Is there an optimal stimulation rate for frequency-tagged visual word-selective responses?

peer reviewedThe existence of inter-individual variability in hemispheric dominance for word recognition processes still needs to be understood. Unfortunately, there are methodological and practical limitations in using neuroimaging techniques and linguistic tasks to determine language lateralisation. Fast Periodic Visual Stimulation (FPVS) coupled with EEG provides objective and sensitive measures of visual recognition processes without explicit tasks required. Indeed, by using a visual word oddball paradigm in which every 5th of the 10 images presented in one second (10Hz base stimulation), a word is inserted (2Hz) in rapid streams of non-words or pseudo-words, a robust index of lexical representation in the left occipito-temporal cortex has been revealed (Lochy et al., 2015). Here we use this promising technique, to determine if there is an optimal stimulation rate for frequency-tagged visual word-selective responses. For this, words are embedded in streams of non-words (i.e., pre-lexical discrimination) or pseudo-words (i.e., lexical discrimination) at a periodic rate, giving rise to frequency-tagged word-selective responses. We used four different frequencies (4 to 20Hz base frequency), to assess if word responses vary in amplitude and topography according to stimulation rate. For all frequencies, words are inserted at 1Hz, at the last frame of the base frequency except for one frequency at 10Hz (i.e., base stimulation) with 2Hz for the oddball frequency. 41 participants were tested both in EEG-FPVS and with reading tests. Reading performance was measured to see if visual word-selective response is modulated by reading speed and/or performance. We found differences in amplitude according to the level of discrimination of the word with a significantly higher amplitude at the visual word-selective response for pre-lexical than lexical discrimination. For both conditions, amplitude and topography differ according to stimulation rate with a strong left activation found at 4Hz and at 10Hz stimulation rate (2Hz at the oddball frequency). Even if responses are more bilateral at 4Hz in non-words condition, no significant difference was found between the left amplitude of these two frequencies. We then found a significant correlation only at 4Hz for lexical word discrimination with reading speed. The faster a person reads a word, the higher the amplitude of the word-selective response in a lexical discrimination over the occipitotemporal cortex. These results suggest that optimal frequencies of stimulation as well as lateralisation vary with the type of word-selective response. However, 4Hz seems to be the most adapted frequency to lead to a stronger left response for word-selective discrimination depending on the reading performance

The biotope of branchial ectoparasites of fishes : factors of variations in the pattern sea bass - monogeneans

International audienceFor the analysis of functional structure of communities, the ecologists are obliged to extend their investigations to the heterogeneity of their environment and colonized biotopes. The gills of sea bass Dicentrarchus labrax serve as a biotope for several ectoparasites ; some aspects of the heterogeneity of this biotope were studied quantitatively. The models expressing the variations of number of branchial filaments, and branchial area that can be colonized by monogeneans, were established in function of the lenght of fishes. Such biotopes being subjected to significant physical modifications, the effects of the latter over the organization of parasitic settlements are then discussed

Factitious lymphoedema as a psychiatric condition mimicking reflex sympathetic dystrophy: a case report

<p>Abstract</p> <p>Introduction</p> <p>Reflex sympathetic dystrophy can result in severe disability with only one in five patients able to fully resume prior activities. Therefore, it is important to diagnose this condition early and begin appropriate treatment. Factitious lymphoedema can mimic reflex sympathetic dystrophy and is caused by self-inflicted tourniquets, blows to the arm or repeated skin irritation. Patients with factitious lymphoedema have an underlying psychiatric disorder but usually present to emergency or orthopaedics departments. Factitious lymphoedema can then be misdiagnosed as reflex sympathetic dystrophy. The treatment for factitious lymphoedema is dealing with the underlying psychiatric condition.</p> <p>Case presentation</p> <p>We share our experience of treating a 33-year-old man, who presented with factitious lymphoedema, initially diagnosed as reflex sympathetic dystrophy.</p> <p>Conclusion</p> <p>Awareness of this very similar differential diagnosis allows early appropriate treatment to be administered.</p

HIV-1/M+O INTERGROUP DUAL INFECTIONS AND ASSOCIATED HIV-MO RECOMBINANTS IN FRANCE FROM 2004 TO 2014

International audienc

Intracerebral electrical stimulation of the left word-selective temporal cortex induces pure alexia

peer reviewedThe ability to read relies on the rapid mapping of perceived visual letters and their combinations (i.e., visual word forms) to phonology and meaning. The central role of the left ventral occipito-temporal cortex (VOTC) in processing letter strings, initially suggested by pure alexia in lesion studies, is now widely accepted. While this region has been intensely studied with functional MRI, direct electrical stimulation (DES) has rarely been used, although it allows a more direct assessment of causality between region(s) and function(s). Moreover, the few DES case studies reported did not provide stringent evaluation of the stimulation effect on reading performance. Here we report a comprehensive case of pure alexia during DES of the left VOTC (subject LV, female, 38 y.o, implanted with SEEG electrodes for refractory epilepsy). During DES of the left posterior occipito-temporal sulcus, but not of other sites, LV was transiently impaired at reading single words (performance on paper without time constraint: 99% correct before and after stimulation vs. 71% during stimulation) but was still able to slowly read letter-by-letter. LV was also impaired at making lexical decision on written words/pseudo-words (performance on paper: 100% vs. 75%; on computer screen: 92% vs. 72%), showing that she had impaired access to the lexico-semantic representation of the words. By contrast, performance was intact during stimulation for oral naming, auditory naming, reading numbers, writing, auditory lexical decision or semantic matching of pictures. Independent functional mapping using a frequency-tagging approach in SEEG showed that the stimulated site was located in a highly word-selective region. Altogether, our results show that DES of the word-selective left VOTC induced pure alexia remarkably selective to words readin

Probabilistic functional tractography of the human cortex revisited

In patients with pharmaco-resistant focal epilepsies investigated with intracranial electroencephalography (iEEG), direct electrical stimulations of a cortical region induce cortico-cortical evoked potentials (CCEP) in distant cerebral cortex, which properties can be used to infer large scale brain connectivity. In 2013, we proposed a new probabilistic functional tractography methodology to study human brain connectivity. We have now been revisiting this method in the F-TRACT project (f-tract.eu) by developing a large multicenter CCEP database of several thousand stimulation runs performed in several hundred patients, and associated processing tools to create a probabilistic atlas of human cortico-cortical connections. Here, we wish to present a snapshot of the methods and data of F-TRACT using a pool of 213 epilepsy patients, all studied by stereo-encephalography with intracerebral depth electrodes. The CCEPs were processed using an automated pipeline with the following consecutive steps: detection of each stimulation run from stimulation artifacts in raw intracranial EEG (iEEG) files, bad channels detection with a machine learning approach, model-based stimulation artifact correction, robust averaging over stimulation pulses. Effective connectivity between the stimulated and recording areas is then inferred from the properties of the first CCEP component, i.e. onset and peak latency, amplitude, duration and integral of the significant part. Finally, group statistics of CCEP features are implemented for each brain parcel explored by iEEG electrodes. The localization (coordinates, white/gray matter relative positioning) of electrode contacts were obtained from imaging data (anatomical MRI or CT scans before and after electrodes implantation). The iEEG contacts were repositioned in different brain parcellations from the segmentation of patients' anatomical MRI or from templates in the MNI coordinate system. The F-TRACT database using the first pool of 213 patients provided connectivity probability values for 95% of possible intrahemispheric and 56% of interhemispheric connections and CCEP features for 78% of intrahemisheric and 14% of interhemispheric connections. In this report, we show some examples of anatomo-functional connectivity matrices, and associated directional maps. We also indicate how CCEP features, especially latencies, are related to spatial distances, and allow estimating the velocity distribution of neuronal signals at a large scale. Finally, we describe the impact on the estimated connectivity of the stimulation charge and of the contact localization according to the white or gray matter. The most relevant maps for the scientific community are available for download on f-tract. eu (David et al., 2017) and will be regularly updated during the following months with the addition of more data in the F-TRACT database. This will provide an unprecedented knowledge on the dynamical properties of large fiber tracts in human.Peer reviewe

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio