Quantification of cortical proprioceptive processing through a wireless and miniaturized EEG amplifier.

Corticokinematic coherence (CKC) is computed between limb kinematics and cortical activity (e.g. MEG, EEG), and it can be used to detect, quantify and localize the cortical processing of proprioceptive afference arising from the body. EEG-based studies on CKC have been limited to lab environments due to bulky, non-portable instrumentations. We recently proposed a wireless and miniaturized EEG acquisition system aimed at enabling EEG studies outside the laboratory. The purpose of this work is to compare the EEG-based CKC values obtained with this device with a conventional wired-EEG acquisition system to validate its use in the quantification of cortical proprioceptive processing. Eleven healthy right-handed participants were recruited (six males, four females, age range: 24-40 yr). A pneumatic-movement actuator was used to evoke right index-finger flexion-extension movement at 3 Hz for 4 min. The task was repeated both with the wireless-EEG and wired-EEG devices using the same 30-channel EEG cap preparation. CKC was computed between the EEG and finger acceleration. CKC peaked at the movement frequency and its harmonics, being statistically significant (p < 0.05) in 8-10 out of 11 participants. No statistically significant differences (p < 0.05) were found in CKC strength between wireless-EEG (range 0.03-0.22) and wired-EEG (0.02-0.33) systems, that showed a good agreement between the recording systems (3 Hz: r = 0.57, p = 0.071, 6 Hz: r = 0.82, p = 0.003). As expected, CKC peaked in sensors above the left primary sensorimotor cortex contralateral to the moved right index finger. As the wired-EEG device, the tested wireless-EEG system has proven feasible to quantify CKC, and thus can be used as a tool to study proprioception in the human neocortex. Thanks to its portability, the wireless-EEG used in this study has the potential to enable the examination of cortical proprioception in more naturalistic conditions outside the laboratory environment. Clinical Relevance-Our study will contribute to provide innovative technological foundations for future unobtrusive EEG recordings in naturalistic conditions to examine human sensorimotor system.

Design and Validation of a Wireless Body Sensor Network for Integrated EEG and HD-sEMG Acquisitions.

Sensorimotor integration is the process through which the human brain plans the motor program execution according to external sources. Within this context, corticomuscular and corticokinematic coherence analyses are common methods to investigate the mechanism underlying the central control of muscle activation. This requires the synchronous acquisition of several physiological signals, including EEG and sEMG. Nevertheless, physical constraints of the current, mostly wired, technologies limit their application in dynamic and naturalistic contexts. In fact, although many efforts were made in the development of biomedical instrumentation for EEG and High Density-surface EMG (HD-sEMG) signal acquisition, the need for an integrated wireless system is emerging. We hereby describe the design and validation of a new fully wireless body sensor network for the integrated acquisition of EEG and HD-sEMG signals. This Body Sensor Network is composed of wireless bio-signal acquisition modules, named sensor units, and a set of synchronization modules used as a general-purpose system for time-locked recordings. The system was characterized in terms of accuracy of the synchronization and quality of the collected signals. An in-depth characterization of the entire system and an head-to-head comparison of the wireless EEG sensor unit with a wired benchmark EEG device were performed. The proposed device represents an advancement of the State-of-the-Art technology allowing the integrated acquisition of EEG and HD-sEMG signals for the study of sensorimotor integration.

Validation of Polymer-Based Screen-Printed Textile Electrodes for Surface EMG Detection.

In recent years, the variety of textile electrodes developed for electrophysiological signal detection has increased rapidly. Among the applications that could benefit from this advancement, those based on surface electromyography (sEMG) are particularly relevant in rehabilitation, training, and muscle function assessment. In this work, we validate the performance of polymer-based screen-printed textile electrodes for sEMG signal detection. We obtained these electrodes by depositing poly-3,4-ethylenedioxythiophene doped with poly(styrene sulfonate) (PEDOT:PSS) onto cotton fabric, and then selectively changing the physical properties of the textile substrate. The manufacturing costs are low and this process meets the requirements of textile-industry production lines. The validation of these electrodes was based on their functional and electrical characteristics, assessed for two different electrode sizes and three skin-interface conditions (dry, solid hydrogel, or saline solution), and compared to those of conventional disposable gelled electrodes. Results show high similarity in terms of noise amplitude and electrode-skin impedance between the conventional and textile electrodes with the addition of solid hydrogel or saline solution. Furthermore, we compared the shape of the electrically induced sEMG, as detected by conventional and textile electrodes from tibialis anterior. The comparison yielded an [Formula: see text] value higher than 97% for all measurement conditions. Preliminary tests in dynamic conditions (walking) revealed the exploitability of the proposed electrode technology with saline application for the monitoring of sEMG for up to 35 min of activity. These results suggest that the proposed screen-printed textile electrodes may be an effective alternative to the conventional gelled electrodes for sEMG acquisition, thereby providing new opportunities in clinical and wellness fields.

Development and testing of acoustically-matched hydrogel-based electrodes for simultaneous EMG-ultrasound detection.

In this manuscript we describe the development and testing of a bipolar electrode for the simultaneous acquisition of ultrasound (US) images and surface electromyograms (EMGs) from the same muscle region. The developed electrode (bEMG-US) consists of two circular sensing regions (20 mm diameter) with fixed inter-electrode distance (3.5 cm, center-to-center). Both the sensing regions and the external structure of the electrode are made of hydrogel layers separated by insulating materials. The electrical properties (i.e., impedance and noise of the electrode-skin interface) and the quality of EMGs detected with the developed electrodes during electrically elicited contractions were assessed and compared with those provided by commercially available EMG electrodes. The effect of the bEMG-US electrode on US images was evaluated by comparing images detected from the same muscle region with and without the electrode interposed between the US probe and the skin. Tests on five subjects showed that the electrode-skin impedance of bEMG-US electrodes was higher than that of conventional EMG electrodes (mean (range): 15.6 (8.5-21.1) kΩ vs. 8.2 (4.9-16.5) kΩ). Despite higher impedance values, both electrode systems provided comparable, electrode-skin noise levels (1.4 (1.1-1.7) µV vs. 1.3 (1.0-1.5) µV) and M waves (normalized mean square error: 2.6 (0.6-6.8)%). The quality of US images detected with and without the bEMG-US electrode between the US probe and the skin was comparable, as demonstrated by the low errors in the estimation of anatomical variables in the two experimental conditions (range: (0.37-2.35) deg for pennation angle and (-0.31-0.1) cm for muscle thickness). Results demonstrate that bEMG-US can be used to acquire concurrently EMGs and US images from the same muscle region with a negligible effect on the quality of the two detected signals, thus allowing for a simultaneous, multimodal evaluation of muscle activation.

Does the amplitude of biceps brachii M waves increase similarly in both limbs during staircase, electrically elicited contractions?

OBJECTIVE: Humans usually tend to control more finely muscle force production in dominant than non-dominant upper limbs. It is well established that motor unit recruitment is a key mechanism by which muscle force is controlled, and we hypothesized that a relatively smaller number of motor units may be recruited in muscles of dominant than non-dominant limbs for any given increase in synaptic input. Hence, we investigated peripheral properties of dominant and non-dominant biceps brachii through the analysis of M-wave responses to incremental electrical stimulation. APPROACH: Current pulses at progressively greater intensities were applied in the proximal region of biceps brachii of 16 subjects while surface electromyograms were recorded with a grid of electrodes in the distal region. M-wave amplitude was averaged across channels and normalized with respect to the maximum amplitude value, separately for each stimulation intensity and limb. Amplitude-current intensity curves were interpolated to provide an equal number of stimulation levels between limbs. Differences between dominant and non-dominant arms were assessed through the average increase in M-wave amplitude for consecutive stimulation intensities (increments). MAIN RESULTS: Wilcoxon's signed-rank test showed that increments in the M-wave amplitude were significantly smaller (p = 0.017) in dominant than non-dominant biceps brachii. SIGNIFICANCE: The results suggest that there was a more gradual recruitment of motor units in biceps brachii of dominant than non-dominant arms. This is in agreement with the hypothesis of a broader spectrum of motor unit recruitment thresholds in the dominant arm, which may contribute to a finer regulation of force production.

A novel system of electrodes transparent to ultrasound for simultaneous detection of myoelectric activity and B-mode ultrasound images of skeletal muscles.

Application of two-dimensional surface electrode arrays can provide a means of mapping motor unit action potentials on the skin surface above a muscle. The resulting muscle tissue displacement can be quantified, in a single plane, using ultrasound (US) imaging. Currently, however, it is not possible to simultaneously map spatio-temporal propagation of activation and resulting tissue strain. In this paper, we developed and tested a material that will enable concurrent measurement of two-dimensional surface electromyograms (EMGs) with US images. Specific protocols were designed to test the compatibility of this new electrode material, both with EMG recording and with US analysis. Key results indicate that, for this new electrode material, 1) the electrode-skin impedance is similar to that of arrays of electrodes reported in literature; 2) the reflection of US at the electrode-skin interface is negligible; 3) the likelihood of observing missing contacts, short-circuits, and artifacts in EMGs is not affected by the US probe; 4) movement of tissues sampled by US can be tracked accurately. We, therefore, conclude this approach will facilitate multimodal imaging of muscle to provide new spatio-temporal information regarding electromechanical function of muscle. This is relevant to basic physiology-biomechanics of active and passive force transmission through and between muscles, of motor unit spatio-temporal activity patterns, of their variation with architecture and task-related function, and of their adaptation with aging, training-exercise-disuse, neurological disease, and injury.

Variability in muscle adaptation to electrical stimulation.

The aims were to investigate the plasticity of the myosin heavy chain (MHC) phenotype following neuromuscular electrical stimulation (NMES) and to assess the correlation between MHC isoform distribution and muscle fibre conduction velocity (MFCV).14 men were subjected to 24 sessions of quadriceps NMES. Needle biopsies were taken from the dominant vastus lateralis and neuromuscular tests were performed on the dominant thigh before and after training. NMES significantly increased the quadriceps maximal force by 14.4±19.7% (P=0.02), vastus lateralis thickness by 10.7±8.6% (P=0.01), vastus lateralis MFCV by 11.1±3.5% (P<0.001), vastus medialis MFCV by 8.4±1.8% (P<0.001). The whole spectrum of possible MHC isoform adaptations to training was observed: fast-to-slow transition (4 subjects), bi-directional transformation from MHC-1 and MHC-2X isoforms toward MHC-2A isoform (7 subjects), shift toward MHC-2X (2 subjects), no MHC distribution change (1 subject). No significant correlation was observed between MHC-2 relative content and vastus lateralis MFCV (pre-training: R2=0.04, P=0.46; post-training: R2=0.02, P=0.67). NMES elicited distinct adaptations in the MHC composition and increased force, muscle thickness, and MFCV. The MHC isoform distribution did not correlate with MFCV, thus implying that the proportion of different fibre types cannot be estimated from this electrophysiological variable.

Time and frequency domain analysis of surface myoelectric signals during electrically-elicited cramps.

OBJECTIVES: To examine if different frequencies of electrical stimulation trigger different sized cramps in the abductor hallucis muscle and to analyze their surface electromyographic (EMG) behaviour in both time and frequency domains. METHODS: Fifteen subjects were studied. Stimulation trains of 150 pulses were applied to the muscle motor point. Frequency was increased (starting from 4pps with 2-pps steps) until a cramp developed. Current intensity was 30% higher than that eliciting maximal M-waves. After the first cramp ("threshold cramp"), a 30-minute rest was provided before a second cramp ("above-threshold cramp") was elicited with a frequency increased by 50% with respect to that eliciting the first cramp. RESULTS: We found greater EMG amplitude and a compression of the power spectrum for above-threshold cramps with respect to threshold cramps. M-wave changes (ranging between small decreases of M-wave amplitude to complete M-wave disappearance) occurred and progressively increased throughout stimulation trains. Significant positive correlations were found between estimates of EMG amplitude during cramps and estimated reductions of M-wave amplitude. CONCLUSIONS: Varying frequencies of electrical stimulation triggered different sized cramps. Moreover, decreases in M-wave amplitude were observed during both threshold and above-threshold stimulations. The choice of the stimulation frequency has relevance for optimizing electrical stimulation protocols for the study of muscle cramps in both healthy and pathological subjects.

Myoelectric fatigue profiles of three knee extensor muscles.

Aims of the present study were to: 1) investigate the differences between the myoelectric fatigue profiles of the vasti muscles of the quadriceps during electrically evoked contractions; 2) compare the myoelectric fatigue profiles of the vasti muscles between sedentary subjects and rowers; 3) analyze motor unit activation order during stimulation of the vasti muscles. In nine sedentary subjects and nine rowers surface EMG signals were detected during electrically elicited contractions of the following three muscles: vastus medialis obliquus (VMO), vastus lateralis (VL), and vastus medialis longus (VML). M-waves were recorded as the muscles were stimulated with both variable (increasing-decreasing) and constant stimulation intensities. Changes in M-wave conduction velocity (CV) during trains with non-constant current were adopted for the study of the motor unit recruitment order. Rates of change of myoelectric signal variables were adopted to assess myoelectric manifestations of fatigue during stimulation trains with constant current. We found that: 1) VL muscle was more fatigable than vastus medialis muscles; 2) VL and VML muscles of rowers resulted less fatigable than sedentary subjects; and 3) in the three muscles, motor units tended to be recruited in order of increasing CV and derecruited in order of decreasing CV with increasing/decreasing stimulation current.

Pulse charge and not waveform affects M-wave properties during progressive motor unit activation.

The aim of this study was to investigate changes in experimentally recorded M-waves with progressive motor unit (MU) activation induced by transcutaneous electrical stimulation with different pulse waveforms. In 10 subjects, surface electromyographic signals were detected with a linear electrode array during electrically elicited contractions of the biceps brachii muscle. Three different monophasic waveforms of 304-micros duration were applied to the stimulation electrode on the main muscle motor point: triangular, square, and sinusoidal. For each waveform, increasing stimulation current intensities were applied in 10 s (frequency: 20 Hz). It was found that: (a) the degree of MU activation, as indicated by M-wave average rectified value, was a function of the injected charge and not of the stimulation waveform, and (b) MUs tended to be recruited in order of increasing conduction velocity with increasing charge of transcutaneous stimulation. Moreover, the subjects reported lower discomfort during the contractions elicited by the triangular waveform with respect to the others. Since subject tolerance to the stimulation protocol must be considered as important as MU recruitment in determining the effectiveness of neuromuscular electrical stimulation (NMES), we suggest that both charge and waveform of the stimulation pulses should be considered relevant parameters for optimizing NMES protocols.

[Usefulness of surface electromyography of hand muscles in the assessment of myoelectric parameters changes due to repetitive manual tasks]. / Applicazione dell'elettromiografia di superficie dei muscoli della mano nello studio delle patologie da sovraccarico biomeccanico.

The aim of this project was to investigate the possible role of sEMG in the diagnosis of Carpal tunnel syndrome (CTS). The study group consisted of 37 subjects, of whom 14 (control group) were not employed in manual tasks and 23 (exposed) were engaged in repetitive and forceful manual tasks. Of the 23 exposed workers, 10 reported CTS symptoms, whereas all the subjects of the control group resulted asymptomatic. The surface electromyography signal was recorded from the abductor pollicis brevis muscle, using different levels of isometric contraction: 20% and 50% of the maximum voluntary contraction (MVC), respectively. The initial values and rate of change of the average rectified value (ARV), mean power spectral frequency (MNF) and conduction velocity (CV) were calculated. Moreover the study protocol included clinical evaluation and electrodiagnostic study of the median nerve. Data from the exposed and control group were compared. Statistically significant differences between the two groups were found for ARV initial value and for CV and MNF rate of change at 50% MVC. These parameters resulted lower in the exposed group, with the lowest values among symptomatic subjects. Possible explanations may be the loss of motor units, particularly affecting the fast and fatigable type II muscle fibers, involved in the myoelectric manifestation of fatigue. In conclusion, this technique was able to show different myoelectric patterns and manifestations of fatigue between subjects exposed and nonexposed to manual intensive work, suffering or not suffering from CTS.