Non-linear EEG synchronization during observation and execution of simple and complex sequential finger movements

The main aim of this study was to examine the temporal aspects of neuronal changes during the observation and execution of simple and complex tasks to gain a greater understanding of the mirror neuron system’s involvement in complex motor tasks. Eleven right-handed subjects observed simple and complex finger movement sequences. Electroencephalograms were recorded from 19 electrodes. Activity was considered in four frequency bands (8–10, 10–13, 13–20, and 20–30 Hz) using a new measure, synchronization likelihood. The results show that motor tasks of different levels of complexity did not have a significant influence on cortical synchronization. The results also provide additional indirect evidence for mirror neuron activity associated with intransitive tasks. Data are discussed in the light of recent findings from the cognitive and behavioral neuroscience literature.     

Audio-visual facilitation of the mu rhythm

Previous studies demonstrate that perception of action presented audio-visually facilitates greater mirror neuron system (MNS) activity in humans (Kaplan and Iacoboni in Cogn Process 8(2):103–113, 2007) and non-human primates (Keysers et al. in Exp Brain Res 153(4):628–636, 2003) than perception of action presented unimodally. In the current study, we examined whether audio-visual facilitation of the MNS can be indexed using electroencephalography (EEG) measurement of the mu rhythm. The mu rhythm is an EEG oscillation with peaks at 10 and 20 Hz that is suppressed during the execution and perception of action and is speculated to reflect activity in the premotor and inferior parietal cortices as a result of MNS activation (Pineda in Behav Brain Funct 4(1):47, 2008). Participants observed experimental stimuli unimodally (visual-alone or audio-alone) or bimodally during randomized presentations of two hands ripping a sheet of paper, and a control video depicting a box moving up and down. Audio-visual perception of action stimuli led to greater event-related desynchrony (ERD) of the 8–13 Hz mu rhythm compared to unimodal perception of the same stimuli over the C3 electrode, as well as in a left central cluster when data were examined in source space. These results are consistent with Kaplan and Iacoboni’s (in Cogn Process 8(2):103–113, 2007), findings that indicate audio-visual facilitation of the MNS; our left central cluster was localized approximately 13.89 mm away from the ventral premotor cluster identified in their fMRI study, suggesting that these clusters originate from similar sources. Consistency of results in electrode space and component space support the use of ICA as a valid source localization tool.     

Preparatory band specific premotor cortical activity differentiates upper and lower extremity movement

Event related desynchronization (ERD) allows evaluation of brain signals in multiple frequency dimensions. The purpose of this study was to determine left hemispheric non-primary motor cortex differences at varying frequencies of premovement ERD for similar movements by end-effectors of the upper and lower extremities. We recorded 32-channel electroencephalography (EEG) while subjects performed self-paced right ankle dorsiflexion and wrist extension. Electromyography (EMG) was recorded over the tibialis anterior and extensor carpi ulnaris. EEG was analyzed for premovement ERD within the alpha (8–12 Hz), low beta (13–18 Hz) and high beta (18–22 Hz) frequencies over the premotor, motor, and sensory areas of the left and mesial cortex from −1.5 to 0 s before movement. Within the alpha and high beta bands, wrist movements showed limited topography, but greater ERD over posterior premotor cortex areas. Alpha ERD was also significantly greater over the lateral motor cortex for wrist movements. In the low beta band, wrist movements provided extensive ERD differences to include the left motor and mesial/lateral premotor areas, whereas ankle movements showed only limited ERD activity. Overall, alpha and high beta activity demonstrated distinctions that are consistent with mapping of wrist and ankle representations over the sensorimotor strip, whereas the low beta representation demonstrated the clearest distinctions between the limbs over widespread brain areas, particularly the lateral premotor cortex. This suggests limited leg premovement activity at the dorsolateral premotor cortex. Low beta ERD may be reflect joint or limb specific preparatory activity in the premotor area. Further work is required to better evaluate the extent of this low beta activity for multiple comparative joints.     

Event-related desynchronization of motor cortical oscillations in patients with multiple system atrophy

Multiple system atrophy (MSA) is a progressive neurodegenerative disease characterized by parkinsonism (MSA-P), cerebellar and autonomic deficits. In Parkinson’s disease (PD), an impaired modulation of motor cortical mu and beta range oscillations may be related to the pathophysiology of bradykinesia. Event-related desynchronization (ERD) of these oscillations occur for 1–2 s preceding a voluntary movement in normal subjects and patients with PD treated with levodopa while only lasting around 0.5 s in untreated patients. Motor cortical rhythms were recorded from subdural strip electrodes in three patients with MSA-P while taking their regular dopaminergic medications. Following a ready cue, patients performed an externally cued wrist extension movement to a go cue. In addition, recordings were obtained during imagined wrist extension movements to the same cues and during self-paced wrist extensions. ERD and event-related synchronization were examined in subject-specific frequency bands. All patients showed movement-related ERD in subject-specific frequency bands below ~40 Hz in both externally cued and self-paced conditions. Preparatory ERD latency preceding self-cued movement was 900 ms in one patient and at or after movement onset in the other two patients. In the externally cued task, a short lasting (<1.3 s) ready cue-related ERD that was not sustained to movement onset was observed in two patients. Imagined movements resulted in go cue-related ERD with a smaller magnitude in the same two patients. These results indicate that the modulation of motor cortical oscillations in patients with MSA that are treated with levodopa is similar to that occurring in untreated patients with PD. The findings suggest that cortical activation in patients with MSA is diminished, may be related to pathophysiological changes occurring in the basal ganglia and correlates with the poor clinical response that these patients typically obtain with dopaminergic therapy.     

EEG Correlates of Action Observation in Humans

To investigate electrophysiological correlates of action observation electroencephalogram (EEG) was recorded while participants observed repetitive biological (human) or non-biological movements (at a rate of 2 Hz). Steady-state evoked potentials were analyzed and their neural sources were investigated using low resolution electromagnetic tomography analysis (LORETA). Results revealed significantly higher activation in the primary motor and premotor cortex, supplementary motor area as well as the posterior parietal cortices during observation of biological movements, supporting mirror properties of cortical motor neurons. In addition interregional communication was analyzed. Increased coherence for distributed networks at delta (0.5–4 Hz) and lower alpha (8–10 Hz) frequencies were obtained suggesting integration and functional coupling between the activated cortical regions during human action observation.     

Noninvasive Epileptic Seizure Localization from Stochastic Behavior of Short Duration Interictal High Density Scalp EEG Data

The stochastic behavior of the phase synchronization index (SI) in different EEG bands was examined for noninvasive localization of the epileptogenic areas from the short duration (30–60 s), seizure-free and spike-free high density (256 channel) scalp EEG data. We also examined the cross-frequency and cross-electrode coupling in different EEG bands. EEG data of four subjects was used. The seizure areas were localized with subdural recordings with an 8×8 grid electrode array. It was found that the stochastic behavior of the SI in low gamma band (30–50 Hz) was higher in epileptogenic areas. The beta (12–30 Hz) band also showed similar tendencies. The stochastic behavior in theta (3–7 Hz) band was depressed in the seizure area while it was widespread in large areas over the scalp in the alpha (7–12 Hz) band. The stochastic behavior of the cross-frequency and cross-electrode couplings in theta–gamma, alpha–gamma and beta–gamma bands were decreased in the seizure areas for all four subjects. These findings suggest that it is possible to localize the epileptogenic areas from the short duration seizure-free and spike-free high density scalp EEG data.     

Spatiotemporal analysis of alpha frequency components with the ERD technique

EEG data from 30 channels were recorded during movement and reading tasks and analyzed in the three frequency bands 6- 8 Hz, 8-10 Hz and 10-12 Hz. For each frequency band, the ERD (event-related desynchronization) was quantified and displayed in the form of time courses and maps. The results show that the ERD pattern varies with the frequency component analyzed. In general, upper alpha components (10-12 Hz) demonstrate a short-lasting, task-specific and localized ERD; the ERD of lower alpha components is long-lasting (greater than 1 sec) and widespread. The ERD can be interpreted as a sign of cortical activation, whereby desynchronization of upper alpha components may reflect more task-specific processes, and desynchronization of middle and lower alpha components may be related to the level of expectancy and attention.     

Event-Related Desynchronization evoked by auditory stimuli

Summary Event-Related Desynchronization (ERD) and Synchronization (ERS) of several EEG alpha frequencies was studied in 19 subjects during the presentation of linguistic and/or melodic auditory stimuli. The stimulus length was 1300 msec (+/–100 msec) and the interstimulus interval was 2000 msec. A significant ERD was found during auditory stimulation in the 8–10 Hz and 10–12 Hz alpha frequency bands, and there were also significant differences in the spatiotemporal pattern of the ERD between these frequency bands. Significant ERD was elicited also in the 10–11 and 11–12 Hz frequency bands by auditory stimulation. There were no significant differences between these one-hertz frequency bands. The subjects were assigned to two analysis groups according to their individual alpha peak frequency (10–11 or 11–12 Hz) at rest. The ERD in these groups reached statistical significance and there were significant differences between the groups. The ERD of the two groups differed significantly also when their EEG data was studied in the 10–12 Hz frequency band. The results from this study show that ERD is not modality-specific, i.e., it can be elicited also by auditory stimuli. Moreover, they indicate that it is important to control over interindividual variation in the EEG when studying the ERD phenomenon.This study was financially supported by the The Cultural Scholarship Foundation of Southwestern Finland (Varsinais-Suomen Kulttruurirahasto) and by the Council for Social Sciences, Academy of Finland (project 7338).     

Investigating the relationship between fetus EEG,respiratory, and blood pressure signals during maturation using wavelet transform

In this study, we introduce the fast wavelet transform as a method for characterizing maturational changes in electrocortical activity, respiratory activity, and blood pressure in fetal lambs in early (110–122 days), mid (123–135 days), and late (136–144 days) third trimester (term 145 days). Each recording was 2 hr in duration. Wavelet decomposition was performed for six sets of parametersD _2j where 1≤j≤6. The six series wavelet transforms represent the following signal frequency bands: 1. 16–32 Hz; 2. 8–16 Hz; 3. 4–8 Hz; 4. 2–4 Hz; 5. 1–2 Hz; 6. 0.5–1 Hz. In the early group, power in the electrocephalogram (EEG) was highest in the fourth wavelet band, with relatively low power in the other bands. Increase in gestational age was characterized by increased power in all four wavelet bands. Power in the first wavelet band was significantly increased during low-voltage fast activity (LVFA) in the late group. The respiratory and blood pressure signals showed common frequency components with respect to time and were coincident with the LVFA EEG signal. Respiratory activity was only observed during some of the LVFA periods and was completely absent during high-voltage slow activity (HVSA) EEG. The respiratory signal showed dominant power in the fourth wavelet band, and less power in the third and fifth band. The blood pressure signal was also characterized by dominant power in the fourth wavelet band. This power was significantly increased during periods of respiratory activity. These results suggest a strong relationship between fetal EEG, blood pressure, and breathing movements.     

Movement-related changes in cortical oscillatory activity in ballistic,sustained and negative movements

We studied movement-related EEG oscillatory changes in the alpha, beta and low-gamma frequency bands in three different paradigms of movement, namely ballistic, sustained, and negative (muscle relaxation). A time-frequency analysis of non-phase-locked activity in the 7–47 Hz range was performed on movement-centred EEG sweeps using wavelet filters and Gabor transforms. All three movements were accompanied by a decrease in beta activity that began contralaterally about 1.5 s prior to the onset of movement but that extended to both sides near the beginning of the movement. This decrease was followed by a rebound after the end of the movement in the ballistic and negative movements. A decrease was also seen in the alpha band during the three paradigms, which began later (1 s before movement) and lasted longer. An increase in gamma activity was only seen during ballistic and sustained movements, while a decrease in gamma energy was observed during negative movements. It was concluded that changes in the beta band of the EEG before movement are related to the preparation for the movement, but an important afferent component may be present in the later changes. Gamma band activity may be just involved in the execution of the movement, related to muscle contraction. Electronic Publication     

Changes in the Mu Rhythm in Different Types of Motor Activity and on Observation of Movements

A complex study of the characteristics of the mu rhythm with subjects in different states was performed: during observation of movements and during execution of their own movements. Stimuli for movement observation were presented on a monitor screen and consisted of a set of movements for which published data show that mirror neurons mount different responses. In particular, these are movements with or without an expressed goal and various tool manipulations. Studies of the effects of the subjects’ movements on the mu rhythm were performed using situations in which subjects executed their own movements and situations in which they imitated movements seen on a monitor screen. Different methods of processing EEG traces and analyzing evoked desynchronization (suppression) of the mu rhythm were used. These experiments showed that presentation of video recordings of different types of movements induced moderate suppression of the spectral power of the mu rhythm. There were no significant differences in the depression of the mu rhythm on observation of movements performed with or without a clear movement goal or movements for which the goal was reached with a tool. Thus, changes in the mu rhythm and suppression of the mirror neuron system on observation of an executed movement were significantly different. Analysis of the time development of mu rhythm depression showed that changes which were quite clearly apparent at the beginning of observation gradually weakened, generally decreasing to statistically insignificant values at the final stages. The “habituation” effect seen in changes in the mu rhythm indicates a possible role for the mechanisms of involuntary and voluntary attention in mu rhythm depression. The “habituation” effect was also characteristic of more marked changes in the mu rhythm seen on execution of movements by the subjects. Significant differences were seen between depression of the mu rhythm evoked by the subjects’ own movements and on imitation of movements. The habituation effect was more marked in the latter case. These differences in the nature of mu rhythm depression may be associated with differences in activation of those areas of the cortex responsible for movement preparation and programming and with changes associated with the rapid development of motor automation.     

Frequency analysis of electroencephalogram recorded from a bottlenose dolphin (<Emphasis Type="Italic">Tursiops</Emphasis> <Emphasis Type="Italic">truncatus</Emphasis>) with a novel method during transportation by truck

In order to obtain information regarding the correlation between an electroencephalogram (EEG) and the state of a dolphin, we developed a noninvasive recording method of EEG of a bottlenose dolphin (Tursiops truncatus) and an extraction method of true-EEG (EEG) from recorded-EEG (R-EEG) based on a human EEG recording method, and then carried out frequency analysis during transportation by truck. The frequency detected in the EEG of dolphin during apparent awakening was divided conveniently into three bands (5–15, 15–25, and 25–40 Hz) based on spectrum profiles. Analyses of the relationship between power ratio and movement of the dolphin revealed that the power ratio of dolphin in a situation when it was being quiet was evenly distributed among the three bands. These results suggested that the EEG of a dolphin could be detected accurately by this method, and that the frequency analysis of the detected EEG seemed to provide useful information for understanding the central nerve activity of these animals.     

Modulation of the human mirror neuron system during cognitive activity

In this experiment we examined the relationship between the mirror neuron system and increased attention caused by task demands. Whole head MEG recordings were made from 13 participants who were asked to passively observe finger movement sequences, observe these sequences with the knowledge they would later have to perform the sequence presented, and finally, to perform a nonmotor mathematics task based on the finger-movement sequences. Beta-band (15-35 Hz) sensorimotor desynchronization was found in overlapping areas during passive observation and in a separate motor execution condition, indicating the activity of the human mirror neuron system. The beta desynchronization in these areas was enhanced relative to passive viewing when participants had to watch the stimuli to later imitate and when they performed the mathematics task, indicating that mirror neuron system activity can be modulated by attention.     

Three-dimensional Localization of Abnormal EEG Activity in Migraine

Investigating the brain of migraine patients in the pain-free interval may shed light on the basic cerebral abnormality of migraine, in other words, the liability of the brain to generate migraine attacks from time to time. Twenty unmedicated “migraine without aura” patients and a matched group of healthy controls were investigated in this explorative study. 19-channel EEG was recorded against the linked ears reference and was on-line digitized. 60 × 2-s epochs of eyes-closed, waking-relaxed activity were subjected to spectral analysis and a source localization method, low resolution electromagnetic tomography (LORETA). Absolute power was computed for 19 electrodes and four frequency bands (delta: 1.5–3.5 Hz, theta: 4.0–7.5 Hz, alpha: 8.0–12.5 Hz, beta: 13.0–25.0 Hz). LORETA “activity” (=current source density, ampers/meters squared) was computed for 2394 voxels and the above specified frequency bands. Group comparison was carried out for the specified quantitative EEG variables. Activity in the two groups was compared on a voxel-by-voxel basis for each frequency band. Statistically significant (uncorrected P < 0.01) group differences were projected to cortical anatomy. Spectral findings: there was a tendency for more alpha power in the migraine that in the control group in all but two (F4, C3) derivations. However, statistically significant (P < 0.01, Bonferroni-corrected) spectral difference was only found in the right occipital region. The main LORETA-finding was that voxels with P < 0.01 differences were crowded in anatomically contiguous cortical areas. Increased alpha activity was found in a cortical area including part of the precuneus, and the posterior part of the middle temporal gyrus in the right hemisphere. Decreased alpha activity was found bilaterally in medial parts of the frontal cortex including the anterior cingulate and the superior and medial frontal gyri. Neither spectral analysis, nor LORETA revealed statistically significant differences in the delta, theta, and beta bands. LORETA revealed the anatomical distribution of the cortical sources (generators) of the EEG abnormalities in migraine. The findings characterize the state of the cerebral cortex in the pain-free interval and might be suitable for planning forthcoming investigations.     

Spatial and Frequency Differences of Neuromagnetic Activities Between the Perception of Open- and Closed-class Words

The present study investigated the spatial and frequency differences of neuromagnetic activities between the perception of open- and closed-class words by using a 275-channel whole head magnetoencephalography (MEG) system. Two groups of words, 110 open-class and 110 closed-class, were presented visually and auditorily simultaneously. The data of 12 healthy subjects were analyzed with synthetic aperture magnetometry (SAM) which can identify the frequency-dependent volumetric distribution of evoked magnetic fields (EMFs). Both vocabulary classes elicited spectral power changes in the left inferior frontal gyrus (Broca’s area) and left posterior-superior temporal gyrus (Wernicke’s area) within 70–120 Hz. However, the open-class words elicited event-related desynchronization (ERD) while the closed-class words elicited event-related synchronization (ERS) in the two areas within 70–120 Hz. In addition, the open-class words also elicited ERS in the right inferior frontal gyrus, right middle frontal gyrus and right inferior parietal lobe within 1–8 Hz, but the closed-class words only elicited ERD in the right inferior frontal gyrus within 1–8 Hz. Furthermore, there were ERD in the right posterior-superior temporal gyrus within 120–200 Hz for the open-class words, but not for the closed-class words. These results indicate that open- and closed-class words are processed differently in the brain, not only in the anatomical substrates, but also in the frequency range of neuromagnetic activity.     

EEG inter/intra-hemispheric coherence and asymmetric responses to visual stimulations

In the past, many studies have claimed that extremely low frequency (ELF) magnetic field (MF) exposures could alter the human electroencephalographic (EEG) activity. This study aims at extending our ELF pilot study to investigate whether MF exposures at ELF in series from 50, 16.66, 13, 10, 8.33 to 4 Hz could alter relative power within the corresponding EEG bands. 33 human subjects were tested under a double-blind and counter-balanced conditions. The multiple repeated three-way analysis of variance (ANOVA) mixed design (within and between-subject) analysis was employed followed by post-hoc t-tests and Bonferroni alpha-correction. The results from this study have shown that narrow alpha1 (7.5–9.5 Hz) and alpha2 (9–11 Hz) bands, associated with 8.33 and 10 Hz MF exposures, were significantly (p < 0.0005) lower than control over the temporal and parietal regions within the 10–16 min of first MF exposure session and the MF exposures were significantly higher than control of the second session MF exposure (60–65 min from the commencement of testing). Also, it was found that the beta1 (12–14 Hz) band exhibited a significant increase from before to after 13-Hz first MF exposure session at frontal region. The final outcome of our result has shown that it is possible to alter the human EEG activity of alpha and beta bands when exposed to MF at frequencies corresponding to those same bands, depending on the order and period of MF conditions. This type of EEG synchronisation of driving alpha and beta EEG by alpha and beta sinusoidal MF stimulation, demonstrated in this study, could possibly be applied as therapeutic treatment(s) of particular neurophysiological abnormalities such as sleep and psychiatric disorders.     

Observation of static gestures influences speech production

Research investigating ‘mirror neurons’ has demonstrated the presence of an observation–execution matching system in humans. One hypothesized role for this system might be to aid in action understanding by encoding the underlying intentions of the actor. To investigate this hypothesis, we asked participants to observe photographs of an actor making orofacial gestures (implying verbal or non-verbal acts), and to produce syllables that were compatible or incompatible with the gesture they observed. We predicted that if mirror neurons encode the intentions of an actor, then the pictures implying verbal gestures would affect speech production, whereas the non-verbal gestures would not. Our results showed that the observation of compatible verbal gestures facilitated verbal responses, while incompatible verbal gestures caused interference. Although this compatibility effect did not reach statistical significance when the photographs implied a non-verbal act, responses were faster on average when the gesture implied the use of similar articulators as those involved with the production of the target syllable. Altogether, these behavioral findings compliment previous neuroimaging studies indicating that static pictures portraying gestures activate brain regions associated with an observation–execution matching system.     

Interactive visuo-motor therapy system for stroke rehabilitation

We present a virtual reality (VR)-based motor neurorehabilitation system for stroke patients with upper limb paresis. It is based on two hypotheses: (1) observed actions correlated with self-generated or intended actions engage cortical motor observation, planning and execution areas (“mirror neurons”); (2) activation in damaged parts of motor cortex can be enhanced by viewing mirrored movements of non-paretic limbs. We postulate that our approach, applied during the acute post-stroke phase, facilitates motor re-learning and improves functional recovery. The patient controls a first-person view of virtual arms in tasks varying from simple (hitting objects) to complex (grasping and moving objects). The therapist adjusts weighting factors in the non-paretic limb to move the paretic virtual limb, thereby stimulating the mirror neuron system and optimizing patient motivation through graded task success. We present the system’s neuroscientific background, technical details and preliminary results.     

Beta- and gamma-frequency coupling between olfactory and motor brain regions prior to skilled,olfactory-driven reaching

A major question in neuroscience concerns how widely separated brain regions coordinate their activity to produce unitary cognitive states or motor actions. To investigate this question, we employed multisite, multielectrode recording in rats to study how olfactory and motor circuits are coupled prior to the execution of an olfactory-driven, GO/NO-GO variant of a skilled, rapidly executed (∼350–600 ms) reaching task. During task performance, we recorded multi-single units and local field potentials (LFPs) simultaneously from the rats’ olfactory cortex (specifically, the posterior piriform cortex) and from cortical and subcortical motor sites (the caudal forepaw M1, and the magnocellular red nucleus, respectively). Analyses on multi-single units across areas revealed an increase in beta-frequency spiking (12–30 Hz) during a ∼100 ms window surrounding the Final Sniff of the GO cue before lifting the arm (the “Sniff-GO window”) that was seldom seen when animals sniffed the NO-GO cue. Also during the Sniff-GO window, LFPs displayed a striking increase in beta, low-gamma, and high-gamma energy (12–30, 30–50, and 50–100 Hz, respectively), and oscillations in the high gamma band appeared to be coherent across the recorded sites. These results indicate that transient, multispectral coherence across cortical and subcortical brain sites is part of the coordination process prior to sensory-guided movement initiation. Raymond Hermer-Vazquez, Linda Hermer-Vazquez these two authors contributed equally.     

Spatiotemporal study of bereitschaftspotential and Event-Related Desynchronization during voluntary movement in Parkinson's disease

Summary Bereitschaftspotential (BP) and Event-Related Desynchronization (ERD) were simultaneously recorded during a voluntary wrist flexion in 10 patients with Parkinson's disease (PD) treated with L-Dopa therapy and 10 control subjects. BP and ERD were analyzed 2 s before and 0.5 s after the movement, during two successive left and right experimental conditions. ERD (9–11 Hz) was computed from 11 source derivations (frontocentral, central, parietocentral). The BP was averaged from these 11 electrodes. For the BP, no spatiotemporal difference was found between the two groups. BP began bilaterally over the 3 groups of electrodes, 1250 ms before movement onset for the right flexion and 1500 ms for the left flexion. A contralateral predominance appeared 500 ms before movement onset over the central area. ERD began in the control group 1750 ms before movement over the contralateral central area, and then appeared bilaterally after its execution. In the PD group, the ERD appeared with a shorter latency than in the control group, 1250 ms (left flexion) and 1000 ms (right flexion) before movement onset; diffusion over the ipsilateral side was found 500 ms before movement onset. ERD also involved the frontocentral area and could be interpreted as a compensatory activity of the supplementary motor area. These findings suggest that with Parkinsonian and control subjects, ERD gives additional and maybe more information than the BP about changes of cortical activity during the motor preparation period. In the PD group the delay of ERD appearance seems to confirm that the programming of movement would be affected, thus explaining partially akinesia.