No-stimulation Condition Research Articles

Illusory Directional Sensation Induced by Asymmetric Vibrations Influences Sense of Agency and Velocity in Wrist Motions.

Illusory directional sensations are generated through asymmetric vibrations applied to the fingertips and have been utilized to induce upper-limb motions in the rehabilitation and training of patients with visual impairment. However, its effects on motor control remain unclear. This study aimed to verify the effects of illusory directional sensations on wrist motion. We conducted objective and subjective evaluations of wrist motion during a motor task, while inducing an illusory directional sensation that was congruent or incongruent with wrist motion. We found that, when motion and illusory directional sensations were congruent, the sense of agency for motion decreased. This indicates an induction sensation of the hand being moved by the illusion. Interestingly, although no physical force was applied to the hand, the angular velocity of the wrist was higher in the congruent condition than that in the no-stimulation condition. The angular velocity of the wrist and electromyography signals of the agonist muscles were weakly positively correlated, suggesting that the participants may have increased their wrist velocity. In other words, the congruence between the direction of motion and illusory directional sensation induced the sensation of the hand being moved, even though the participants' wrist-motion velocity increased. This phenomenon can be explained by the discrepancy between the sensation of active motion predicted by the efferent copy, and that of actual motion caused by the addition of the illusion. The findings of this study can guide the design of novel rehabilitation methods.

Hybrid and adaptive control of functional electrical stimulation to correct hemiplegic gait for patients after stroke.

Introduction: Gait, as a fundamental human movement, necessitates the coordination of muscles across swing and stance phases. Functional electrical stimulation (FES) of the tibialis anterior (TA) has been widely applied to foot drop correction for patients with post-stroke during the swing phase. Although the gastrocnemius (GAS) during the stance phase is also affected, the Functional electrical stimulation of the gastrocnemius received less attention. Methods: To address this limitation, a timing- and intensity-adaptive Functional electrical stimulation control strategy was developed for both the TA and GAS. Each channel incorporates a speed-adaptive (SA) module to control stimulation timing and an iterative learning control (ILC) module to regulate the stimulation intensity. These modules rely on real-time kinematic or kinetic data during the swing or stance phase, respectively. The orthotic effects of the system were evaluated on eight patients with post-stroke foot drop. Gait kinematics and kinetics were assessed under three conditions: no stimulation (NS), Functional electrical stimulation to the ankle dorsiflexor tibialis anterior (SA-ILC DS) and FES to the tibialis anterior and the ankle plantarflexor gastrocnemius (SA-ILC DPS). Results: The ankle plantarflexion angle, the knee flexion angle, and the anterior ground reaction force (AGRF) in the SA-ILC DPS condition were significantly larger than those in the NS and SA-ILC DS conditions (p < 0.05). The maximum dorsiflexion angle during the swing phase in the SA-ILC DPS condition was similar to that in the SA-ILC DS condition, with both being significantly larger than the angle observed in the NS condition (p < 0.05). Furthermore, the angle error and force error relative to the set targets were minimized in the SA-ILC DPS condition. Discussion: The observed improvements can be ascribed to the appropriate stimulation timing and intensity provided by the SA-ILC DPS strategy. This study demonstrates that the hybrid and adaptive control strategy of functional electrical stimulation system offers a significant orthotic effect, and has considerable potential for future clinical application.

Adaptions in back muscle activity in long-haul truck drivers during prolonged driving with and without seat-integrated stimulation

ObjectiveThe aim of this study was to investigate the development of back muscle activity during a simulated 4.5-h truck drive with professional long-haul truck drivers and to assess the effects of a seat-integrated stimulation on muscle activity during the drive. MethodMuscle activity was compared intra-individually between a stimulation condition (with seat-integrated stimulation) and a no-stimulation condition (without seat-integrated stimulation) in a simulated driving study (N = 16). During the drive, sEMGs of the m. trapezius pars descendens, m. trapezius pars ascendens and m. erector spinae were recorded bilaterally and the RMS values of the sEMG amplitudes were analyzed. ResultsThere was a significant increase in muscle activity within 1-h driving periods (in m. trapezius pars descendens and m. trapezius pars ascendens) in both the stimulation and the no-stimulation condition but not within the whole sitting duration (in all muscles). Contrary to our expectations, the RMS values did not differ between conditions. ConclusionShort-term effects on back muscle activity of long-haul truck drivers during 1-h driving periods were found with and without the seat-integrated stimulation. However, interruptions of the driving task seemed to be sufficient to eliminate these effects. These findings on back muscle activity in long-haul drivers reveal new insights as to what affects the musculoskeletal system in prolonged driving. OutlookIn future studies, an uninterrupted driving task under real conditions should be used to investigate possible effects of prolonged driving on truck drivers’ muscle activity in general and of seat-integrated stimulation on back muscle activity in particular.

Subthreshold electrical stimulation with pink noise enhances feedback control as evaluated by scaling exponent of postural sway

Subthreshold somatosensory stimulation with pink noise has been shown to attenuate postural sway better than stimulation with white noise. This might be due to the different frequency structures of the noise signals. However, their effects on the underlying somatosensory feedback pathway are still unknown. Thus, we aimed to determine whether pink noise enhances the somatosensory feedback pathway more effectively than other noises with different frequency structures, such as white and red noises. Sixteen young adults stood quietly for 65 s under four stimulation conditions: no stimulation and stimulations with white-, pink-, and red-noise-like signals. Based on a stabilogram-diffusion analysis, we calculated the long-term diffusion coefficient and scaling exponent in the radial direction to evaluate the effects of these noise signals on their somatosensory feedback control. The root mean square (CoPRMS) and mean velocity of the foot center of pressure were also computed to assess the amount of postural sway. The results showed that the stimulation condition had a significant effect on the scaling exponent, with the value under the pink-noise-like signal significantly lower than that under the no-stimulation condition. We also found that among the participants, the percentage of reduction in CoPRMS by the pink-noise-like signal was positively correlated with the CoPRMS value under the no-stimulation condition. Altogether, the somatosensory feedback control for balancing for quiet standing posture was improved by pink noise, and its effect on the variability of postural sway correlated with inherent postural sway variability.

Robust enhancement of motor sequence learning with 4 mA transcranial electric stimulation

Background and objectivesMotor learning experiments with transcranial direct current stimulation (tDCS) at 2 mA have produced mixed results. We hypothesize that tDCS boosts motor learning provided sufficiently high field intensity on the motor cortex. MethodsIn a single-blinded design, 108 healthy participants received either anodal (N = 36) or cathodal (N = 36) tDCS at 4 mA total, or no stimulation (N = 36) while they practiced a 12-min sequence learning task. Anodal stimulation was delivered across four electrode pairs (1 mA each), with anodes above the right parietal lobe and cathodes above the right frontal lobe. Cathodal stimulation, with reversed polarities, served as an active control for sensation, while the no-stimulation condition established baseline performance. fMRI-localized targets on the primary motor cortex in 10 subjects were used in current flow models to optimize electrode placement for maximal field intensity. A single electrode montage was then selected for all participants. ResultsWe found a significant difference in performance with anodal vs. cathodal stimulation (Cohen's d = 0.71) and vs. no stimulation (d = 0.56). This effect persisted for at least 1 h, and subsequent learning for a new sequence and the opposite hand also improved. Sensation ratings were comparable in the active groups and did not exceed moderate levels. Current flow models suggest the new electrode montage can achieve stronger motor cortex polarization than alternative montages. ConclusionThe present paradigm shows a medium to large effect size and is well-tolerated. It may serve as a go-to experiment for future studies on motor learning and tDCS.

Effects of subthreshold electrical stimulation with white noise, pink noise, and chaotic signals on postural control during quiet standing

BackgroundThe stochastic resonance (SR) phenomenon has been used to improve postural control through the application of imperceptible noise to the somatosensory system. White noise signals have been applied in numerous SR studies on postural control. However, because the SR effect depends on the noise structure, the stimulation effects of signals with different structures, such as pink noise and chaotic signals, on postural control, must be determined to achieve better clinical applications of SR technology. Research questionDuring quiet standing, how is postural control affected by subthreshold electrical stimulation to the knee joints when signals with different structures (white noise, pink noise, and chaotic signals) are used? MethodsSixteen healthy young adults stood quietly for 40 s with their eyes closed. To evaluate postural sway, we calculated the mean velocity, root mean square (CoPRMS), and range (CoPRange) values for the center of pressure (CoP) in the anteroposterior direction. The standing task was conducted under subthreshold electrical stimulation with white noise, pink noise, and chaotic signals based on the Lorenz system, in addition to the no-stimulation condition. The four stimulation conditions were randomized within each set and repeated seven times. ResultsSignificant effects of stimulation were observed in the CoPRMS and CoPRange values. The CoPRMS value under the pink noise signal was significantly lower than that under the no-stimulation condition. The CoPRange value also tended to decrease under the pink noise signal compared with the no-stimulation condition; however, the differences were not statistically significant. No significant changes were found with the white noise and chaotic signals compared with the no-stimulation condition. SignificanceWe demonstrated that the pink noise signal was more effective in reducing postural sway than the white noise and chaotic signals based on the Lorenz system during quiet standing.

Weak closed-loop vibrational stimulation improves the depth of slow-wave sleep and declarative memory consolidation.

Sleep is a unique behavioral state that affects body functions and memory. Although previous studies suggested stimulation methods to enhance sleep, a new method is required that is practical for long-term and unconstrained use by people. In this study, we used a novel closed-loop vibration stimulation method that delivers a stimulus in interaction with the intrinsic heart rhythm and examined the effects of stimulation on sleep and memory. Twelve volunteers participated in the experiment and each underwent one adaptation night and two experimental conditions-a stimulation condition (STIM) and a no-stimulation condition (SHAM). The heart rate variability analysis showed a significant increase in the normalized high frequency and the normalized low frequency significantly decreased under the STIM during the slow-wave sleep (SWS) stage. Furthermore, the synchronization ratio between the heartbeat and the stimulus significantly increased under the STIM in the SWS stage. From the electroencephalogram (EEG) spectral analysis, EEG relative powers of slow-wave activity and theta frequency bands showed a significant increase during the STIM in the SWS stage. Additionally, memory retention significantly increased under the STIM compared to the SHAM. These findings suggest that the closed-loop stimulation improves the SWS-stage depth and memory retention, and further provides a new technique for sleep enhancement.

Individual alpha frequency increases during a task but is unchanged by alpha-band flicker.

Visual perception fluctuates in sync with ongoing neural oscillations in the delta, theta, and alpha frequency bands of the human EEG. Supporting the relationship between alpha and perceptual sampling, recent work has demonstrated that variations in individual alpha frequency (IAF) correlate with the ability to discriminate one from two stimuli presented briefly in the same location. Other studies have found that, after being presented with a flickering stimulus at alpha frequencies, perception of near-threshold stimuli fluctuates for a short time at the same frequency. Motivated by previous work, we were interested in whether this alpha entrainment involves shifts in IAF. While recording EEG, we tested whether two-flash discrimination (a behavioral correlate of IAF) can be influenced by~1s of rhythmic visual stimulation at two different alpha frequencies (8.3 and 12.5Hz). Speaking against the bottom-up malleability of IAF, we found no change in IAF during stimulation and no change in two-flash discrimination immediately afterward. We also found synchronous activity that persisted after 12.5Hz stimulation, which suggests that a separate source of alpha was entrained. Importantly, we replicated the correlation between IAF and two-flash discrimination in a no-stimulation condition, demonstrating the sensitivity of our behavioral measure. We additionally found that IAF increased during the task compared to rest, which demonstrates that IAF is influenced by top-down factors but is not involved in entrainment.

Proceedings #11: Replay of Endogenous Sleep Rhythms to Produce Sleepiness

Varying modes of non-invasive electrical stimulation techniques have been investigated to induce endogenous sleep-like states (historically called Electrosleep). These include transcranial pulsed current stimulation (tPCS) such as Cranial Electrical Stimulation, transcranial direct current stimulation (tDCS), and transcranial alternating current stimulation (tACS) such as 10 Hz sinusoidal stimulation. Prior efforts used synthetic (simple) waveforms selected to modulate excitability (e.g. tDCS) or reproduce a single predominant frequency of endogenous neuronal rhythms of sleep induction (e.g. 10 Hz). To examine the effects of electrical stimulation with a complete spectrum sleep-related endogenous neural activity, we designed and applied an endogenous sleep-derived stimulation waveform to subjects while assessing a range subjective performance and objective physiological data. We hypothesized that a stimulation with complex high-bandwidth waveform reflecting endogenous sleep-associated neuronal activity patterns (transcranial Endogenous Sleep-Derived; tESD) would be more effective, than synthetic frequency-specific waveforms such at tACS, in supporting the transition to sleepiness. The basis for the transcranial Endogenous Sleep-Derived (tESD) waveform was acquired during a resting, sleepy-state EEG session. Data were examined for markers of sleepiness and corresponding segments were extracted, compressed, and scaled to produce a current signal. Stimulation was applied through a custom, high-bandwidth current-control stimulator. Subjects were supine in a light and sound attenuated environment. Using HD bipolar montage (AF7, AF8) with a maximal current amplitude of 0.5 mA over 10 minutes. tESD was also simulated in a computational model. Physiology (EEG, ECG, respiration, EOG, EMG) and behavior (questionnaires, reaction time) was assessed before, during (only for physiology), and after stimulation. Each subject underwent tESD, 10 Hz tACS, and a no-stimulation (non-interventional) sessions in a counterbalanced manner with at least 24 hours between each session. tESD polarized the frontal lobe. Changes in the no-stimulation condition confirms the testing environment was conducive to a wakefulness–sleep transition. Preliminary data indicate an enhanced shift in physiological measures in directions consistent with a relaxed and sleepy state with tESD compared to tACS and no-stimulation conditions. Behavioral data indicate a delay in reactions times post stimulation and subjective sleepiness reports indicate higher sleepiness post stimulation. tESD was well tolerated and blinding was effective. tESD aims to “replay” the endogenous neuronal signature of sleep. Neurophysiological (EEG), physiological (heart rate, respiration) and behavioral (simple reaction time, PVT) indicate that tESD, directed to frontal brain regions, that are associated with top-down thalamo-cortical sleep control mechanisms, accelerated wakefulness–sleep transition in subjects in a baseline relaxed state.

Low and medium frequency auditory steady-state responses decrease during NREM sleep.

Previous research on auditory steady-state responses (ASSRs) demonstrated sensitivity of 40 Hz ASSR to changes in the level of arousal, both in sleep and in general anaesthesia. In this study we extended the range of stimulation frequencies, using also low and medium stimulation frequencies (4, 6, 8, 12, 20, 40 Hz) and studied their susceptibility to the loss of consciousness in NREM sleep (N2 and N3 stages). Effects of NREM sleep were examined in power domain with relative power (RP), and in phase domain using inter-trial phase coherence (PC) parameter. The activity in power domain was also compared to no-stimulation data. Regions displaying significant waking-NREM sleep differences were selected using non-parametric suprathreshold cluster test. For 4, 6, 20 and 40 Hz stimulation relative power of ASSRs was lower in NREM sleep, with maximal change for 40 Hz stimulation. This decrease was not seen in no-stimulation condition. For all stimulation frequencies (except 12 Hz) we observed decrease of phase coherence of ASSR during NREM sleep. Our results demonstrate that low and medium frequency ASSRs are state-sensitive, thus susceptible to loss of consciousness during NREM sleep. Diminishing of power and phase coherence may result from cortical down states and/or thalamic inhibition. Our results support possible use of low- and medium-frequency ASSRs for discrimination between states of altered consciousness and emphasize the role of the auditory system in determining these variations.

Computationally Developed Sham Stimulation Protocol for Multichannel Desynchronizing Stimulation.

A characteristic pattern of abnormal brain activity is abnormally strong neuronal synchronization, as found in several brain disorders, such as tinnitus, Parkinson's disease, and epilepsy. As observed in several diseases, different therapeutic interventions may induce a placebo effect that may be strong and hinder reliable clinical evaluations. Hence, to distinguish between specific, neuromodulation-induced effects and unspecific, placebo effects, it is important to mimic the therapeutic procedure as precisely as possibly, thereby providing controls that actually lack specific effects. Coordinated Reset (CR) stimulation has been developed to specifically counteract abnormally strong synchronization by desynchronization. CR is a spatio-temporally patterned multichannel stimulation which reduces the extent of coincident neuronal activity and aims at an anti-kindling, i.e., an unlearning of both synaptic connectivity and neuronal synchrony. Apart from acute desynchronizing effects, CR may cause sustained, long-lasting desynchronizing effects, as already demonstrated in pre-clinical and clinical proof of concept studies. In this computational study, we set out to computationally develop a sham stimulation protocol for multichannel desynchronizing stimulation. To this end, we compare acute effects and long-lasting effects of six different spatio-temporally patterned stimulation protocols, including three variants of CR, using a no-stimulation condition as additional control. This is to provide an inventory of different stimulation algorithms with similar fundamental stimulation parameters (e.g., mean stimulation rates) but qualitatively different acute and/or long-lasting effects. Stimulation protocols sharing basic parameters, but inducing nevertheless completely different or even no acute effects and/or after-effects, might serve as controls to validate the specific effects of particular desynchronizing protocols such as CR. In particular, based on our computational findings we propose a multichannel sham (i.e., inactive) stimulation protocol as control condition for phase 2 and phase 3 studies with desynchronizing multichannel stimulation techniques.

Frequency-specific disruptions of neuronal oscillations reveal aberrant auditory processing in schizophrenia.

Individuals with schizophrenia exhibit abnormalities in evoked brain responses in oddball paradigms. These could result from (a) insufficient salience-related cortical signaling (P300), (b) insufficient suppression of irrelevant aspects of the auditory environment, or (c) excessive neural noise. We tested whether disruption of ongoing auditory steady-state responses at predetermined frequencies informed which of these issues contribute to auditory stimulus relevance processing abnormalities in schizophrenia. Magnetoencephalography data were collected for 15 schizophrenia and 15 healthy subjects during an auditory oddball paradigm (25% targets; 1-s interstimulus interval). Auditory stimuli (pure tones: 1 kHz standards, 2 kHz targets) were administered during four continuous background (auditory steady-state) stimulation conditions: (1) no stimulation, (2) 24 Hz, (3) 40 Hz, and (4) 88 Hz. The modulation of the auditory steady-state response (aSSR) and the evoked responses to the transient stimuli were quantified and compared across groups. In comparison to healthy participants, the schizophrenia group showed greater disruption of the ongoing aSSR by targets regardless of steady-state frequency, and reduced amplitude of both M100 and M300 event-related field components. During the no-stimulation condition, schizophrenia patients showed accentuation of left hemisphere 40 Hz response to both standard and target stimuli, indicating an effort to enhance local stimulus processing. Together, these findings suggest abnormalities in auditory stimulus relevance processing in schizophrenia patients stem from insufficient amplification of salient stimuli.

Alleviating simulator sickness with galvanic cutaneous stimulation.

In a driving simulation, we investigated the efficacy of galvanic cutaneous stimulation (GCS) provided during curves or intermittently during the whole circuit to mitigate simulator syndrome (SS). The literature on how GCS decreases SS, although scarce, has demonstrated the effectiveness of this technique. Stimulation with this and similar techniques has usually been provided in curves or continuously during the whole circuit but never intermittently. This stimulation method could generate a continued activation of processes related to GCS mitigating SS. Fifteen drivers (8 men; mean age = 25.5 years) participated in this experiment. We compared the total scores of the Simulator Sickness Questionnaire (SSQ) across three stimulation conditions: (a) curve GCS condition, whereby GCS was provided in curves; (b) intermittent GCS condition, whereby GCS was provided intermittently during the whole circuit; and (c) no-stimulation condition, whereby no stimulation was provided (baseline condition). The experimental outcomes revealed that GCS decreased SS in both the curve and intermittent stimulation conditions. We provide evidence that GCS is an effective countermeasure to decrease SS. It could be applied indifferently in curves or intermittently during the whole circuit. For future interventions, we recommend the use of GCS to mitigate SS with similar intermittent stimulation programs. These programs have a crucial advantage as they are easily integrated into the simulator setup without the necessity of generating a complicated experimental design to stimulate during the curves.

Transcranial electrical brain stimulation modulates neuronal tuning curves in perception of numerosity and duration

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation method with many putative applications and reported to effectively modulate behaviour. However, its effects have yet to be considered at a computational level. To address this we modelled the tuning curves underlying the behavioural effects of stimulation in a perceptual task. Participants judged which of the two serially presented images contained more items (numerosity judgement task) or was presented longer (duration judgement task). During presentation of the second image their posterior parietal cortices (PPCs) were stimulated bilaterally with opposite polarities for 1.6s. We also examined the impact of three stimulation conditions on behaviour: anodal right-PPC and cathodal left-PPC (rA-lC), reverse order (lA-rC) and no-stimulation condition. Behavioural results showed that participants were more accurate in numerosity and duration judgement tasks when they were stimulated with lA-rC and rA-lC stimulation conditions respectively. Simultaneously, a decrease in performance on numerosity and duration judgement tasks was observed when the stimulation condition favoured the other task. Thus, our results revealed a double-dissociation of laterality and task. Importantly, we were able to model the effects of stimulation on behaviour. Our computational modelling showed that participants' superior performance was attributable to a narrower tuning curve — smaller standard deviation of detection noise. We believe that this approach may prove useful in understanding the impact of brain stimulation on other cognitive domains.

Postural Perturbations Induced by a Moving Virtual Environment Are Reduced in Persons With Brain Injury When Gripping a Mobile Object

Gripping a mobile (unfixed) object increases standing postural stability in healthy individuals. We tested whether the same strategy is effective for stabilizing upright posture perturbed by a moving environment (virtual perturbation) in participants with traumatic brain injury (TBI). Fifteen participants with mild-to-moderate postural deficits after TBI and a comparison group of 15 age-matched healthy subjects participated in the study. Participants stood for 1 minute in front of a large screen with a projected three-dimensional image of a boat; for 30 seconds the boat remained stationary (no visual stimulation condition), and for 30 seconds the boat rocked on the water at a speed of 15°/s (visual stimulation condition). The visual stimulation was applied in pseudorandom order (during either the first or second half of the 1-minute trial). To analyze postural stability, the displacement and velocity of the center of mass in the sagittal and frontal planes were compared between groups and across 4 experimental conditions, including standing with/without visual stimulation and with/without gripping a 300-g object (short wooden stick) in the dominant hand. Participants with TBI showed greater instability under all experimental conditions. The visual stimulation significantly increased postural oscillations in the sagittal plane by 35% to 63% across groups. Gripping a stick significantly reduced the stimulation-induced instability in the sagittal plane by 19% to 29%, although not to the level of the no-stimulation condition in either group. The stabilizing effect of gripping an external object in participants with TBI was confirmed. A possibility of using this effect as a balance aid strategy requires further investigation.

From Oscillatory Transcranial Current Stimulation to Scalp EEG Changes: A Biophysical and Physiological Modeling Study

Both biophysical and neurophysiological aspects need to be considered to assess the impact of electric fields induced by transcranial current stimulation (tCS) on the cerebral cortex and the subsequent effects occurring on scalp EEG. The objective of this work was to elaborate a global model allowing for the simulation of scalp EEG signals under tCS. In our integrated modeling approach, realistic meshes of the head tissues and of the stimulation electrodes were first built to map the generated electric field distribution on the cortical surface. Secondly, source activities at various cortical macro-regions were generated by means of a computational model of neuronal populations. The model parameters were adjusted so that populations generated an oscillating activity around 10 Hz resembling typical EEG alpha activity. In order to account for tCS effects and following current biophysical models, the calculated component of the electric field normal to the cortex was used to locally influence the activity of neuronal populations. Lastly, EEG under both spontaneous and tACS-stimulated (transcranial sinunoidal tCS from 4 to 16 Hz) brain activity was simulated at the level of scalp electrodes by solving the forward problem in the aforementioned realistic head model. Under the 10 Hz-tACS condition, a significant increase in alpha power occurred in simulated scalp EEG signals as compared to the no-stimulation condition. This increase involved most channels bilaterally, was more pronounced on posterior electrodes and was only significant for tACS frequencies from 8 to 12 Hz. The immediate effects of tACS in the model agreed with the post-tACS results previously reported in real subjects. Moreover, additional information was also brought by the model at other electrode positions or stimulation frequency. This suggests that our modeling approach can be used to compare, interpret and predict changes occurring on EEG with respect to parameters used in specific stimulation configurations.

Effects of Motor Cortical Stimulation during Planar Reaching Movement

Background : The purpose was to examine the effects of single pulse transcranial magnetic stimulation (TMS) over primary motor cortex delivered at different times during a center-out reaching task in a robot reaching environment. Methods : Eleven right-handed subjects participated. Movement hotspots and thresholds were determined for each subject, and the stimulation intensity was set at 120% of the movement threshold. TMS was delivered at rest and when subjects performed a series of reaching tasks. The 5 different conditions were: no stimulation, sham stimulation, and stimulation at 150, 500, or 1000 ms post go cue. Outcome measures included TMS-evoked movement during rest and in the 150ms condition, trajectory deviations (no stimulation, sham, and 150ms conditions), and peak velocity (PV), path length, reaction time, acceleration time, and deceleration time for all conditions. Results : When TMS was applied at 150 ms, the evoked path lengths were significantly shorter than at rest and had less deviation than the no-stimulation condition ( p < 0.05). Peak velocities were lowest during the no-stimulation condition and highest during the 500ms condition ( p < 0.05). Path lengths were significantly shorter during the no-stimulation, sham, and 150ms condition compared to the 500ms and 1000ms conditions. Conclusions : TMS applied during the reaction time phase suppressed movements evoked by TMS, decreased trajectory deviations, and shortened path length, while TMS delivered after movement onset increased PV and path length. TMS stimulation may be delivered to enhance movement parameters and potentially facilitate reach training in the robotic rehabilitation environment.

High‐frequency deep brain stimulation of the putamen improves bradykinesia in Parkinson's disease

Deep brain stimulation is effective for a wide range of neurological disorders; however, its mechanisms of action remain unclear. With respect to Parkinson's disease, the existence of multiple effective targets suggests that putamen stimulation also may be effective and raises questions as to the mechanisms of action. Are there as many mechanisms of action as there are effective targets or some single or small set of mechanisms common to all effective targets? During the course of routine surgery of the globus pallidus interna in patients with Parkinson's disease, the deep brain stimulation lead was placed in the putamen en route to the globus pallidus interna. Recordings of hand opening and closing during high-frequency and no stimulation were made. Speed of the movements, based on the amplitude and frequency of the repetitive hand movements as well as the decay in amplitude, were studied. Hand speed in 6 subjects was statistically significantly faster during active deep brain stimulation than the no-stimulation condition. There were no statistically significant differences in decay in the amplitude of hand movements. High-frequency deep brain stimulation of the putamen improves bradykinesia in a hand-opening and -closing task in patients with Parkinson's disease. Consequently, high-frequency deep brain stimulation of virtually every structure in the basal ganglia-thalamic-cortical system improves bradykinesia. These observations, together with microelectrode recordings reported in the literature, argue that deep brain stimulation effects may be system specific and not structure specific.

Prior state of cortical activity influences subsequent practicing of a visuomotor coordination task

According to the Bienenstock–Cooper–Munro (BCM) rule, a low overall cortical activity level is suggested to enhance synaptic strength of active neuronal connections, while a high level of activity should diminish it. Whereas the relevance of this mechanism for neuroplasticity in humans has been ascertained on the neurophysiological level, its functional relevance remains unclear so far. The aim of this study was to explore the impact of the pre-performance cortical activity and excitability state on subsequent performance practicing a visuomotor paradigm. Excitability of the primary motor cortex (M1) or the visual area MT/V5 was modulated by 10min of anodal or cathodal transcranial direct current stimulation (tDCS) in healthy subjects before practice of a visuomotor tracking task. The percentage of correct tracking movements increased significantly in the early phase of practice after both anodal and cathodal stimulations over both cortical areas compared to the no-stimulation condition showing a behavioral improvement at the beginning of the practice process. Stimulation of a control cortical area did not result in significant difference with regard to the practice between cathodal, anodal and sham stimulation. However, the steepness of improvement between the different time-points was significantly increased only at the beginning of the task, and was reduced at the 5′–10′ (V5) and 10′–15′ (M1) time-window with regard to anodal stimulation, compared to the ‘no-stimulation’ condition. With regard to cathodal stimulation, the steepness of improvement was significantly lower at the 10′–15′ time-window (M1) compared to the ‘no-stimulation’ condition. The results of our study underline the principal functional relevance of the BCM rule for the efficacy of visuomotor practice, but imply that also other mechanisms have to be taken into account.

ADHD and delay aversion: the influence of non‐temporal stimulation on choice for delayed rewards

Delay aversion, the motivation to escape or avoid delay, results in preference for small immediate over large delayed rewards. Delay aversion has been proposed as one distinctive psychological process that may underlie the behavioural symptoms and cognitive deficits of attention deficit/hyperactivity disorder (ADHD). Furthermore, the delay aversion hypothesis predicts that ADHD children's preference for immediate small over large delayed rewards will be reduced when stimulation, which makes time appear to pass more quickly, is added to the delay interval. The current paper tests these predictions. A group of children with a diagnosis of ADHD (with or without oppositional defiant disorder (ODD)), a group with a diagnosis of high-functioning autism (HFA), and a normal control group were compared on an experimental paradigm giving repeated choices between small immediate and large delayed rewards (Maudsley Index of Delay Aversion-MIDA) under two conditions (stimulation and no stimulation). As predicted, ADHD children displayed a stronger preference than the HFA and control children for the small immediate rewards under the no-stimulation condition. The ADHD children preferences were normalised under the stimulation condition with no differences between the groups. This pattern of results was the same whether the ADHD children had comorbid ODD or not. The findings from the MIDA are consistent with the delay aversion hypothesis of ADHD in showing that preference for small immediate rewards over large delayed rewards is a specific feature of ADHD and that this preference can be reduced by the addition of stimulation. Further research is required to better understand the emotional and motivational mechanisms underpinning delay aversion.