Measuring the electrophysiological effects of direct electrical stimulation after awake brain surgery.

OBJECTIVE: Direct electrical stimulation (DES) at 60 Hz is used to perform real-time functional mapping of the brain, and guide tumour resection during awake neurosurgery. Nonetheless, the electrophysiological effects of DES remain largely unknown, both locally and remotely. APPROACH: In this study, we lowered the DES frequency to 1-10 Hz and we used a differential recording mode of electro-corticographic (ECoG) signals to improve the focality with a simple algorithm to remove the artefacts due to the response of the acquisition chain. MAIN RESULTS: Doing so, we were able to observe different components in the evoked potentials triggered by simulating the cortex or the subcortical white matter pathways near the recording electrodes and by stimulating the cortex remotely from the recording site. More particularly, P0 and N1 components were repeatedly observed on raw ECoG signals without the need to average the data. SIGNIFICANCE: This new methodology is important to probe the electrophysiological states and the connectivity of the brain in vivo and in real time, namely to perform electrophysiological brain mapping on human patients operated in the neurosurgical room and to better understand the electrophysiological spreading of DES.

Characterization of multi-channel intraneural stimulation in transradial amputees.

Although peripheral nerve stimulation using intraneural electrodes has been shown to be an effective and reliable solution to restore sensory feedback after hand loss, there have been no reports on the characterization of multi-channel stimulation. A deeper understanding of how the simultaneous stimulation of multiple electrode channels affects the evoked sensations should help in improving the definition of encoding strategies for bidirectional prostheses. We characterized the sensations evoked by simultaneous stimulation of median and ulnar nerves (multi-channel configuration) in four transradial amputees who had been implanted with four TIMEs (Transverse Intrafascicular Multichannel Electrodes). The results were compared with the characterization of single-channel stimulation. The sensations were characterized in terms of location, extent, type, and intensity. Combining two or more single-channel configurations caused a linear combination of the sensation locations and types perceived with such single-channel stimulations. Interestingly, this was also true when two active sites from the same nerve were stimulated. When stimulating in multi-channel configuration, the charge needed from each electrode channel to evoke a sensation was significantly lower than the one needed in single-channel configuration (sensory facilitation). This result was also supported by electroencephalography (EEG) recordings during nerve stimulation. Somatosensory potentials evoked by multi-channel stimulation confirmed that sensations in the amputated hand were perceived by the subjects and that a perceptual sensory facilitation occurred. Our results should help the future development of more efficient bidirectional prostheses by providing guidelines for the development of more complex stimulation approaches to effectively restore multiple sensations at the same time.

A sensor fusion approach for inertial sensors based 3D kinematics and pathological gait assessments: toward an adaptive control of stimulation in post-stroke subjects.

Pathological gait assessment and assistive control based on functional electrical stimulation (FES) in post-stroke individuals, brings out a common need to robustly quantify kinematics facing multiple constraints. This study proposes a novel approach using inertial sensors to compute dorsiflexion angles and spatio-temporal parameters, in order to be later used as inputs for online close-loop control of FES. 26 post-stroke subjects were asked to walk on a pressure mat equipped with inertial measurement units (IMU) and passive reflective markers. A total of 930 strides were individually analyzed and results between IMU-based algorithms and reference systems compared. Mean absolute (MA) errors of dorsiflexion angles were found to be less than 4°, while stride lengths were robustly segmented and estimated with a MA error less than 10 cm. These results open new doors to rehabilitation using adaptive FES closed-loop control strategies in "foot drop" syndrome correction.

Neural and muscular mechanisms of electrically induced fatigue in patients with spinal cord injury.

STUDY DESIGN: Intervention study. OBJECTIVES: The present study aimed at examining whether spinal and/or peripheral alterations are in the origin of neuromuscular fatigue development induced by intermittent neuromuscular electrical stimulation (NMES) in subjects with complete spinal cord injury (SCI). SETTING: Neurological Rehabilitation Center CMN Propara, Montpellier, France. METHODS: Thirteen volunteers with complete SCI participated in the study. The right triceps surae muscle was fatigued using a 30-Hz NMES protocol (2 s ON-2 s OFF) composed of three series of five trains. Spinal excitability (assessed by the H-reflex), muscle excitability (assessed by the M-wave), muscle contractile properties (assessed by mechanical response parameters) and torque evoked by NMES were tested before and after each five-train series. RESULTS: NMES-evoked torque significantly decreased throughout the protocol (P<0.001). This decrease was accompanied by a significant increase in M-wave amplitude (P<0.001), whereas H-reflex and the Hmax/Mmax ratio were not significantly modified. The amplitude of the mechanical response was significantly decreased at the end of the protocol (P<0.05). CONCLUSION: The results indicate significant fatigue development, which was attributed to impaired cross-bridge force-generating capacity, without modification of spinal excitability nor muscle excitability.

Development of an implantable transverse intrafascicular multichannel electrode (TIME) system for relieving phantom limb pain.

Phantom limb pain frequently follows amputation. Currently there is no fully effective treatment available. Our aim is to develop an innovative Human Machine Interface (HMI) where we apply multi-channel microstimulation to the nerve stump of an amputee subject to manipulate the phantom limb sensations and explore the possibility of using microstimulation as a treatment for phantom limb pain.

Application of an artificial neural network to the control of an active external orthosis of the lower limb.

The object of this paper is to present a real-time application of an artificial neural network (ANN). The application for which this network is demonstrated is a motorised orthosis with six degrees-of-freedom for use by a paraplegic; a 'walking machine'. Theoretical networks and training methods need modification to function correctly with a real application. Several complex phenomena that are very difficult to model have to be accommodated; the starting threshold of the activators, non-linearity, noise, and the non-biunivocity between successive system states (position, velocity, actuator controls). The modifications made to the network and the associated training method partially alleviate these difficulties.

Determination of fatigue in the electrically stimulated quadriceps muscle and relative effect of ischaemia.

The creation of muscle fatigue using surface electrical stimulation represents a highly reproducible phenomenon in spinal cord injured patients. The torque output was recorded as a function of time. The fatigue curves recorded over 110s exhibited three main parts: first, a plateau of short duration, followed by a more or less steep slope and then a second plateau which was maintained for a long time. This phenomenon was fitted using an exponential equation which had been developed and four parameters introduced that outlined to the muscle behaviour. A set of fatigue indices was defined to characterize the asymptotic value, the slope, the coordinates of the inflexion point, the time constant and the vertical amplitude of the curve recorded. Two populations were studied; a group of 11 thoracic level of injury paraplegic patients and a group of 10 able-bodied control subjects. The computed coefficients of determination, r2, were of very high values (0.99). Therefore, fatigue indices gave reliable information. Torque output did not differ between the two populations until 25 s had elapsed, but from 30 s onwards it was markedly lower in paraplegics. The residual torque output was 21.1 +/- 10.6% in the paraplegic group while it was 58.5 +/- 8.9% in the control group. The effect of blood supply in the production of fatigue was also studied by repeating the same tests using a tourniquet at the groin level. The residual torque became 14.7 +/- 2.3% in the paraplegic group and 42.9 +/- 6.3% in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

[Determination of the instantaneous center of rotation of the shoulder using the ELITE system. Application to the study of normal and pathological abduction]. / Détermination du centre instantané de rotation de l'épaule par le système ELITE. Application à l'étude de l'abduction normale et pathologique.

The authors determined the in vivo displacement of the instantaneous center of rotation (ICR) of the shoulder from data supplied by an optoelectronic system (ELITE System) which uses a specifically designed software program to achieve 3-dimensional analysis of abduction. The study involved 10 control subjects and 20 patients suffering from a periarticular disorder of the shoulder capsule retraction in 10 cases and rotator cuff tears before and after rehabilitation in 10 cases. This method provides an objective assessment of humeral head misalignment in relation to the glenoid cavity induced by the periarticular shoulder disorder and of the realignment achieved through rehabilitation. The proposed ICR calculation technique is entirely harmless for the patient in (particular because it requires no radiation analysis).