Differential Regulation of Human Paired Associative Stimulation-Induced and Theta-Burst Stimulation-Induced Plasticity by L-type and T-type Ca2+ Channels.

Activity-dependent changes of postsynaptic Ca2+-concentration are influenced by a variety of different Ca2+-channels and play an important role in synaptic plasticity. Paired associative stimulation (PAS) and theta-burst stimulation (TBS) are noninvasive magnetic stimulation protocols used in human subjects to induce lasting corticospinal excitability changes that have been likened to synaptic long-term potentiation and long-term depression. To better characterize the Ca2+-related physiological mechanisms underlying PAS- and TBS-induced plasticity, we examined the impact of different Ca2+-sources. PAS-induced facilitation of corticospinal excitability was blocked by NMDA-receptor blocker dextromethorphan (DXM) and L-type voltage gated Ca2+ channels (VGCC) blocker nimodipine (NDP), but turned into depression by T-type VGCC blocker ethosuximide (ESM). Although, surprisingly, static corticospinal excitability was increased by the combination of DXM and NDP, PAS-induced facilitation was blocked. TBS-induced facilitation of corticospinal excitability, which has previously been shown to be turned into depression by L-type VGCC blocker NDP (Wankerl K, Weise D, Gentner R, Rumpf J, Classen J. 2010. L-type voltage-gated Ca2+ channels: a single molecular switch for long-term potentiation/long-term depression-like plasticity and activity-dependent metaplasticity in humans. J Neurosci. 30(18):6197-6204.), was blocked, but not reverted, by T-type VGCC blocker ESM. The different patterns of Ca2+-channel modulation of PAS- and TBS-induced plasticity may point to an important role of backpropagating action potentials in PAS-induced plasticity, similar as in spike-timing dependent synaptic plasticity, and to a requirement of dendritic Ca2+-dependent spikes in TBS-induced plasticity.

A reconfigurable all-fiber polarization-diversity coherent Doppler lidar: principles and numerical simulations.

This paper shows an efficient adaptation of a polarization diversity optical front-end, commonly used in high-speed fiber-optic communications, in a coherent Doppler lidar (CDL). The adopted architecture can be employed in a modified transceiver design for an all-fiber micropulsed coherent Doppler wind lidar where the performance limits of such systems are pushed beyond the conventionally available wind CDLs. As a result, either a longer measurement range, crucial in clear-air environments with low concentration of aerosols, or a shorter integration time (resulting in a faster scanning) can be achieved. Alternatively, in certain aerosol loading conditions where the presence of nonspherical aerosols is considerable, the system can be reconfigured on the fly to analyze the cross polarization of the backscatter optical signal. The result is the capability to analyze the nature of aerosol particles for the detected range of interest. Due to full utilization of the backscatter signal, i.e., detection of co-polarization and cross polarization components, the signal-to-noise-ratio (SNR) as well as detection range is improved in this configuration. Moreover, the system is capable of providing a more reliable estimation of the aerosol backscatter coefficient when compared with the contemporary CDLs. This system employs robust and compact all-fiber subsystems, which are cost effective and widely available as off-the-shelf components.

An all-fiber image-reject homodyne coherent Doppler wind lidar.

In this paper, we present an alternative approach to the down-conversion (translation) of the received optical signals collected by the antenna of an all-fiber coherent Doppler lidar (CDL). The proposed method, widely known as image-reject, quadrature detection, or in-phase/quadrature-phase detection, utilizes the advances in fiber optic communications such that the received signal can be optically down-converted into baseband where not only the radial velocity but also the direction of the movement can be inferred. In addition, we show that by performing a cross-spectral analysis, enabled by the presence of two independent signal observations with uncorrelated noise, various noise sources can be suppressed and a more simplified velocity estimation algorithm can be employed in the spectral domain. Other benefits of this architecture include, but are not limited to, a more reliable measurement of radial velocities close to zero and an improved bandwidth. The claims are verified through laboratory implementation of a continuous wave CDL, where measurements both on a hard and diffuse target have been performed and analyzed.

Microcircuit mechanisms involved in paired associative stimulation-induced depression of corticospinal excitability.

Synaptic weight changes induced by temporal correlations between the spikes of pre- and postsynaptic neurons are referred to as spike-timing-dependent plasticity (STDP). Transcranial magnetic stimulation (TMS) induces long-lasting effects on corticospinal excitability, if it is repetitively paired with stimulation of afferents from a corresponding contralateral hand region at short intervals (paired associative stimulation, PAS). PAS-induced plasticity has been linked with synaptic STDP. We aimed to investigate which elements of the cortical microcircuitry sustain and govern PAS-induced depression of corticospinal excitability in the target muscle representation (and enhancement of excitability in its functional surround). We show that the time window during which the interaction between both stimulus-induced cortical events leads to immediate post-interventional depression is short (<4.5 ms). The depressant PAS effects at the target representation were completely blocked by applying a subthreshold magnetic pulse 3 ms before the principal TMS pulse, even when the strength of the latter was adjusted to generate a motor-evoked potential of similar amplitude to that with the unconditioned magnetic pulse. Epidural recordings from the cervical cord of a patient showed that under this condition late TMS-evoked I-waves remain suppressed. When the intensity of the TMS component during PAS was lowered - sufficient to allow activation of inhibitory neurons, but insufficient to activate corticospinal neurons - excitability of short-latency intracortical inhibition remained unchanged. PAS-induced facilitation in the functional surround followed the same pattern as the centre-depressant effects. These findings may suggest that excitability-depressant PAS-induced effects are due to weakening of excitatory synapses between upper cortical layer principal neurons, but not those located on the corticospinal neuron, or inhibitory synapses. Inhibitory interneurons involved in short-latency intracortical inhibition are gate-keepers to producing centre-depressant/surround-facilitatory PAS effects. Based on these and earlier findings we propose a model specifying the composition and laminar location of the involved microcircuit of PAS-induced plasticity that may enhance its utility as a model of STDP in humans.

[Arthroscopic-assisted management of intra-articular scapular fractures in a rugby player]. / Arthroskopisch assistierte Versorgung einer intraartikulären Skapulafraktur bei einem Rugbyspieler.

Scapular fractures are a rare injury entity accounting for 0,4-1 % of all fractures and 3-5 % of fractures involving the shoulder girdle. This study focuses on a 29-year-old male patient who sustained an intraarticular scapular fracture during a "Rugby Bundesliga" match after direct impact with another player. The clinical and radiological examinations showed a dislocated multifragmentary transverse scapular fracture involving the superior border, the medial border and the glenoid (Euler and Rüedi D2b/AO 14 F1.3e). The patient was subjected to arthroscopic surgery and underwent early postoperative functional rehabilitation without weight-bearing and with a limited range of motion of 90° abduction/anteversion. In the first match of the second half of the season (5 months post-operatively), the patient was available to play, and in the clinical follow-up 6 months post-operatively, he was pain-free with excellent clinical results (CS 100 pt, SSV 98 %, OSS 12 pt, ASES 100 pt). No pain or restrictions in the range of motion were reported. In conclusion, the arthroscopic-assisted management of intra-articular scapular fractures is a safe and effective choice of treatment in young and active patients.

Experimental investigation of Lagrangian structure functions in turbulence.

Lagrangian properties obtained from a particle tracking velocimetry experiment in a turbulent flow at intermediate Reynolds number are presented. Accurate sampling of particle trajectories is essential in order to obtain the Lagrangian structure functions and to measure intermittency at small temporal scales. The finiteness of the measurement volume can bias the results significantly. We present a robust way to overcome this obstacle. Despite no fully developed inertial range, we observe strong intermittency at the scale of dissipation. The multifractal model is only partially able to reproduce the results.

Novel box trainer for taTME - prospective evaluation among medical students.

BACKGROUND: Transanal total mesorectal excision (taTME) has been subject to extensive research and increasing clinical application. It allows further reduction of trauma by accessing via a natural orifice. Manifold platforms and instruments have been introduced and heterogeneity in surgical techniques exists. Because of the technique's complexity there is a persistent need for dedicated training devices and concepts. MATERIALS AND METHODS: The key steps of taTME were analyzed and a box trainer with three modules resembling these steps was designed and manufactured. Twenty-one surgically inexperienced medical students performed five repetitions of the three tasks with the new box trainer. Time and error count were analyzed for assessment of a learning curve. RESULTS: A significant reduction of processing time could be demonstrated for tasks 1-3 (p < 0.001; p < 0.001; p = 0.001). The effect size was high for comparison of repetition 1 and 5 and decreased over the course (task 1: r = 0.88 vs. r = 0.21; task 2: r = 0.86 vs. r = 0.23; task 3: r = 0.74 vs. r = 0.44). Also, a significant reduction of errors was demonstrated for tasks 1 and 2. The decrease of effect size was analogously demonstrated. CONCLUSIONS: The trainer might help to reduce the use of animal models for testing of platforms and instruments as well as gaining first-hand experience in transanal rectal resection.

Backwards and forwards relative dispersion in turbulent flow: an experimental investigation.

From particle tracking velocimetry we present an experimental measure of the ratio between backwards and forwards relative dispersion in an intermediate Reynolds number turbulent flow. Lack of time-reversal symmetry implies that their ratio may be different from 1. From a stochastic model, this has recently been studied by Sawford et al [Phys. Fluids 17, 095109 (2005)] giving ratios between 5 and 20. We find a value of approximately 2 and discuss it in the context of the characteristics of the rate of strain tensor s(ij). An analysis of a direct numerical simulation by Biferale et al [Phys. Rev. Lett. 93, 064502 (2004) and Phys. Fluids 17, 021701 (2004)] gives the same result.

Direct measurement of the spectral transfer function of a laser based anemometer.

The effect of a continuous-wave (cw) laser based anemometer's probe volume on the measurement of wind turbulence is studied in this paper. Wind speed time series acquired by both a remote sensing cw laser anemometer, whose line-of-sight was aligned with the wind direction, and by a reference sensor (sonic anemometer) located in the same direction, were used. The spectral transfer function, which describes the attenuation of the power spectral density of the wind speed turbulence, was calculated and found to be in good agreement with the theoretical exponential function, which is based on the properties of the probe volume of a focused Gaussian laser beam. Parameters such as fluctuations of the wind direction, as well as the overestimation of the laser Doppler spectrum threshold, were found to affect the calculation of the spectral transfer function by introducing high frequency noise.