Alpha and beta oscillatory activity during a sequence of two movements

Enhanced Post-Movement Beta Rebound: Unraveling the Impact of Preplanned Sequential Actions

The Post-Movement Beta Rebound (PMBR) is the increase in beta-band power after voluntary movement ends, but its specific role in cognitive processing is unclear. Current theory links PMBR with updates to internal models, mental frameworks that help anticipate and react to sensory feedback. However, research has not explored how reactivating a preexisting action plan, another source for internal model updates, might affect PMBR intensity. To address this gap, we recruited 20 participants (mean age 18.55 ± 0.51; 12 females) for an experiment involving isolated (single-step) or sequential (two-step) motor tasks based on predetermined cues. We compared PMBR after single-step movements with PMBR after the first movement in two-step tasks to assess the influence of a subsequent action on the PMBR power associated with the first action. The results show a significant increase in PMBR magnitude after the first movement in sequential tasks compared to the second action and the isolated movements. Notably, this increase is more pronounced for right-hand movements, suggesting lateralized brain activity in the left hemisphere. These findings indicate that PMBR is influenced not only by external stimuli but also by internal cognitive processes such as working memory. This insight enhances our understanding of PMBR's role in motor control, emphasizing the integration of both external and internal information.

Connectivity of neural signals to the primary motor area during preparatory periods for movement following external and internal cues

PURPOSE

We investigated the connectivity of neural signals from movement-related cortical areas to the primary motor area (M1) in the hemisphere contralateral to the movement side during the period of movement-related magnetic fields before movement.

MATERIALS AND METHODS

Participants were 13 healthy adults, and nerual signals were recorded using magnetoencephalography. Spontaneous extension of the right wrist was performed at the participant's own pace and following a visual cue in internal (IC) and external (EC) cue tasks. The connectivity of neural signals to M1 from each movement-related motor area was assessed by Granger causality analysis (GCA). The GCA was performed on the neural activity elicited in a frequency band between 7.8 and 46.9 Hz during the pre-movement periods, which occurred durng the readiness field (RF) and the negative slope prime (NSp). F-values, as connectivity values obtained by GCA, were compared between the EC and IC cue tasks.

RESULTS

For NSp periods, the connectivity of neural signals from the left superior frontal area (SF-L) to M1 was dominant in the IC task, whereas that from the left superior parietal area (SP-L) to M1 was dominant in the EC task. The F value in the GCA from SP-L to M1 was greater in the EC task during RF than in the IC task during equivalent periods.

CONSLUSIONS

In the present study, there were differences in the connectivity of neural signals to M1 between IC and EC tasks. The present results suggested that the pattern of pre-movement neural activity that resulted in a movement was not uniform but differed between movement tasks just before the movement.

Unique Neural Mechanisms Underlying Speed Control of Low-Force Ballistic Contractions

According to the speed-control hypothesis, the rate of force development (RFD) during ballistic contractions is dictated by force amplitude because time to peak force (TPF) remains constant regardless of changes in force amplitude. However, this hypothesis has not been tested at force levels below 20% of an individual's maximum voluntary contraction (MVC). Here, we examined the relationship between the RFD and force amplitude from 2 to 85% MVC and the underlying structure of muscle activity in 18 young adults. Participants exerted ballistic index finger abductions for 50 trials in each of seven randomly assigned force levels (2, 5, 15, 30, 50, 70, and 85% MVC). We quantified TPF, RFD, and various EMG burst characteristics. Contrary to the speed-control hypothesis, we found that TPF was not constant, but significantly varied from 2 to 85% MVC. Specifically, the RFD slope from 2 to 15% MVC was greater than the RFD slope from 30 to 85% MVC. Longer TPF at low force levels was associated with the variability of EMG burst duration, whereas longer TPF with higher force levels was associated with the EMG burst integral. Contrary to the speed-control hypothesis, we found that the regulation of TPF for low and high force levels was different, suggesting that neuronal variability is critical for force levels below 30% MVC and neuronal amplitude for force levels above 30% MVC. These findings present compelling new evidence highlighting the limitations of the speed-control hypothesis underscoring the need for a new theoretical framework.

Altered Functional Networks of Alpha and Low-Beta Bands During Upper Limb Movement and Association with Motor Impairment in Chronic Stroke

Background: Impaired movement after stroke is closely associated with altered brain functions, and thus the investigation on neural substrates of patients with stroke can pave a way for not only understanding the underlying mechanisms of neuropathological traits, but also providing an innovative solution for stroke rehabilitation. The objective of this study was to precisely investigate altered brain functions in terms of power spectral and brain network analyses. Methods: Altered brain function was investigated by using electroencephalography (EEG) measured while 34 patients with chronic stroke performed movement tasks with the affected and unaffected hands. The relationships between functional brain network indices and Fugl-Meyer Assessment (FMA) scores were also investigated. Results: A stronger low-beta event-related desynchronization was found in the contralesional hemisphere for both affected and unaffected movement tasks compared with that of the ipsilesional hemisphere. More efficient whole-brain networks (increased strength and clustering coefficient, and prolonged path length) in the low-beta frequency band were revealed when moving the unaffected hand compared with when moving the affected hand. In addition, the brain network indices of the contralesional hemisphere indicated higher efficiency and cost-effectiveness than those of the ipsilesional hemisphere in both the alpha and low-beta frequency bands. Moreover, the alpha network indices (strength, clustering coefficient, path length, and small-worldness) were significantly correlated with the FMA scores. Conclusions: Efficient functional brain network indices are associated with better motor outcomes in patients with stroke and could be useful biomarkers to monitor stroke recovery during rehabilitation.

Cortical processing during robot and functional electrical stimulation

Introduction

Like alpha rhythm, the somatosensory mu rhythm is suppressed in the presence of somatosensory inputs by implying cortical excitation. Sensorimotor rhythm (SMR) can be classified into two oscillatory frequency components: mu rhythm (8-13 Hz) and beta rhythm (14-25 Hz). The suppressed/enhanced SMR is a neural correlate of cortical activation related to efferent and afferent movement information. Therefore, it would be necessary to understand cortical information processing in diverse movement situations for clinical applications.

Methods

In this work, the EEG of 10 healthy volunteers was recorded while fingers were moved passively under different kinetic and kinematic conditions for proprioceptive stimulation. For the kinetics aspect, afferent brain activity (no simultaneous volition) was compared under two conditions of finger extension: (1) generated by an orthosis and (2) generated by the orthosis simultaneously combined and assisted with functional electrical stimulation (FES) applied at the forearm muscles related to finger extension. For the kinematic aspect, the finger extension was divided into two phases: (1) dynamic extension and (2) static extension (holding the extended position).

Results

In the kinematic aspect, both mu and beta rhythms were more suppressed during a dynamic than a static condition. However, only the mu rhythm showed a significant difference between kinetic conditions (with and without FES) affected by attention to proprioception after transitioning from dynamic to static state, but the beta rhythm was not.

Discussion

Our results indicate that mu rhythm was influenced considerably by muscle kinetics during finger movement produced by external devices, which has relevant implications for the design of neuromodulation and neurorehabilitation interventions.

EEG Oscillations in Specific Frequency Bands Are Differently Coupled with Angular Joint Angle Kinematics during Rhythmic Passive Elbow Movement

Rhythmic passive movements are often used during rehabilitation to improve physical functions. Previous studies have explored oscillatory activities in the sensorimotor cortex during active movements; however, the relationship between movement rhythms and oscillatory activities during passive movements has not been substantially tested. Therefore, we aimed to quantitatively identify changes in cortical oscillations during rhythmic passive movements. Twenty healthy young adults participated in our study. We placed electroencephalography electrodes over a nine-position grid; the center was oriented on the transcranial magnetic stimulation hotspot of the biceps brachii muscle. Passive movements included elbow flexion and extension; the participants were instructed to perform rhythmic elbow flexion and extension in response to the blinking of 0.67 Hz light-emitting diode lamps. The coherence between high-beta and low-gamma oscillations near the hotspot of the biceps brachii muscle and passive movement rhythms was higher than that between alpha oscillation and passive movement rhythm. These results imply that alpha, beta, and gamma oscillations of the primary motor cortex are differently related to passive movement rhythm.

Robustness of individualized inferences from longitudinal resting state EEG dynamics

Tracking how individual human brains change over extended timescales is crucial to clinical scenarios ranging from stroke recovery to healthy aging. The use of resting state (RS) activity for tracking is a promising possibility. However, it is unresolved how a person's RS activity over time can be decoded to distinguish neurophysiological changes from confounding cognitive variability. Here, we develop a method to screen RS activity changes for these confounding effects by formulating it as a problem of change classification. We demonstrate a novel solution to change classification by linking individual-specific change to inter-individual differences. Individual RS-EEG was acquired over five consecutive days including task states devised to simulate the effects of inter-day cognitive variation. As inter-individual differences are shaped by neurophysiological differences, the inter-individual differences in RS activity on one day were analyzed (using machine learning) to identify distinctive configurations in each individual's RS activity. Using this configuration as a decision-rule, an individual could be re-identified from 2-second samples of the instantaneous oscillatory power spectrum acquired on a different day both from RS and confounded-RS with a limited loss in accuracy. Importantly, the low loss in accuracy in cross-day vs same-day classification was achieved with classifiers that combined information from multiple frequency bands at channels across the scalp (with a concentration at characteristic fronto-central and occipital zones). Taken together, these findings support the technical feasibility of screening RS activity for confounding effects and the suitability of longitudinal RS for robust individualized inferences about neurophysiological change in health and disease.

Cognitive and emotional regulation processes of spontaneous facial self-touch are activated in the first milliseconds of touch: Replication of previous EEG findings and further insights

Spontaneously touching one’s own face (sFST) is an everyday behavior that occurs in people of all ages, worldwide. It is—as opposed to actively touching the own face—performed without directing one’s attention to the action, and it serves neither instrumental (scratching, nose picking) nor communicative purposes. These sFST have been discussed in the context of self-regulation, emotional homeostasis, working memory processes, and attention focus. Even though self-touch research dates back decades, neuroimaging studies of this spontaneous behavior are basically nonexistent. To date, there is only one electroencephalography study that analyzed spectral power changes before and after sFST in 14 participants. The present study replicates the previous study on a larger sample. Sixty participants completed a delayed memory task of complex haptic relief stimuli while distracting sounds were played. During the retention interval 44 of the participants exhibited spontaneous face touch. Spectral power analyses corroborated the results of the replicated study. Decreased power shortly before sFST and increased power right after sFST indicated an involvement of regulation of attentional, emotional, and working memory processes. Additional analyses of spectral power changes during the skin contact phase of sFST revealed that significant neurophysiological changes do not occur while skin contact is in progress but at the beginning of sFST (movement toward face and initial skin contact). The present findings clearly illustrate the complexity of sFST and that the specific trigger mechanisms and functions of this spontaneous behavior need to be further investigated in controlled, experimental studies.

Cortical sensorimotor activity in the execution and suppression of discrete and rhythmic movements

Although the engagement of sensorimotor cortices in movement is well documented, the functional relevance of brain activity patterns remains ambiguous. Especially, the cortical engagement specific to the pre-, within-, and post-movement periods is poorly understood. The present study addressed this issue by examining sensorimotor EEG activity during the performance as well as STOP-signal cued suppression of movements pertaining to two distinct classes, namely, discrete vs. ongoing rhythmic movements. Our findings indicate that the lateralized readiness potential (LRP), which is classically used as a marker of pre-movement processing, indexes multiple pre- and in- movement-related brain dynamics in a movement-class dependent fashion. In- and post-movement event-related (de)synchronization (ERD/ERS) observed in the Mu (8-13 Hz) and Beta (15-30 Hz) frequency ranges were associated with estimated brain sources in both motor and somatosensory cortical areas. Notwithstanding, Beta ERS occurred earlier following cancelled than actually performed movements. In contrast, Mu power did not vary. Whereas Beta power may reflect the evaluation of the sensory predicted outcome, Mu power might engage in linking perception to action. Additionally, the rhythmic movement forced stop (only) showed a post-movement Mu/Beta rebound, which might reflect an active "clearing-out" of the motor plan and its feedback-based online control. Overall, the present study supports the notion that sensorimotor EEG modulations are key markers to investigate control or executive processes, here initiation and inhibition, which are exerted when performing distinct movement classes.

Temporal Context Actively Shapes EEG Signatures of Time Perception

Our subjective perception of time is optimized to temporal regularities in the environment. This is illustrated by the central tendency effect: When estimating a range of intervals, short intervals are overestimated, whereas long intervals are underestimated to reduce the overall estimation error. Most models of interval timing ascribe this effect to the weighting of the current interval with previous memory traces after the interval has been perceived. Alternatively, the perception of the duration could already be flexibly tuned to its temporal context. We investigated this hypothesis using an interval reproduction task in which human participants (both sexes) reproduced a shorter and longer interval range. As expected, reproductions were biased toward the subjective mean of each presented range. EEG analyses showed that temporal context indeed affected neural dynamics during the perception phase. Specifically, longer previous durations decreased contingent negative variation and P2 amplitude and increased beta power. In addition, multivariate pattern analysis showed that it is possible to decode context from the transient EEG signal quickly after both onset and offset of the perception phase. Together, these results suggest that temporal context creates dynamic expectations which actively affect the perception of duration.SIGNIFICANCE STATEMENT The subjective sense of duration does not arise in isolation, but is informed by previous experiences. This is demonstrated by abundant evidence showing that the production of duration estimates is biased toward previously experienced time intervals. However, it is yet unknown whether this temporal context actively affects perception or only asserts its influence in later, postperceptual stages as proposed by most current formal models of this task. Using an interval reproduction task, we show that EEG signatures flexibly adapt to the temporal context during perceptual encoding. Furthermore, interval history can be decoded from the transient EEG signal even when the current duration was identical. Thus, our results demonstrate that context actively influences perception.

Stance leg and surface stability modulate cortical activity during human single leg stance

Mobile Electroencephalography (EEG) provides insights into cortical contributions to postural control. Although changes in theta (4–8 Hz) and alpha frequency power (8–12 Hz) were shown to reflect attentional and sensorimotor processing during balance tasks, information about the effect of stance leg on cortical processing related to postural control is lacking. Therefore, the aim was to examine patterns of cortical activity during single-leg stance with varying surface stability. EEG and force plate data from 21 healthy males (22.43 ± 2.23 years) was recorded during unipedal stance (left/right) on a stable and unstable surface. Using source-space analysis, power spectral density was analyzed in the theta, alpha-1 (8–10 Hz) and alpha-2 (10–12 Hz) frequency bands. Repeated measures ANOVA with the factors leg and surface stability revealed significant interaction effects in the left (p = 0.045, η_p² = 0.13) and right motor clusters (F = 16.156; p = 0.001, η_p² = 0.41). Furthermore, significant main effects for surface stability were observed for the fronto-central cluster (theta), left and right motor (alpha-1), as well as for the right parieto-occipital cluster (alpha-1/alpha-2). Leg dependent changes in alpha-2 power may indicate lateralized patterns of cortical processing in motor areas during single-leg stance. Future studies may therefore consider lateralized patterns of cortical activity for the interpretation of postural deficiencies in unilateral lower limb injuries.

The influence of motor preparation on the processing of action-relevant visual features

Action preparation can facilitate performance in tasks of visual perception, for instance by speeding up responses to action-relevant stimulus features. However, it is unknown whether this facilitation reflects an influence on early perceptual processing, or instead post-perceptual processes. In three experiments, a combination of psychophysics and electroencephalography was used to investigate whether visual features are influenced by action preparation at the perceptual level. Participants were cued to prepare oriented reach-to-grasp actions before discriminating target stimuli oriented in the same direction as the prepared grasping action (congruent) or not (incongruent). As expected, stimuli were discriminated faster if their orientation was congruent, compared to incongruent, with the prepared action. However, action-congruency had no influence on perceptual sensitivity, regardless of cue-target interval and discrimination difficulty. The reaction time effect was not accompanied by modulations of early visual-evoked potentials. Instead, beta-band (13-30 Hz) synchronization over sensorimotor brain regions was influenced by action preparation, indicative of improved response preparation. Together, the results suggest that action preparation may not modulate early visual processing of orientation, but likely influences higher order response or decision related processing. While early effects of action on spatial perception are well documented, separate mechanisms appear to govern non-spatial feature selection.

Tracking Keystroke Sequences at the Cortical Level Reveals the Dynamics of Serial Order Production

Response selection is often studied by examining single responses, although most actions are performed within an overarching sequence. Understanding processes that order and execute items in a sequence is thus essential to give a complete picture of response selection. In this study, we investigate response selection by comparing single responses and response sequences as well as unimanual and bimanual sequences. We recorded EEG while participants were typing one- or two-keystroke sequences. Irrespective of stimulus modality (visual or auditory), response-locked analysis revealed distinct contralateral and ipsilateral components previously associated with activation and inhibition of alternative responses. Unimanual sequences exhibited a similar activation/inhibition pattern as single responses, but with the activation component of the pattern expressed more strongly, reflecting the fact that the hand will be used for two strokes. In contrast, bimanual sequences were associated with successive activation of each of the corresponding motor cortices controlling each keystroke and no traceable inhibitory component. In short, the activation component of the two-keystroke sequence EEG pattern can be understood from the addition of activation components of single-stroke sequences; the inhibition of the hand not being used is only evidenced when that hand is not planned for the next stroke.

Effects of Electroacupuncture on Pain Memory-Related Behaviors and Synchronous Neural Oscillations in the Rostral Anterior Cingulate Cortex in Freely Moving Rats

Our previous studies have confirmed that electroacupuncture (EA) can effectively intervene in pain memory, but the neural mechanism involved remains unclear. In this study, we observed the effects of EA in regulating pain memory-related behaviors and synchronous neural oscillations in the rostral anterior cingulate cortex (rACC). During nociceptive behavioral testing, pain memory induced a nonpain stimulus that spurred a neural oscillatory reaction similar to that caused by pain stimuli in the rACC. After EA, nonpain stimuli did not induce decreased neural oscillatory activity in the rACC until the presentation of pain stimuli. During aversive behavioral testing, EA, through the downregulation of theta power, inhibited the retrieval of aversive memory and relieved pain memory-induced aversive behaviors. These changes of oscillatory activity may be the hallmarks of EA therapy for pain memory.

Freely chosen and instructed actions are terminated by different neural mechanisms revealed by kinematics-informed EEG

Neurophysiological accounts of human volition are dominated by debates on the origin of voluntary choices but the neural consequences that follow such choices remain poorly understood. For instance, could one predict whether or not an action was chosen voluntarily based only on how that action is motorically executed? We investigated this possibility by integrating scalp electroencephalograms and index-finger accelerometer recordings acquired while people chose between pressing a left or right button either freely or as instructed by a visual cue. Even though freely selected and instructed actions were executed with equal vigor, the timing of the movement to release the button was comparatively delayed for freely selected actions. This chronometric difference was six-times larger for the β-oscillations over the sensorimotor cortex that characteristically accompany an action's termination. This surprising modulation of an action's termination by volition was traceable to volition-modulated differences in how the competing yet non-selected action was represented and regulated.

Neural activity related to volitional regulation of cortical excitability

To date there exists no reliable method to non-invasively upregulate or downregulate the state of the resting human motor system over a large dynamic range. Here we show that an operant conditioning paradigm which provides neurofeedback of the size of motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS), enables participants to self-modulate their own brain state. Following training, participants were able to robustly increase (by 83.8%) and decrease (by 30.6%) their MEP amplitudes. This volitional up-versus down-regulation of corticomotor excitability caused an increase of late-cortical disinhibition (LCD), a TMS derived read-out of presynaptic GABAB disinhibition, which was accompanied by an increase of gamma and a decrease of alpha oscillations in the trained hemisphere. This approach paves the way for future investigations into how altered brain state influences motor neurophysiology and recovery of function in a neurorehabilitation context.

Error-related modulations of the sensorimotor post-movement and foreperiod beta-band activities arise from distinct neural substrates and do not reflect efferent signal processing

While beta activity has been extensively studied in relation to voluntary movement, its role in sensorimotor adaptation remains largely uncertain. Recently, it has been shown that the post-movement beta rebound as well as beta activity during movement-preparation are modulated by movement errors. However, there are critical functional differences between pre- and post-movement beta activities. Here, we addressed two related open questions. Do the pre- and post-movement error-related modulations arise from distinct neural substrates? Do these modulations relate to efferent signals shaping muscle-activation patterns or do they reflect integration of sensory information, intervening upstream of the motor output? For this purpose, first we exploited independent component analysis (ICA) which revealed a double dissociation suggesting that distinct neural substrates are recruited in error-related beta-power modulations observed before and after movement. Second, we compared error-related beta oscillation responses observed in two bimanual reaching tasks involving similar movements but different interlimb coordination, and in which the same mechanical perturbations induced different behavioral adaptive responses. While the task difference was not reflected in the post-movement beta rebound, the pre-movement beta activity was differently modulated according to the interlimb coordination. Critically, we show an uncoupling between the behavioral and the electrophysiological responses during the movement preparation phase, which demonstrates that the error-related modulation of the foreperiod beta activity does not reflect changes in the motor output from primary motor cortex. It seems instead to relate to higher level processing of sensory afferents, essential for sensorimotor adaptation.

Group and individual analyses of pre-, peri-, and post-movement related alpha and beta oscillations during a single continuous monitoring task

Band power linked to lower and upper alpha (i.e. 8-10Hz; 10-12Hz) and lower and upper beta (i.e. 12-20Hz; 20-30Hz) were examined during response related stages, including anticipation, response execution (RE), response inhibition (RI) and post response recovery (PRR). Group and individual data from 34 participants were considered. The participant's objective was to press a response key immediately following 4 non-repeating, single integer odd digits. These were presented amongst a continuous stream of digits and Xs. Electroencephalogram (EEG) signals were recorded from 32 electrodes (pooled to 12 regions). In the group analyses, participant EEG response was compared to baseline revealing that upper alpha desynchronised during anticipation, RE and RI; lower beta during anticipation and RE; and upper beta just RE. Upper alpha desynchronisation during rapid, unplanned RI is novel. Also, upper alpha and lower/upper beta synchronised during PRR. For upper alpha, we speculate this indexes brief cortical deactivation; for beta we propose this indexes response set maintenance. Lastly, lower alpha fluctuations correlated negatively with RT, indexing neural efficiency. Individual analyses involved calculation of the proportion of individuals displaying the typical RE and PRR trends; these were not reflected by all participants. The former was displayed individually by the largest proportion in upper alpha recorded left fronto-centrally; the latter was most reliably displayed individually in lower beta recorded mid centro-parietally. Therefore, group analyses identified typical alpha and beta synchronisation/desynchronisation trends, whilst individual analyses identified their degree of representation in single participants. Attention is drawn to the clinical relevance of this issue.

The functional role of post-movement beta oscillations in motor termination

Shortly after movement termination, there is a strong increase or resynchronization of the beta rhythm (15-30 Hz) across the sensorimotor network of humans, known as the post-movement beta rebound (PMBR). This response has been associated with active inhibition of the motor network following the completion of a movement, sensory afferentation of the sensorimotor cortices, and other functions. However, studies that have directly probed the role of the PMBR in movement execution have reported mixed results, possibly due to differences in the amount of total motor output and/or movement complexity. Herein, we used magnetoencephalography during an isometric-force control task to examine whether alterations in the timing of motor termination demands modulate the PMBR, independent of differences in the motor output itself. Briefly, we manipulated the amount of time between the cue to initiate the force and the cue to terminate the force, such that participants were either forced to terminate quickly or slowly. We also performed a control experiment to test for temporal predictability effects. Our results indicated that the PMBR was stronger immediately following movement termination in the prefrontal cortices, supplementary motor area, left postcentral gyrus, paracentral lobule, and parietal cortex when participants were forced to terminate more quickly. These results were not attributable to the temporal predictability of each condition. These findings support the notion that the PMBR response at least partially serves motor inhibition, independent of the parameters within the motor output itself, and that particular nodes of the motor network may be differentially modulated by motor termination.

Distinct Modulations in Sensorimotor Postmovement and Foreperiod β-Band Activities Related to Error Salience Processing and Sensorimotor Adaptation

In a recent study, Tan et al. (2014a,b) showed that the increase in β-power typically observed after a movement above sensorimotor regions (β-rebound) is attenuated when movement-execution errors are induced by visual perturbations. Moreover, akin to sensorimotor adaptation, the effect depended on the context in which the errors are experienced. Thus the β-rebound attenuation might relate to neural processes involved in trial-to-trial adaptive mechanisms. In two EEG experiments with human participants, along with the β-rebound, we examine β-activity during the preparation of reaches immediately following perturbed movements. In the first experiment, we show that both foreperiod and postmovement β-activities are parametrically modulated by the sizes of kinematic errors produced by unpredictable mechanical perturbations (force field) independent of their on-line corrections. In the second experiment, we contrast two types of reach errors: movement-execution errors that trigger trial-to-trial adaptive mechanisms and goal errors that do not elicit sensorimotor adaptation. Movement-execution errors were induced by mechanical or visual perturbations, whereas goal errors were caused by unexpected displacements of the target at movement initiation. Interestingly, foreperiod and postmovement β-activities exhibit contrasting patterns, pointing to important functional differences of their underlying neuronal activity. While both types of reach errors attenuate the postmovement β-rebound, only the kinematic errors that trigger trial-to-trial motor-command updates influenced β-activity during the foreperiod. These findings suggest that the error-related modulation of the β-rebound may reflect salience processing, independent of sensorimotor adaptation. In contrast, modulations in the foreperiod β-power might relate to the motor-command adjustments activated after movement-execution errors are experienced.

SIGNIFICANCE STATEMENT

The functional significance of sensorimotor β-band (15-25 Hz) oscillations remains uncertain. Recently β-power was found to be reduced following erroneous movements. We extend and refine this novel finding in two crucial ways. First, by contrasting the EEG correlates of movement errors driving or not driving adaptation we dissociate error-salience processing from error-based adaptation. Second, in addition to β-activity in error trials, we examine β-power during the preparation of the subsequent movements. We find clearly distinct patterns of error-related modulations for β-activities preceding and succeeding movements, highlighting critical functional differences. Postmovement β-power may reflect error-salience processing independent of sensorimotor adaptation. In contrast, modulations in the foreperiod β-band power may directly relate to the motor-command adjustments activated after movement-execution errors are experienced.

Brain oscillatory signatures of motor tasks

Noninvasive brain-computer-interfaces (BCI) coupled with prosthetic devices were recently introduced in the rehabilitation of chronic stroke and other disorders of the motor system. These BCI systems and motor rehabilitation in general involve several motor tasks for training. This study investigates the neurophysiological bases of an EEG-oscillation-driven BCI combined with a neuroprosthetic device to define the specific oscillatory signature of the BCI task. Controlling movements of a hand robotic orthosis with motor imagery of the same movement generates sensorimotor rhythm oscillation changes and involves three elements of tasks also used in stroke motor rehabilitation: passive and active movement, motor imagery, and motor intention. We recorded EEG while nine healthy participants performed five different motor tasks consisting of closing and opening of the hand as follows: 1) motor imagery without any external feedback and without overt hand movement, 2) motor imagery that moves the orthosis proportional to the produced brain oscillation change with online proprioceptive and visual feedback of the hand moving through a neuroprosthetic device (BCI condition), 3) passive and 4) active movement of the hand with feedback (seeing and feeling the hand moving), and 5) rest. During the BCI condition, participants received contingent online feedback of the decrease of power of the sensorimotor rhythm, which induced orthosis movement and therefore proprioceptive and visual information from the moving hand. We analyzed brain activity during the five conditions using time-frequency domain bootstrap-based statistical comparisons and Morlet transforms. Activity during rest was used as a reference. Significant contralateral and ipsilateral event-related desynchronization of sensorimotor rhythm was present during all motor tasks, largest in contralateral-postcentral, medio-central, and ipsilateral-precentral areas identifying the ipsilateral precentral cortex as an integral part of motor regulation. Changes in task-specific frequency power compared with rest were similar between motor tasks, and only significant differences in the time course and some narrow specific frequency bands were observed between motor tasks. We identified EEG features representing active and passive proprioception (with and without muscle contraction) and active intention and passive involvement (with and without voluntary effort) differentiating brain oscillations during motor tasks that could substantially support the design of novel motor BCI-based rehabilitation therapies. The BCI task induced significantly different brain activity compared with the other motor tasks, indicating neural processes unique to the use of body actuators control in a BCI context.

Event-Related Synchronization and Desynchronization of High-Frequency Electroencephalographic Activity during a Visual Go/No-Go Paradigm

OBJECTIVE

High-frequency electroencephalography (EEG) activity has been observed in association with cognitive processing, including stimulus perception, consciousness and selective attention, in humans. The aim of this study was to compare visual-motor integrated processing between execution and inhibition of a motor response using event-related synchronization (ERS) and desynchronization (ERD) in the 15- to 80-Hz range and to investigate a relationship between event-related potentials (ERPs) and ERS/ERD in 10 normal young subjects.

METHODS

EEGs were recorded from 21 scalp sites during a visual go/no-go paradigm. For ERPs, 40 artifact-free trials were averaged off-line referenced to linked ear lobes. In the β and γ bands, ERS and ERD were calculated by time-frequency analysis.

RESULTS

Go N2 and no-go N2 were elicited 200-250 ms after stimuli, and their distributions were predominant at Fz. Go P3 was predominantly elicited 340-360 ms after stimuli at Pz, whereas no-go P3 was predominantly elicited 360-380 ms after stimuli at Cz. ERD of the β band at Fz and Cz during 300-600 ms showed in the go condition, whereas ERD showed between 39 and 42 Hz at F3 in the no-go condition.

CONCLUSION

Oscillatory cortical response-related β and γ activities differ between the processing of execution and inhibition in motor responses. β ERDs in the sensorimotor areas with go stimuli may be related to motor responses, and γ ERDs in the left frontal area with no-go stimuli may be involved in the processing of inhibition of motor responses. © 2015 S. Karger AG, Basel.

Winning the game: brain processes in expert, young elite and amateur table tennis players

This study tested two hypotheses: (1) compared with amateurs and young elite, expert table tennis players are characterized by enhanced cortical activation in the motor and fronto-parietal cortex during motor imagery in response to table tennis videos; (2) in elite athletes, world rank points are associated with stronger cortical activation. To this aim, electroencephalographic data were recorded in 14 expert, 15 amateur and 15 young elite right-handed table tennis players. All subjects watched videos of a serve and imagined themselves responding with a specific table tennis stroke. With reference to a baseline period, power decrease/increase of the sensorimotor rhythm (SMR) during the pretask- and task period indexed the cortical activation/deactivation (event-related desynchronization/synchronization, ERD/ERS). Regarding hypothesis (1), 8–10 Hz SMR ERD was stronger in elite athletes than in amateurs with an intermediate ERD in young elite athletes in the motor cortex. Regarding hypothesis (2), there was no correlation between ERD/ERS in the motor cortex and world rank points in elite experts, but a weaker ERD in the fronto-parietal cortex was associated with higher world rank points. These results suggest that motor skill in table tennis is associated with focused excitability of the motor cortex during reaction, movement planning and execution with high attentional demands. Among elite experts, less activation of the fronto-parietal attention network may be necessary to become a world champion.

Linking motor-related brain potentials and velocity profiles in multi-joint arm reaching movements

The study of the movement related brain potentials (MRPBs) needs accurate technical approaches to disentangle the specific patterns of bran activity during the preparation and execution of movements. During the last forty years, synchronizing the electromyographic activation (EMG) of the muscle with electrophysiological recordings (EEG) has been commonly ussed for these purposes. However, new clinical approaches in the study of motor diseases and rehabilitation suggest the demand of new paradigms that might go further into the study of the brain activity associated with the kinematics of movements. As a response to this call, we have used a 3-D hand-tracking system with the aim to record continuously the position of an ultrasonic sender attached to the hand during the performance of multi-joint self-paced movements. We synchronized time-series of position and velocity of the sender with the EEG recordings, obtaining specific patterns of brain activity as a function of the fluctuations of the kinematics during natural movement performance. Additionally, the distribution of the brain activity during the preparation and execution phases of movements was similar that reported previously using the EMG, suggesting the validity of our technique. We claim that this paradigm could be usable in patients because of its simplicity and the potential knowledge that can be extracted from clinical protocols.

Proprioceptive feedback and brain computer interface (BCI) based neuroprostheses

Brain computer interface (BCI) technology has been proposed for motor neurorehabilitation, motor replacement and assistive technologies. It is an open question whether proprioceptive feedback affects the regulation of brain oscillations and therefore BCI control. We developed a BCI coupled on-line with a robotic hand exoskeleton for flexing and extending the fingers. 24 healthy participants performed five different tasks of closing and opening the hand: (1) motor imagery of the hand movement without any overt movement and without feedback, (2) motor imagery with movement as online feedback (participants see and feel their hand, with the exoskeleton moving according to their brain signals, (3) passive (the orthosis passively opens and closes the hand without imagery) and (4) active (overt) movement of the hand and rest. Performance was defined as the difference in power of the sensorimotor rhythm during motor task and rest and calculated offline for different tasks. Participants were divided in three groups depending on the feedback receiving during task 2 (the other tasks were the same for all participants). Group 1 (n = 9) received contingent positive feedback (participants' sensorimotor rhythm (SMR) desynchronization was directly linked to hand orthosis movements), group 2 (n = 8) contingent “negative” feedback (participants' sensorimotor rhythm synchronization was directly linked to hand orthosis movements) and group 3 (n = 7) sham feedback (no link between brain oscillations and orthosis movements). We observed that proprioceptive feedback (feeling and seeing hand movements) improved BCI performance significantly. Furthermore, in the contingent positive group only a significant motor learning effect was observed enhancing SMR desynchronization during motor imagery without feedback in time. Furthermore, we observed a significantly stronger SMR desynchronization in the contingent positive group compared to the other groups during active and passive movements. To summarize, we demonstrated that the use of contingent positive proprioceptive feedback BCI enhanced SMR desynchronization during motor tasks.

Action-related semantic content and negation polarity modulate motor areas during sentence reading: an event-related desynchronization study

Our study evaluated motor cortex involvement during silent reading of sentences referring to hand actions. We aimed at defining whether sentential polarity (affirmative vs. negative) would modulate motor cortex activation using the event-related desynchronization (ERD) analysis of the mu rhythm. Eleven healthy volunteers performed a reading task involving 160 sentences (80 affirmative: 40 hand-related, 40 abstract; 80 negative: 40 hand-related, 40 abstract). After reading each sentence, subjects had to decide whether the verb was high or low frequency in Italian. Electroencephalographic (EEG) activity was recorded with 32 surface electrodes and mu ERD analyses were performed for each subject. Hand-action related sentences induced a greater mu ERD over the left premotor and motor hand areas compared to abstract sentences. Mu ERD was greater and temporally delayed when the hand-related verbs were presented in the negative versus affirmative form. As predicted by the "embodied semantic" theory of language understanding, motor areas were activated during sentences referring to hand actions. In addition, motor cortex activation was larger for negative than affirmative motor sentences, a finding compatible with the hypothesis that comprehension is more demanding in the specific case of motor content negation.

Source analysis of beta-synchronisation and cortico-muscular coherence after movement termination based on high resolution electroencephalography

We hypothesized that post-movement beta synchronization (PMBS) and cortico-muscular coherence (CMC) during movement termination relate to each other and have similar role in sensorimotor integration. We calculated the parameters and estimated the sources of these phenomena.

We measured 64-channel EEG simultaneously with surface EMG of the right first dorsal interosseus muscle in 11 healthy volunteers. In Task1, subjects kept a medium-strength contraction continuously; in Task2, superimposed on this movement, they performed repetitive self-paced short contractions. In Task3 short contractions were executed alone. Time-frequency analysis of the EEG and CMC was performed with respect to the offset of brisk movements and averaged in each subject. Sources of PMBS and CMC were also calculated.

High beta power in Task1, PMBS in Task2-3, and CMC in Task1-2 could be observed in the same individual frequency bands. While beta synchronization in Task1 and PMBS in Task2-3 appeared bilateral with contralateral predominance, CMC in Task1-2 was strictly a unilateral phenomenon; their main sources did not differ contralateral to the movement in the primary sensorimotor cortex in 7 of 11 subjects in Task1, and in 6 of 9 subjects in Task2. In Task2, CMC and PMBS had the same latency but their amplitudes did not correlate with each other. In Task2, weaker PMBS source was found bilaterally within the secondary sensory cortex, while the second source of CMC was detected in the premotor cortex, contralateral to the movement. In Task3, weaker sources of PMBS could be estimated in bilateral supplementary motor cortex and in the thalamus.

PMBS and CMC appear simultaneously at the end of a phasic movement possibly suggesting similar antikinetic effects, but they may be separate processes with different active functions. Whereas PMBS seems to reset the supraspinal sensorimotor network, cortico-muscular coherence may represent the recalibration of cortico-motoneuronal and spinal systems.

Disturbed post-movement beta synchronization in Wilson's disease with neurological manifestation

We analyzed the changes of post-movement beta synchronization (PMBS) of the electroencephalogram (EEG) in Wilson's disease with neurological manifestation. Our aim was to determine if PMBS in Wilson's disease is altered in a different way than in Parkinson's disease or in essential tremor. Our purpose was to find out whether the analysis of PMBS could help the diagnosis in ambiguous cases. Ten patients with neurological manifestation of Wilson's disease and ten controls performed self-paced movements with the dominant hand during EEG acquisition. Five electrodes above the sensorimotor cortex were selected for evaluation (C3, C1, Cz, C2, C4) as contralateral (C); contralateral medial (CM); medial (M); ipsilateral medial (IM); ipsilateral (I) relative to the dominant hand. Power and latency of PMBS were calculated by time resolved power spectral analysis with multitaper method. PMBS power in the C electrode position was significantly lower in patients than in controls, its contralateral preponderance disappeared in the patient group. In every location, latency of PMBS was significantly longer in the Wilson group compared to controls. More altered PMBS could be measured in patients with both basal ganglia and cerebellar involvements. Since decreased power of PMBS was observed in Parkinson's disease and increased latency in essential tremor, the combined change of PMBS can indicate pathology of different neural circuits and may help the diagnosis in challenging cases.

Stability-dependent behavioural and electro-cortical reorganizations during intentional switching between bimanual tapping modes

This study investigated behavioural and electro-cortical reorganizations accompanying intentional switching between two distinct bimanual coordination tapping modes (In-phase and Anti-phase) that differ in stability when produced at the same movement rate. We expected that switching to a less stable tapping mode (In-to-Anti switching) would lead to larger behavioural perturbations and require supplementary neural resources than switching to a more stable tapping mode (Anti-to-In switching). Behavioural results confirmed that the In-to-Anti switching lasted longer than the Anti-to-In switching. A general increase in attention-related neural activity was found at the moment of switching for both conditions. Additionally, two condition-dependent EEG reorganizations were observed. First, a specific increase in cortico-cortical coherence appeared exclusively during the In-to-Anti switching. This result may reflect a strengthening in inter-regional communication in order to engage in the subsequent, less stable, tapping mode. Second, a decrease in motor-related neural activity (increased beta spectral power) was found for the Anti-to-In switching only. The latter effect may reflect the interruption of the previous, less stable, tapping mode. Given that previous results on spontaneous Anti-to-In switching revealing an inverse pattern of EEG reorganization (decreased beta spectral power), present findings give new insight on the stability-dependent neural correlates of intentional motor switching.

Oscillatory changes related to the forced termination of a movement

OBJECTIVE

Stimulus-induced movements are accompanied by a definite pattern of oscillatory changes, that include a frontal 15 Hz synchronization, a central peri-movement desynchronization, and a contralateral beta rebound after the movement. Our aim was to study the oscillatory changes related to the forced termination of a single complex motor program (signature) and compare them with those observed after the normal termination of the movement.

METHODS

Fifty-eight reference-free EEG channels were analyzed in 10 healthy subjects. A 2000 Hz tone (S1, go signal) indicated the subject to begin to write his/her complete signature. A second 2000 Hz tone 0.8 s afterwards (50% probability: S2, stop signal) indicated the subject to stop immediately. Movement-related energy changes were evaluated by means of time-frequency (Gabor) transforms.

RESULTS

A frontal 15 Hz synchronization was observed after S1, but not after S2. The amplitude of the post-movement beta increase was significantly lower when the movement was abnormally terminated (p=0.005), while the peri-movement decrease was similar.

CONCLUSIONS

The forced termination of a motor program reduces significantly the amplitude of the post-movement beta increment, conserving its temporal pattern. Also, the presence of the 15 Hz frontal synchronization only after S1, together with the results of previous studies, suggests that the frontal mechanisms involved in go/no go and stop signals are very different.

SIGNIFICANCE

Our results indicate that the beta rebound is an active process, independent of the peri-movement beta decrease, which is influenced by how the movement is terminated.

Changes in cortical relative power in patients submitted to a tendon transfer: a pre and post surgery study

The aim of this study is analyze possible modifications in the cerebral cortex, through quantitative electroencephalography (qEEG) in patients submitted to a tendon transfer procedure (posterior tibialis) by the Srinivasan's technique. Four subjects (2 men and 2 women), 49.25 age average (SD +/ 21.4) were studied. All subjects have been through surgical procedure due to leprosy and had, at least, two years of drop foot condition. The qEEG measured the electrocortical activity (relative power) between 8 and 25 Hz frequencies pre and post surgery. A paired t test analyzed all data (p< or =0,05). The results show significant alterations in the alpha relative power, electrodes F7 (p=0.01) and F8 (p=0.021). Altogether, based on findings of the current literature, we can conclude that the tendon transfer procedure suggests electrocortical alterations sensitive to specific qEEG bands.

Changes in the alpha and beta amplitudes of the central EEG during the onset, continuation, and offset of long-duration repetitive hand movements

Electroencephalographic alpha and beta activities recorded from central electrodes are known to display movement-related suppression or enhancement. We investigated whether the suppression that is known to occur during the onset of a single movement would persist or otherwise habituate when the movement is continuously repeated for a long period of time. Fourteen subjects took part in the experiments. They performed repetitive simultaneous extension-flexions of the fingers II-V in one hand, continuously for a period of at least 30 s. They then stopped this self-paced movement and rested for at least 30 s. Bipolar recording was made from C3-Cz and C4-Cz. Patterns of amplitude changes in the alpha and beta bands were calculated against a resting baseline. Following a bilateral alpha and beta suppression at the movement onset, alpha amplitude gradually but not fully recovered towards the baseline during the 30 s post-onset. Habituation of afferences and transfer of the cortical function were discussed as the two alternative explanations for this gradual recovery. Beta amplitude, however, displayed no recovery as long as the movement continued. Considering the relatively rapid beta recovery reported for sustained movements, this finding demonstrated that the sustained and continuous movements are conducted through quite different processes. A transient contralateral beta rebound was observed only after the end of the long movement period, strengthening the viewpoint that links the beta rebound with the closure of the cortical processes running throughout a motor sequence. Modulation of the beta amplitude, rather than the changes in alpha amplitude, appeared to be more closely correlated with the execution of a continuous movement.

Functional oropharyngeal sensory disruption interferes with the cortical control of swallowing

Background

Sensory input is crucial to the initiation and modulation of swallowing. From a clinical point of view, oropharyngeal sensory deficits have been shown to be an important cause of dysphagia and aspiration in stroke patients. In the present study we therefore investigated effects of functional oropharyngeal disruption on the cortical control of swallowing. We employed whole-head MEG to study cortical activity during self-paced volitional swallowing with and without topical oropharyngeal anesthesia in ten healthy subjects. A simple swallowing screening-test confirmed that anesthesia caused swallowing difficulties with decreased swallowing speed and reduced volume per swallow in all subjects investigated. Data were analyzed by means of synthetic aperture magnetometry (SAM) and the group analysis of the individual SAM data was performed using a permutation test.

Results

The analysis of normal swallowing revealed bilateral activation of the mid-lateral primary sensorimotor cortex. Oropharyngeal anesthesia led to a pronounced decrease of both sensory and motor activation.

Conclusion

Our results suggest that a short-term decrease in oropharyngeal sensory input impedes the cortical control of swallowing. Apart from diminished sensory activity, a reduced activation of the primary motor cortex was found. These findings facilitate our understanding of the pathophysiology of dysphagia.

Amplitude and phase dynamics associated with acoustically paced finger tapping

To gain insight into the brain activity associated with the performance of an acoustically paced synchronization task, we analyzed the amplitude and phase dynamics inherent in magnetoencephalographic (MEG) signals across frequency bands in order to discriminate between evoked and induced responses. MEG signals were averaged with respect to motor and auditory events (tap and tone onsets). Principal component analysis was used to compare amplitude and phase changes during listening and during paced and unpaced tapping, allowing a separation of brain activity related to motor and auditory processes, respectively. Motor performance was accompanied by phasic amplitude changes and increased phase locking in the beta band. Auditory processing of acoustic stimuli resulted in a simultaneous increase of amplitude and phase locking in the theta and alpha band. The temporal overlap of auditory-related amplitude changes and phase locking indicated an evoked response, in accordance with previous studies on auditory perception. The temporal difference of movement-related amplitude and phase dynamics in the beta band, on the other hand, suggested a change in ongoing brain activity, i.e., an induced response supporting previous results on motor-related brain dynamics in the beta band.

Synchronized brain activity during rehearsal and short-term memory disruption by irrelevant speech is affected by recall mode

EEG coherence as a measure of synchronization of brain activity was used to investigate effects of irrelevant speech. In a delayed serial recall paradigm 21 healthy participants retained verbal items over a 10-s delay with and without interfering irrelevant speech. Recall after the delay was varied in two modes (spoken vs. written). Behavioral data showed the classic irrelevant speech effect and a superiority of written over spoken recall mode. Coherence, however, was more sensitive to processing characteristics and showed interactions between the irrelevant speech effect and recall mode during the rehearsal delay in theta (4-7.5 Hz), alpha (8-12 Hz), beta (13-20 Hz), and gamma (35-47 Hz) frequency bands. For gamma, a rehearsal-related decrease of the duration of high coherence due to presentation of irrelevant speech was found in a left-lateralized fronto-central and centro-temporal network only in spoken but not in written recall. In theta, coherence at predominantly fronto-parietal electrode combinations was indicative for memory demands and varied with individual working memory capacity assessed by digit span. Alpha coherence revealed similar results and patterns as theta coherence. In beta, a left-hemispheric network showed longer high synchronizations due to irrelevant speech only in written recall mode. EEG results suggest that mode of recall is critical for processing already during the retention period of a delayed serial recall task. Moreover, the finding that different networks are engaged with different recall modes shows that the disrupting effect of irrelevant speech is not a unitary mechanism.

Movement-related frequency modulation of beta oscillatory activity in the human subthalamic nucleus

Event-related changes of brain electrical rhythms are typically analysed as amplitude modulations of local field potential (LFP) oscillations, like radio amplitude modulation broadcasting. In telecommunications, frequency modulation (FM) is less susceptible to interference than amplitude modulation (AM) and is therefore preferred for high-fidelity transmissions. Here we hypothesized that LFP rhythms detected from deep brain stimulation (DBS) electrodes implanted in the subthalamic nucleus (STN) in patients with Parkinson's disease could represent movement-related activity not only in AM but also in FM. By combining adaptive autoregressive identification with spectral power decomposition, we were able to show that FM of low-beta (13-20 Hz) and high-beta (20-35 Hz) rhythms significantly contributes to the involvement of the human STN in movement preparation, execution and recovery, and that the FM patterns are regulated by the dopamine levels in the system. Movement-related FM of beta oscillatory activity in the human subthalamic nucleus therefore provides a novel informational domain for rhythm-based pathophysiological models of cortico-basal ganglia processing.

Asymmetric spatiotemporal patterns of event-related desynchronization preceding voluntary sequential finger movements: a high-resolution EEG study

OBJECTIVE

To study spatiotemporal patterns of event-related desynchronization (ERD) preceding voluntary sequential finger movements performed with dominant right hand and nondominant left hand.

METHODS

Nine subjects performed self-paced movements consisting of three key strokes with either hand. Subjects randomized the laterality and timing of movements. Electroencephalogram (EEG) was recorded from 122 channels. Reference-free EEG power measurements in the beta band were calculated off-line.

RESULTS

During motor preparation (-2 to -0.5s with respect to movement onset), contralateral preponderance of event-related desynchronization (ERD) (lateralized power) was only observed during right hand finger movements, whereas ERD during left hand finger movements was bilateral.

CONCLUSIONS

For right-handers, activation on the left hemisphere during left hand movements is greater than that on the right hemisphere during right hand movements.

SIGNIFICANCE

We provide further evidence for motor dominance of the left hemisphere in early period of motor preparation for complex sequential finger movements.