Frequency Electrical Stimulation Research Articles

P148 Faster recovery of stroke patients through alternative electrical stimulation and rehabilitation movement frequency matching

P148 Faster recovery of stroke patients through alternative electrical stimulation and rehabilitation movement frequency matching

Muscle Fatigue in Response to Electrical Stimulation Pattern and Frequency in Spinal Cord Injury.

Functional electrical stimulation (FES) is widely used to induce functional movements for paralyzed muscles. However, rapid muscle fatigue during FES-induced muscle contractions limits FES clinical efficacy. To investigate muscle fatigue response across stimulation patterns and frequencies during FES in able-bodied individuals and in those with spinal cord injury (SCI). Four stimulation protocols combining 20 and 40 Hz average frequency with either constant frequency trains (CFTs) or with doublet frequency trains (DFTs) were applied to the quadriceps of seven adults with SCI and eight able-bodied participants. A FES-row training laboratory. Seven individuals with SCI (one female; age range, 25 ± 6 years) and eight age-matched able-bodied participants (one female). None. Fatigue was defined as the number of contractions until force decreased by 20% from the target level of 25% maximal contraction force. The number of contractions and the stimulation current used during the four stimulation protocols were compared. There was a significant effect of frequency, as well as interaction between group and stimulation pattern (P < .05). In both groups, 20-Hz trains increased the number of contractions to fatigue compared to 40-Hz trains. However, the responses to the pattern of stimulation differed. In the able-bodied participants, CFT increased the number of contractions to fatigue compared to DFT, whereas in those with SCI, DFT increased the number of contractions to fatigue. In fact, DFT resulted in similar number of contractions to fatigue in both populations. These results indicate that DFT at 20 Hz may be a better stimulation protocol to delay fatigue onset in the SCI population than the other three protocols. In addition, this work implies that results from able-bodied persons may not be directly applicable to those with SCI.

Frequency and Intensity of Electrical Stimulation of Human Sympathetic Ganglia Affect Heart Rate Variability and Pain Threshold

The study relates to the selection of effective clinical treatments based on the changes associated with each electrical stimulation condition. The aim was to investigate the effects of electrical stimulation on the autonomic nervous system by evaluating the heart rate variability (HRV) and pain threshold in response to different interferential current conditions applied to the sympathetic ganglia. Forty five participants were randomly assigned to receive high frequency-low intensity (HF-LI), low frequency-high intensity (LF-HI), or high frequency-high intensity (HF-HI) electrical stimulation. We then used bipolar adhesive pad electrodes to stimulate the thoracic vertebrae T1–T4 for 20 min, and changes were evaluated before, immediately after and 30 min after electrical stimulation. Results revealed significant HRV immediately after HF-LI and LF-HI electrical stimulations. This present study finding of a reduction in HRV immediately after HF-HI electrical stimulation confirms HRV measurement reliability based on electrical stimulation parameters. Results revealed a significant increase in the pain threshold with HF-HI electrical stimulation than for the other conditions; there was also a shorter pain duration. The present study also showed a significant effect of the HF-LI and LF-HI conditions on the pain threshold immediately after electrical stimulation, but the results after 30 min only revealed significant changes in the LF-HI group, indicating a maintenance of the pain control period immediately and 30 min after electrical stimulation. Different conditions of electrical stimulation resulted in distinct changes in HRV and pain control duration.

Heterosynaptic facilitation of mechanical nociceptive input is dependent on the frequency of conditioning stimulation.

High-frequency burstlike electrical conditioning stimulation (HFS) applied to human skin induces an increase in mechanical pinprick sensitivity of the surrounding unconditioned skin (a phenomenon known as secondary hyperalgesia). The present study assessed the effect of frequency of conditioning stimulation on the development of this increased pinprick sensitivity in humans. In a first experiment, we compared the increase in pinprick sensitivity induced by HFS, using monophasic non-charge-compensated pulses and biphasic charge-compensated pulses. High-frequency stimulation, traditionally delivered with non-charge-compensated square-wave pulses, may induce a cumulative depolarization of primary afferents and/or changes in pH at the electrode-tissue interface due to the accumulation of a net residue charge after each pulse. Both could contribute to the development of the increased pinprick sensitivity in a frequency-dependent fashion. We found no significant difference in the increase in pinprick sensitivity between HFS delivered with charge-compensated and non-charge-compensated pulses, indicating that the possible contribution of charge accumulation when non-charge-compensated pulses are used is negligible. In a second experiment, we assessed the effect of different frequencies of conditioning stimulation (5, 20, 42, and 100 Hz) using charge-compensated pulses on the development of increased pinprick sensitivity. The maximal increase in pinprick sensitivity was observed at intermediate frequencies of stimulation (20 and 42 Hz). It is hypothesized that the stronger increase in pinprick sensitivity at intermediate frequencies may be related to the stronger release of substance P and/or neurokinin-1 receptor activation expressed at lamina I neurons after C-fiber stimulation.NEW & NOTEWORTHY Burstlike electrical conditioning stimulation applied to human skin induces an increase in pinprick sensitivity in the surrounding unconditioned skin (a phenomenon referred to as secondary hyperalgesia). Here we show that the development of the increase in pinprick sensitivity is dependent on the frequency of the burstlike electrical conditioning stimulation.

Low-intensity muscle contraction exercise following the onset of arthritis improves hyperalgesia via reduction of joint inflammation and central sensitization in the spinal cord in a rat model

We examined the effect of immobilization, low-intensity muscle contraction exercise, and transcutaneous electrical nerve stimulation (TENS) on tissue inflammation and acute pain following the onset of arthritis in a rat model. Sixty Wistar rats were divided into five groups: (1) Arthritis group, (2) arthritis and immobilization (Immobilization group), (3) arthritis and low intensity muscle contraction (Exercise group), (4) arthritis and TENS (TENS group), and (5) sham arthritis (Sham group). Arthritis was induced in the right knee joints by single injection of 3% kaolin and carrageenan. Immobilization of the right hindlimb was conducted by full extension of the right knee joints and full plantar flexion of the ankle joints using a plaster cast for 7 days after injection. The right quadriceps muscles were subjected to electrical stimulation (frequency: 50 Hz; intensity: 2–3 mA) for 20 min/day as contraction exercise for one week. TENS was delivered at 20 min/day for one week (frequency: 50 Hz; intensity: 1 mA). The pressure pain threshold (PPT) and paw withdrawal response (PWR) were evaluated at 1 and 7 days after injection. We also analyzed the number of CD68-positive cells in the synovium by immunohistochemistry and determined the expression level of calcitonin gene-related peptide (CGRP) in the spinal dorsal horn with immunofluorescence. Improvements of both PPT and PWR were observed in the Exercise group at 7 days after injection compared to those of the Arthritis and Immobilization groups, although only improvement of PPT was observed in the TENS group. The number of CD68-positive cells in the synovium and CGRP expression in the dorsal horn decreased only in the Exercise group. These results suggested that low-intensity muscle contraction exercise might be a better treatment for reduction of arthritis-induced inflammation and acute pain compared to immobilization and TENS.

A low-frequency of electrical stimulation improves wound healing

High frequency of electrical stimulation (ES) can cause patients to become uncomfortable. Therefore, it needs to use a low frequency of ES. However, the use of low frequency of ES (below 20 Hz) on wound healing is still unclear. Therefore, this study aimed to elucidate the effect of low frequency (10 Hz) of ES on wound healing. A wound with a diameter of one cm was created at the dorsal side of rats. The rats were divided into two groups; low frequency of electrical stimulation (LFES), and control group (without ES application). The application of ES was given for ten days. The wound size in the LFES group was smaller in LFES group compared to the control group. The intensity of polymorphonuclear neutrophils was lower in the LFES group, while the intensity of fibroblast was significantly higher in the LFES than in the control group. The formation of new epidermis (reepithelialisation) was faster in LFES group than in the control groups. Low frequency of ES (10 Hz) accelerated wound healing by reducing inflammation, improving the fibroblast intensity, and formation of new epidermis.

Water intake after dehydration makes muscles more susceptible to cramp but electrolytes reverse that effect

ObjectiveNo previous study has compared water and oral rehydration solution (ORS) intake after dehydration induced by exercise in the heat for the effect on muscle cramps. The present study tested...

Abstract #117: Changes in high frequency activity depend on frequency of electrical stimulation in the human cortex

Abstract #117: Changes in high frequency activity depend on frequency of electrical stimulation in the human cortex

The curative effect observation of different frequency of TEAS combined with wristband pressing on Neiguan (PC 6) for nausea and vomiting after laparoscopic cholecystectomy

To compare the effects of different frequency of transcutaneous electrical acupoint stimulation (TEAS) combined with wristband pressing on Neiguan (PC 6) for nausea and vomiting (PONV) after laparoscopic cholecystectomy, and optimize the TEAS frequency selection for treatment of PONV. Eighty patients undergoing laparoscopic cholecystectomy were randomly divided into a postoperative routine care group, a 2 Hz TEAS combined with wristband pressing group (2 Hz TEAS group), a 100 Hz TEAS combined with combined with wristband pressing group (100 Hz TEAS group) and a 2 Hz/100 Hz TEAS wristband pressing group (2 Hz/100 Hz TEAS group), 20 cases in each group (1 patient dropped off in the postoperative routine care group). All the four groups underwent laparoscopic cholecystectomy, and routine nursing was given after the operation. In the postoperative routine nursing group，only routine nursing was received. In the other three groups, 2 Hz TEAS combined with wristband pressing, 100 Hz TEAS combined with wristband pressing, 2 Hz/100 Hz TEAS combined with wristband pressing to simulate Neiguan (PC 6) were treated on the basis of postoperative routine care after surgery. The treatment was given for 30 min each time for a total of 4 treatments. The incidence of PONV in each group was observed at 0-2 h, 2-8 h, 8-24 h and 24-48 h after operation, and the severity of PONV and postoperative pain were evaluated. Compared with the postoperative routine care group, the incidence and severity of PONV in the four time periods after surgery were significantly reduced in the 2 Hz/100 Hz TEAS group (all P<0.05), the incidence and severity of PONV in patients at 2 h and 2-8 h after surgery were significantly reduced in the 2Hz TEAS group and the 100 Hz TEAS group (all P<0.05), the postoperative pain at 8 h and 24 h after surgery was alleviated in the 100 Hz TEAS group and the 2 Hz/100 Hz TEAS group (all P<0.05). Different frequency of TEAS combined with wristband pressing to stimulating Neiguan (PC 6) have certain therapeutic effects on PONV in patients undergoing laparoscopic cholecystectomy. 2 Hz/100 Hz TEAS combined with wristband pressing at Neiguan (PC 6) is more effective in PONV. 2 Hz/100 Hz TEAS and 100 Hz TEAS combined with wristband pressing at Neiguan (PC 6) have postoperative analgesic effect, and 2 Hz/100 Hz TEAS has the better analgesic effect.

Effect of neuromuscular electrical stimulation frequency on postprandial glycemia, current-related discomfort, and muscle soreness. A crossover study.

Consensus is lacking regarding optimal neuromuscular electrical stimulation (NMES) parameters for postprandial glycemic control. Therefore, the aim of this study was to determine the NMES frequency inducing the greatest hypoglycemic effect in healthy individuals. The secondary aim was to compare current-related discomfort and muscle soreness between different frequencies. We conducted an experimental clinical study with a randomized crossover design. Sixteen healthy and sedentary participants received NMES for 20 min at 5, 10, or 50 Hz (pulse duration: 400 μs, on-off ratio: 4:12 s) following a standardized meal. Glycemia, discomfort, and muscle soreness during and after NMES were compared between conditions. Five-hertz NMES generated a significant hypoglycemic effect, contrary to 10 Hz and 50 Hz. Ten-hertz and 50-Hz NMES resulted respectively in lower current-related discomfort and greater muscle soreness compared with the other frequencies. Women reported higher discomfort than men. These findings contribute towards the possibility of more efficient long-term NMES treatments in terms of glycemic response and patient tolerance.

Frequency and state-dependent effects of VTA electrical stimulation on whole brain fMRI activity

Event Abstract Back to Event Frequency and state-dependent effects of VTA electrical stimulation on whole brain fMRI activity Sjoerd Murris1*, John Arsenault1, 2 and Wim Vanduffel1, 2, 3 1 Department of Neurosciences, KU Leuven, Belgium 2 Athinoula A. Martinos Center for Biomedical Imaging, Harvard Medical School, United States 3 Harvard Medical School, United States The Ventral Tegmental Area (VTA) and neighbouring Substantia Nigra are integral structures at the heart of the dopamine system, underlying adaptive behaviour. Endogenous firing rates of dopamine cells in the VTA vary from fast phasic bursts to slow tonic activity, possibly supporting diverse cognitive functionss1. Artificial perturbations of the VTA through electrical and optogenetic stimulation methods generate different and sometimes even contrasting behavioural outcomes depending on stimulation parameters such as frequency, amplitude and pulse width2–4. Here we investigate the brain-wide functional effects of electrical stimulation frequency (10, 20, 50 and 100 Hz) of the VTA of two rhesus macaques implanted with chronic electrodes5. We stimulated both animals while measuring brain-wide fMRI signal changes during a passive fixation task or under anaesthesia. In the awake state, activity in many cortical and subcortical structures followed an inverted u-shape as a function of stimulation frequency, with highest evoked activity when stimulating at 20 and 50 Hz and less activity at 10 and 100 Hz. In addition, we tested whether the state of the animals had an effect on stimulation-induced network activity by performing the same experiment under ketamine-induced anaesthesia. Under anaesthesia, the hemodynamic responses in connected brain areas were slightly positive at 10Hz stimulation, but became negative and decreased linearly as a function of higher stimulation frequencies. In conclusion, brain wide network effects induced by electrical stimulation of the VTA are to a large degree frequency and state-dependent. The remarkably different stimulation-induced amplitudes and patterns of fMRI activity may explain varying and even opposing behavioural effects observed using Deep Brain Stimulation in patients. In addition, they call for a careful design and interpretation of electrical microstimulation procedures in fundamental research. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Acknowledgements This work received funding from KU Leuven C14/17/109; Hercules II funds; Fonds Wetenschappelijk Onderzoek-Vlaanderen G0D5817N, G090714N and Odysseus G0007.12; and the European Union's Horizon 2020 Framework Programme for Research and Innovation under Grant Agreement No 785907 (Human Brain Project SGA2).

A novel technique for in situ uniaxial tests of self-assembled soft biomaterials.

We introduce a novel method to form 3D biomimetic tissues from a droplet of a cell-extracellular matrix (ECM) mixture on a sensor stage and to quantify tissue force and stiffness as a function of time under optical microscopes. This method exploits advances in micro-nano fabrication and capillarity for self-assembly and self-alignment of tissues on the stage. It allows simultaneous investigation of the microstructure of the tissue in situ while its mechanical response is quantified, thus linking tissue biophysics with physiology and revealing structural-functional properties of 3D tissues. We demonstrate the functionality of the stage by studying the mechanical behavior of different cell-collagen mixtures under mechanical, chemical and electrical stimulation. This includes force evolution in cell-free collagen during curing, myotubes differentiated from muscle cell-collagen/Matrigel ECM subjected to electrical stimulation, and fibroblast-collagen tissue subjected to cancer cell conditioned media (CM) and a Rho-kinase inhibitor, Y27632. Muscle contraction decreases with increasing frequency of electrical stimulation, and fibroblasts respond to CM by increasing contractility for a short time and completely relax in the presence of Y27632 but restore force with Y27632 washout.

Effect of neuromuscular electrical stimulation frequency on muscles of the tongue.

Neuromuscular electrical stimulation (NMES) for the treatment of swallowing disorders is delivered at a variety of stimulation frequencies. We examined the effects of stimulation frequency on tongue muscle plasticity in an aging rat model. Eighty-six young, middle-aged, and old rats were assigned to either bilateral hypoglossal nerve stimulation at 10 or 100 Hz (5 days/week, 8 weeks), sham, or no-implantation conditions. Muscle contractile properties and myosin heavy chain (MyHC) composition were determined for hyoglossus (HG) and styloglossus (SG) muscles. Eight weeks of 100-Hz stimulation resulted in the greatest changes in muscle contractile function with significantly longer contraction and half-decay times, the greatest reduction in fatigue, and a transition toward slowly contracting, fatigue-resistant MyHC isoforms. NMES at 100-Hz induced considerable changes in contractile and phenotypic profiles of HG and SG muscles, suggesting higher frequency NMES may yield a greater therapeutic effect. Muscle Nerve, 2018.

The effectiveness of electrical stimulation on muscle tone, elasticity and stiffness of gastrocnemius muscle in children with spastic cerebral palsy

Introduction/Background The aim of this study was to demonstrate the therapeutic effectiveness of electrical stimulation on muscle tone, elasticity and stiffness in children with spastic cerebral palsy. Material and method Thirty-one lower extremities of 18 patients with spastic cerebral palsy (5 diplegic, 8 quadriplegic and 5 hemiplegic) were evaluated. Biomechanical measurements of gastrocnemius muscle were performed using a myotonometry device. The MyotonPro was used to measure the muscle tone, elasticity and stiffness of the gastrocnemius muscle (medial and lateral parts) on bilateral sides of the patients with diplegic/quadriplegic cerebral palsy and from the paretic side of the patients with hemiplegic cerebral palsy. Patients were treated for five days of electrical stimulation (frequency of 50 Hz, pulse duration 300 ms, ramp of 0,5 ms, on:off time 5 s:5 s, session time of 30 minutes) which was applied on the gastrocnemius muscle aiming for the management of spasticity. The measurements were repeated after the fifth session. Results The mean age of the patients were 6.44 ± 3.6 (2.5–13). The mean Gross Motor Function Classification System level of the patients were 3.11 ± 1.6 (1–5) and Ashworth scale were 2.06 ± 0.75 (1–3). The muscle tone and stiffness of medial and lateral gastrocnemius muscle decreased significantly (P Conclusion Our results suggest that electrical stimulation for the treatment of spasticity had improvements on muscle tone, elasticity and stiffness of spastic cerebral palsy patients. And MyotonPro can be used to measure the effects of treatment in spasticity.

Contractile Protein Expression and Phosphorylation and Contractility of Gastric Smooth Muscles from Obese Patients and Patients with Obesity and Diabetes.

Ingested food is received, mixed, and ground into chyme by distinct gastric motility patterns. Diabetes impairs gastric muscle function, but the mechanisms underlying diabetes-induced gastric muscle dysfunction are unknown. Here, we compared the expression and phosphorylation of Ca2+ sensitization and contractile proteins in human gastric muscles from obese nondiabetic and diabetic patients. We also compared the spontaneous phasic contractions and the contractile responses evoked by electrical field stimulation of cholinergic motor neurons. Fundus and antrum muscles were obtained from sleeve gastrectomies and were used in in vitro myobath contractile studies and for capillary electrophoresis and immunodetection of γ-actin, CPI-17, pT38-CPI-17, MYPT1, pT853-MYPT1, pT696-MYPT1, myosin light chain (MYL9), pS19-MYL9, myosin light chain kinase (MYLK), protein phosphatase-1δ (PP1δ), and Rho-associated kinase (ROCK2). In diabetic fundus muscles, MYLK, ROCK2, and PP1δ expression was unchanged; MYPT1 and CPI-17 expression was decreased; and the pT853/MYPT1 and pT38/CPI-17 ratios, but not the pT696/MYPT1 ratio, were increased. Although MYL9 expression was increased, the pS19/MYL9 ratio was unchanged in diabetic fundus muscles. In diabetic antrum muscles, MYLK and MYL9 expression was unchanged, but ROCK2, CPI-17, and PP1δ expression was decreased. The pT38/CPI-17 ratio was unchanged, while the pS19/MYL9, pT853/MYPT1, and pT696/MYPT1 ratios were decreased, consistent with the reduced ROCK2 expression. The frequencies of spontaneous phasic contractions from nondiabetic and diabetic gastric fundus and antrum muscles did not significantly differ from each other, regardless of age, sex, or diabetic status. The fold increases in the contractions of diabetic fundus and antrum muscles in response to increased frequencies of electrical field stimulation were significantly lower compared to nondiabetic fundus and antrum muscles. The altered contractile responses and the protein expression and phosphorylation in gastric muscles of obese patients with diabetes illustrate the importance of understanding how smooth muscle Ca2+ sensitization mechanisms contribute to gastric motility.

Effect of Electrical Stimulation Frequency and Pattern on Muscle Fatigue in Spinal Cord Injured Individuals

Spinal cord injury (SCI) leads to an extensive skeletal muscle atrophy in the regions below the level of injury. Moreover, the paralyzed skeletal muscles shift towards predominantly Type II (fast‐twitch and highly fatigable) fibers. Functional electrical stimulation (FES) has been used to produce purposeful and controlled muscle contractions to restore functional movements, but rapid muscle fatigue remains a problem. Both pattern and frequency of stimulation can influence muscle fatigue rate, but optimization of stimulation parameters has rarely been investigated for those with SCI. FES has traditionally used constant‐frequency trains (CFT; brief stimulation pulses separated by regular interpulse intervals). However, it has been suggested that doublet‐frequency trains (DFT; close‐spaced pulse trains separated by longer intervals) can result in lesser fatigue. Also, stimulation frequency may determine muscle fatigue, with high‐frequency trains resulting in lesser fatigue compared to low‐frequency trains. However, most studies comparing muscle fatigue across stimulation parameters have been only examined in able‐bodied individuals and it is unknown whether paralyzed muscles respond similarly. There are a few studies suggesting that low‐frequency trains produce less fatigue than high‐frequency trains in those with SCI, in direct contrast to the able‐bodied. Therefore, we examined differences in muscle fatigue across and within able‐bodied individuals (N=8) and those with SCI (N=6) during CFT and DFT stimulation patterns at high‐ (40 Hz) and low‐ (20 Hz) frequencies. Fatigue was defined as a sustained reduction in force of &gt;20% at a constant stimulation intensity. Differences were considered significant at p&lt;0.05 and values are mean ± SEM. For both groups, low‐frequency trains delayed fatigue onset compared to high‐frequency trains, on average by 30 ± 3 %. In the able‐bodied, CFT resulted in slower fatigue onset (#contractions to fatigue CFT vs DFT: 20 Hz 39 ± 4 vs. 34 ± 4, 40 Hz 26 ± 4 vs. 23 ± 3). In those with SCI, DFT resulted in slower fatigue onset (#contractions to fatigue CFT vs DFT: 20 Hz 26 ± 2 vs. 35 ± 4, 40 Hz 20 ± 2 vs. 25 ± 2). In fact, DFT resulted in similar #contractions to fatigue in both populations, whereas CFT induced muscle fatigue significantly faster in those with SCI. These results may indicate that DFT preferentially recruit fast‐twitch fibers, leading to similar fatigue in both able‐bodied and those with SCI. DFT has been previously shown to limit fatigue potentially by increasing calcium release from the sarcoplasmic reticulum and/or by increasing muscle stiffness. These data indicate that DFT trains appear to be preferable for fatigue reduction in the SCI population.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Investigation of the Relationship Between Electrical Stimulation Frequency and Muscle Frequency Response Under Submaximal Contractions.

Neuromuscular electrical stimulation (NMES) is a common tool that is used in clinical and laboratory experiments and can be combined with mechanomyography (MMG) for biofeedback in neuroprostheses. However, it is not clear if the electrical current applied to neuromuscular tissues influences the MMG signal in submaximal contractions. The objective of this study is to investigate whether the electrical stimulation frequency influences the mechanomyographic frequency response of the rectus femoris muscle during submaximal contractions. Thirteen male participants performed three maximal voluntary isometric contractions (MVIC) recorded in isometric conditions to determine the maximal force of knee extensors. This was followed by the application of nine modulated NMES frequencies (20, 25, 30, 35, 40, 45, 50, 75, and 100 Hz) to evoke 5% MVIC. Muscle behavior was monitored by the analysis of MMG signals, which were decomposed into frequency bands by using a Cauchy wavelet transform. For each applied electrical stimulus frequency, the mean MMG spectral/frequency response was estimated for each axis (X, Y, and Z axes) of the MMG sensor with the values of the frequency bands used as weights (weighted mean). Only with respect to the Z (perpendicular) axis of the MMG signal, the stimulus frequency of 20 Hz did not exhibit any difference with the weighted mean (P = 0.666). For the frequencies of 20 and 25 Hz, the MMG signal displayed the bands between 12 and 16 Hz in the three axes (P < 0.050). In the frequencies from 30 to 100 Hz, the muscle presented a higher concentration of the MMG signal between the 22 and 29 Hz bands for the X and Z axes, and between 16 and 34 Hz bands for the Y axis (P < 0.050 for all cases). We observed that MMG signals are not dependent on the applied NMES frequency, because their frequency contents tend to mainly remain between the 20- and 25-Hz bands. Hence, NMES does not interfere with the use of MMG in neuroprosthesis.

Closed-Loop Efficient Searching of Optimal Electrical Stimulation Parameters for Preferential Excitation of Retinal Ganglion Cells.

The ability for visual prostheses to preferentially activate functionally-distinct retinal ganglion cells (RGCs) is important for improving visual perception. This study investigates the use of high frequency stimulation (HFS) to elicit RGC activation, using a closed-loop algorithm to search for optimal stimulation parameters for preferential ON and OFF RGC activation, resembling natural physiological neural encoding in response to visual stimuli. We evaluated the performance of a wide range of electrical stimulation amplitudes and frequencies on RGC responses in vitro using murine retinal preparations. It was possible to preferentially excite either ON or OFF RGCs by adjusting amplitudes and frequencies in HFS. ON RGCs can be preferentially activated at relatively higher stimulation amplitudes (>150 μA) and frequencies (2–6.25 kHz) while OFF RGCs are activated by lower stimulation amplitudes (40–90 μA) across all tested frequencies (1–6.25 kHz). These stimuli also showed great promise in eliciting RGC responses that parallel natural RGC encoding: ON RGCs exhibited an increase in spiking activity during electrical stimulation while OFF RGCs exhibited decreased spiking activity, given the same stimulation amplitude. In conjunction with the in vitro studies, in silico simulations indicated that optimal HFS parameters could be rapidly identified in practice, whilst sampling spiking activity of relevant neuronal subtypes. This closed-loop approach represents a step forward in modulating stimulation parameters to achieve appropriate neural encoding in retinal prostheses, advancing control over RGC subtypes activated by electrical stimulation.

Characterizing the transcutaneous electrical recruitment of lower leg afferents in healthy adults: implications for non-invasive treatment of overactive bladder

BackgroundAs a potential new treatment for overactive bladder (OAB), we investigated the feasibility of non-invasively activating multiple nerve targets in the lower leg.MethodsIn healthy participants, surface electrical stimulation (frequency = 20 Hz, pulse width = 200 μs) was used to target the tibial nerve, saphenous nerve, medial plantar nerve, and lateral plantar nerve. At each location, the stimulation amplitude was increased to define the thresholds for evoking (1) cutaneous sensation, (2) target nerve recruitment and (3) maximum tolerance.ResultsAll participants were able to tolerate stimulation amplitudes that were 2.1 ± 0.2 (range = 2.0 to 2.4) times the threshold for activating the target nerve.ConclusionsNon-invasive electrical stimulation can activate neural targets at levels that are consistent with evoking bladder-inhibitory reflex mechanisms. Further work is needed to test the clinical effects of stimulating one or more neural targets in OAB patients.

Electrical Stimulation Frequency and Skeletal Muscle Characteristics: Effects on Force and Fatigue.

This investigation aimed to determine the force and muscle surface electromyography (EMG) responses to different frequencies of electrical stimulation (ES) in two groups of muscles with different size and fiber composition (fast- and slow-twitch fiber proportions) during a fatigue-inducing protocol. Progression towards fatigue was evaluated in the abductor pollicis brevis (APB) and vastus lateralis (VL) when activated by ES at three frequencies (10, 35, and 50Hz). Ten healthy adults (mean age: 23.2 ± 3.0 years) were recruited; participants signed an IRB approved consent form prior to participation. Protocols were developed to 1) identify initial ES current intensity required to generate the 25% maximal voluntary contraction (MVC) at each ES frequency and 2) evaluate changes in force and EMG activity during ES-induced contraction at each frequency while progressing towards fatigue. For both muscles, stimulation at 10Hz required higher current intensity of ES to generate the initial force. There was a significant decline in force in response to ES-induced fatigue for all frequencies and for both muscles (p<0.05). However, the EMG response was not consistent between muscles. During the progression towards fatigue, the APB displayed an initial drop in force followed by an increase in EMG activity and the VL displayed a decrease in EMG activity for all frequencies. Overall, it appeared that there were some significant interactions between muscle size and fiber composition during progression towards fatigue for different ES frequencies. It could be postulated that muscle characteristics (size and fiber composition) should be considered when evaluating progression towards fatigue as EMG and force responses are not consistent between muscles.