L’érosion différentielle dans les reliefs de l’Estrie et de la Nouvelle-Angleterre, entre Montréal et le piedmont sud-est des White Mountains

Entre Montréal et Granby, dans une véritable plaine à inselbergs, ces derniers correspondent à des intrusions tantôt syénitiques, tantôt basiques : ils sont plus résistants que les calcaro-schistes cambro-ordoviciens. L'intrusion la plus orientale est celle du mont Mégantic, qui comporte un croissant syénitique enveloppant une bosse de granite. Les intrusions de granite dévonien de l'Estrie et du nord du Vermont sont souvent en creux, ce qui peut s'expliquer soit par leur composition granodioritique (alvéole d'Island Pond), soit par une intense microfissuration (alvéole de Scotstown). La position culminante des White Mountains paraît due (en grande partie) à l'érosion différentielle. Les séries de Littleton, où les unités schisteuses sont aussi résistantes que les éléments quartzitiques et gneissiques. dominent, au nord, les gneiss olivériens, dont la position déprimée est attribuable à leur fracturation, non suivie de recristallisation, et ailleurs, les granites de Bickford, pourtant relativement acides. En position culminante se placent également les syenites et les granites à hastingsite mésozoïques. Quant aux granites dits de Conway, tantôt ils sont troués par d'amples cuvettes, tantôt ils constituent des fiers monolithes limités par des diaclases espacées. C'est que ces roches sont très hétérogènes, tantôt blanches et acides, tantôt grises et riches en biotite et en hornblende, ainsi qu'en plagioclases. Au total, les roches occupant le sommet de l'échelle de dureté sont celles où les perthites et les microperthites constituent une trame continue. Pour les autres variétés de roches, le degré de microfissuration et la composition minéralogique jouent alternativement le rôle principal.Between Montréal and Granby, the studied profile cuts across a true erosion plain where inselbergs coincide with syenitic and basic intrusions more resistant than the Cambro-Ordovician calcareous shales and schists. Mount Mégantic, the most eastern intrusion consists of a syenitic crescent and a granitic boss. In the Eastern Townships and northern Vermont, Devonian granitic intrusions are often hollowed out into basins. This derives either from their granodioritic composition (Island Pond) or from severe microfissuration (Scotstown). The prominent position of the White Mountains seems to be due to selective erosion. The Littleton Series, where schistous units are as resistant as the quartzitic and gneissic elements, rise on their northern boundary above the oliverian gneisses. These were easily eroded since no recrystallization occurred after fracturing. Elsewhere, the Littleton Series rise above Bickford granites despite the rather acid composition of the latter. Mesozoic hastingsite syenites and granites also have a prominent position. As for the granites classified as Conway granites, they range from white and acid varieties to grey varieties with a high content of plagioclases, biotites and hornblende. This heterogeneity may explain the topographic contrast between huge basins and monoliths, the latter being limited by spaced joints. The rocks at the top of the hardness scale are those where the main components, perthites and microperthites, form the structural grain. As for the other types of rocks, the degree of microfissuration (determined after microscopic examination and measurement of the filtration rate of coloured water) and the mineralogical composition oalternately intervene as the main element.Zwischen Montréal und Granby uberquert das erforschte Profil eine echte Erosionsebene, wo lnselberge mit syenetischen und basischen lntrusionen zusammenfallen, die widerstandsfâhiger als die Cambro-Ordovician Kalkâr Schalen und Schiefer sind. In der Estrie und im nôrd-lichen Vermont, sind devoniasniche Graniti intrusionen oft zu Becken ausgehôlt. Das kommt entweder von ihrer granodioritischen Zusammensetzung (Island Pond) Oder von hâftiger Mikrospaltung (Scotstown) her. Die hervorstehende Stellung der White Mountains scheint hauptsâchlich, aber nicht ausschliesslich, von selektiver Erosion zu stammen. Die Littleton Series, wo schieferhaltige Einheiten aus noch unbekannten Grunden, ebenso widerstandsfàhig wie die Quartzund Gneisselemente sind, erheben sich an ihrer nôrdlichen Grenze uber die oliveranischen Gneisse. Die wurden leicht erodiert weil es nach der Frakturation keine Rekristalisation gab. Anderswo erheben sich die Littleton Series uber Bickford Granite, trotz deren ziemlich saurer Beschaffenheit. Diese Mannigfaltigkeit kann vielleich den topographischen Kontrast zwischen grossen Becken und Monolithen erklâren, letztere findet man hauptsâchlich in durch Fugen begrenzten Randstellungen. Das Gestein am Gipfel der Hârteskala, hat als Hauptkomponenten Bethite und Mikroperthite, die, die strukturelle Kôrnung bilden. Fur die anderen Gesteinstypen kommen der Grad der Mikrospaltung (bestimmt durch mikroskopische Prufung und Messung der Filtrationsgeschwindigkeit von gefarbtem Wasser) und die mineralogische Zusammensetzung abwechselnd las Hauptelement vor

Electrical source imaging and connectivity analysis to localize the seizure-onset zone based on high-density ictal scalp EEG recordings

Functional connectivity analysis of ictal intracranial EEG (icEEG) recordings can help with seizure-onset zone (SOZ) localization in patients with focal epilepsy1. However, it would be of high clinical value to be able to localize the SOZ based on non-invasive ictal EEG recordings to better target or avoid icEEG and improve surgical outcome. In this work, we propose an approach to localize the SOZ based on non-invasive ictal high- density EEG (hd-EEG) recordings. We considered retrospective ictal hd-EEG recordings of two patients who were rendered seizure free after surgery. Furthermore, we simulated 1000 ictal hd-EEG epochs of 10s with an underlying network consisting of 3 randomly placed epileptic patches in the brain. EEG source imaging (ESI) was performed in CARTOOL using an individual head model (LSMAC) to calculate the forward model2. We considered dipoles uniformly distributed in the brain with a spacing of 5mm. LORETA3 was used as inverse solution method. Center dipoles of clusters with high activation were determined as dipoles for which there was no higher power in their neighborhood. The time-varying connectivity pattern between the time series of these dipoles was calculated using the integrated, full-frequency, and spectrum-weighted Adaptive Directed Transfer Function4. This was done in the frequency band containing the seizure information, 3-30Hz. The outdegree of each selected dipole was determined as the sum over time of all outgoing connections. Around the dipole with the highest outdegree, we determined a region of dipoles that had a power that was at least 90% of the power of the center dipole. This region was then considered as the SOZ. We were able to successfully localize the driver in the resected zone for both patients. For the simulation data, the results can be quantified: in 71% of the simulations, the localization error remained below 25mm. If the selection of the dipole would be solely based on the highest power, the error would be more than 82mm. ESI in combination with connectivity analysis can successfully localize the SOZ in non- invasive ictal hd-EEG recordings and outperforms localization based on power. This could have important clinical relevance for the presurgical evaluation in focal epilepsy. References: 1. van Mierlo, P et al. (2014) Prog Neurobiol. 121:19-35. 2. Brunet, D. et al. (2011) Comput. Intell. Neurosci. 2. 3. Pascal-Marqui, R.D., et al. (1994) Int. J. Psychophysiol. 18(1):49-65. 4. van Mierlo, P. et al. (2013) Epilepsia 54.8:1409-1418

Seizure onset zone localization from ictal high-density EEG in five patients

Rationale Because epilepsy is a network disease, localization of the exact seizure onset zone (SOZ) is difficult because the epileptic activity can spread to other regions within milliseconds. Functional connectivity metrics quantify how the activity in different brain regions is interrelated. In the past, it has been shown that functional connectivity analysis of ictal intracranial EEG (icEEG) recordings can help with SOZ localization in patients with focal epilepsy (van Mierlo et al., 2014). However, it would be of high clinical value to be able to localize the SOZ based on non-invasive ictal EEG recordings to optimize the icEEG implantation scheme or to avoid invasive monitoring and improve surgical outcome. In this work, we propose an approach to localize the SOZ based on non-invasive ictal high-density EEG (hd-EEG) recordings. Methods We considered retrospective ictal epochs of 2.4 s up to 10 s recorded with hd-EEG (256 electrodes) in five patients who were rendered seizure free after surgery. From the 256 electrodes, the facial electrodes were removed, resulting in a subset of 204 electrodes. A 28-channel subset was constructed to mimic a low-density (ld) electrode setup used in clinical practice. EEG source imaging (ESI) was performed in the CARTOOL software using an individual head model (LSMAC) to calculate the forward model (Brunet et al., 2011). We considered sources uniformly distributed in the brain with a spacing of 5 mm. LORETA (Pascal-Marqui et al., 1994) was used as inverse solution method. In each cluster of activity, we determined a central source based on the criterion that there was no higher power in its neighborhood. The time-varying connectivity pattern between the time series of these sources was calculated using Granger causality (van Mierlo et al., 2013). This was done in the frequency band containing the fundamental seizure frequency, 3-30Hz. The outdegree of each selected dipole was determined as the sum over time of all outgoing connections. Around the dipole with the highest outdegree, we determined a region of dipoles that had a power that was at least 90% of the power of the center dipole. This region was then considered as the SOZ. Results We were able to successfully localize the driver in the resected zone for all patients based on ESI followed by connectivity analysis of the hd-EEG (mean localization error (LE) = 0 mm). If we chose the cluster with the highest power as driver, the mean LE was 59.69 mm. For the ld-EEG, ESI followed by connectivity analysis resulted in a mean LE of 23.30 mm and when selecting the cluster with the highest power as driver, the mean LE was 31.21 mm. Conclusions ESI in combination with connectivity analysis can successfully localize the SOZ in non-invasive ictal hd-EEG recordings and greatly outperforms localization based on power. For ld-EEG recordings, the localization error remains significant but still outperforms localization based on power. This could have important clinical relevance for the presurgical evaluation in focal epilepsy

Localization of extended brain sources from EEG/MEG: The ExSo-MUSIC approach.

International audienceWe propose a new MUSIC-like method, called 2q-ExSo-MUSIC (q≥1). This method is an extension of the 2q-MUSIC (q≥1) approach for solving the EEG/MEG inverse problem, when spatially-extended neocortical sources ("ExSo") are considered. It introduces a novel ExSo-MUSIC principle. The novelty is two-fold: i) the parameterization of the spatial source distribution that leads to an appropriate metric in the context of distributed brain sources and ii) the introduction of an original, efficient and low-cost way of optimizing this metric. In 2q-ExSo-MUSIC, the possible use of higher order statistics (q≥2) offers a better robustness with respect to Gaussian noise of unknown spatial coherence and modeling errors. As a result we reduced the penalizing effects of both the background cerebral activity that can be seen as a Gaussian and spatially correlated noise, and the modeling errors induced by the non-exact resolution of the forward problem. Computer results on simulated EEG signals obtained with physiologically-relevant models of both the sources and the volume conductor show a highly increased performance of our 2q-ExSo-MUSIC method as compared to the classical 2q-MUSIC algorithms

Recherche et développement : idées reçues et réalités

Il existe une certaine confusion entre les termes études, expérimentations, recherche fondamentale, recherche finalisée... Plus largement, la position de la recherche dans la société et plus particulièrement dans le milieu des espaces forestiers méditerranéens mériterait d'être mieux appréhendée. Dans cet article, Yves Birot nous apporte un éclairage sur tous ces points, en écartant au passage mythes, idées reçues et stéréotypes

Science serving forestry in the Mediterranean Region : the ways ahead -

The aim of the first session of the Mediterranean Forestry Week, held in Avignon on April 5-8, 2011, was to present the current context: the environment of the Mediterranean Rim in a mutating world and, especially, an account of the role of forests and science faced with the major challenges and issues. In this context Yves Birot gave a synopsis of the different approaches science has to offer on these questions: what has been learnt and achieved, pooling knowledge, perspectives..

La science au service de la foresterie en région méditerranéenne : les voies du futur -

La première session de la Semaine forestière méditerranéenne qui s'est déroulée à Avignon du 5 au 8 avril 2011, avait pour objectif de présenter le contexte actuel : l'environnement de la Méditerranée dans un monde en mutation et, plus particulièrement, d'y décrire le rôle des forêts et de la science face aux grands défis. C'est dans ce cadre qu'Yves Birot fait, dans cet article, le tour des différentes approches de la science sur ces questions : acquis, partage des connaissances, perspectives..

Artificial canopy bridges improve connectivity in fragmented landscapes: The case of Javan slow lorises in an agroforest environment

Canopy bridges are increasingly used to reduce fragmentation in tropical habitats yet monitoring of their impact on the behavior of primates remains limited. The Javan slow loris (Nycticebus javanicus) is endemic to Java, Indonesia, where the species most often occurs in human-dominated, highly patchy landscapes. Slow lorises cannot leap, are highly arboreally adapted, and are vulnerable on the ground. To increase arboreal connectivity, as part of a long-term conservation project in Cipaganti, West Java, we built and monitored seven slow lorises bridges of two types – waterline or rubber – and monitored their use by seven adult individuals from 2016-2017. Motion triggered camera traps collected data for 195 ± SD 85 days on each bridge. We collected 341.76 hours (179.67 h before and 162.09 h after the installation of bridges) of behavioral and home range data via instantaneous sampling every 5-min, and terrestrial behavior (distance and duration of time spent on the ground) via all occurrences sampling. We found that slow lorises used bridges on average 12.9 ± SD 9.7 days after their instalment mainly for travelling. Slow lorises showed a trend towards an increase in their home range size (2.57 ha before, 4.11 ha after; p=0.063) and reduced ground use (5.98 s/h before, 0.43 s/h; p=0.063) after implementation of bridges. Although the number of feeding trees did not change, new feeding trees were included in the home range, and the proportion of data points spent travelling and exploring significantly decreased (p=0.018). Waterline bridges serve a purpose to irrigate the crops of local farmers who thus help to maintain the bridges, and also ascribe value to the presence of slow lorises. Other endemic mammal species also used the bridges. We advocate the use and monitoring of artificial canopy bridges as an important supplement for habitat connectivity in conservation interventions