The role of vision in spatial representation

A complex link exists between vision and unilateral spatial neglect (USN). Firstly, USN is not a perceptual deficit, secondly, USN is not necessarily accompanied by a visual deficit and finally, USN can be observed in non-visual modalities as well as in mental spatial imagery. This apparent supramodality of USN stands in sharp contrast to the fact that neglect signs are often more severe and more durable in the visual than in other sensory modalities (Chokron et al., 2002). The influence of vision on spatial representation has rarely been studied. In the present study we assessed six right brain-damaged patients suffering from left USN on two tasks involving spatial representations: a clock-drawing task and a drawing from memory task in two experimental conditions, with and without visual control. We confirm that even in mental imagery, the absence of visual feedback may decrease and even suppress left neglect signs (Bartolomeo and Chokron, 2001b; 2002). Since vision is largely involved in the orientation of attention in space, suppressing visual control could reduce the magnetic attraction towards the right ipsilesional hemispace and in this way could allow a re-orientation of attention towards the left neglected hemispace. We discuss the theoretical and therapeutic implications of these findings.     

Individual voxel-based analysis of gray matter in focal cortical dysplasia

High-resolution MRI of the brain has made it possible to identify focal cortical dysplasia (FCD) in an increasing number of patients. There is evidence for structural abnormalities extending beyond the visually identified FCD lesion. Voxel-based morphometry (VBM) has the potential of detecting both lesions and extra-lesional abnormalities because it performs a whole brain voxel-wise comparison. However, on T1-weighted MRI, FCD lesions are characterized by a wide spectrum of signal hyperintensity that may compromise the results of the segmentation step in VBM. Our purpose was to investigate gray matter (GM) changes in individual FCD patients using voxel-based morphometry (VBM). In addition, we sought to assess the performance of this technique for FCD detection with respect to lesion intensity using an operator designed to emphasize areas of hyperintense T1 signal. We studied 27 patients with known FCD and focal epilepsy and 39 healthy controls. We compared the GM map of each subject (controls and patients) with the average GM map of all controls and obtained a GM z-score map for each individual. The protocol being designed to achieve a maximal specificity, no differences in GM concentration were found in the control group. The z-score maps showed an increase in GM that coincided with the lesion in 21/27 (78%) patients. Five of the six remaining patients whose lesions were not detected by VBM presented with a strong lesion hyperintensity, and a significant part of their lesion was misclassified as white matter. In 16/27 (59%) patients, there were additional areas of GM increase distant from the primary lesion. Areas of GM decrease were found in 8/27 (30%) patients. In conclusion, individual voxel-based analysis was able to detect FCD in a majority of patients. Moreover, FCD was often associated with widespread GM changes extending beyond the visible lesion. In its current form, however, individual VBM may be unable to detect lesions characterized by strong signal intensity abnormalities.     

In vivo profiling of focal cortical dysplasia on high-resolution MRI with computational models

PURPOSE: On MRI, focal cortical dysplasia (FCD) is characterized by a combination of increased cortical thickness, hyperintense signal within the dysplastic lesion, and blurred transition between gray and white matter (GM-WM). The visual identification of these abnormal characteristics may be difficult, and it is unclear to what degree these features occur among different FCD lesions. Our purpose was to investigate the pattern of occurrence of abnormal MRI characteristics in FCD by using a set of computational models and to generate quantitative lesion profiling. METHODS: A set of voxel-wise operators was applied to high-resolution 3D T1-weighted MRI in 23 patients with histologically proven FCD and 39 healthy controls, creating maps of GM thickness, maps of relative intensity highlighting areas with hyperintense signal, and maps of gradient magnitude modeling the GM-WM transition. All FCD lesions were segmented manually on the T1-weighted MRI. RESULTS: FCD volumes ranged from 734 mm3 to 80,726 mm3 (mean, 8,629 mm3 +/- 16,238). The manually segmented FCD lesions were used to estimate features in the lesional area and to determine possible local variations of each feature by means of a histogram. In 78% of the patients, FCD lesions were characterized by simultaneous GM thickening, hyperintense signal, and blurring of the GM-WM transition. Moreover, in all patients, the FCD lesion had at least two of these three characteristics. CONCLUSIONS: The three features occurred regardless of the lesion volume, and they characterized not only large FCD lesions, but also subtle ones that had been overlooked by conventional radiologic inspection before surgery.     

Distinct Patterns of Antiamyloid-β Antibodies in Typical and Atypical Alzheimer Disease

OBJECTIVE To compare serum antiamyloid-β (Aβ) antibodies in typical and atypical Alzheimer disease (AD). DESIGN Preliminary observations. SUBJECTS Thirteen patients with AD, 8 patients with posterior cortical atrophy with evidence of AD (PCA-AD) pathophysiological process by both cerebrospinal fluid (CSF) biomarkers and amyloid imaging, and 12 age-matched control individuals. INTERVENTIONS The class and subclass levels of serum anti-Aβ antibodies were measured using an oligomer-based enzyme-linked immunosorbent assay. This method allowed measuring both free antibodies and, after acidic treatment, the total fraction that includes all antibodies complexed with circulating Aβ40/42 and any cross-reacting antigen. RESULTS Anti-Aβ IgG were restricted to the IgG1 and IgG3 subclasses. Their total levels were strikingly lower and more homogeneous in patients with PCA compared with both typical AD and controls, while biomarkers of amyloid deposition (CSF Aβ42 and positron emission tomography amyloid imaging) were similar in patients with AD and patients with PCA. CONCLUSIONS Serum anti-Aβ IgG1 and IgG3 antibodies differ between distinct forms of AD. Its significance is discussed for possible implications as immune effectors in the specific pathophysiology of AD variants.     

Tissue at risk in the deep middle cerebral artery territory is critical to stroke outcome

Introduction  

The clinical efficacy of thrombolysis in stroke patients is explained by the increased rate of recanalization, which limits infarct growth. However, the efficacy could also be explained by the protection of specific sites of the brain. Here, we investigate where is this outcome-related tissue at risk using voxel-based analysis.     

Differential adhesion of Pseudomonas aeruginosa to human respiratory epithelial cells in primary culture.

Human nasal polyps in outgrowth culture were used to study the Pseudomonas aeruginosa adhesion to respiratory cells. By scanning electron microscopy, P. aeruginosa were seen associated with ciliated cells, but by transmission electron microscopy, bacteria were never seen at the interciliary spaces or attached along cilia, but were identified trapped at the extremities of cilia, usually as bacterial aggregates. A fibronectin-containing fibrillar material was seen associated with aggregated bacteria. By time-lapse video microscopy, bacteria were seen to aggregate in the culture medium following their addition to the culture wells. Progressively, these aggregates were trapped by cilia or attached to migrating cells of a lower cell layer that protruded beneath the upper layer cells, at the outgrowth periphery. P. aeruginosa adhesion to these lower cell layer migrating cells was significantly higher than to ciliated or nonciliated cells of the upper cell layer. Migrating cells were intensely labeled by the complexes Con A and arachis hypogea agglutinin (PNA)-FITC, in contrast to the other cells. The percentage of PNA-labeled cells with attached bacteria was significantly higher than that without bacteria. These results suggest that changes of cell surface glycoconjugates related with cell migration may favor P. aeruginosa adhesion to respiratory cells.     

Magnetic resonance imaging for diagnosis of early Alzheimer's disease

A major challenge for neuroimaging is to contribute to the early diagnosis of Alzheimer's disease (AD). In particular, magnetic resonance imaging (MRI) allows detecting different types of structural and functional abnormalities at an early stage of the disease. Anatomical MRI is the most widely used technique and provides local and global measures of atrophy. The recent diagnostic criteria of “mild cognitive impairment due to AD” include hippocampal atrophy, which is considered a marker of neuronal injury. Advanced image analysis techniques generate automatic and reproducible measures both in the hippocampus and throughout the whole brain. Recent modalities such as diffusion-tensor imaging and resting-state functional MRI provide additional measures that could contribute to the early diagnosis but require further validation.     

Is radiological evaluation as good as computer-based volumetry to assess hippocampal atrophy in Alzheimer’s disease?

Introduction

Hippocampus volumetry is a useful surrogate marker for the diagnosis of Alzheimer??s disease (AD). Our purpose was to compare visual assessment of medial temporal lobe atrophy made by radiologists with automatic hippocampal volume and to compare their performances for the classification of AD, mild cognitive impairment (MCI) and cognitively normal (CN).

Methods

We studied 30 CN, 30 MCI and 30 AD subjects. Six radiologists with two levels of expertise performed two readings of medial temporal lobe atrophy. Medial temporal lobe atrophy was evaluated on coronal three-dimensional T1-weighted images using Scheltens scale and compared with hippocampal volume obtained using a fully automatic segmentation method (Spearman??s rank coefficient).

Results

Visual assessment of medial temporal lobe atrophy was correlated with hippocampal volume (p?<?0.01). Classification performances between MCI converter and CN was better using volumetry than visual assessment of non-expert readers whereas classification of AD and CN did not differ between visual assessment and volumetry except for the first reading of one non-expert (p?=?0.03).

Conclusions

Visual assessment of medial temporal lobe atrophy by radiologists was well correlated with hippocampal volume. Radiological assessment is as good as computer-based volumetry for the classification of AD, MCI non-converter and CN and less good for the classification of MCI converter versus CN. Use of Scheltens scale for assessing hippocampal atrophy in AD seems thus justified in clinical routine.     

Spatial regularization of SVM for the detection of diffusion alterations associated with stroke outcome

In this paper, we propose a new method to detect differences at the group level in brain images based on spatially regularized support vector machines (SVM). We propose to spatially regularize the SVM using a graph Laplacian. This provides a flexible approach to model different types of proximity between voxels. We propose a proximity graph which accounts for tissue types. An efficient computation of the Gram matrix is provided. Then, significant differences between two populations are detected using statistical tests on the outputs of the SVM. The method was first tested on synthetic examples. It was then applied to 72 stroke patients to detect brain areas associated with motor outcome at 90 days, based on diffusion-weighted images acquired at the acute stage (median delay one day). The proposed method showed that poor motor outcome is associated to changes in the corticospinal bundle and white matter tracts originating from the premotor cortex. Standard mass univariate analyses failed to detect any difference on the same population.