Cortical Plasticity Induced by Transcranial Magnetic Stimulation during Wakefulness Affects Electroencephalogram Activity during Sleep

BACKGROUND:Sleep electroencephalogram (EEG) brain oscillations in the low-frequency range show local signs of homeostatic regulation after learning. Such increases and decreases of slow wave activity are limited to the cortical regions involved in specific task performance during wakefulness. Here, we test the hypothesis that reorganization of motor cortex produced by long-term potentiation (LTP) affects EEG activity of this brain area during subsequent sleep. METHODOLOGY/PRINCIPAL FINDINGS:By pairing median nerve stimulation with transcranial magnetic stimulation over the contralateral motor cortex, one can potentiate the motor output, which is presumed to reflect plasticity of the neural circuitry. This paired associative stimulation increases M1 cortical excitability at interstimulus intervals of 25 ms. We compared the scalp distribution of sleep EEG power following paired associative stimulation at 25 ms to that following a control paradigm with 50 ms intervals. It is shown that the experimental manipulation by paired associative stimulation at 25 ms induces a 48% increase in amplitude of motor evoked potentials. This LTP-like potentiation, induced during waking, affects delta and theta EEG power in both REM and non-REM sleep, measured during the following night. Slow-wave activity increases in some frontal and prefrontal derivations and decreases at sites neighboring and contralateral to the stimulated motor cortex. The magnitude of increased amplitudes of motor evoked potentials by the paired associative stimulation at 25 ms predicts enhancements of slow-wave activity in prefrontal regions. CONCLUSIONS/SIGNIFICANCE:An LTP-like paradigm, presumably inducing increased synaptic strength, leads to changes in local sleep regulation, as indexed by EEG slow-wave activity. Enhancement and depression of slow-wave activity are interpreted in terms of a simultaneous activation of both excitatory and inhibitory circuits consequent to the paired associative stimulation at 25 ms

Corrélation entre les altérations structurales et la thrombogénicité aiguë des valves percutanées en péricarde après sertissage et expansion

INTRODUCTION : Transcathether heart valve replacement has gained considerable acceptance during the last decades. It is now part of the armamentarium for aortic valve replacement. The procedure proved to be highly efficient. However the issues of the blood compatibility and tissue durability were not raised and the adverse events were probably under-reported, according to observations of thrombosis after deployment. MATERIAL AND METHOD : Bovine pericardium leaflets were sewn inside a 26mm diameter stainless steel stent to manufacture these valves (one control and two experimental). The correlation between the trauma and the acute thombogenicity of bovine pericardium leaflets, after crimping and ballooning, was investigated via an in vitro blood flow with labeled platelets. These leaflets were processed for histology: scanning electron microscopy, light microscopy, and transmission electron microscopy. RESULTS : The control specimens showed a regular pericardium structure with some blood cells deposited on the collagen fibrous surface (inflow) and scarce blood cells deposited on the serous surface (outflow). After crimping and ballooning, the structure of the pericardium was severely injured, eventually with delaminations and ruptures. The blood cell uptake was considerably increased compared to the control. CONCLUSION : It would therefore be appropriate to pay more attention to the design of the valves. Specifically, the incorporation of a buffer tissue or fabric between the pericardium and the metallic stent is suggested. The issue of ballooning deserves detailed and in depth investigation regarding the lifetime of the device.INTRODUCTION : Le remplacement percutané de valves cardiaques s’est imposé au cours des dernières décennies. Ce type d’implant est maintenant accepté pour le remplacement des valves aortiques. Cette intervention a démontré son efficacité, cependant la compatibilité sanguine à long terme demeure incertaine et les complications évolutives sont vraisemblablement sous-évaluées, notamment les thromboses après déploiement. MATÉRIEL ET MÉTHODE : Des feuillets de péricarde bovin ont été suturés à l’intérieur d’une endoprothèse en acier inoxydable de 26 mm de diamètre, pour fabriquer 3 valves (1 contrôle et 2 expérimentales). La corrélation entre les lésions et la thrombogénicité aiguë des feuillets de péricarde bovin a été évaluée. Après sertissage et expansion, les feuillets furent investigués dans un circuit sanguin in vitro avec des plaquettes marquées. Les feuillets furent ensuite examinés au plan histologique : microscopie électronique à balayage, microscopie optique et microscopie électronique à transmission. RÉSULTATS : Les feuillets de référence présentaient une structure régulière de péricarde avec quelques cellules sanguines retenues sur la surface fibreuse (côté de l’afflux sanguin), et plus rares sur la surface séreuse (côté de l’éjection). Après sertissage et expansion, la structure du péricarde était sévèrement endommagée, avec des délaminations occasionnelles et des fractures. La rétention d’éléments cellulaires était considérable par rapport aux feuillets de référence. CONCLUSION : Il serait souhaitable d’accorder davantage d’attention au design des valves. Plus spécifiquement, l’incorporation d’un coupon textile entre le péricarde et le stent métallique est suggérée. L’expansion à l’aide d’un ballon requiert des analyses détaillées du traumatisme susceptible de remettre en cause la biofonctionalité des implants