Surface EEG-Transcranial Direct Current Stimulation (tDCS) Closed-Loop System.

Conventional transcranial direct current stimulation (tDCS) protocols rely on applying electrical current at a fixed intensity and duration without using surrogate markers to direct the interventions. This has led to some mixed results; especially because tDCS induced effects may vary depending on the ongoing level of brain activity. Therefore, the objective of this preliminary study was to assess the feasibility of an EEG-triggered tDCS system based on EEG online analysis of its frequency bands. Six healthy volunteers were randomized to participate in a double-blind sham-controlled crossover design to receive a single session of 10[Formula: see text]min 2[Formula: see text]mA cathodal and sham tDCS. tDCS trigger controller was based upon an algorithm designed to detect an increase in the relative beta power of more than 200%, accompanied by a decrease of 50% or more in the relative alpha power, based on baseline EEG recordings. EEG-tDCS closed-loop-system was able to detect the predefined EEG magnitude deviation and successfully triggered the stimulation in all participants. This preliminary study represents a proof-of-concept for the development of an EEG-tDCS closed-loop system in humans. We discuss and review here different methods of closed loop system that can be considered and potential clinical applications of such system.

Higher-order power harmonics of pulsed electrical stimulation modulates corticospinal contribution of peripheral nerve stimulation.

It is well established that electrical-stimulation frequency is crucial to determining the scale of induced neuromodulation, particularly when attempting to modulate corticospinal excitability. However, the modulatory effects of stimulation frequency are not only determined by its absolute value but also by other parameters such as power at harmonics. The stimulus pulse shape further influences parameters such as excitation threshold and fiber selectivity. The explicit role of the power in these harmonics in determining the outcome of stimulation has not previously been analyzed. In this study, we adopted an animal model of peripheral electrical stimulation that includes an amplitude-adapted pulse train which induces force enhancements with a corticospinal contribution. We report that the electrical-stimulation-induced force enhancements were correlated with the amplitude of stimulation power harmonics during the amplitude-adapted pulse train. In an exploratory analysis, different levels of correlation were observed between force enhancement and power harmonics of 20-80 Hz (r = 0.4247, p = 0.0243), 100-180 Hz (r = 0.5894, p = 0.0001), 200-280 Hz (r = 0.7002, p < 0.0001), 300-380 Hz (r = 0.7449, p < 0.0001), 400-480 Hz (r = 0.7906, p < 0.0001), 500-600 Hz (r = 0.7717, p < 0.0001), indicating a trend of increasing correlation, specifically at higher order frequency power harmonics. This is a pilot, but important first demonstration that power at high order harmonics in the frequency spectrum of electrical stimulation pulses may contribute to neuromodulation, thus warrant explicit attention in therapy design and analysis.

Contribution of Corticospinal Modulation and Total Electrical Energy for Peripheral-Nerve-Stimulation-Induced Neuroplasticity as Indexed by Additional Muscular Force.

BACKGROUND: Protocols to induce motor related neuroplasticity are usually directed to central neural structures such as the motor cortex or the spinal cord. OBJECTIVE: Herein, we aimed to evaluate the effects of peripheral nerve stimulation using a current intensity (stimulation intensity) approach to understand the contribution of the corticospinal system and total energy to electrically-induced neuroplasticity. METHODS: Electrical stimulation trains of lower intensity, interlaced with 2-s bursts of higher intensity, were applied to anesthetized rabbits. Nerve blocks were applied to the proximal side of the stimulation site with identical stimulation trains in a different session to block the contribution of corticospinal volleys during intensity-modulated electrical stimulation. RESULTS: Additional force corresponding to additional recruitment of motoneurons was observed when a 2-s burst of high intensity was present (burst/constant: 24.7 ± 3.6%/2.09 ± 4.8%; p < .001). Additional force was absent in sessions when the neural pathway to the spinal cord was blocked (unblocked/blocked: 29.3 ± 3.8%/-2.49 ± 4.8%; p < .001). CONCLUSIONS: The results suggest that induced neuroplasticity indexed by the additional force is dependent on the total energy applied and connectivity to central structures. These results give additional evidence for the contribution of two factors for induced neuroplasticity: (i) modulation by corticospinal structures and (ii) total energy of stimulation. Further protocols should explore simultaneous peripheral and central stimulation.

5 Hz Repetitive Transcranial Magnetic Stimulation with Maximum Voluntary Muscle Contraction Facilitates Cerebral Cortex Excitability of Normal Subjects.

BACKGROUND: Recently, high-frequency repetitive transcranial magnetic stimulation (rTMS) is reported to evaluating the corticospinal pathway and improving both cortical excitability and motor function significantly in subjects. According to some previous reports, the maximum voluntary muscle contraction (MVC) of target muscle can reinforce the influence by rTMS. The aim of this study was to confirm 5 Hz rTMS with MVC in healthy individuals is an effective method to facilitate motor neuron excitability and the efficiency can last at least 30 min post stimulation. OBJECTIVE: To compare the motor evoked potentials (MEPs) elicited by 5Hz rTMS and 5Hz rTMS combined with MVC. METHODS: In this randomized, controlled, assessor-blinded, crossover trial, 40 healthy right-handed subjects were divided into group A (n=20) and group B (n=20). All subjects received rTMS over the primary motor cortex area (M1) in the left hemisphere. The parameters of rTMS were 5 Hz, 90.of the resting motor threshold (RMT), for a total of 500 pulses in 100 trains (1-sec inter-stimulus and 8- sec inter-interval). Method 1: All subjects received rTMS over the hand area of left M1. Method 2: All subjects received rTMS at the same stimulated point, combined with maximum voluntary hand griping in each 10 trains. Test 1: group A underwent method 1, while group B underwent method 2. Test 2: A week later, group B underwent method 1, while group A underwent method 2. In each test, the MEP amplitude and latency was measured before (P-rTMS), 5 min after (Post 1) and 30 min after (Post 2) the rTMS intervention. RESULTS: MEP amplitude increased significantly from baseline at 5 minutes post intervention under both treatment regimes. However for both sequences, it decreased towards baseline under the rTMS intervention at 30 minutes post intervention but remained relatively high when rTMS was combined with MVC. MEP latency decreased significantly from baseline at 5 minutes post intervention under both treatment regimes. For both sequences, it then increased again towards baseline under both treatment regimes at 30 minutes post intervention. Although there was a trend for a less pronounced increase under the combined treatment, this effect was not significant. CONCLUSION: Both 5 Hz rTMS and 5 Hz rTMS combined with MVC facilitate motor cortical excitability, but the enhancement in rTMS with MVC is more pronounced and maintained longer than simple rTMS.

Comparison of the Effects of Contralaterally Controlled Functional Electrical Stimulation and Neuromuscular Electrical Stimulation on Upper Extremity Functions in Patients with Stroke.

BACKGROUND: Contralaterally controlled functional electrical stimulation (CCFES) is an innovative method to improve upper extremity functions after stroke. OBJECTIVE: To compare the effects of CCFES versus neuromuscular electrical stimulation (NMES) on the upper extremity functions in patients with stroke. METHODS: Sixty patients with stroke were randomly assigned into CCFES group (n=30) or NMES group (n=30). All patients were also treated with conventional medical treatment and rehabilitation training. Patients in CCFES group received CCFES to the affected wrist extensors while the NMES group received NMES. The stimulus current was biphasic wave with a pulse duration of 200 µs and a frequency of 60 Hz. The electrical stimulation lasted for 20 min per session, 5 sessions per week for 3 weeks. The intensity of the CCFES was based on the electromyography (EMG) value of the unaffected side while the subjects voluntarily extended their unaffected wrist slightly (<10% range of motion, ROM), moderately (about 50% ROM) and completely (100% ROM). Fugl-Meyer assessment (FMA), motricity index (MI), the Hong Kong version of functional test for the hemiplegic upper extremity (FTHUE-HK) and active range of motion (AROM) of wrist extension were measured before and after 3 weeks of treatment. RESULTS: Compared with the baseline values, both groups showed significant improvements in all the measurements after treatment (p<0.05). Patients in CCFES group showed significantly higher upper extremity FMA, FTHUE-HK scores and AROM of wrist extension than those in NMES group (p<0.05). CONCLUSION: Compared with the conventional NMES, CCFES provides better recovery of upper extremity function in patients with stroke.

Reducing anterior tibial translation by applying functional electrical stimulation in dynamic knee extension exercises: quantitative results acquired via marker tracking.

BACKGROUND: Pain that accompanies anterior cruciate ligament deficiency during dynamic knee extension exercises is usually caused by excessive anterior tibial translation, which can be restricted if the anterior cruciate ligament was intact. METHODS: A functional electrical stimulator is incorporated with a training device to induce hamstring contractions during certain degrees of knee extension to replicate effects similar to those generated by an intact anterior cruciate ligament and to reduce anterior tibial translation. By using a camera that tracks markers placed on bony prominences of the femur and tibia, the anterior tibial translations corresponding to various settings were determined by customized image processing procedures. FINDINGS: In the electrical stimulation sessions, the knee extensions with electrical stimulation feedback induced significantly (n=6, P<.05) less anterior tibial translation over the range of 20 to 50° when compared to those using the standard isokinetic shank restraint. Likewise, the knee extensions with an anti-shear device that blocks tibia displacement mechanically also induced significantly (n=6, P<.05) less anterior tibial translation, but over a different range of knee extension (30 to 70°). INTERPRETATION: Despite the fact that both the electrical stimulator and the anti-shear device assisted in reducing anterior tibial translation, the tendency of the curves generated with the functional electrical stimulation was generally more similar to those generated when using the standard isokinetic shank restraint.

Pulse energy as a reliable reference for twitch forces induced by transcutaneous neuromuscular electrical stimulation.

Voltage-controlled neuromuscular electrical stimulation has been considered to be safer in noninvasive applications notwithstanding the fact that voltage-controlled devices purportedly generate forces less predictable than their current-controlled equivalents. This prompted us to evaluate relevant electrical parameters to determine whether forces induced by voltage-controlled stimuli were able to match to those induced by current-controlled ones, which tend to evoke forces that were more predictable. Force magnitudes corresponding to current- and voltage-controlled stimuli were aligned with respect to electric charge (equivalent to average current intensity) and electrical energy (equivalent to average power) of the same stimulation pulse to determine which provided a better coherence. Consistency of forces evaluated with energy was significantly (p < 0.001) better than that evaluated with electric charges, suggesting that electrically stimulated forces can be reliably predicted by monitoring the energy parameter of stimulation pulses. The above results appear to show that electrode-tissue impedance, a factor that makes charge and energy evaluations different, redefined the actual effects of current intensities in generating favorable results. Accordingly, novel schemes that track the energy (or average power) of a stimulation pulse may be used as a reliable benchmark to associate mechanical (force) and electrical (stimulation pulse) characteristics in transcutaneous applications of electrical stimulation.

A pelvic motion driven electrical stimulator for drop-foot treatment.

Foot switches operating with force sensitive resistors placed in the shoe sole were considered as an effective way for driving FES assisted walking systems in gait restoration. However, the reliability and durability of the foot switches run down after a certain number of steps. As an alternative for foot switches, a simple, portable, and easy to handle motion driven electrical stimulator (ES) is provided for drop foot treatment. The device is equipped with a single tri-axis accelerometer worn on the pelvis, a commercial dual channel electrical stimulator, and a controller unit. By monitoring the pelvic rotation and acceleration during a walking cycle, the events including heel strike and toe off of each step is thereby predicted by a post-processing neural network model.

Safety measures implemented for modular functioning electrical stimulators.

The modular architecture allows for greater flexibility in the building of neural prostheses with a variety of channels but may result in unpredictable accidents under circumstances such as sensor displacements, improper coordination of the connected modules and malfunction of any individual module. A novel fail-safe interface is offered as a solution that puts in place the necessary safety measures when building a module based functional electrical stimulator. By using a single reference line in the interconnecting bus of the modules, various commands would immediately be directed to each module so that proper actions may be taken.

Safety assurance of assistive devices based on a two-level checking scheme.

The increasing number of physically challenged individuals has boosted the demand of powered wheelchairs. This paper is on the subject of a DSP (Digital Signal Processors) based assistive system, which is associated with a two-level checking scheme. The assistive system takes on the M3S (Multiple Master Multiple Slave) regulation for the assurance of safety. The CAN (Control Area Networks) embedded module in the DSP provides robust transmission of information within the system. The hardware interfaces based on the two-level checking scheme is implemented in input devices (e.g. joystick, head control apparatus) and in output devices (e.g. manipulator, prime mover motors).

Monitoring and Transmission via Wireless Network for an Assistive Device.

Owing to the increasing number of disabled individuals, technical aids are acting more aggressively in the era of modern medicine. The M3S (Multiple Master Multiple Slave) system developed for the physically challenged, utilizes intelligent transmission and integration mechanisms to arrange all hooked-up devices with proper control. To overcome certain limitations of the system (e.g. distance), an RF (Radio Frequency) wireless module would be in charge of the wireless communication between a remote bus and a local bus. It is demonstrated here as assistance for parking assistive vehicles (e.g. powered wheelchair) located in a remote region, which also includes monitoring and usage of accessorial data transmissions shown in our man-machine interface.

Use of M3S for mobile/local controls over a remote/fixed environment.

The M3S (Multiple Master Multiple Slave) is an intelligent transmission system for the disabled. This integrated system combines technical aids for mobility, manipulation, environment control and communication. However, signals must be transmitted by a RF (Radio Frequency) module to overcome critical limitations of the CAN Bus (e.g. length). Appliances in different rooms are attached to different "remote" M3S Busses, while the user's "local" M3S Bus controls these remote links by manipulating all output devices on the remote end with input devices on the local end. Signals may also be transferred singly through remote M3S Busses, allowing the neighborhood remote Busses to interface between origin and destination.

A generic input device for the multiple master multiple slave system.

The growing demand for input devices designed for the severely handicapped led to development of modular features for the open architecture multiple master multiple slave (M3S) system. With its central safety monitor, M3S allows individuals suffering from cerebral palsy, paraplegia, or multiple sclerosis, and other physically debilitating illnesses greater autonomy by allowing them to access a wide range of input devices tailored to a specific user, e.g., joysticks, keypads, head-control modules and speech recognizers. These input devices, which are equipped with basic configuration abilities, are operated with DSP cores and additional circuitries to maintain optimal control and high levels of safety, and may be modified or expanded with minimal adjustments.