Electrical stimulation of the motor system after stroke.

After an electrical stimulus within the motor system there will follow a compulsion, a reflexlike process in functional dependency, naturally in illness (function disturbance) dependency as well. We can detect this process with the evoked potentials at the non-stimulated sites of the motor system and with the motor answers at the periphery. Because the motor system acts as a whole, it is certain that every process at a site has its correlates at the other sites, but the different part of the same process will be in a different grade pronounced (many times in opposite direction) at the different sites. If we want to know something from the basic process and to find the real correlates, we have to compare different evoked potentials within the motor system and motor responses at the periphery, or we have to enhance or depress the whole process or its parts. For the latter the double stimulation technique is suitable, but we have to take into consideration that during this investigation two alternating processes affect each other and therefore the result will not be direct.

The modulation of rolandic oscillation induced by digital nerve stimulation and self-paced movement of the finger: A MEG study

CB1 receptor antagonism/inverse agonism increases motor system excitability in humans

Brain plasticity refers to changes in the organization of the brain as a result of different environmental stimuli. The aim of this study was to assess the genetic variation of brain plasticity, by comparing intrapair differences between monozygotic (MZ) and dizygotic (DZ) twins. Plasticity was examined by a paired associative stimulation (PAS) in 32 healthy female twins (9 MZ and 7 DZ pairs, aged 22.6±2.7 and 23.8±3.6 years, respectively). Stimulation consisted of low frequency repetitive application of single afferent electric stimuli, delivered to the right median nerve, paired with a single pulse transcranial magnetic stimulation (TMS) for activation of the abductor pollicis brevis muscle (APB). Corticospinal excitability was monitored for 30 min following the intervention. PAS induced an increase in the amplitudes of the motor evoked potentials (MEP) in the resting APB, compared to baseline. Intrapair differences, after baseline normalization, in the MEP amplitudes measured at 25-30 min post-intervention, were almost double for DZ (1.25) in comparison to MZ (0.64) twins (P =0.036). The heritability estimate for brain plasticity was found to be 0.68. This finding implicates that genetic factors may contribute significantly to interindividual variability in plasticity paradigms. Genetic factors may be important in adaptive brain reorganization involved in motor learning and rehabilitation from brain injury.

One of the main central processes affecting the cortical representation of conspecific vocalizations is the collateral output from the extended motor system for call generation. Before starting to study this interaction we sought to compare the characteristics of calls produced by stimulating four different parts of the brain in guinea pigs (Cavia porcellus). By using anaesthetised animals we were able to reposition electrodes without distressing the animals. Trains of 100 electrical pulses were used to stimulate the midbrain periaqueductal grey (PAG), hypothalamus, amygdala, and anterior cingulate cortex (ACC). Each structure produced a similar range of calls, but in significantly different proportions. Two of the spontaneous calls (chirrup and purr) were never produced by electrical stimulation and although we identified versions of chutter, durr and tooth chatter, they differed significantly from our natural call templates. However, we were routinely able to elicit seven other identifiable calls. All seven calls were produced both during the 1.6 s period of stimulation and subsequently in a period which could last for more than a minute. A single stimulation site could produce four or five different calls, but the amygdala was much less likely to produce a scream, whistle or rising whistle than any of the other structures. These three high-frequency calls were more likely to be produced by females than males. There were also differences in the timing of the call production with the amygdala primarily producing calls during the electrical stimulation and the hypothalamus mainly producing calls after the electrical stimulation. For all four structures a significantly higher stimulation current was required in males than females. We conclude that all four structures can be stimulated to produce fictive vocalizations that should be useful in studying the relationship between the vocal motor system and cortical sensory representation.

Neuroprosthetic systems are designed to interface with the nervous system, for the replacement or restoration of damaged functions in the motor and/or sensory systems. In order to have an efficient communication with the nervous tissue leading to optimized clinical outcomes, achieving neural stimulation with high selectivity is essential. This thesis aims at finding technological routes to enable spatial, structural and cell-type selective surface neuromodulation using electrical and optogenetic stimulation and to validate them in in vivo models. Thin and conformable electrode arrays enable close contact with the target tissue, thereby leading to minimal distances with the target neurons and maximal spatial selectivity. Flexible polymer technologies based on polyimide (PI) are used to design thin (< 10 IŒm thick) electrode arrays with small feature size (< 100 IŒm), resulting in miniaturized conformable arrays for surface stimulation. PEDOT conducting polymer coatings are used on the miniaturized electrical stimulation sites (100 IŒm diameter) to improve their charge injection properties. This implant is used for auditory brainstem stimulation in a rat model, and is shown to generate robust activation of the auditory system. Analysis of the multiunit recordings obtained from the inferior colliculus (IC), an auditory structure of the midbrain, led to the identification of different phases in the responses, with various frequency tuning properties. The stimulation configuration is shown to influence the tonotopic organisation of the frequency-tuned responses. Bipolar stimulation with small interelectrode distances (400 IŒm) is shown to generate responses that are more frequency-selective than with larger interelectrode distances (800 IŒm). The orientation of the electrode pair and the waveformof stimulation current are also shown to influence the response properties. An updated design of the clinical auditory brainstem implant(ABI) is then proposed, integrating higher electrode density and guidelines for a more tissue-conformal format. The main steps in the road towards improvement of ABI outcomes are then discussed, with proposed changes in the stimulation protocol and electrode array in parallel. Another approach to cell-specific neuromodulation is the implementation of optogenetics. This requires not only genetic engineering of the neurons but also the manufacturing of implantable light-emitting devices. Here, we introduce a fabrication process for the integration of thin (50 IŒm) LEDs into a polyimide-based device. A proof-of-concept in vivo study shows that stimulation of the spinal cord of a mouse model generates robust EMG responses in both legs over the course of several weeks. The walking integrity is confirmed, showing the absence of functional damages to the spinal cord. These results show that the presented LED array can provide a way of stimulating key elements of the locomotor neural circuitry, potentially leading to a greater understanding of the role of each neuronal subtypes in the spinal cord. Through the applications of ABI and spinal cord stimulation, this thesis thus highlights the importance and potential use of specifically tailored technologies enabling selective surface stimulation of the nervous system.

Short-term high-frequency transcutaneous electrical nerve stimulation decreases human motor cortex excitability

Electrical Stimulation of the Motor System

Locomotion induced by non-contingent intracranial electrical stimulation: Dopamine dependence and general characteristics.

Deep brain stimulation for Parkinson's disease: disrupting the disruption

Introduction: Motor control requires a reciprocal volley between somatosensory and motor systems, with somatosensory feedback being essential for the online updating of motor commands to achieve behavioral outcomes. However, this dynamic interplay among sensorimotor brain systems serving motor control remains poorly understood. Methods: To address this, we designed a novel somatosensory entrainment-movement task, which 25 adults completed during magnetoencephalography (MEG). Specifically, participants completed a quasi-paced finger-tapping paradigm while subthreshold electrical stimulation was applied to the right median nerve at a sensorimotor-relevant frequency (15 Hz) and during a second condition where no electrical stimulation was applied. The MEG data were transformed into the time-frequency domain and imaged by using a beamformer to evaluate the effect of somatosensory feedback (i.e., entrainment) on movement-related oscillations and motor performance at the single trial level. Results: Our results indicated spectrally specific reductions in movement-related oscillatory power (i.e., theta, gamma) during 15 Hz stimulation in the contralateral motor cortex during motor execution. In addition, we observed robust cross-frequency coupling within the motor cortex and further, stronger theta-gamma coupling was predictive of faster reaction times, irrespective of condition (i.e., stim vs. no stim). Finally, in the presence of electrical stimulation, cross-frequency coupling of movement-related oscillations was reduced, and the stronger the entrained neuronal populations (i.e., increased oscillatory power) were before movement onset, the weaker the inherent theta-gamma coupling became in the motor cortex. Discussion: This novel exogenous manipulation paradigm provides key insights on how the somatosensory system modulates the motor cortical oscillations required for volitional movement in the normative sensorimotor system.

Smile and laughter elicited by electrical stimulation of the frontal operculum

The present study aimed to investigate neurophysiologic mechanisms mediating the newly discovered phenomenon of respiratory-motor interactions and to explore its potential clinical application for motor recovery. First, young and healthy subjects were instructed to breathe normally (NORM); to exhale (OUT) or inhale (IN) as fast as possible in a self-paced manner; or to voluntarily hold breath (HOLD). In experiment 1 (n = 14), transcranial magnetic stimulation (TMS) was applied during 10% maximal voluntary contraction (MVC) finger flexion force production or at rest. The motor-evoked potentials (MEPs) were recorded from flexor digitorum superficialis (FDS), extensor digitorum communis (EDC), and abductor digiti minimi (ADM) muscles. Similarly, in experiment 2 (n = 11), electrical stimulation (ES) was applied to FDS or EDC during the described four breathing conditions while subjects maintained 10%MVC of finger flexion or extension and at rest. In the exploratory clinical experiments (experiment 3), four patients with chronic neurological disorders (three strokes, one traumatic brain injury) received a 30-min session of breathing-controlled ES to the impaired EDC. In experiment 1, the EDC MEP magnitudes increased significantly during IN and OUT at both 10%MVC and rest; the FDS MEPs were enhanced only at 10%MVC, whereas the ADM MEP increased only during OUT, compared with NORM for both at rest and 10%MVC. No difference was found between NORM and HOLD for all three muscles. In experiment 2, when FDS was stimulated, force response was enhanced during both IN and OUT, but only at 10%MVC. When EDC was stimulated, force response increased at both 10%MVC and rest, only during IN, but not OUT. The averaged response latency was 83 ms for the finger extensors and 79 ms for the finger flexors. After a 30-min intervention of ES to EDC triggered by forced inspiration in experiment 3, we observed a significant reduction in finger flexor spasticity. The spasticity reduction lasted for ≥ 4 wk in all four patients. TMS and ES data, collectively, support the phenomenon that there is an overall respiration-related enhancement on the motor system, with a strong inspiration-finger extension coupling during voluntary breathing. As such, breathing-controlled electrical stimulation (i.e., stimulation to finger extensors delivered during the voluntary inspiratory phase) could be applied for enhancing finger extension strength and finger flexor spasticity reduction in poststroke patients.

Optimal levels of noise stimulation have been shown to enhance the detection and transmission of neural signals thereby improving the performance of sensory and motor systems. The first series of experiments in the present study aimed to investigate whether subsensory electrical noise stimulation applied over the triceps surae (TS) in seated subjects decreases torque variability during a force-matching task of isometric plantar flexion and whether the same electrical noise stimulation decreases postural sway during quiet stance. Correlation tests were applied to investigate whether the noise-induced postural sway decrease is linearly predicted by the noise-induced torque variability decrease. A second series of experiments was conducted to investigate whether there are differences in torque variability between conditions in which the subsensory electrical noise is applied only to the TS, only to the tibialis anterior (TA) and to both TS and TA, during the force-matching task with seated subjects. Noise stimulation applied over the TS muscles caused a significant reduction in force variability during the maintained isometric force paradigm and also decreased postural oscillations during quiet stance. Moreover, there was a significant correlation between the reduction in force fluctuation and the decrease in postural sway with the electrical noise stimulation. This last result indicates that changes in plantar flexion force variability in response to a given subsensory random stimulation of the TS may provide an estimate of the variations in postural sway caused by the same subsensory stimulation of the TS. We suggest that the decreases in force variability and postural sway found here are due to stochastic resonance that causes an improved transmission of proprioceptive information. In the second series of experiments, the reduction in force variability found when noise was applied to the TA muscle alone did not reach statistical significance, suggesting that TS proprioception gives a better feedback to reduce force fluctuation in isometric plantar flexion conditions.

Voluntary motor drive is an important central command that descends via the corticospinal tract to initiate muscle contraction. When electrical stimulation (ES) is applied to an antagonist or agonist muscle, it changes the agonist muscle’s representative motor cortex and thus its voluntary motor drive. In this study, we used a reaction time task to compare the effects of weak and strong ES of the antagonist or agonist muscle during the premotor period of a wrist extension. We recorded motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) that was applied to the extensor carpi radialis (ECR; agonist) and flexor carpi radialis (FCR; antagonist). When stronger ES intensities were applied to the antagonist, the MEP control ratio in the ECR significantly increased during the premotor time. Furthermore, the MEP control ratio with stronger antagonist ES intensity was significantly larger than that in the agonist for the same ES intensity. In the FCR, the MEP control ratio was also significantly greater at the strong ES intensity than at the weak ES intensity. Furthermore, the MEP control ratio in the antagonist with a strong ES intensity was significantly larger than that in the agonist with the same ES intensity. These results suggest that agonist corticomotor excitability might be enhanced by ES of the antagonist, which in turn strongly activates the descending motor system in the preparation of agonist contraction.