Nouvelles techniques de stimulation cérébrale: perspectives thérapeutiques en psychiatrie [Novel brain stimulation techniques: therapeutic perspectives in psychiatry]

Recent advances have allowed the development of new physical techniques in neurology and psychiatry, such as Transcranial Magnetic Stimulation (TMS), Vagus Nerve Stimulation (VNS), and Deep Brain Stimulation (DBS). These techniques are already recognized as therapeutic approaches in several late stage refractory neurological disorders (Parkinson's disease, tremor, epilepsy), and currently investigated in psychiatric conditions, refractory to medical treatment (obsessive-compulsive disorder, resistant major depression). In Paralell, these new techniques offer a new window to understand the neurobiology of human behavior.

Growth and demise of Permian biogenic chert along northwest Pangea: evidence for end-Permian collapse of thermohaline circulation

The Permian Chert Event (PCE) was a 30 Ma long episode of unusual chert accumulation along the northwest margin of Pangea, and possibly worldwide. The onset of the PCE occurred at about the Sakmarian-Artinskian boundary in the Sverdrup Basin, Canadian Arctic, where it coincides with a maximum flooding event, the ending of high-frequency/high-amplitude shelf cyclicity, the onset of massive biogenic chert deposition in deep-water distal areas, and a long-term shift from warm- to cool-water carbonate sedimentation in shallow-water proximal areas. A similar and coeval shift is observed from the Barents Sea to the northwestern USA. A landward and southward expansion of silica factories occurred during the Middle and Late Permian at which time warm-water carbonate producers disappeared completely from the northwest margin of Pangea. Biotically impoverished and increasingly narrow cold-water carbonate factories (characterised by non-cemented bioclasts of sponges, bryozoans, echinoderms and brachiopods) were then progressively replaced by silica factories. By Late Permian time, little carbonate sediments accumulated in the Barents Sea and in the Sverdrup Basin. where the deep- to shallow-water sedimentary spectrum was occupied by siliceous sponge spicules. By that time, biogenic silica sedimentation was common throughout the world. Silica factories collapsed in the Late Permian, abruptly bringing the PCE to an end. In northwest Pangea, the end- Permian collapse of the PCE was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions. Chert deposition resumed in the distal oceanic areas during the early Middle Triassic (Anisian) after a 8-10 Ma interruption (Early Triassic Chert Gap). The conditions necessary for the onset, expansion and zenith of the PCE were provided by the thermohaline circulation of nutrient-rich cold waters along the northwestern and western margin of Pangea, and possibly throughout the world oceans. These conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area, created a nutrient- and oxygen-rich environment favouring siliceous biogenic productivity. established cold sea-floor conditions, hindering silica dissolution, while increasing calcium carbonate solubility, and provided conditions adverse to organic and inorganic carbonate production, The northwest margin of Pangea was, for nearly 30 Ma. bathed by cold waters presumably derived from the seasonal melting of northern sea ice, the assumed engine for thermohaline circulation. This process started near the Sakmarian-Artinskian boundary. intensified throughout Middle and Late Permian time and ceased suddenly in latest Permian time, It led to oceanic conditions much colder than normally expected from the palaeolatitudes. and the influence of cold northerly-derived water was felt as far south southern Nevada. The demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean. Complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production. accumulation and preservation of biogenic silica.

Syndrome de vasoconstriction cérébrale réversible : identifications de facteurs pronostiques = [Reversible cerebral vasoconstriction syndrome identification of pronostic factors]

Objectif : Le syndrome de vasoconstriction cérébrale réversible (SVCR) est une entité clinico-radiologique associant des céphalées paroxystiques à un vasospasme uni- ou multifocal réversible des artères cérébrales avec ou sans déficit neurologique transitoire ou crise comitiale. Le but de notre étude est de rechercher les facteurs de mauvais pronostic des patients présentant un SVCR. Méthode : Nous avons réalisé une étude rétrospective des imageries vasculaires cérébrales invasives et non invasives entre janvier 2006 et 2011 et avons retenu 10 patients présentant les critères du RCVS. Les données démographiques, facteurs de risque vasculaires ainsi que l'évolution de chaque patient ont été noté. Résultats : Sept des 10 patients sont des femmes, avec un âge médian de 46 ans. Quatre patients ne présentaient pas de facteur étiologique, deux femmes se trouvaient en période post-partum (entre la première et la troisième semaine) et les trois autres cas sont induits par des drogues vaso-actives (cannabis pour 2 cas dont un associé à la cyclosporine, sumatriptan pour un cas). La durée moyenne du suivi est de 10,2 mois (0¬28 mois). Deux patients ont présentés une séquelle neurologique : un a gardé des troubles phasiques et l'autre une hémianopsie latérale homonyme. Deux autres patients sont décédés dans les suites, ce qui est inhabituel. Nous n'avons pas trouvé de corrélation d'évolution différente entre les cas de SVCR primaire ou secondaire. Les seules facteurs corrélaient à l'évolution clinique sont le status neurologique à l'admission et la présence de lésion parenchymateuse (ischémie ou hématome) à l'imagerie. Conclusion : La vasoconstriction cérébrale réversible impliquant des déficits neurologiques ou la mort a été, rarement, rapportée. Nous devons garder à l'esprit qu'une telle évolution peut survenir notamment pour les cas présentant un état neurologique dégradé à l'admission ou présentant des lésions parenchymateuses à l'imagerie.

Effect of Noncondensable Gases on Circulation of Primary Coolant in Nuclear Power Plants in Abnormal Situations

The present study focuses on two effects of the presence of a noncondensable gas on the thermal-hydraulic behavior of thecoolant of the primary circuit of a nuclear reactor in the VVER-440 geometry inabnormal situations. First, steam condensation with the presence of air was studied in the horizontal tubes of the steam generator (SG) of the PACTEL test facility. The French thermal-hydraulic CATHARE code was used to study the heat transfer between the primary and secondary side in conditions derived from preliminary experiments performed by VTT using PACTEL. In natural circulation and single-phase vapor conditions, the injection of a volume of air, equivalent to the totalvolume of the primary side of the SG at the entrance of the hot collector, did not stop the heat transfer from the primary to the secondary side. The calculated results indicate that air is located in the second half-length (from the mid-length of the tubes to the cold collector) in all the tubes of the steam generator The hot collector remained full of steam during the transient. Secondly, the potential release of the nitrogen gas dissolved in the water of the accumulators of the emergency core coolant system of the Loviisa nuclear power plant (NPP) was investigated. The author implemented a model of the dissolution and release ofnitrogen gas in the CATHARE code; the model created by the CATHARE developers. In collaboration with VTT, an analytical experiment was performed with some components of PACTEL to determine, in particular, the value of the release time constant of the nitrogen gas in the depressurization conditions representative of the small and intermediate break transients postulated for the Loviisa NPP. Such transients, with simplified operating procedures, were calculated using the modified CATHARE code for various values of the release time constant used in the dissolution and release model. For the small breaks, nitrogen gas is trapped in thecollectors of the SGs in rather large proportions. There, the levels oscillate until the actuation of the low-pressure injection pumps (LPIS) that refill the primary circuit. In the case of the intermediate breaks, most of the nitrogen gas is expelled at the break and almost no nitrogen gas is trapped in the SGs. In comparison with the cases calculated without taking into account the release of nitrogen gas, the start of the LPIS is delayed by between 1 and 1.75 h. Applicability of the obtained results to the real safety conditions must take into accountthe real operating procedures used in the nuclear power plant.