Nicolas Chauveau

LIMO EEG: a toolbox for hierarchical linear modeling of electroencephalographic data

Magnetic- and electric-evoked brain responses have traditionally been analyzed by comparing the peaks or mean amplitudes of signals from selected channels and averaged across trials. More recently, tools have been developed to investigate single trial response variability (e.g., EEGLAB) and to test differences between averaged evoked responses over the entire scalp and time dimensions (e.g., SPM, Fieldtrip). LIMO EEG is a Matlab toolbox (EEGLAB compatible) to analyse evoked responses over all space and time dimensions, while accounting for single trial variability using a simple hierarchical linear modelling of the data. In addition, LIMO EEG provides robust parametric tests, therefore providing a new and complementary tool in the analysis of neural evoked responses.

Effects of the audiovisual conflict on auditory early processes.

Auditory alarm misperception is one of the critical events that lead aircraft pilots to an erroneous flying decision. The rarity of these alarms associated with their possible unreliability may play a role in this misperception. In order to investigate this hypothesis, we manipulated both audiovisual conflict and sound rarity in a simplified landing task. Behavioral data and event related potentials (ERPs) of thirteen healthy participants were analyzed. We found that the presentation of a rare auditory signal (i.e., an alarm), incongruent with visual information, led to a smaller amplitude of the auditory N100 (i.e., less negative) compared to the condition in which both signals were congruent. Moreover, the incongruity between the visual information and the rare sound did not significantly affect reaction times, suggesting that the rare sound was neglected. We propose that the lower N100 amplitude reflects an early visual-to-auditory gating that depends on the rarity of the sound. In complex aircraft environments, this early effect might be partly responsible for auditory alarm insensitivity. Our results provide a new basis for future aeronautic studies and the development of countermeasures.

Modular Cole phantom for parametric electrical impedance tomography

A phantom was designed for studying in vitro acquisition procedures and reconstruction algorithms for multifrequency electrical impedance tomography (EIT). The phantom mimics a circular region discretized in 208 square pixels whose sides are composed of Cole models. A modular design, based on plug-in boards, provides facilities for modifying the electrical parameters of any pixel. This phantom is used especially for studying tissue characterization by imaging the characteristic frequency.

A Case of Logopenic Primary Progressive Aphasia with C9ORF72 Expansion and Cortical Florbetapir Binding

We report the case of a 65-year-old woman, clinically diagnosed with the logopenic variant of primary progressive aphasia (PPA), and carrier of C9ORF72 expansion, despite cerebrospinal fluid biomarkers suggesting Alzheimers disease (AD). She underwent structural MRI, metabolic PET, and amyloid PET imaging using florbetapir. Comparison with healthy controls revealed widespread hypometabolism, left sided cortical atrophy, and an increased cortical amyloid load. No difference in amyloid binding was found between the patient and predemential AD patients. This case provides evidence of amyloidopathy in a carrier of C9ORF72 expansion exhibiting a clinical profile of the logopenic variant of PPA.

Brain Gray Matter Mri Morphometry for Neuroprognostication After Cardiac Arrest

Objectives: We hypothesize that the combined use of MRI cortical thickness measurement and subcortical gray matter volumetry could provide an early and accurate in vivo assessment of the structural impact of cardiac arrest and therefore could be used for long-term neuroprognostication in this setting. Design: Prospective cohort study. Setting: Five Intensive Critical Care Units affiliated to the University in Toulouse (France), Paris (France), Clermont-Ferrand (France), Liège (Belgium), and Monza (Italy). Patients: High-resolution anatomical T1-weighted images were acquired in 126 anoxic coma patients (“learning” sample) 16 ± 8 days after cardiac arrest and 70 matched controls. An additional sample of 18 anoxic coma patients, recruited in Toulouse, was used to test predictive model generalization (“test” sample). All patients were followed up 1 year after cardiac arrest. Interventions: None. Measurements and Main Results: Cortical thickness was computed on the whole cortical ribbon, and deep gray matter volumetry was performed after automatic segmentation. Brain morphometric data were employed to create multivariate predictive models using learning machine techniques. Patients displayed significantly extensive cortical and subcortical brain volumes atrophy compared with controls. The accuracy of a predictive classifier, encompassing cortical and subcortical components, has a significant discriminative power (learning area under the curve = 0.87; test area under the curve = 0.96). The anatomical regions which volume changes were significantly related to patient’s outcome were frontal cortex, posterior cingulate cortex, thalamus, putamen, pallidum, caudate, hippocampus, and brain stem. Conclusions: These findings are consistent with the hypothesis of pathologic disruption of a striatopallidal-thalamo-cortical mesocircuit induced by cardiac arrest and pave the way for the use of combined brain quantitative morphometry in this setting.

N270 sensitivity to conflict strength and working memory: A combined ERP and sLORETA study

The event-related potential N270 component is known to be an electrophysiological marker of the supramodal conflict processing. However little is know about the factors that may modulate its amplitude. In particular, among all studies that have investigated the N270, little or no control of the conflict strength and of the load in working memory have been done leaving a lack in the understanding of this component. We designed a spatial audiovisual conflict task with simultaneous target and cross-modal distractor to evaluate the N270 sensitivity to the conflict strength (i.e., visual target with auditory distractor or auditory target with visual distractor) and the load in working memory (goal task maintenance with frequent change in the target modality). In a first session, participants had to focus on one modality for the target position to be considered (left-hand or right-hand) while the distractor could be at the same side (compatible) or at opposite side (incompatible). In a second session, we used the same set of stimuli as in the first session with an additional distinct auditory signal that clued the participants to frequently switch between the auditory and the visual targets. We found that (1) reaction times and N270 amplitudes for conflicting situations were larger within the auditory target condition compared to the visual one, (2) the increase in target maintenance effort led to equivalent increase of both reaction times and N270 amplitudes within all conditions and (3) the right dorsolateral prefrontal cortex current density was higher for both conflicting and active maintenance of the target situations. These results provide new evidence that the N270 component is an electrophysiological marker of the supramodal conflict processing that is sensitive to the conflict strength and that conflict processing and active maintenance of the task goal are two functions of a common executive attention system.

Gray matter characteristics associated with trait anxiety in older adults are moderated by depression.

BACKGROUND Structural gray matter characteristics of anxiety remain unclear. The aim of this study was to assess the influence of current depressive symptoms and history of depression on the gray matter characteristics of trait anxiety. METHODS Structural magnetic resonance imaging (MRI) data from 393 individuals aged 65 years or older were used. Regions of interest (ROIs) included the amygdala, anterior cingulate cortex (ACC), insula, orbitofrontal cortex (OFC), and temporal cortex. Trait anxiety was measured by the State-Trait Anxiety Inventory (STAI). Depression and depressive symptoms were measured using DSM-IV criteria and the Center for Epidemiological Studies Depression Scale (CESD). RESULTS After adjustments for sociodemographics and health-related variables, anxiety had a significant influence on the gray matter characteristics in all cortical ROIs. First, in participants without depression antecedents, higher trait anxiety was associated with a larger cortical thickness in all cortical ROIs. Second, in participants with a previous history of depression, higher trait anxiety was associated with a smaller cortical thickness in all cortical ROIs. CONCLUSIONS These results suggest that anxiety is related to cortical thickness differently in healthy older adults and in older adults with psychiatric antecedents. Anxiety associated with thinner cortical areas could reflect symptoms of a specific type of depression or a vulnerability to develop depression.