Competition of Heavy Quark Radiative and Collisional Energy Loss in Deconfined Matter

We extend our recently advanced model on collisional energy loss of heavy quarks in a quark gluon plasma (QGP) by including radiative energy loss. We discuss the approach and present first preliminary results. We show that present data on nuclear modification factor of non photonic single electrons hardly permit to distinguish between those 2 energy loss mechanisms.Comment: 8 pages, extended to 11 pages for v2; accepted for publication in Journal of Physics

Bringing sensation to prosthetic hands—chronic assessment of implanted thin-film electrodes in humans

Direct stimulation of peripheral nerves with implantable electrodes successfully provided sensory feedback to amputees while using hand prostheses. Longevity of the electrodes is key to success, which we have improved for the polyimide-based transverse intrafascicular multichannel electrode (TIME). The TIMEs were implanted in the median and ulnar nerves of three trans-radial amputees for up to six months. We present a comprehensive assessment of the electrical properties of the thin-film metallization as well as material status post explantationem. The TIMEs stayed within the electrochemical safe limits while enabling consistent and precise amplitude modulation. This lead to a reliable performance in terms of eliciting sensation. No signs of corrosion or morphological change to the thin-film metallization of the probes was observed by means of electrochemical and optical analysis. The presented longevity demonstrates that thin-film electrodes are applicable in permanent implant systems

A high-performance 4 nV/√ analog front-end architecture for artefact suppression in local field potential recordings during deep brain stimulation

Objective. Recording of local field potentials (LFPs) during deep brain stimulation (DBS) is necessary to investigate the instantaneous brain response to stimulation, minimize time delays for closed-loop neurostimulation and maximise the available neural data. To our knowledge, existing recording systems lack the ability to provide artefact-free high-frequency (> 100 Hz) LFP recordings during DBS in real time primarily because of the contamination of the neural signals of interest by the stimulation artefacts. Approach. To solve this problem, we designed and developed a novel, low-noise and versatile analog front-end (AFE) that uses a high-order (8th) analog Chebyshev notch filter to suppress the artefacts originating from the stimulation frequency. After defining the system requirements for concurrent LFP recording and DBS artefact suppression, we assessed the performance of the realised AFE by conducting both in vitro and in vivo experiments using unipolar and bipolar DBS (monophasic pulses, amplitude ranging from 3 to 6 V peak-to-peak, frequency 140 Hz and pulse width 100 μs). A full performance comparison between the proposed AFE and an identical AFE, equipped with an 8th order analog Bessel notch filter, was also conducted. Main results. A high-performance, 4 nV/√ AFE that is capable of recording nV-scale signals was designed in accordance with the imposed specifications. Under both in vitro and in vivo experimental conditions, the proposed AFE provided real-time, low-noise and artefact-free LFP recordings (in the frequency range 0.5 – 250 Hz) during stimulation. Its sensing and stimulation artefact suppression capabilities outperformed the capabilities of the AFE equipped with the Bessel notch filter. Significance. The designed AFE can precisely record LFP signals, in and without the presence of either unipolar or bipolar DBS, which renders it as a functional and practical AFE architecture to be utilised in a wide range of applications and environments. This work paves the way for the development of externalized research tools for closed-loop neuromodulation that use low- and higher-frequency LFPs as control signals

Impact of direct epispinal stimulation on bladder and bowel functions in pigs: A feasibility study

International audienceAims: This study assesses the potential of epispinal (subdural) stimulation applicationin the treatment of urinary and bowel neurological disorders. Acute experiments wereperformed on a large animal model — the domestic pig — to develop a newmethodology facilitating future results and technology transfers to human.Methods: After rectal and bladder catheterization, four Landrace pigs (45-50 kg)underwent spinal cord surgery— that is, lumbosacral incision, laminectomy [L4-S4],dural opening and microsurgical arachnoid dissection. Three successive electricalstimulation sessions were carried out: 1) nerve roots stimulation, 2) epispinalstimulation with a matrix electrode, 3) epispinal stimulation with a small diameterneedle electrode. Changes in rectal and bladder pressures were monitored throughoutthe various procedures to identify spinal areas inducing responseswhile evaluating theinfluence of electrode contacts size in the measured responses amplitudes.Results: Aninteresting areawas identified in the upper portion of the spinal myelomeres(ie, spinal cord segment delimited by two successive pairs of spinal roots) directlyadjoining root with best pressures (either rectal or vesical). Significant responses (up to40 cmH2O) were also obtained with a needle electrode. Furthermore, bowel evacuationwas triggered in one of the animals. Despite the use of smaller electrode contacts, nodetrusor or rectum selective responses were observed in none of the sessions.Conclusion: This study showed, for the first time, that epispinal stimulation causessignificant detrusor and rectal responses in pigs and allows considering further studieswith the objective of treating urinary and rectal disorders in spinal cord injurypatients

Validation of a methodology for neuro-urological and lumbosacral stimulation studies in domestic pigs: a humanlike animal model

OBJECTIVESpinal cord injuries (SCIs) result in loss of movement and sensory feedback, but also organ dysfunction. Nearly all patients with complete SCI lose bladder control and are prone to kidney failure if intermittent catheterization is not performed. Electrical stimulation of sacral spinal roots was initially considered to be a promising approach for restoring continence and micturition control, but many patients are discouraged by the need for surgical deafferentation as it could lead to a loss of sensory functions and reflexes. Nevertheless, recent research findings highlight the renewed interest in spinal cord stimulation (SCS). It is thought that synergic recruitment of spinal fibers could be achieved by stimulating the spinal neural networks involved in regulating physiological processes. Paradoxically, most of these recent studies focused on locomotor issues, while few addressed visceral dysfunction. This could at least partially be attributed to the lack of methodological tools. In this study, the authors aim to fill this gap by presenting a comprehensive method for investigating the potential of SCS to restore visceral functions in domestic pigs, a large-animal model considered to be a close approximation to humans.METHODSThis methodology was tested in 7 female pigs (Landrace pig breed, 45-60 kg, 4 months old) during acute experiments. A combination of morphine and propofol was used for anesthesia when transurethral catheterization and lumbosacral laminectomy (L4-S4) were performed. At the end of the operation, spinal root stimulation (L6-S5) and urodynamic recordings were performed to compare the evoked responses with those observed intraoperatively in humans.RESULTSNervous excitability was preserved despite long-term anesthesia (mean 8.43 +/- 1.5 hours). Transurethral catheterization and conventional laminectomy were possible while motor responses (gluteus muscle monitoring) were unaffected throughout the procedure. Consistent detrusor (approximately 25 cm H2O) and sphincter responses were obtained, whereas spinal root stimulation elicited detrusor and external urethral sphincter co-contractions similar to those observed intraoperatively in humans.CONCLUSIONSPigs represent an ideal model for SCS studies aimed at visceral function investigation and restoration because of the close similarities between female domestic pigs and humans, both in terms of anatomical structure and experimental techniques implemented. This article provides methodological keys for conducting experiments with equipment routinely used in clinical practice