusion tensor tractography is a powerful tool for the non-invasive depiction of the white matter architecture in the human brain. However, due to limitations in the underlying tensor model, the technique is often unable to reconstruct correct trajectories in heterogeneous fiber arrangements, such as axonal crossings. A novel tractography method based on fast marching (FM) is proposed which is capable of resolving fiber crossings and also permits trajectories to branch. It detects heterogeneous fiber arrangements by incorporating information from the entire diffusion tensor. The FM speed function is adapted to the local tensor characteristics, allowing in particular to maintain the front evolution direction in crossing situations. In addition, the FM's discretization error is reduced by increasing the number of considered possible front evolution directions. The performance of the technique is demonstrated in artificial data and in the healthy human brain. Comparisons with standard FM tractography and conventional line propagation algorithms show that, in the presence of interfering structures, the proposed method is more accurate in reconstructing trajectories. The in vivo results illustrate that the elucidated major white matter pathways are consistent with known anatomy and that multiple crossings and tract branching are handled correctly.

Diffusion Tensor Imaging and Tractography of Human Brain Development

Over the past decade, diffusion tensor imaging (DTI) has offered researchers and clinicians a new noninvasive window into the developing human brain, from preterm infants through adolescents and young adults. DTI improves on conventional MR imaging, such as T1-weighted and T2-weighted sequences, through its sensitivity to many microstructural features of neural organization. This has enabled visualization of the early cerebral laminar architecture in premature infants, of developing white matter before myelination, and of the microarchitecture of the cerebral cortex during preterm maturation. DTI provides reproducible quantitative measures, such as mean diffusivity and fractional anisotropy, that reflect the underlying tissue properties of gray matter and white matter and may therefore become useful as developmental milestones for the improved assessment of abnormal brain maturation. Furthermore, three-dimensional fiber tractography based on DTI can reveal the developing axonal connectivity of the human brain as well as aberrant connectivity in structural brain malformations. In this article, applications of DTI and fiber tractography to the study of human brain development are reviewed. The new insights into brain maturation afforded by DTI promise to improve the diagnostic evaluation of an array of congenital, metabolic, and neurodevelopmental disorders.

Fiber tracking in the cervical spine and inferior brain regions with reversed gradient diffusion tensor imaging

Diffusion tensor echo planar magnetic resonance imaging of the inferior brain regions and the spinal cord suffers from tissue-air and tissue-bone interfaces, which cause severe susceptibility-induced artifacts. These artifacts consist of image distortions in the phase encode direction and also affect signal intensity. To correct for these distortions, we used the reversed gradient method. We find that most in-plane voxel displacements in the inferior brain regions and the cervical spine can be corrected, yielding a good match of white matter fiber tracts with anatomical reference images. Furthermore, uninterrupted white matter fiber tracts going from the cervical spine up to cortical areas, derived from data acquired in a single acquisition, are presented.

Functional magnetic resonance imaging in the treatment of epilepsy

Although structural magnetic resonance imaging (MRI) is now in routine use in the evaluation and management of epilepsy, functional MRI (fMRI) has recently begun to provide a noninvasive and widely available modality for assessing regional brain function. fMRI studies of language and memory are able to show discrete areas of activation in cerebral cortex, are useful in lateralizing language and memory during presurgical evaluation, and are providing further insight into the processes underlying cerebral plasticity in the brains of epilepsy patients. The use of fMRI for localization of ictal phenomena may also contribute to the localization of seizure foci and to a better understanding of the pathophysiology of electrographic spikes. The combination of fMRI with electroencephalogram and other advanced structural imaging techniques may not only improve seizure localization, but may also contribute valuable information towards a better understanding of the pathophysiology of epilepsy and its consequences on brain development.

Frontostriatal Microstructure Modulates Efficient Recruitment of Cognitive Control

Many studies have linked activity in a frontostriatal network with the capacity to suppress inappropriate thoughts and actions, but relatively few have examined the role of connectivity between these structures. Here, we use diffusion tensor imaging to assess frontostriatal connectivity in 21 subjects (ages 7-31 years). Fifteen subjects were tested on a go/no-go task, where they responded with a button press to a visual stimulus and inhibited a response to a second infrequent stimulus. An automated fiber tracking algorithm was used to delineate white matter fibers adjacent to ventral prefrontal cortex and the striatum, and the corticospinal tract, which was not expected to contribute to control per se. Diffusion in frontostriatal and corticospinal tracts became more restricted with age. This shift was paralleled by an increase in efficiency of task performance. Frontostriatal radial diffusivities predicted faster reaction times, independent of age and accuracy, and this correlation grew stronger for trials expected to require greater control. This was not observed in the corticospinal tract. On trials matched for speed of task performance, adults were significantly more accurate, and accuracies were correlated with frontostriatal, but not corticospinal, diffusivities. These findings suggest that frontostriatal connectivity may contribute to developmental and individual differences in the efficient recruitment of cognitive control.

Changes in cerebral functional organization during cognitive development

It has been just under a decade since contemporary neuroimaging tools, such as functional magnetic resonance imaging, were first applied to developmental questions. These tools provide invaluable information on how brain anatomy, function and connectivity change during development. Studies using these methods with children and adolescents show that brain regions that support motor and sensory function mature earliest, whereas higher-order association areas, such as the prefrontal cortex, which integrate these functions, mature later.

Diffusion-Tensor MR Tractography of Somatotopic Organization of Corticospinal Tracts in the Internal Capsule: Initial Anatomic Results in Contradistinction to Prior Reports

The goal of this study was to use diffusion-tensor magnetic resonance (MR) imaging to define the location and organization of corticospinal tracts (CSTs) in the posterior limb of the internal capsule (PLIC). The Institutional Review Board approved the study, and informed consent was obtained from all subjects. Eight volunteers and two patients with brain tumor were imaged at 3 T. All CSTs were found to lie in a compact area in one part of the PLIC: If the PLIC is divided into four equal quarters from anterior to posterior, the CST was shown to be in the third quarter. Seventeen of 20 CSTs were organized somatotopically, with hand fibers anterolateral to foot fibers, not anteromedial as is currently believed. In three of 20, hand and foot fibers were intermixed. Classically, it was thought that the CST was located in the anterior third of the PLIC. The present data confirm recent results that the CST is located more posteriorly. In the majority of cases, however, the CST is organized somatotopically.

White matter imaging in holoprosencephaly in children

PURPOSE OF REVIEW

Holoprosencephaly is a disorder of forebrain development characterized by a failure of the brain to separate into two hemispheres during early development. It is now clear that many cases of holoprosencephaly are caused by alterations in the genetic programmes that pattern the nervous system. Less is known about how a holoprosencephalic brain either forms or fails to form connections between various brain structures.

RECENT FINDINGS

Abnormalities in the corpus callosum, corticospinal tract, medial lemniscus and cerebellar peduncles can be seen in holoprosencephaly. Diffusion tensor imaging has been and will continue to be an important tool for imaging white matter in the brain, and will be reviewed here. Furthermore, recent evidence suggests that holoprosencephaly can be associated with delays or abnormalities in myelination. The functional implications of white matter abnormalities in children with holoprosencephaly is only beginning to be understood.

SUMMARY

Modern neuroimaging has led to a better appreciation of the variability seen in holoprosencephaly, an anomaly known to have multiple etiologies. Recent reviews of the biology of holoprosencephaly identify the condition as a defect in dorsoventral patterning. More detailed white and grey matter structure-function studies are likely to shed light on how a brain with drastically altered composition and connectivity does or does not organize itself to accomplish increasingly complex developmental functions.

The development of reading impairment: a cognitive neuroscience model

This review discusses recent cognitive neuroscience investigations into the biological bases of developmental dyslexia, a common disorder impacting approximately 5 to 17 percent of the population. Our aim is to summarize central findings from several lines of evidence that converge on pivotal aspects of the brain bases of developmental dyslexia. We highlight ways in which the approaches and methodologies of developmental cognitive neuroscience that are addressed in this special issue-including neuroimaging, human genetics, refinement of cognitive and biological phenotypes, neural plasticity and computational model-can be employed in uncovering the biological bases of this disorder. Taking a developmental perspective on the biological bases of dyslexia, we propose a simple cascading model for the developmental progression of this disorder, in which individual differences in brain areas associated with phonological processing might influence the specialization of visual areas involved in the rapid processing of written words. We also discuss recent efforts to understand the impact of successful reading interventions in terms of changes within cortical circuits associated with reading ability.

Imaging the developing brain with fMRI

Advancements in magnetic imaging techniques have revolutionized our ability to study the developing human brain in vivo. The ability to noninvasively image both anatomy and function in healthy volunteers, including young children, has already enhanced our understanding of brain and behavior relations. The application of these techniques to developmental research offers the opportunity to further explore these relationships and allows us to ask questions about where, when and how cognitive abilities develop in relation to changes in underlying brain systems. It is also possible to explore the contributions of maturation versus learning in the development of these abilities through cross-sectional and longitudinal research involving training and intervention procedures. Current imaging methodologies, in conjunction with new and rapidly evolving techniques, hold the promise of even greater insights into developmental issues in the near future. These methodologies and their application to development and learning are discussed in the current paper.

A systems neuroscience approach to autism: biological, cognitive, and clinical perspectives

Autism is a behaviorally defined disorder characterized by a broad constellation of symptoms. Numerous studies directed to the biological substrate demonstrate clear effects of neurodevelopmental differences that will likely point to the etiology, course, and long-term outcomes of the disorder. Consistently replicated research on the neural underpinnings of autism is reviewed. In general, results suggest several main conclusions: First, autism is a heterogeneous disorder and is likely to have multiple possible etiologies; second, structural brain studies have indicated a variety of diffuse anatomical differences, reflective of an early developmental change in the growth or pruning of neural tissue, rather than localized lesions; similarly, neurochemical studies suggest early, neuromodulatory discrepancies rather than gross or localized abnormalities; and finally, there are a number of limitations on studies of brain activity that to date preclude definitive answers to questions of how the brain functions differently in autism. The large number of active research programs investigating the cognitive neuroscience of autism spectrum disorders, in combination with the exciting development of new methodologies and tools in this area, indicates the drama and excitement of work in this area.

A review of the biological bases of ADHD: what have we learned from imaging studies?

Attention Deficit Hyperactivity Disorder (ADHD) is a common and impairing neuropsychiatric disorder with onset at preschool age. Although a significant amount of progress has been made investigating the neurobiology of this disorder, its precise etiology still remains unclear. Converging evidence from studies of the neuropharmacology, genetics, neuropsychology, and neuroimaging of ADHD imply the involvement of fronto-striatal circuitry in ADHD. However, while it does appear that poor inhibitory control and the deficits in fronto-striatal circuitry associated with it are central, there is evidence to suggest that more posterior cerebral areas are also implicated in this disorder. Anatomical studies suggest widespread reductions in volume throughout the cerebrum and cerebellum, while functional imaging studies suggest that affected individuals activate more diffuse areas than controls during the performance of cognitive tasks. The future impact of new MR imaging methodologies on the field is discussed.