Studying Network Mechanisms Using Intracranial Stimulation in Epileptic Patients

Patients suffering from focal drug-resistant epilepsy who are explored using intracranial electrodes allow to obtain data of exceptional value for studying brain dynamics in correlation with pathophysiological and cognitive processes. Direct electrical stimulation (DES) of cortical regions and axonal tracts in those patients elicits a number of very specific perceptual or behavioral responses, but also abnormal responses due to specific configurations of epileptic networks. Here, we review how anatomo-functional brain connectivity and epilepsy network mechanisms can be assessed from DES responses measured in patients. After a brief summary of mechanisms of action of brain electrical stimulation, we recall the conceptual framework for interpreting DES results in the context of brain connectivity and review how DES can be used for the characterization of functional networks, the identification of the seizure onset zone, the study of brain plasticity mechanisms, and the anticipation of epileptic seizures. This pool of exceptional data may be underexploited by fundamental research on brain connectivity and leaves much to be learned

MOMAC: a SAXS/WAXS laboratory instrument dedicated to nanomaterials

International audienceThis article presents the technical characteristics of a newly built small-and wide-angle X-ray scattering (SAXS/WAXS) apparatus dedicated to structural characterization of a wide range of nanomaterials in the powder or dispersion form. The instrument is based on a high-flux rotating anode generator with a molybdenum target, enabling the assessment of highly absorbing samples containing heavy elements. The SAXS part is composed of a collimation system including a multilayer optic and scatterless slits, a motorized sample holder, a vacuum chamber, and a two-dimensional image-plate detector. All the control command is done through a TANGO interface. Normalization and data correction yield scattering patterns at the absolute scale automatically with a q range from 0.03 to 3.2 A ˚ À1. The WAXS part features a multilayer collimating optic and a two-dimensional image-plate detector with variable sample-to-detector distances. The accessible q range is 0.4–9 A ˚ À1 , ensuring a large overlap in q range between the two instruments. A few examples of applications are also presented, namely coupled SAXS/WAXS structure and symmetry determination of gold nanocrystals in solution and characterization of imogolite nanotubes and iron-filled carbon nanotube samples

Introduction of a urodynamic score to detect pre- and postoperative neurological deficits in children with a primary tethered cord

Object: An increasing number of asymptomatic children are diagnosed with occult spinal dysraphism, raising the question of their optimal management. Urodynamic study (UDS) is the most reliable method of detecting neuro-urological abnormalities in these children. The rate of postoperative retethering ranges from 10 to 20% and is not always immediately clinically significant. The aim of this prospective study was to develop a reliable method that could be used in the preoperative assessment and postoperative follow-up of children with a tethered cord syndrome (TCS). Methods: From 1989 to 1997, 15 children underwent spinal cord untethering for TCS. Preoperatively, patients were assessed with MRI and UDS. Postoperative UDS were repeated at 6- to 12-month intervals. Four UDS parameters were identified, graded, and added to obtain a UDS score. A group of 38 children without dysraphic condition was used as control and allowed the calculation of a normal score. Conclusions: There was a statistically significant difference in the preoperative UDS scores between the control group and the study group (p<0.001). Postoperatively, there was a statistically significant improvement (p<0.001) in UDS scores. UDS score is a reliable tool for identifying and quantifying neuro-urological disorders in patients with TCS. Postoperatively, this score was useful in the early diagnosis of spinal cord retetherin

Mesure de la Largeur Spectrale d'un Laser Cohérent par Injection Optique

session VII « Cristaux photoniques en optique planaire I, fonctions spéciales » [704]National audienceNous proposons une nouvelle méthode de mesure de faibles largeurs spectrales pour des lasers métrologiques. La mesure comparative repose sur une injection optique. Nous présentons la mesure expérimentale en bande C d'un laser de pleine largeur spectrale à mi-hauteur 50 kHz, en comparaison à une référence de largeur 125 kHz. Un modèle théorique reposant sur la fonction d'Airy généralisée est aussi présenté, tenant compte des outils d'analyse expérimentaux utilisés

: Seizure onset zone imaging

International audienceStereo-electroencephalography is used to localize the seizure onset zone and connected neuronal networks in surgical candidates suffering from intractable focal epilepsy. The concept of an epileptogenicity index has been proposed recently to represent the likelihood of various regions being part of the seizure onset zone. It quantifies low-voltage fast activity, the electrophysiological signature of seizure onset usually assessed visually by neurologists. Here, we revisit epileptogenicity in light of neuroimaging tools such as those provided in statistical parametric mapping software. Our goal is to propose a robust approach, allowing easy exploration of patients' brains in time and space. The procedure is based upon statistical parametric mapping, which is an established framework for comparing multi-dimensional image data that allows one to correct for inherent multiple comparisons. Statistics can also be performed at the group level, between seizures in the same patient or between patients suffering from the same type of epilepsy using normalization of brains to a common anatomic atlas. Results are obtained from three case studies (insular reflex epilepsy, cryptogenic frontal epilepsy and lesional occipital epilepsy) where tailored resection was performed, and from a group of 10 patients suffering from mesial temporal lobe epilepsy. They illustrate the basics of the technique and demonstrate its very good reproducibility and specificity. Most importantly, the proposed approach to the quantification of the seizure onset zone allows one to summarize complex signals in terms of a time-series of statistical parametric maps that can support clinical decisions. Quantitative neuroimaging of stereo-electroencephalographic features of seizures might thus help to provide better pre-surgical assessment of patients undergoing resective surgery

Spectral and Time Phenomena in Optical Injection Using Distributed Feedback Semiconductor or Fiber Lasers

http://www.iop.vast.ac.vn/activities/5-8April/Proceedings_IWPA2004/proceeding_IWPA_2004.htmlInternational audienceOptical injection is compared for distributed feedback semiconductor and fibre lasers whose wavelength is around 1550 nm. A spectral description of an injected semiconductor laser is presented for usual injected power (> 30 dBm), by mapping out several phenomena, such as bistable areas, undamped relaxation and chaos synchronization. For weak injection levels (< 30 dBm), the slave acts as a highquality amplifier of spectrally narrow signals. In this case, the slave frequency is pulled by the master one. Theory of weak injection is demonstrated using a generalized Airy's function method. We also present the temporal response of a fibre laser output power for static injection, and observe original dynamics linked to relaxation processes. A new method using optical injection is proposed to measure narrow linewidth or spontaneous emission rate

Aesthetic discomfort in hand osteoarthritis: results from the LIège Hand Osteoarthritis Cohort (LIHOC)

Characteristics of patients reporting high (HAD) or low (LAD) (aesthetic discomfort). (DOC 55 kb