Montreal Neurological Institute Space Research Articles

Electrical Source Imaging of Sleep Spindles

To identify and compare cortical source generators of slow and fast sleep spindles in healthy subjects, electroencephalographic (EEG) signals were obtained from 256 channels, and sources on neuroanatomical Montreal Neurological Institute (MNI) space estimated with low-resolution brain electromagnetic tomography analysis (LORETA). Spindle activity was recorded in 18 healthy volunteers during daytime napping. Because of lack of sleep or excessive artifacts, data from 13 subjects were analyzed off-line. Spindles were visually scored, marked, and bandpass filtered (slow 10-12 Hz or fast 12-14 Hz). EEG was segmented on the marker, and segments separately averaged. LORETA projected cortical sources on the MNI brain. Maximal intra- and inter-individual intensities were compared using the Wilcoxon test (P < .05) and cortical sources distribution compared using a chi2 test. Two to three slow spindles generators were consistently identified in frontal lobes, with additional sources in parietal and limbic lobes in half cases. Fast spindles had multiple temporo-parietal sources, with an inconstant frontal source. Inter-individual (P = 0.44), and intra-individual (P = 0.09 slow and P = 0.10 fast spindles) source intensities were comparable. Slow spindles sources were preferentially concentrated over frontal cortices in comparison with fast spindles (P = 0.0009). Our results demonstrate multiple, synchronous, and equipotent spindles cortical generators in healthy subjects, with more anterior generators for slow spindles.

Slow spindles’ cortical generators overlap with the epileptogenic zone in temporal epileptic patients: An electrical source imaging study

ObjectiveTo determine whether temporal epileptic patients and normal volunteers display similar sleep spindles’ cortical generators as determined by electrical source imaging (ESI), and whether such generators overlap in epilepsy patients with the epileptogenic zone identified by ESI. MethodsTwelve healthy subjects and twelve temporal lobe pharmaco-resistant epileptic patients underwent a 256-channel EEG recording during a daytime nap. Sleep spindles were analyzed off line, distinguishing slow (10–12Hz) and fast (12–14Hz) ones, and the final averaged signal was projected onto a MNI (Montreal Neurological Institute) space to localize cortical generators. The same procedure was performed for averaged epileptic spikes, obtaining their cortical source. Intra- and inter-group statistical analyses were conducted. ResultsMultiple, concomitant generators were detected in both populations for slow and fast spindles. Slow spindles in epileptics displayed higher source amplitude in comparison to healthy volunteers (Z=0.001), as well as a preferential localization over the affected temporal cortices (p=0.039). Interestingly, at least one of slow spindles’ generators overlapped with the epileptogenic zone. ConclusionSlow spindles, but not fast ones, in temporal epilepsy are mainly generated by the affected temporal lobe. SignificanceThese results point to the strict relation between sleep and epilepsy and to the possible cognitive implications of spikes arising from memory-encoding brain structures.

White matter microstructural abnormalities in patients with late-onset schizophrenia identified by a voxel-based diffusion tensor imaging

Reduced fractional anisotropy (FA) has been previously found in diffusion tensor imaging (DTI) studies of white matter in schizophrenic patients. However, there are no reports in the literature that address FA alterations in late-onset schizophrenia (LOS). The current study measured FA in whole white matter and subsequently analyzed its association with psychotic symptoms in LOS. DTI was carried out in 20 patients with LOS and 17 age-, gender- and education-matched healthy subjects. Fractional anisotropy in different areas of white matter was compared between groups using a voxelwise analysis after inter-subject registration to standard Montreal Neurological Institute (MNI) space. Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). Cognitive functions were measured using the Wisconsin Card Sorting Test (WCST), the Digit Span Test, and the Trail-making Test. Significant reduction in FA was found in the left parietal lobe and right posterior cingulum in LOS patients compared with healthy subjects. Significant deficits in cognitive functions were observed in LOS. No significant correlation was found between FA value and PANSS scores, cognitive test scores, age, or antipsychotic medication dosages in LOS patients. Our study suggests that abnormalities in white matter integrity may contribute to the pathophysiology of LOS. However, these microstructural abnormalities provided no evidence for the emergence of psychotic symptoms in LOS.

Effect of Local Anesthesia on Trigeminal Somatosensory-evoked Magnetic Fields

For objective neurophysiological evaluation of the function of the trigeminal system, magnetoencephalography- based TSEF (trigeminal somatosensory-evoked field) assessment would be valuable in providing spatial and temporal profiles of cortical responses. However, this necessitates knowledge of how TSEF varies with trigeminal nerve dysfunctions. We introduced a conduction block of the trigeminal nerve using local anesthesia (lidocaine) to temporally mimic nerve dysfunctions, and monitored TSEF changes. Following an electrical stimulation of the lower lip, a magnetic response with peak latency of approximately 20 ms was identified in all participants. Dipole for the peak was estimated on the post-central gyrus in the participant’s own magnetic resonance image. After normalization to Montreal Neurological Institute (MNI) space and inter-participant data integration, the summary equivalent current dipole localization among participants remained in the post-central gyrus, suggesting validity of the use of MNI space. Partial anesthesia of the lower lip led to a loss of the waveform characteristics of TSEF for electrical stimulation to the trigeminal nerve. We verified that the 20-ms latency cortical response of TSEF components localized at the primary sensory cortex can serve as a robust neurofunctional marker of experimental trigeminal nerve dysfunction.

312 Increased Regional Cerebral Type 1 Cannabinoid Receptor Availability in Functional Dyspepsia: A [18F]MK9470 PET Study

INTRODUCTION: Functional dyspepsia (FD) is defined as the presence of chronic epigastric symptoms in the absence of underlying structural or biochemical abnormalities likely to explain them. These dyspeptic symptoms are often meal-related and disturbances in appetite regulation and food intake might lead to unexplained weight loss. FD patients are also characterized by abnormal regional cerebral activity in key areas of the ‘pain neuromatrix'. However, it is unknown which neurotransmitter mechanisms underlie these abnormalities. Endocannabinoids are involved in pain processing, regulation of gastrointestinal function and reward/food intake AIM: To compare the regional cerebral availability of the type 1 cannabinoid (CB1) receptor between FD patients and healthy controls. METHODS: 12 FD patients (mean age 29.4 ± 10.6, 11 women) with significant weight loss (mean 13.2 kg) and 12 age-, genderand BMI-matched healthy controls participated in the study; psychiatric co-morbidity and intake of centrally acting medication or (recreational) drugs were exclusion criteria. Each subject underwent a 30 minute dynamic positron emission tomography scan consisting of 6 frames at 90 min postinjection of the CB1 receptor-selective radioligand [18F]MK9470. Parametric maps of CB1 receptor availability were constructed using modified standard uptake value (mSUV) values as estimate of receptor availability. These maps were spatially normalized to Montreal Neurological Institute space to allow whole-brain voxelbased analysis. A significance level of pheight < 0.001 (uncorrected) was used to compare CB1 receptor availability between both groups. RESULTS: Significantly higher CB1 receptor availability was found in FD patients with local maxima in the following brain regions: anterior cingulate cortex (ACC, perigenual), caudate head, insular cortex (INS, anterior/mid, bilateral), orbitofrontal cortex (bilateral) and putamen (Table 1). The large cluster also included the amygdala, globus pallidus, hypothalamus, PAG and ventral striatum (nucleus accumbens) (Figure 1). CONCLUSION: We report the first study demonstrating a significantly higher CB1 receptor availability in regions involved in the regulation of visceral sensation (ant/mid INS, ACC and amygdala), and reward/food intake (hypothalamus and (ventral) striatum) in FD patients compared to controls. Whether this elevated receptor availability predisposes to or is a consequence of FD symptoms remains to be elucidated. However, within the patients group weight loss was not associated with receptor binding in any of the brain regions. These results may indicate that the abnormal brain activity in several of these regions previously demonstrated in FD may be due to abnormal functioning of the endocannabinoid system, identifying it as a potential novel target for treatment. Table1

Transcallosal sensorimotor fiber tract structure‐function relationships

Recent studies have demonstrated neuroanatomically selective relationships among white matter tract microstructure, physiological function, and task performance. Such findings suggest that the microstructure of transcallosal motor fibers may reflect the capacity for interhemispheric inhibition between the primary motor cortices, although full characterization of the transcallosal inhibitory sensorimotor network is lacking. Thus, the goal of this study was to provide a comprehensive description of transcallosal fibers connecting homologous sensorimotor cortical regions and to identify the relationship(s) between fiber tract microstructure and interhemispheric inhibition during voluntary cortical activity. To this end, we assessed microstructure of fiber tracts connecting homologous sensorimotor regions of the cortex with diffusion tensor imaging. We also assessed interhemispheric inhibition by eliciting the ipsilateral silent period (iSP) within the same participants. We mapped mutually exclusive transcallosal connections between homologous sensorimotor regions and computed quantitative metrics of each fiber tract. Paralleling work in non-human primates, we found the densest interhemispheric sensorimotor connections to be between the medial motor areas. Additionally, we provide a midsagittal callosal atlas in normalized Montreal Neurological Institute (MNI) space for future studies to use when investigating callosal fiber tracts connecting primary and secondary sensorimotor cortices. Finally, we report a strong, positive relationship (r = 0.76) between strength of interhemispheric inhibition (iSP) and microstructure of interhemispheric fibers that is specific to tracts connecting the primary motor cortices. Thus, increased fiber microstructure in young adults predicts interhemispheric inhibitory capacity.

A comparison of F-18 FDG-PET imaging in differential diagnosis of Alzheimer's disease and dementia with Lewy body disease

Dementia with Lewy bodies (DLB) is the second most common cause of degenerative dementia after Alzheimer's disease (AD). Clinically it is characterized by attentional fluctuation, recurrent visual hallucinations and motor features of Parkinsonism, while histopathologically by cortical and sub-cortical Lewy bodies. However, due to overlapping clinical features and low sensitivity of clinical diagnostic criteria, the differential diagnosis of AD and DLB remains a major problem in clinical practice. The aim of this study was to investigate the diagnostic value of metabolism in the diagnosis of DLB and AD in comparison with [F-18] fluoro-2-deoxy-D-glucose (FDG)-PET imaging. Investigations which could help improve the accuracy of discrimination between DLB and AD would be a major advance. All subjects underwent 18F-FDG-PET and MRI. We compared regional cerebral metabolic images by a voxel-by-voxel analysis with statistical parametric mapping among DLBD, AD and NC subjects, and evaluated differences of hypometabolic regions. All PET scans be visually rated from equivalent slices, each image volume was registered to match a 18F-FDG-PET template in standard MNI (Montreal Neurological Institute) space using statistical parametric mapping. Accurate normalization is essential for quantitative pattern analysis to neurodegenerative disease; the cerebellum or pons was often used as a reference region in the MR image, which assumed no significant regional influence of physiological fluctuations for quantitative. 18F-FDG-PET revealed evidence of diffuse hypometabolism in both DLBD and AD with Parkinsonism marked declines in association cortices with relative sparing of subcortical structures and primary somatomotor cortex, a pattern reported previously in AD. Unlike AD, DLBD subjects also had hypometabolism in the occipital association cortex and primary visual cortex. Significant changes in hypometabolism in the volume of interest were assessed in the posterior cingulate gyrus, precuneus and parietal cortices. The severity of the decrease in metabolism in AD patients was significantly greater than in vascular dementia and frontotemporal dementia patients and controls. These findings indicate the presence of diffuse cortical abnormalities in DLBD and suggest that FDG-PET may be useful in discriminating DLBD from AD.

Atlas Learning in Fetal Brain Development

Magnetic resonance imaging has become an important noninvasive technique to gain insight into fetal brain development. Its capabilities go beyond ultrasound when diagnosing high-risk pregnancies. To summarize observations across a population in magnetic resonance imaging studies, reference systems such as atlases that establish correspondences across a cohort are key. In this article, we review the evolution of atlas-building methods in light of their relevance, limitations, and benefits for the modeling of human brain development. Starting with single anatomical templates to which brain scans where mapped to such as Talairach and Montreal Neurological Institute space, we explore the uses of atlases as a means to establish correspondences across a cohort and as a model that captures the population characteristics of the cases the atlas is built from. We discuss methods that capture features of increasingly heterogeneous populations and approaches that are able to generalize with only minimal annotation. The main focus of this review are methods that explicitly model the variability in the population with regard to time, such as in the modeling of disease progression and brain development. We highlight the applicability and limitations of state-of-the art approaches, how insights from the study of disease progression are helpful in developmental studies, and point to the directions of future research that is still necessary.

Atlas‐based automated positioning of outer volume suppression slices in short‐echo time 3D MR spectroscopic imaging of the human brain

Spatial suppression of peripheral lipid-containing regions in volumetric MR spectroscopic imaging of the human brain requires placing large numbers of outer volume suppression (OVS) slices, which is time-consuming, prone to operator error and may introduce subject-dependent variability in volume coverage. We developed a novel, computationally efficient atlas-based approach for automated positioning of up to 16 OVS slices and the MR spectroscopic imaging slab. Standardized positions in Montreal Neurological Institute atlas space were established offline using a recently developed iterative optimization procedure. During the scanning session, positions in subject space were computed using affine transformation of standardized positions in Montreal Neurological Institute space. Offline analysis using magnetization prepared rapid gradient echo scans from 11 subjects demonstrated reliable OVS placement, comparable with but faster than iterative placement in subject space. This atlas-based method was further validated in 14 subjects using 3D short-echo time proton-echo-planar-spectroscopic-imaging at 3 T. Comparison of manual and automatic placement using 8 OVS slices demonstrated consistent MR spectroscopic imaging volume selection and comparable spectral quality with similar degree of lipid suppression and number of usable voxels. Automated positioning of 16 OVS slices enabled larger volume coverage, while maintaining similar spectral quality and lipid suppression. Atlas-based automatic prescription of short echo time MR spectroscopic imaging is expected to be advantageous for longitudinal and cross-sectional studies.

P02-553 - Database of MNI stereotactic coordinates for deep brain stimulation targets in neuropsychiatric disorders

IntroductionDeep brain stimulation (DBS) is a promising therapy option for otherwise treatment-resistant neuropsychiatrie disorders, especially in obsessive-compulsive disorder (OCD), major depression (TRD) and Tourette's Syndrome (TS).ObjectiveThe brain coordinates of the DBS targets are mainly reported using measurements in original, unnormalized brains. In the neuroimaging community stereotactic data are mainly indicated in the standardized Montreal Neurological Institute (MNI) space, i.e. a three-dimensional proportional grid system.AimsImproved comparability between targets in DBS studies and molecular and functional neuroimaging data from PET, SPECT, MRI, fMRI, mostly published with stereotactic data.MethodsA comprehensive and systematic literature search for published DBS case reports or studies in TRD, OCD and TS was performed. We extracted the tip positions of electrode leads as provided in the publications or by the authors, and transferred individual coordinates to the standard brain in the MNI space.Results46 publications fulfilled the inclusion criteria. The main targets for the specific disorders and one or two examples of their calculated MNI coordinates are indicated in the table:[MNI coordinates of the main DBS targets]ConclusionsWe provide DBS data of neuropsychiatrie disorders in the MNI space, improving the comparability to molecular, functional and structural neuroimaging data.

Hemispheric asymmetries in the resting-sate functional connectivity patterns of the brain regions critical for language comprehension

Hemispheric asymmetries in the resting-sate functional connectivity patterns of the brain regions critical for language comprehension

SU‐GG‐I‐158: A Comparison of F‐18 FDG‐PET Imaging in Differential Diagnosis of Alzheimer's Disease with Parkinsonism and Dementia with Lewy Bodies Disease

Purpose: Dementia with Lewy bodies (DLB) is the second most common cause of degenerative dementia after Alzheimer's disease (AD). The aim of this study was to investigate the diagnostic value of metabolism in the diagnosis of DLB and AD in comparison with [F‐18]fluoro‐2‐deoxy‐D‐glucose(FDG)—PET imaging. Investigations which could help improve the accuracy of discrimination between DLB and AD would be a major advance. Methods: All Subjects underwent 18F‐FDG‐PET and MRI. We compared regional cerebral metabolic images by a voxel‐by‐voxel analysis with statistical parametric mapping (SPM) among DLBD, AD and NC subjects, and evaluated differences of hypometabolic regions. All PET scans be visually rated from equivalent slices, each image volume was registered to match a 18F‐FDG‐PET template in standard MNI (Montreal Neurological Institute) space using statistical parametric mapping. Accurate normalization is essential for quantitative pattern analysis to neurodegenerative disease; the cerebellum or pons was often used as a reference region in the MR image, which assumed no significant regional influence of physiological fluctuations for quantitative. Results: 18F‐FDG‐PET revealed evidence of diffuse hypometabolism in both DLBD and AD with Parkinsonism marked declines in association cortices with relative sparing of subcortical structures and primary somatomotor cortex, a pattern reported previously in AD. Unlike AD, DLBD subjects also had hypometabolism in the occipital association cortex and primary visual cortex. Significant changes in hypometabolism in the volume of interest were assessed in the posterior cingulate gyrus, precuneus and parietal cortices. The severity of the decrease in metabolism in AD patients was significantly greater than in vascular dementia and frontotemporal dementia patients and controls. Conclusion: These findings indicate the presence of diffuse cortical abnormalities in DLBD and suggest that FDG‐PET may be useful in discriminating DLBD from AD.

Changes in the Frontotemporal Cortex and Cognitive Correlates in First-Episode Psychosis

BackgroundLoss of cortical volume in frontotemporal regions has been reported in patients with schizophrenia and their relatives. Cortical area and thickness are determined by different genetic processes, and measuring these parameters separately may clarify disturbances in corticogenesis relevant to schizophrenia. Our study also explored clinical and cognitive correlates of these parameters.MethodsThirty-seven patients with first-episode psychosis (34 schizophrenia, 3 schizoaffective disorder) and 38 healthy control subjects matched for age and sex took part in the study. Imaging was performed on an magnetic resonance imaging 1.5-T scanner. Area and thickness of the frontotemporal cortex were measured using a surface-based morphometry method (Freesurfer). All subjects underwent neuropsychologic testing that included measures of premorbid and current IQ, working and verbal memory, and executive function.ResultsReductions in cortical area, more marked in the temporal cortex, were present in patients. Overall frontotemporal cortical thickness did not differ between groups, although regional thinning of the right superior temporal region was observed in patients. There was a significant association of both premorbid IQ and IQ at disease onset with area, but not thickness, of the frontotemporal cortex, and working memory span was associated with area of the frontal cortex. These associations remained significant when only patients with schizophrenia were considered.ConclusionsOur results suggest an early disruption of corticogenesis in schizophrenia, although the effect of subsequent environmental factors cannot be excluded. In addition, cortical abnormalities are subject to regional variations and differ from those present in neurodegenerative diseases.

Abnormal anterior cingulum integrity in first episode, early-onset schizophrenia: A diffusion tensor imaging study

Adolescents with early-onset schizophrenia (EOS) provide a unique opportunity to examine regional and disease-specific early abnormal brain development in schizophrenia. There is currently a general agreement that clinical symptoms and cognitive dysfunctions of schizophrenia may arise from a failure of adequate communication between different brain regions. This disturbed connectivity may be related to alterations in the numbers, distribution, and ultrastructural integrity of oligodendrocytes of white matter. Diffusion tensor imaging provides a relatively new approach for quantifying possible connectivity of white matter in vivo. In this study, thirty-eight adolescents with early-onset schizophrenia (EOS; onset of psychotic symptoms by age 18 years) and 38 age- and gender-matched healthy volunteers received diffusion tensor imaging examinations. Fractional anisotropy images were compared between groups in the white matter using a voxelwise analysis after inter-subject registration to standard Montreal Neurological Institute (MNI) space. Adolescents with EOS demonstrated significantly reduced fractional anisotropy in right anterior cingulum compared to healthy volunteers. Increased fractional anisotropy was not observed in any brain region in patients compared to controls. ROI analysis also reported a trend-level negative correlation between mean regional FA in right anterior cingulum and PANSS positive symptom score. These findings indicate that white matter abnormalities in the anterior cingulum are associated with adolescent EOS.

A robust method to estimate the intracranial volume across MRI field strengths (1.5T and 3T)

As population-based studies may obtain images from scanners with different field strengths, a method to normalize regional brain volumes according to intracranial volume (ICV) independent of field strength is needed. We found systematic differences in ICV estimation, tested in a cohort of healthy subjects (n=5) that had been imaged using 1.5T and 3T scanners, and confirmed in two independent cohorts. This was related to systematic differences in the intensity of cerebrospinal fluid (CSF), with higher intensities for CSF located in the ventricles compared with CSF in the cisterns, at 3T versus 1.5T, which could not be removed with three different applied bias correction algorithms. We developed a method based on tissue probability maps in MNI (Montreal Neurological Institute) space and reverse normalization (reverse brain mask, RBM) and validated it against manual ICV measurements. We also compared it with alternative automated ICV estimation methods based on Statistical Parametric Mapping (SPM5) and Brain Extraction Tool (FSL). The proposed RBM method was equivalent to manual ICV normalization with a high intraclass correlation coefficient (ICC=0.99) and reliable across different field strengths. RBM achieved the best combination of precision and reliability in a group of healthy subjects, a group of patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI) and can be used as a common normalization framework.

Nicotinic 123I-5IA-85380 Single Photon Emission Computed Tomography as a Predictor of Cognitive Progression in Alzheimer's Disease and Dementia With Lewy Bodies

To investigate normalized I-5-Iodo-3-[2(S)-2-azetidinylmethoxy] pyridine (5IA-85380) single photon emission computed tomography (SPECT) imaging, a marker for the alpha4beta2 nicotinic receptor, as a predictor of cognitive progression in Alzheimer's disease (AD) and dementia with Lewy bodies (DLB). Thirty-one patients with dementia (16 patients with AD and 15 patients with DLB) underwent I-5IA-85380 SPECT scanning. Image analysis was performed using statistical parametric mapping (SPM2), which involved spatial preprocessing of scans to standard Montreal Neurological Institute space and intensity normalization of each image to its mean global brain activity. Regression analysis revealed that reduced normalized I-5IA-85380 uptake in left superior, middle, and inferior frontal gyri and prepost central and anterior cingulate regions significantly correlated with decline in executive function in a pooled group comprising AD and DLB. The findings, although preliminary, suggest that the cholinergic system may be more involved in neurodegenerative processes affecting some cognitive processes more than others, as such, this procedure may be useful for increased understanding of the pathophysiological mechanisms responsible for neurodegeneration.

Evaluation of atlas-based segmentation of hippocampi in healthy humans

Region of interest (ROI)-based functional magnetic resonance imaging (fMRI) data analysis relies on extracting signals from a specific area which is presumed to be involved in the brain activity being studied. The hippocampus is of interest in many functional connectivity studies for example in epilepsy as it plays an important role in epileptogenesis. In this context, ROI may be defined using different techniques. Our study aims at evaluating the spatial correspondence of hippocampal ROIs obtained using three brain atlases with hippocampal ROI obtained using an automatic segmentation algorithm dedicated to the hippocampus. High-resolution volumetric T1-weighted MR images of 18 healthy volunteers (five females) were acquired on a 3T scanner. Individual ROIs for both hippocampi of each subject were segmented from the MR images using an automatic hippocampus and amygdala segmentation software called SACHA providing the gold standard ROI for comparison with the atlas-derived results. For each subject, hippocampal ROIs were also obtained using three brain atlases: PickAtlas available as a commonly used software toolbox; automated anatomical labeling (AAL) atlas included as a subset of ROI into PickAtlas toolbox and a frequency-based brain atlas by Hammers et al. The levels of agreement between the SACHA results and those obtained using the atlases were assessed based on quantitative indices measuring volume differences and spatial overlap. The comparison was performed in standard Montreal Neurological Institute space, the registration being obtained with SPM5 (http://www.fil.ion.ucl.ac.uk/spm/). The mean volumetric error across all subjects was 73% for hippocampal ROIs derived from AAL atlas; 20% in case of ROIs derived from the Hammers atlas and 107% for ROIs derived from PickAtlas. The mean false-positive and false-negative classification rates were 60% and 10% respectively for the AAL atlas; 16% and 32% for the Hammers atlas and 6% and 72% for the PickAtlas. Though atlas-based ROI definition may be convenient, the resulting ROIs may be poor representations of the hippocampus in some studies critical to under- or oversampling. Performance of the AAL atlas was inferior to that of the Hammers atlas. Hippocampal ROIs derived from PickAtlas are highly significantly smaller, and this results in the worst performance out of three atlases. It is advisable that the defined ROIs should be verified with knowledge of neuroanatomy before using it for further data analysis.

Probabilistic topography of human corpus callosum using cytoarchitectural parcellation and high angular resolution diffusion imaging tractography

The function of the corpus callosum (CC) is to distribute perceptual, motor, cognitive, learned, and voluntary information between the two hemispheres of the brain. Accurate parcellation of the CC according to fiber composition and fiber connection is of upmost important. In this work, population-based probabilistic connection topographies of the CC, in the standard Montreal Neurological Institute (MNI) space, are estimated by incorporating anatomical cytoarchitectural parcellation with high angular resolution diffusion imaging (HARDI) tractography. First, callosal fibers are extracted using multiple fiber assignment by continuous tracking algorithm based on q-ball imaging (QBI), on 12 healthy and young subjects. Then, the fiber tracts are aligned in the standard MNI coordinate system based on a tract-based transformation scheme. Next, twenty-eight Brodmann's areas on the surface of cortical cortex are registered to the MNI space to parcellate the aligned callosal fibers. Finally, the population-based topological subdivisions of the midsagittal CC to each cortical target are then mapped. And the resulting subdivisions of the CC that connect to the frontal and somatosensory associated cortex are also showed. To our knowledge, it is the first topographic subdivisions of the CC done using HARDI tractography and cytoarchitectonic information. In conclusion, this sophisticated topography of the CC may serve as a landmark to further understand the correlations between the CC, brain intercommunication, and functional cytoarchitectures.

Visualization of disconnection syndromes in humans

Knowledge of the relationship between structure and function is essential to the exploration of the architecture of cognition. Cognitive processes require the coordinated activity of large-scale brain networks consisting of distant cortical regions, connected by long-range white matter tracts. Despite decades of connectional tracing studies in monkeys, the backwardness of human anatomy makes it difficult to draw conclusions from lesion studies and functional neuroimaging when brain connectivity is at issue. We propose an approach to clinico-anatomical correlation, based on a standardized atlas of white matter tracts derived from diffusion tensor imaging tractography. Using OVER-TRACK, a method based on tracking and overlapping white matter tracts, we mapped the course of three rostro-caudal association pathways in the Montreal Neurological Institute space. For each voxel we defined the probability of finding fibers belonging to individual tracts. This method is defined to localize in the white matter the overlapping lesion derived from a group of patients with brain damage. Our study provides a general approach for establishing anatomo-functional correlations by estimating the cortical areas connected in normal subjects, or disconnected by white matter lesions. This method will help researchers and clinicians to identify the neural bases of cognitive abilities and the behavioral consequences of brain lesions.

A diffusion tensor imaging tractography atlas for virtual in vivo dissections

Diffusion tensor imaging (DTI) tractography allows perform virtual dissections of white matter pathways in the living human brain. In 2002, Catani et al. published a method to reconstruct white matter pathways using a region of interest (ROI) approach. The method produced virtual representations of white matter tracts faithful to classical post-mortem descriptions but it required detailed a priori anatomical knowledge. Here, using the same approach, we provide a template to guide the delineation of ROIs for the reconstruction of the association, projection and commissural pathways of the living human brain. The template can be used for single case studies and case–control comparisons. An atlas of the 3D reconstructions of the single tracts is also provided as anatomical reference in the Montreal Neurological Institute (MNI) space.