D. Rafolt

Modulation of motor cortex excitability by different levels of whole-hand afferent electrical stimulation

OBJECTIVE In a previous transcranial magnetic stimulation (TMS) study we demonstrated that suprathreshold mesh-glove (MG) whole-hand stimulation elicits lasting changes in motor cortical excitability. Currently, there is no consensus with regard to the optimal parameters for the induction of sensorimotor cortical plasticity using peripheral electrical stimulation. Thus, in the present study we explore the modulatory effects of MG stimulation at different stimulus intensities and different frequencies in order to identify an optimal stimulation protocol. METHODS MG stimulation was performed on 12 healthy subjects in separate sessions at different stimulation levels: sub-sensory at 50 Hz, sensory at 50 Hz and motor at 2 Hz. To verify if stimulation at lower frequencies is less effective, an additional experiment at sensory level with 2 Hz was performed. TMS was used to assess motor threshold (MT), motor evoked potentials (MEPs) recruitment curve (RC), short latency intracortical inhibition (SICI) and intracortical facilitation (ICF) to paired-pulse TMS at baseline (T0), immediately after (T1) and 1h (T2) after 30 min of MG stimulation. F-wave studies were performed to assess spinal motoneuron excitability. RESULTS MG stimulation at sub-sensory/50 Hz and sensory/2 Hz level determines no significant cortical excitability changes; at sensory/50 Hz level and at motor/2 Hz level we found decreased MT, increased MEP RC as well as reduced SICI and increased ICF at T1 and T2. CONCLUSIONS MG stimulation at sensory/50 Hz and motor/2 Hz level induces similar long-lasting modulatory effects on motor cortical excitability. Both the strength of the corticospinal projections and the intracortical networks are influenced to the same extend. SIGNIFICANCE The study provides further evidence that stimulation intensity and frequency can independently modulate motor cortical plasticity. The selection of optimal stimulation parameters has potentially important implications for the neurorehabilitation of patients after brain damage (e.g. stroke, traumatic brain injury) with hand motor deficits.

Instrumentation for assessment of tremor, skin vibrations, and cardiovascular variables in MIR space missions

A versatile and simple to use biomedical instrumentation for noninvasive examinations of cosmonauts at the Russian MIR space station was developed. It consists of a comfortable sensor jacket to assess signals from the body surface, a precision hand dynamometer to produce muscular and cardiovascular loads, and a small interactive microprocessor unit that controls the examination and stores measurement data. The sensor jacket includes highly sensitive piezo-resistive accelerometers, pulse sensors, an ECG system, and a skin-mountable mechanical vibrator. The functionality of this instrumentation was evaluated during long-term space flights and also proved very useful in laboratory and clinical studies.

Cuff-type pneumatic stimulator for studying somatosensory evoked responses with fMRI.

For quantitative somatosensory testing in the clinical environment a microprocessor controlled MR-compatible stimulation device was developed. A main feature of this device is the use of an inflatable cuff allowing the application of defined test pressures (0-1000 mbar) to the skin surface. The cuff is pressurized by a piezoelectric proportional valve with embedded closed loop controller. The distortion of the pressure pulses, introduced by the tube between valve and cuff (tube lengths of 2 and 6 m), was evaluated. Two kinds of stimulation patterns were implemented by the microprocessor: constant frequency stimulation (selectable between 1 and 20 Hz) and stimulation with stepwise changing frequencies according to a pseudorandom sequence. Imaging tests (n=8, index finger) showed more robust responses in S1 (contralateral) and S2 (bilaterally) if evoked by the random sequence. Both, the technical tests and the imaging results, demonstrate that this new stimulation system is well suited to set a standard for somatosensory stimulation in individual longitudinal studies or multicenter comparisons.

Vibration stimulation during non-fatiguing tonic contraction induces outlasting neuroplastic effects

The objective was to explore if vibration superposed to tonic contraction induces plastic changes in the contra- and ipsilateral motor cortex. Healthy subjects (n=12) abducted the right index finger with a force 5% of maximal voluntary contraction (MVC) against the lever of a torque motor while a 60 Hz vibration stimulus of 10 min was delivered. Motor evoked potentials (MEPs) after single and paired-pulse transcranial magnetic stimulation (TMS) were recorded from the first dorsal interosseous muscle of right and left hand pre, during, post and 30 min post-stimulation. The TMS assessments were employed with tonic contraction alone (TONIC) and with superposed vibrostimulation (VIBRO), each for the ipsi- and contralateral cortex separately. In the contralateral cortex: resting motor threshold (rMT) decreased, MEP amplitudes increased, short-interval intracortical inhibition (SICI) reduced and intracortical facilitation (ICF) increased post VIBRO, while no changes occurred post TONIC. In the ipsilateral cortex: rMT decreased, MEP amplitude increased and SICI reduced during TONIC, while no changes occurred post TONIC, during and post VIBRO. Vibration superposed to tonic contraction, induces lasting (30 min) plastic changes, whereas contraction alone caused no outlasting effects. Mainly intrinsic intracortical mechanisms are involved because spinal adaptation could be excluded (F-wave assessments). These findings have a therapeutic potential in the functional recovery of motor deficits with robot-aided devices.

Increased motor cortical excitability after whole-hand electrical stimulation: A TMS study

OBJECTIVE To examine the neuromodulatory effect of whole-hand mesh-glove (MG) stimulation on motor cortical pathways, we explored motor cortical excitability before and after suprathreshold whole-hand MG stimulation using transcranial magnetic stimulation (TMS). METHODS Twenty-eight healthy volunteers (14 controls) were studied at baseline, immediately post and 1h post-MG stimulation for 30 min. Motor thresholds (MTs), motor evoked potentials (MEPs) recruitment curve, short intracortical inhibition (SICI) and intracortical facilitation (ICF) after paired magnetic stimuli were evaluated. RESULTS After MG stimulation the MTs were significantly reduced and slope of MEP recruitment curve significantly increased; furthermore, the stimulation led to a sustained decrease of SICI and increase of ICF in the contralateral motor cortex. These effects lasted for at least 60 min and were stronger 1h post-stimulation compared with testing immediately after stimulation. A sham group did not show any differences before and after MG stimulation. CONCLUSIONS We provide a first demonstration that MG whole-hand stimulation induces increases in motor cortical excitability lasting at least 1h. Both the strength of the corticospinal projections and the inhibitory and facilitatory intracortical mechanisms are involved. Synaptic modifications such as long-term potentiation mechanisms may underlie this stimulation-induced cortical plasticity changes. SIGNIFICANCE Present results prove the MG stimulation to be a promising tool in neurorehabilitation.

Pruritometer 2: Portable recording system for the quantification of scratching as objective criterion for the pruritus

Studies to evaluate therapies for itching (pruritus) related diseases often require the quantification of the itch sensation. Like all subjective symptoms the evaluation of itching is difficult and can only be done indirectly. With the Pruritometer 2 a measuring system is introduced that evaluates itching by detecting scratching movements. Based on the Pruritometer 1, that processes the signals of a piezoelectric vibration sensor, fixed on the midfinger of the patients dominant hand, and triggers a simple counter, the Pruritometer 2 allows to store the scratch activity during a 24 hours period. For each adjustable time slice of this time period, the amount of scratches and the scratch intensity are recorded. All data can be transferred to a PC via infrared link for further processing with a standard software package. An additional PC-software allows to set various parameters for optimal scratch detection and to test the patient attached system, also via the infrared link. All electronic components are shockproof encapsulated in a milled housing and are attached to a textile watchstrap that is worn by the patient like a wristwatch.

Pruritometer 1: Portables Meßsystem zur Quantifizierung des Kratzens als objektives Maß für den cholestatischen Pruritus - Pruritometer 1: A Portable Measuring System for the Quantification of Scratching as an Objective Criterion of Cholestatic Pruritus

Objective assessment of subjective symptoms such as pruritus always presents problems, which can often be resolved only indirectly. The objectification of pruritus was necessitated by a study on the efficacy of a serotonin antagonist used as treatment of cholestatic pruritus. In the present paper, a portable measuring system for the indirect objective assessment of pruritus via the quantification of scratching is described. A piezoelectric scratch-vibration sensor for attachment to the middle finger of the patients dominant hand was developed. A sensor interface detects the scratching signals and generates pulses that are then summed in an adapted sports watch. The entire system-Pruritometer 1- is worn by the patient like a wrist watch, and is characterized by ease of handling. Acceptance by the patient is reported to be good. A statistically good correlation between measured (Pruritometer) and visually counted scratches was demonstrated. Pruritometer 2, which will enable scratch frequency and intensity distribution over time to be determined, is presently being developed.

Mechanical flutter stimulation induces a lasting response in the sensorimotor cortex as revealed with BOLD fMRI.

It has been recently shown that 20 min of mechanical flutter stimulation induces lasting motor cortical excitability changes, as assessed by transcranial magnetic stimulation in relaxed hand muscles. The present functional magnetic resonance imaging (fMRI) study aims to examine if such neuromodulatory changes are reflected in the BOLD signal during a motor test. Therefore, two groups were recruited: one group receiving whole‐hand flutter stimulation with a frequency of 25 Hz (FSTIM group, n = 22) and a second group receiving no stimulation (NOSTIM group, n = 22). As motor test finger‐to‐thumb tapping was performed to activate a wide sensorimotor network during the fMRI measurements. Three fMRI measurements were obtained with this test: before stimulation (PRE), after stimulation (POST1), and 1 h after stimulation (POST2). Three regions of interest (ROIs) were defined: primary motor area (M1), primary somatosensory area (S1), and supplementary motor area. In the absence of baseline differences between both groups, the FSTIM group showed increased movement‐related brain activations compared with the NOSTIM group, both at POST1 and POST2. ROI analysis revealed increased blood‐oxygenation‐level‐dependent (BOLD) responses within contralateral S1 (+20%) and M1 (+25%) at POST1, which lasted until POST2. These poststimulatory effects within S1 and M1 obviously reflect neuroplastic changes associated with augmented cortical excitability. These findings are of high clinical relevance, for example, to improve the treatment of stroke patients. Hum Brain Mapp 34:2767–2774, 2013.

Mobile gait analysis via eSHOEs instrumented shoe insoles: a pilot study for validation against the gold standard GAITRite®

Abstract Clinical gait analysis contributes massively to rehabilitation support and improvement of in-patient care. The research project eSHOE aspires to be a useful addition to the rich variety of gait analysis systems. It was designed to fill the gap of affordable, reasonably accurate and highly mobile measurement devices. With the overall goal of enabling individual home-based monitoring and training for people suffering from chronic diseases, affecting the locomotor system. Motion and pressure sensors gather movement data directly on the (users) feet, store them locally and/or transmit them wirelessly to a PC. A combination of pattern recognition and feature extraction algorithms translates the motion data into standard gait parameters. Accuracy of eSHOE were evaluated against the reference system GAITRite in a clinical pilot study. Eleven hip fracture patients (78.4 ± 7.7 years) and twelve healthy subjects (40.8 ± 9.1 years) were included in these trials. All subjects performed three measurements at a comfortable walking speed over 8 m, including the 6-m long GAITRite mat. Six standard gait parameters were extracted from a total of 347 gait cycles. Agreement was analysed via scatterplots, histograms and Bland–Altman plots. In the patient group, the average differences between eSHOE and GAITRite range from −0.046 to 0.045 s and in the healthy group from −0.029 to 0.029 s. Therefore, it can be concluded that eSHOE delivers adequately accurate results. Especially with the prospect as an at home supplement or follow-up to clinical gait analysis and compared to other state of the art wearable motion analysis systems.

New Synthetic Prosthesis for Peripheral Nerve Injuries An Experimental Pilot Study

Introduction. Even the most modern technology has failed to induce satisfactory functional regeneration of traumatically severed peripheral nerves. Delayed neural regeneration and in consequence, slower neural conduction seriously limit muscle function in the area supplied by the injured nerve. This study aimed to compare a new nerve coaptation system involving an innovative prosthesis with the classical clinical method of sutured nerve coaptation. Besides the time and degree of nerve regeneration, the influence of electrostimulation was also tested. Methods. The sciatic nerve was severed in 14 female Göttingen minipigs with an average weight of 40.4 kg. The animals were randomized into 2 groups: One group received the new prosthesis and the other underwent microsurgical coaptation. In each group, according to the randomization a part of the animals received postoperative electrostimulation. Postoperative monitoring and the stimulation schedule covered a period of 9 months, during which axonal budding was evaluated monthly. Results. The data from the pilot study indicate that results with the nerve prosthesis were comparable with those of conventional coaptation. Conclusion. The results indicate that implantation of the nerve prosthesis allows for good and effective neural regeneration. This new and simple treatment option for peripheral nerve injuries can be performed in any hospital with surgical facilities as it does not involve the demanding microsurgical suture technique that can only be performed in specialized centers.