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International audience; Abstract The superior temporal sulcus (STS) is a conserved fold that divides the middle and superior temporal gyri. In humans, there is considerable variation in the shape, folding pattern, lateralization, and depth of the STS that have been reported to be associated with social cognition and linguistic functions. We examined the role that genetic factors play on individual variation in STS morphology in chimpanzees. The surface area and depth of the STS were quantified in sample of 292 captive chimpanzees comprised of two genetically isolated population of individuals. The chimpanzees had been previously genotyped for AVPR1A and KIAA0319, two genes that play a role in social cognition and communication in humans. Single nucleotide polymorphisms in the KIAA0319 and AVPR1A genes were associated with average depth as well as asymmetries in the STS. By contrast, we found no significant effects of these KIA0319 and AVPR1A polymorphism on surface area and depth measures for the central sulcus. The overall findings indicate that genetic factors account for a small to moderate amount of variation in STS morphology in chimpanzees. These findings are discussed in the context of the role of the STS in social cognition and language in humans and their potential evolutionary origins.

International audience; Introduction: Approximately 40% of dementia cases could be delayed or prevented acting on modifiable risk factors including hypertension. However, the mechanisms underlying the hypertension-dementia association are still poorly understood.Methods: We conducted a cross-sectional analysis in 2048 patients from the MEMENTO cohort, a French multicenter clinic-based study of outpatients with either isolated cognitive complaints or mild cognitive impairment. Exposure to hypertension was defined as a combination of high blood pressure (BP) status and antihypertensive treatment intake. Pathway associations were examined through structural equation modeling integrating extensive collection of neuroimaging biomarkers and clinical data.Results: Participants treated with high BP had significantly lower cognition compared to the others. This association was mediated by higher neurodegeneration and higher white matter hyperintensities load but not by Alzheimer's disease (AD) biomarkers.Discussion: These results highlight the importance of controlling hypertension for prevention of cognitive decline and offer new insights on mechanisms underlying the hypertension-dementia association.Highlights: Paths of hypertension-cognition association were assessed by structural equation models. The hypertension-cognition association is not mediated by Alzheimer's disease biomarkers. The hypertension-cognition association is mediated by neurodegeneration and leukoaraiosis. Lower cognition was limited to participants treated with uncontrolled blood pressure. Blood pressure control could contribute to promote healthier brain aging.

We present an automatic algorithm for the group-wise parcellation of the cortical surface. The method is based on the structural connectivity obtained from representative brain fiber clusters, calculated via an inter-subject clustering scheme. Preliminary regions were defined from cluster-cortical mesh intersection points. The final parcellation was obtained using parcel probability maps to model and integrate the connectivity information of all subjects, and graphs to represent the overlap between parcels. Two inter-subject clustering schemes were tested, generating a total of 171 and 109 parcels, respectively. The resulting parcels were quantitatively compared with three state-of-the-art atlases. The best parcellation returned 69 parcels with a Dice similarity coefficient greater than 0.5. To the best of our knowledge, this is the first diffusion-based cortex parcellation method based on whole-brain inter-subject fiber clustering.

International audience; Objective: To assess the role of biomarkers of Alzheimer's Disease (AD), neurodegeneration and small vessel disease (SVD) as mediators in the association between diabetes mellitus and cognition.Methods: The study sample was derived from MEMENTO, a cohort of French adults recruited in memory clinics and screened for either isolated subjective cognitive complaints or mild cognitive impairment. Diabetes was defined based on blood glucose assessment, use of antidiabetic agent or self-report. We used structural equation modelling to assess whether latent variables of AD pathology (PET mean amyloid uptake, Aβ42/Aβ40 ratio and CSF phosphorylated tau), SVD (white matter hyperintensities volume and visual grading), and neurodegeneration (mean cortical thickness, brain parenchymal fraction, hippocampal volume, and mean fluorodeoxyglucose uptake) mediate the association between diabetes and a latent variable of cognition (five neuropsychological tests), adjusting for potential confounders.Results: There were 254 (11.1%) participants with diabetes among 2,288 participants (median age 71.6 years; 61.8% women). The association between diabetes and lower cognition was significantly mediated by higher neurodegeneration (standardized indirect effect: -0.061, 95% confidence interval: -0.089; -0.032), but not mediated by SVD and AD markers. Results were similar when considering latent variables of memory or executive functioning.Conclusion: In a large clinical cohort in the elderly, diabetes is associated with lower cognition through neurodegeneration, independently of SVD and AD biomarkers.

International audience; Imaging-genetics cohorts allow to find associations between genotyped variants and brain imaging features. They are invaluable tools to evaluate the part of genetics and environment in the brain characteristic variance observed in normal and pathological populations. The present analyses were conducted using the 2018 UK Biobank (UKB) data release, and included 15,040 subjects for which sulcal opening, a measure of sulcus width, are extracted for 126 sulci using BrainVisa/Morphologist pipeline. Based on genetic maps, continuous blocks of high-confidence phase are extracted using the haplotype dataset of UK Biobank. The feasibility study analyzes 13,942 haplotypes of 1,756 blocks on chromosome 21, obtained with a stringent block definition, and shows that block-based test seems underpowered compared to haplotype-based association test.

Background and Purpose— Recently, in a mouse model of cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy, a monogenic cerebral small vessel disease, intramyelinic edema was detected in the white matter (WM) early during the course of the disease. We hypothesized that if this mechanism holds true in patients, it would translate in larger WM volume. We aimed to measure WM volume in patients with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy in comparison with age- and sex-matched controls, along with the ratio of cortical surface area to the volume of brain hemispheres as an indirect measure that should be reduced in patients. Methods— Twenty patients at the early stage of the disease (Mini Mental State Examination >24 and modified Rankin scale ≤1) and 27 age- and sex-matched controls had high-quality 3-Tesla 3DT1 MRI acquisitions. Volumes of brain hemispheres and of WM were determined. The ratio of cortical surface area to the volume of brain hemispheres was evaluated as a proxy of underlying WM volume. Results— Patients had larger volumes of WM than controls (patients: 479.4±71.7; controls: 463.9±44.2; P =0.03). They presented a lower cortical surface area and cortical volume leading to a lower ratio of cortical surface area to the volume of brain hemispheres (patients: 15.7±0.7; controls: 16.1±0.5; P =0.004). Volume of WM tended to be associated with that of WM hyperintensities ( P =0.06). Conclusions— Patients with cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy have larger WM volume than age- and sex-matched controls, a finding compatible with the hypothesis of intramyelinic edema as observed recently in mice.

Background and Purpose— Lacunes are a major manifestation of cerebral small vessel disease. Although still debated, the morphological features of lacunes may offer mechanistic insights. We systematically analyzed the shape of incident lacunes in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, a genetically defined small vessel disease. Methods— A total of 88 incident lacunes from 57 patients were segmented from 3-dimensional T1 magnetic resonance images and 3 dimensionally reconstructed. Anatomic location, diameter, volume, surface area, and compactness of lacunes were assessed. The shape was analyzed using a size, orientation, and position invariant spectral shape descriptor. We further investigated the relationship with perforating arteries and fiber tracts. Results— Lacunes were most abundant in the centrum semiovale and the basal ganglia. Diameter, volume, and surface area of lacunes in the basal ganglia and centrum semiovale were larger than in other brain regions. The spectral shape descriptor revealed a continuum of shapes with no evidence for distinct classes of lacunes. Shapes varied mostly in elongation and planarity. The main axis and plane of lacunes were found to align with the orientation of perforating arteries but not with fiber tracts. Conclusions— Elongation and planarity are the primary shape principles of lacunes. Their main axis and plane align with perforating arteries. Our findings add to current concepts on the mechanisms of lacunes.

IC-P-166 AUTOMATIC DIFFUSION-BASED FRACTIONAL ANISOTROPY MEASUREMENTS WEIGHTED BY FIBER DENSITY Adam Schwarz, Clarisse Longo dos Santos, Delphine Duclap, Cyril Poupon, Lea Marais, Derek Hill, Adam Schwarz, Jean-Francois Mangin, Eli Lilly and Company, Indianapolis, Indiana, United States; CEA, Gif-sur-Yvette, ~ A Zle-de-France, France; CEA IBM NeuroSpin, Gif-sur-Yvette, ~ A Zle-de-France, France; IXICO, London, United Kingdom; IXICO Ltd., London, United Kingdom; Eli Lilly, Indianapolis, Indiana, United States. Contact e-mail: a.schwarz@lilly.com

Space geodetic techniques of artificial satellites tracking have been greatly improved since this last decade. Particularly, the successful development of radio tracking systems like GPS, DORIS, and PRARE has to be emphasized, concerning precise positioning, orbit determination, and gravity field determination. All these techniques are able to operate under all weather conditions and are of very easy use. In fact, all the complexity of systems is to be found in space on board the satellites. To some extent, for laser satellite tracking, the situation is the opposite. It is weather dependent and comparatively complex and costly at the ground level. However, this technique is the most straightforward in concept for accurate measuring of the Earth-satellite distance. But, it is true, provided that instrumental biases can be well understood and precisely estimated. As a result, the role of laser tracking has to be reassessed and the control of range biases is nowadays of the utmost importance. Therefore, the international organization for laser cooperation has been reconsidered and the purpose of this paper is to present the effort made in this field at the Grasse, France observatory.

Analysis of functional images of the brain increasingly relies on individual anatomy of subjects. The aim is the construction of accurate anatomy-indexed functional mappings which would be of crucial importance for neurosurgical planning. The major difficulty relies in the important inter-subject structural variability of the cortical anatomy. In this paper, we assume that a large part of this variability can be overcome if more elementary and stable units than sulci and gyri are chosen to analyse cortex anatomy. Hence, we try to highlight such features using differential geometry. A method extracting cortical fold crest lines is described first. Then a morphological decomposition of sulci along crest lines is proposed. Finally, the relevance of this approach is demonstrated by a segmentation of central sulcus into two stable parts for ten subjects.

At the Wettzell Laser Ranging System [1] (WLRS, Germany), the AvalanchePhotodiode 5P1141 was operated successfully at a wavelength of 532 nm as wellas at 1.064 m. The detector was found to have a high sensitivity, a high accu-racy and was convenient to use. To analyze it's sensitivity in detail, a commonexperiment was planned and carried out, at the Lunar Laser Ranging Station in GRASSE [2] (France). This ranging experiment to the most demanding targets allowed a direct comparison between the well known characteristics ofthe RCA 31034a photomultiplier and the 5P114. Under varying configurations,measurements were taken from all lunar targets. It was found, that the SP114had a sensitivity and accuracy far above the photomultiplier. 1. THE EXPERIMENTAL SETUP Figure 1 outlines the optical receive path of the LLR- Station GRASSE. The field ofview of the 1.5 m aperture telescope is focused onto a diaphragm for spatial filtering.A dichroic mirror separates the two different laser frequencies used, before the beam

We propose a method to calculate brain attenuation correction factors (ACF) for quantitative PET using MRI data in clinical protocols that require both modalities. In that case the elimination of the transmission scan will simplify the protocol and reduce the patient dose while preserving the accurate quantification. Moreover possible mispositioning between transmission and emission acquisitions, which is not usually accounted for, may be avoided.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

P18 Background and Purpose: Variable microstructural changes have been reported within the white-matter in CADASIL. Lacunar infarcts are frequently observed in the subcortical grey matter. However, whether microstructural tissular alterations are also present within the non-infarcted putamen (NIP) or thalamus (NIT), remains unknown. Methods: We used diffusion tensor imaging, a MRI method highly sensitive to the cerebral microstructure, in 20 CADASIL patients and 12 age-matched controls. Both Trace(D) and anisotropy (volume-ratio index) of diffusion were measured within the NIP and NIT. In addition, diffusion parameters and the load of small infarcts were calculated within the white-matter of the centrum semi-ovale. A one way ANOVA was performed to compare the diffusion parameters between patients and controls. Thereafter, correlations between the significant results in our patients and the diffusion parameters in the white-matter or the MMSE scores were tested. Results: A significant increase in Trace(D) and decrease in anisotropy were observed in both the NIP and NIT in our patients. Conversely to the results in the NIP, only significant in the presence of associated putaminal infarcts, the diffusion changes in the NIT were significant both in the presence and absence of associated thalamic infarcts. The asymmetry indices of Trace(D) in the NIT and in the white-matter were strongly correlated. The diffusion increase in the NIT was also positively correlated both to Trace(D) and to the load of small deep infarcts within the centrum semi-ovale. Elsewhere, the diffusion increase in the NIT, but not in the NIP, was negatively correlated to the MMSE score in our patients. Conclusions: These results suggest that microstructural alterations are present in both the NIP and NIT in CADASIL. In the NIT, microstructural alterations appear secondary to remote lesions of thalamo-cortical pathways. Diffusion measured in the NIT mirror both the degree of white-matter tissular damage and the clinical severity in CADASIL. This study highlights the importance of secondary neurodegeneration in a typical model of “pure vascular dementia”.

This second issue of the French Complex Systems Roadmap is the outcome of the Entretiens de Cargese 2008, an interdisciplinary brainstorming session organized over one week in 2008, jointly by RNSC, ISC-PIF and IXXI. It capitalizes on the first roadmap and gathers contributions of more than 70 scientists from major French institutions. The aim of this roadmap is to foster the coordination of the complex systems community on focused topics and questions, as well as to present contributions and challenges in the complex systems sciences and complexity science to the public, political and industrial spheres.