Mu Rhythm Research Articles

Characterization of the Mu rhythm during the sleep of children with autism spectrum disorder level 1

Introduction. Autistic spectrum disorder (ASD) is characterized by difficulties in communication and social interaction. The theory of mind (TM) links social deficiencies in ASD with a difficulty in representing the mental states of other people. The Mu rhythm (8-13Hz) has been studied as an expression of the possible neuronal basis of TM. In ASD, the physiological reactivity of the Mu rhythm to motor events is affected. During sleep, there are also phenomena related to sensorimotor processing. Objective. To characterize the Mu rhythm in the sleep of children with level 1 ASD, ages six to 10, and compare it with control children paired by age and sex. Method. Polysomnographic records for two consecutive nights. The record of the second night was analyzed visually (the first was considered habituation) to identify and select Mu rhythm segments throughout the night. The extracted segments were analyzed using the fast Fourier transform and subsequently with t tests on the data of C3 and C4. Results. A significant difference was found in the power spectrums of C3 and C4 t (1, 144) = 3.038, p = .003 and t (1, 144) = -2.301, p = .023, respectively. Discussion and conclusion. The results of this study are consistent with the morphological and topographic characteristics found in studies conducted during wakefulness. The results suggest that the Mu rhythm is caused intrinsically, without external sensory stimulation, and that there is a difference in this generation in the population with ASD.

Effect of visual orientation on mu suppression in children: a comparative EEG study with adults

BackgroundThe human mirror neuron system exists in adults, and even in children. However, a significant, unanswered question in the literature concerns age differences in the effect of visual orientation of human body movements. The observation of actions performed by others is known to activate populations of neural cells called mirror neuron system. Moreover, the power of mu rhythms (8–13 Hz) in the EEG is known to decrease while performing and observing human movements. Therefore, the mu rhythm could be related to the activity of the mirror neuron system. This study investigated the effects of the visual perspective on electroencephalography responses to hand actions in two age groups.MethodsThe participants were 28 elementary school students and 26 university students. Videos of the two hands operating switches were used as stimuli. The electroencephalogram mu rhythm (8–13 Hz) was measured during stimuli presentation as an index of mirror neuron system activity.ResultsAdult participants showed significant mirror neuron system activation under both conditions, although no effect of visual perspectives was observed. On the other hand, children only reacted to egocentric stimuli and not to the others.ConclusionsThese findings confirmed the suggested differences in the activity of the mirror neuron system between different age groups. The demonstration that brain activities related to mirroring change during development could help explain previous findings in the literature.

Mu Suppression Is Sensitive to Observational Practice but Results in Different Patterns of Activation in Comparison with Physical Practice.

Research has shown the effectiveness of observational practice for motor learning, but there continues to be debate about the mechanisms underlying effectiveness. Although cortical processes can be moderated during observation, after both physical and observational practice, how these processes change with respect to behavioural measures of learning has not been studied. Here we compared short-term physical and observational practice during the acquisition and retention of a novel motor task to evaluate how each type of practice modulates EEG mu rhythm (8–13 Hz). Thirty healthy individuals were randomly assigned to one of three groups: (1) physical practice (PP), (2) observational practice (OP), and (3) no practice (NP) control. There were four testing stages: baseline EEG, practice, postpractice observation, and delayed retention. There was significant bilateral suppression of mu rhythm during PP but only left lateralized mu suppression during OP. In the postpractice observation phase, mu suppression was bilateral and larger after PP compared to that after OP. NP control showed no evidence of suppression and was significantly different to both the OP and PP groups. When comparing the three groups in retention, the groups did not differ with respect to tracing times, but the PP group showed fewer errors, especially in comparison to the NP group. Therefore, although the neurophysiological measures index changes in the OP group, which are similar but moderated in comparison to PP, changes in these processes are not manifest in observational practice outcomes when assessed in a delayed retention test.

Common Interferences Removal from Dense Multichannel EEG Using Independent Component Decomposition.

To improve the spatial resolution, dense multichannel electroencephalogram with more than 32 leads has gained more and more applications. However, strong common interference will not only conceal the weak components generated from the specific isolated neural source, but also lead to severe spurious correlation between different brain regions, which results in great distortion on brain connectivity or brain network analysis. Starting from the fast independent component analysis algorithm, we first derive the mixing matrix of independent source components based on the baseline signals prior to tasks. Then, we identify the common interferences as those components whose mixing vectors span the minimum angles with respect to the unitary vector. By assuming that both the common interferences and their corresponding mixing vectors stay consistent during the entire experiment, we apply the demixing and mixing matrix to the task signals and remove the inferred common interferences. Subsequently, we validate the method using simulation. Finally, the index of global coherence is calculated for validation. It turns out that the proposed method can successfully remove the common interferences so that the prominent coherence of mu rhythms in motor imagery tasks is unmasked. The proposed method can gain wide applications because it reveals the true correlation between the local sources in spite of the low signal-to-noise ratio.

S128. Oscillatory responses evoked by single-pulse electrical stimulation in human cerebral cortex – A Cortico-Cortical Evoked Potential (CCEP) study

Introduction Human brain operates with oscillatory activity in different frequency bands. For example, mu rhythm is well known as an idling rhythm observed in the central area related to motor function. We observed some rhythmic pattern in the averaged waveforms in the CCEP investigation (called “oscillatory response” here), which is originally a method to trace connectivity by single electrical pulse stimulation. We report on the frequency and distribution of the oscillatory responses in CCEP. Methods Subjects are 5 intractable epilepsy patients who underwent chronic implantation of subdural electrodes for presurgical evaluation. Written informed consents were obtained from all subjects. Single-pulse stimuli (0.3 ms, 8–10 mA, alternating polarity, 30 × 2 trials) were applied through two adjacent electrodes (52.8 ± 15.3 stimulus sites per patient). CCEP was recorded from subdural electrodes (105.2 ± 31.8 electrodes per patient) placed on the lateral and medial aspect of the cerebral hemisphere. Lateral fronto-parietal area was covered in all subjects. An oscillatory response in CCEP was detected by visual inspection on the averaged waveform according to the following criteria; (1) it has at least two pairs of peak and trough spaced equally, (2) it can be overlapped with other evoked responses (typical N1/ N2 response). If more than one rhythms with different frequencies were observed in the same electrode, we counted the largest one in amplitude. Results Totally, 2362 oscillatory responses (7.9%) were detected in 29891 observations in 5 subjects, including 443 alpha-band responses (7.5–13.5 Hz), 312 beta-band responses (13.5–30 Hz) and 1505 theta-band responses (3.5–7.5 Hz). Theta rhythm was observed predominantly in the temporal lobe including the basal temporal area (the occurrence rate was 12.45%). Alpha rhythm was observed more often in the parietal lobe including the postcentral gyrus (the occurrence rate was 4.57%), while beta rhythm was often observed around precentral gyrus (the occurrence rate was 1.98%). The frequency of the resting rhythmic activity was equal to that of oscillatory CCEP response in the alpha band in the postcentral gyrus in all subjects. This alpha activity was considered as mu rhythm in all the 3 subjects who performed a hand grasping task. Conclusion Single pulse electrical stimulation evoked oscillatory CCEP responses preferentially in the temporal lobe and the perirolandic area. The correspondence of frequency between the oscillatory response and mu rhythm implies the phase resetting of the physiological oscillation by exogenous input. This unique oscillatory CCEP may help to map these functionally important cortical regions.

Suppression of EEG mu rhythm during action observation corresponds with subsequent changes in behavior

Movement is intrinsically linked to perception such that observing an action induces in the observer behavioral changes during execution of similar actions. Electroencephalogram (EEG) studies have revealed that at the group level, action observation suppresses oscillatory power in mu (8–12 Hz) and beta (15–25 Hz) bands over the sensorimotor cortex – a phenomenon associated with increased excitability of cortical neurons. However, it is unclear whether differences in suppression level across individuals is linked with individual differences in subsequent behavioral changes. Here 32 subjects performed self-paced finger tapping with their right hand before and after observation of a video displaying finger-tapping at either 2 or 4 Hz. Behaviorally, subjects’ rate of self-pace tapping increased following observation, with higher increases following 4 Hz observation. The level of EEG power suppression in the low frequency range (low mu; 8–10 Hz) during observation corresponded to subsequent behavioral changes in tapping rate across individuals. Our results demonstrate that observing actions implicitly shifts subsequent execution rates, and that individual differences in the level of this implicit shift can be explained by activity in the sensorimotor cortex during observation.

Novice Shooters With Lower Pre-shooting Alpha Power Have Better Performance During Competition in a Virtual Reality Scenario.

Competition changes the environment for athletes. The difficulty of training for such stressful events can lead to the well-known effect of “choking” under pressure, which prevents athletes from performing at their best level. To study the effect of competition on the human brain, we recorded pilot electroencephalography (EEG) data while novice shooters were immersed in a realistic virtual environment representing a shooting range. We found a differential between-subject effect of competition on mu (8–12 Hz) oscillatory activity during aiming; compared to training, the more the subject was able to desynchronize his mu rhythm during competition, the better was his shooting performance. Because this differential effect could not be explained by differences in simple measures of the kinematics and muscular activity, nor by the effect of competition or shooting performance per se, we interpret our results as evidence that mu desynchronization has a positive effect on performance during competition.

The Effects of Fluency Enhancing Conditions on Sensorimotor Control of Speech in Typically Fluent Speakers: An EEG Mu Rhythm Study.

Objective: To determine whether changes in sensorimotor control resulting from speaking conditions that induce fluency in people who stutter (PWS) can be measured using electroencephalographic (EEG) mu rhythms in neurotypical speakers.Methods: Non-stuttering (NS) adults spoke in one control condition (solo speaking) and four experimental conditions (choral speech, delayed auditory feedback (DAF), prolonged speech and pseudostuttering). Independent component analysis (ICA) was used to identify sensorimotor μ components from EEG recordings. Time-frequency analyses measured μ-alpha (8–13 Hz) and μ-beta (15–25 Hz) event-related synchronization (ERS) and desynchronization (ERD) during each speech condition.Results: 19/24 participants contributed μ components. Relative to the control condition, the choral and DAF conditions elicited increases in μ-alpha ERD in the right hemisphere. In the pseudostuttering condition, increases in μ-beta ERD were observed in the left hemisphere. No differences were present between the prolonged speech and control conditions.Conclusions: Differences observed in the experimental conditions are thought to reflect sensorimotor control changes. Increases in right hemisphere μ-alpha ERD likely reflect increased reliance on auditory information, including auditory feedback, during the choral and DAF conditions. In the left hemisphere, increases in μ-beta ERD during pseudostuttering may have resulted from the different movement characteristics of this task compared with the solo speaking task. Relationships to findings in stuttering are discussed.Significance: Changes in sensorimotor control related feedforward and feedback control in fluency-enhancing speech manipulations can be measured using time-frequency decompositions of EEG μ rhythms in neurotypical speakers. This quiet, non-invasive, and temporally sensitive technique may be applied to learn more about normal sensorimotor control and fluency enhancement in PWS.

A Neurovisceral Approach to Autism: Targeting Self-Regulation and Core Symptoms Using Neurofeedback and Biofeedback

Mu Rhythm Synchrony Neurofeedback (MRS-NFB) has shown promise in improving electrophysiological and behavioral deficits in autism spectrum disorder (ASD). Heart rate variability biofeedback (HRV-BFB), a method for improving self-regulation of the autonomic nervous system (ANS), has yet to be tested as a clinical intervention for ASD. This study evaluated the impact of HRV-BFB on symptoms of ASD; and whether a combined HRV-BFB + MRS-NFB intervention would be more efficacious than HRV-BFB alone. Fifteen children with a verified diagnosis of ASD completed the study. Participants were assigned to either an HRV-BFB group (Group 1) or a combined HRV-BFB + MRS-NFB group (Group 2). All children underwent pre- and postassessments of electroencephalography (EEG), heart rate variability (HRV), and parent-reported behaviors. No significant between-groups differences were observed on any parent-reported behaviors. Group 1 showed significant pre–post improvements in emotion regulation and social behavior, while Group 2 showed significant pre–post improvements in emotional lability and autistic behaviors. Group 2 also showed significant improvements in RMSSD and lnHF (vagal tone) indices of HRV over time, while Group 1 displayed no significant changes in HRV over time. Group 1 showed an increase in mu suppression posttraining, and Group 2 showed a reduction in mu suppression posttraining. The results suggest that HRV-BFB, alone or in combination with MRS-NFB, may improve behavioral features of autism. A combined approach may be more efficacious in enhancing HRV, while the implications of each approach on mu suppression are mixed. Neurovisceral approaches that teach self-regulation offer a novel treatment avenue for ASD.

Analysis of Electroencephalography Event-Related Desynchronisation and Synchronisation Induced by Lower-Limb Stepping Motor Imagery

Bilateral upper-limb motor imagery has been demonstrated to be a useful mental task in electroencephalography (EEG)-based brain–computer interfaces (BCIs). By contrast, few studies have examined bilateral lower-limb motor imagery, and all of them have focused on imaginary foot movements. The left–right classification accuracy reported in these studies based on the EEG mu rhythm (8–13 Hz) and beta band (13–30 Hz) remains unsatisfactory. The present study investigated the possibility of using lower-limb stepping motor imagery as the mental task and analysed the EEG difference between imaginary left-leg stepping (L-stepping) and right-leg stepping (R-stepping) movements. An experimental paradigm was designed to collect 5-s motor imagery EEG signals at nine recording sites around the vertex of the brain. Results from eight able-bodied participants indicated that the commonly used mu event-related desynchronisation (ERD) feature exhibited no significant difference between the two imaginary movements for all recording sites and all time intervals within the 5-s motor imagery period. Regarding the other commonly used feature, beta event-related synchronisation, no significant difference between the two imagery tasks was observed for most of the recording sites and time intervals. Instead, theta band (4–8 Hz) ERD significantly differed between the L- and R-stepping imagery tasks at five sites (FC4, C3, CP3, Cz, CPz) within the first 2 s after motor imagery cue onset. The findings from the present study may be a basis for further development of BCI systems for decoding left and right stepping during mental exercise where the two motions are alternately imagined.

Event-related changes detection in sensorimotor rhythm

Brain activities initiate motion in the human body. In our research we try to detect brain electrical activities and generate control signals for robotic devices like prosthetic legs. Human legs are associated with a small representation area in the sensorimotor (SMR) cortex, which is located deep inside the inter hemispheric fissure. It is difficult to observe any electroencephalographic activity related to the legs. Detection of sensorimotor signals, based on leg imagery, could potentially be useful in medical applications, i.e. for systems that are using brain-computer interface for lower limbs assistance. We investigate reactivity of sensorimotor rhythm i.e., mu rhythm, as a result of given tasks, such as, motor execution (ME) and motor imagery (MI) of the leg. Resulting SMR was analyzed, for each task state and evaluated in terms of eventrelated de synchronization and event-related synchronization patterns. Higher power concentration was observed in the foot representation and peripheral areas, during both ME and MI tasks. No contralateral dominance was detected during left or right discrimination tasks. Results provide a foundation for leg imagery based, interfacing and control signals creation. This could be used for locomotion functions' restoration in a lower limb wearable rehabilitation system. Spinal cord injury patients could, also, be potential users of this type of biomechanical systems.

Simultaneous scalp recorded EEG and local field potentials from monkey ventral premotor cortex during action observation and execution reveals the contribution of mirror and motor neurons to the mu-rhythm

The desynchronization of alpha and beta oscillations (mu rhythm) in the central scalp EEG during action observation and action execution is thought to reflect neural mirroring processes. However, the extent to which mirror neurons (MNs) or other populations of neurons contribute to such EEG desynchronization is still unknown. Here, we provide the first evidence that, in the monkey, the neuronal activity recorded from the ventral premotor cortex (PMv) strongly contributes to the EEG changes occurring in the beta band over central scalp electrodes, during executed and observed actions. We simultaneously recorded scalp EEG and extracellular activity, Multi Unit Activity (MUA) and Local Field Potentials (LFP), from area F5 of two macaques executing and observing grasping actions. We found that MUA highly correlates with an increase in high gamma LFP power and, interestingly, such LFP power increase also correlates to EEG beta – and in part also to alpha – desynchronization. In terms of timing of signal changes, the increase in high gamma LFP power precedes the EEG desynchronization, during both action observation and execution, thus suggesting a causal role of PMv neuronal activity in the modulation of the alpha and beta mu-rhythm. Lastly, neuronal signals from deeper layers of PMv exert a greater contribution than superficial layers to the EEG beta rhythm modulation, especially during the motor task. Our findings have clear implications for EEG studies in that they demonstrate that the activity of different populations of neurons in PMv contribute to the generation of the mu-rhythm.

Electroencephalographic modulations during an open- or closed-eyes motor task.

There is fundamental knowledge that during the resting state cerebral activity recorded by electroencephalography (EEG) is strongly modulated by the eyes-closed condition compared to the eyes-open condition, especially in the occipital lobe. However, little research has demonstrated the influence of the eyes-closed condition on the motor cortex, particularly during a self-paced movement. This prompted the question: How does the motor cortex activity change between the eyes-closed and eyes-open conditions? To answer this question, we recorded EEG signals from 15 voluntary healthy subjects who performed a simple motor task (i.e., a voluntary isometric flexion of the right-hand index) under two conditions: eyes-closed and eyes-open. Our results confirmed strong modulation in the mu rhythm (7–13 Hz) with a large event-related desynchronisation. However, no significant differences have been observed in the beta band (15–30 Hz). Furthermore, evidence suggests that the eyes-closed condition influences the behaviour of subjects. This study gives us greater insight into the motor cortex and could also be useful in the brain-computer interface (BCI) domain.

Childhood emotional invalidation and right hemispheric mu suppression during a pain empathy task: An EEG study

ABSTRACTEmpathy is a critical aspect of social behavior, and impairment in empathic processing is linked to hindered social interactions and several disorders. Despite much interest in this topic, our understanding of the developmental and neural involvement for empathic processing is limited. Recent evidence suggests the Mirror Neuron System (MNS) may play a role in this behavior, and that mu rhythm suppression found over the sensorimotor cortices may be a proxy for the MNS. Therefore, we aimed to measure mu rhythm oscillations in response to empathic processing during observation of painful action-based situations using electroencephalogram (EEG). Our second goal was to examine how perceived parental emotional invalidation (EI) during childhood may relate to empathy and influence mu suppression. Our results showed that mu rhythm suppression was strongest over the right hemisphere. EI had a significant influence on this suppression between painful and non-painful images, and was negatively correlated with behavioral measures of empathy. Our findings suggest that perceived childhood EI may decrease empathizing abilities and influence neural responses to the painful experiences of others. Implications from this study could entail clinical intervention targeted at emotional invalidation to foster the healthy development of empathy.

Mu rhythm in the implementation of bimanual coordination task among active versus inactive children with autism spectrum disorder

Mu rhythm in the implementation of bimanual coordination task among active versus inactive children with autism spectrum disorder

EEG beta desynchronization during hand goal-directed action observation in newborn monkeys and its relation to the emergence of hand motor skills

Previous developmental research suggests that motor experience supports the development of action perception across the lifespan. However, it is still unknown when the neural mechanisms underlying action-perception coupling emerge in infancy. The goal of this study was to examine the neural correlates of action perception during the emergence of grasping abilities in newborn rhesus macaques. Neural activity, recorded via electroencephalogram (EEG), while monkeys observed grasping actions, mimed actions and means-end movements during the first (W1) and second week (W2) of life was measured. Event-related desynchronization (ERD) during action observation was computed from the EEG in the alpha and beta bands, two components of the sensorimotor mu rhythm associated with activity of the mirror neuron system (MNS). Results revealed age-related changes in the beta band, but not the alpha band, over anterior electrodes, with greater desynchronization at W2 than W1 for the observation of grasping actions. Additionally, desynchronization to observed grasping actions at W2 was associated with infants’ motor skills – measured by a separate behavioral task – such that more grasping attempts were associated to greater beta ERD. These findings suggest the emergence of an early action-perception system, that relies on motor experience, shortly after birth.

Behavioral preference in sequential decision-making and its association with anxiety.

In daily life, people often make consecutive decisions before the ultimate goal is reached (i.e., sequential decision-making). However, this kind of decision-making has been largely overlooked in the literature. The current study investigated whether behavioral preference would change during sequential decisions, and the neural processes underlying the potential changes. For this purpose, we revised the classic balloon analogue risk task and recorded the electroencephalograph (EEG) signals associated with each step of decision-making. Independent component analysis performed on EEG data revealed that four EEG components elicited by periodic feedback in the current step predicted participants' decisions (gamble vs. no gamble) in the next step. In order of time sequence, these components were: bilateral occipital alpha rhythm, bilateral frontal theta rhythm, middle frontal theta rhythm, and bilateral sensorimotor mu rhythm. According to the information flows between these EEG oscillations, we proposed a brain model that describes the temporal dynamics of sequential decision-making. Finally, we found that the tendency to gamble (as well as the power intensity of bilateral frontal theta rhythms) was sensitive to the individual level of trait anxiety in certain steps, which may help understand the role of emotion in decision-making.

Localizing bicoherence from EEG and MEG

We propose a new method for the localization of nonlinear cross-frequency coupling in EEG and MEG data analysis, based on the estimation of bicoherences at the source level. While for the analysis of rhythmic brain activity, source directions are commonly chosen to maximize power, we suggest to maximize bicoherence instead. The resulting nonlinear cost function can be minimized effectively using a gradient approach. We argue, that bicoherence is also a generally useful tool to analyze phase-amplitude coupling (PAC), by deriving formal relations between PAC and bispectra. This is illustrated in simulated and empirical LFP data. The localization method is applied to EEG resting state data, where the most prominent bicoherence signatures originate from the occipital alpha rhythm and the mu rhythm. While the latter is hardly visible using power analysis, we observe clear bicoherence peaks in the high alpha range of sensorymotor areas. We additionally apply our method to resting-state data of subjects with schizophrenia and healthy controls and observe significant bicoherence differences in motor areas which could not be found from analyzing power differences.

Event-related desynchronization of mu and beta oscillations during the processing of novel tool names

According to the embodied cognition framework, the formation of conceptual representations integrates the type of experience during learning. In this electroencephalographic study, we applied a linguistic variant of a training paradigm, in which participants learned to associate novel names to novel tools while either manipulating or visually exploring them. The analysis focused on event-related desynchronization (ERD) of oscillations in the mu and beta frequency range, which reflects activation of sensorimotor brain areas. After three training sessions, processing names of manipulated tools elicited a stronger ERD of the beta (18–25 Hz, 140–260 ms) and the lower mu rhythm (8–10 Hz, 320–440 ms) than processing names of visually explored tools, reflecting a possible reactivation of experiential sensorimotor information. Given the unexpected result that familiarized pseudo-words elicited an ERD comparable to names of manipulated tools, our findings could reflect a suppression of sensorimotor activity during the processing of objects with exclusively visual features.

Giving A Hand To Pilots With Animated Alarms Based On Mirror System Functioning

Controlled Flight Into Terrain (CFIT) accidents are among the most frequent and deadly accidents in aviation (IATA, 2016). Pilots have sometimes only a few seconds to react to the ‘Pull-Up’ alarm that indicates an imminent collision with the ground. The auditory modality of the alarm can generate stress, which can disrupt cognitive processes (Porcelli et al., 2008) and negatively impact the ability to take timely and appropriate actions (Scholz et al., 2009). While in general humans are less sensitive to auditory stimuli than to visual stimuli (Mrugalska et al. 2016), the auditory component of the ‘Pull-Up’ alarm is loud and prominent whereas its visual component is more discreet (i.e., small text). Consequently, a first step to enhance the efficiency of this alarm would be to increase the conspicuity of its visual component by enlarging the ‘Pull-Up’ text size and to increase its salience by displacing it from the artificial horizon to the bottom of the Primary Flight Display (PFD). However, enlarging the inscription may not be sufficient to cope with the loss of cognitive performance due to stress (BEA, 2009). Previous researched found that watching an action activates premotor cortex and pre-initiates the gesture imitation through the mirror neuron system (Ocampo & Kritikos, 2011). Therefore, presenting a video of the gesture to perform (i.e., a hand pulling the sidestick), in case of imminent impact with the ground, should pre-activate the motor reaction to the alarm and then improve the pilots’ performance in terms of reaction time. The present experiment aimed at assessing whether these ‘Pull-Up’ video better performance than more conventional ‘Pull-Up’ alarms. Both behavioral and electroencephalographic (EEG) results were used to assess the best alarm design.