Event-related Desynchronization Responses Research Articles

Exploring altered oscillatory activity in the anterior cingulate cortex after nerve injury: Insights into mechanisms of neuropathic allodynia

While neural oscillations play a critical role in sensory perception, it remains unclear how these rhythms function under conditions of neuropathic allodynia. Recent studies demonstrated that the anterior cingulate cortex (ACC) is associated with the affective-aversive component of pain, and plasticity changes in this region are closely linked to abnormal allodynic sensations. Here, to study the mechanisms of allodynia, we recorded local field potentials (LFPs) in the bilateral ACC of awake-behaving rats and compared the spectral power and center frequency of brain oscillations between healthy and CCI (chronic constriction injury) induced neuropathic pain conditions. Our results indicated that activation of the ACC occurs bilaterally in the presence of neuropathic pain, similar to the healthy condition. Furthermore, CCI affects both spontaneous and stimulus-induced activity of ACC neurons. Specifically, we observed an increase in spontaneous beta activity after nerve injury compared to the healthy condition. By stimulating operated or unoperated paws, we found more intense event-related desynchronization (ERD) responses in the theta, alpha, and beta frequency bands and faster alpha center frequency after CCI compared to before CCI. Although the behavioral manifestation of allodynia was more pronounced in the operated paw than the unoperated paw following CCI, there was no significant difference in the center frequency and ERD responses observed in the ACC between stimulation of the operated and unoperated limbs. Our findings offer evidence supporting the notion that aberrancies in ACC oscillations may contribute to the maintenance and development of neuropathic allodynia.

Development of an Application That Implements a Brain–Computer Interface to an Upper-Limb Motor Assistance Robot to Facilitate Active Exercise in Patients: A Feasibility Study

In this study, we aimed to evaluate the effectiveness of a brain robot in rehabilitation that combines motor imagery (MI), robotic motor assistance, and electrical stimulation. Thirteen in-patients with severe post-stroke hemiplegia underwent electroencephalography (EEG), measured according to the international 10–20 method, during MI. The dicephalus robotic system (DiC) was activated by detecting event-related desynchronization (ERD) using the Markov switching model (MSM) and relative power (RP) from the EEG of the motor cortex (C3 and C4). The reaction times (the time between ERD detection and DiC activation) of the MSM and RP were compared using Wilcoxon’s signed rank sum test. ERD was detected in all 13 and 12 patients with the MSM and RP, respectively. The DiC reaction time for the ERD detection process was significantly shorter for the MSM (13.02 ± 0.16 s) than for the RP (19.95 ± 7.45 s) (W = 9, p = 0.0037). The results of this study suggest that ERD responses can be detected in the motor cortex during MI in patients with severe upper-extremity paralysis; the MSM is more effective than the RP in detecting ERD when the EEG signal is used as a switch to activate the robot, and the reaction time to detect the signal is shorter.

Decreased neural inhibitory state in fibromyalgia pain: A cross-sectional study

Chronic pain is one of the most common and challenging symptoms in fibromyalgia (FM). Currently, self-reported pain is the main criterion used by clinicians assessing patients with pain. However, it is subjective, and multiple factors can affect pain levels. In this study, we investigated the neural correlates of FM pain using conditioned pain modulation (CPM), electroencephalography (EEG), and transcranial magnetic stimulation (TMS). In this cross-sectional neurophysiological analysis of a randomized, double-blind controlled trial, 36 patients with fibromyalgia were included. We analyzed CPM, EEG variables and TMS measures and their correlation with pain levels as measured by a visual analog scale. Univariate and multivariate linear regression analyses were performed to identify the predictors of pain severity. We found: (1) no association between pain levels and CPM; (2) an association between reduced alpha and beta power over the central region in resting-EEG and higher pain levels; (3) an association between smaller event-related desynchronization (ERD) responses in theta and delta bands over the central region and higher pain levels; (4) an association between smaller ERD responses in theta and delta bands and smaller intracortical inhibition and higher intracortical facilitation ratios; (5) an association between smaller ERD responses in delta band and reduced CPM. Our results do not support CPM as a biomarker for pain intensity in FM. However, our specific EEG findings showing the relationship between pain, CPM and TMS measures suggest that FM leads to a disruption of inhibitory neural modulators and thus support CPM as a likely predictive marker of disrupted pain modulation system. These neurophysiological markers need to be further explored in potential future trials as to find novel targets for the treatment of FM.

Action Observation of Own Hand Movement Enhances Event-Related Desynchronization.

A stroke occurs when blood flow to the brain is critically reduced or blocked, potentially resulting in motor paralysis. One of the most promising and effective neurorehabilitation methods for strokes is a closed-loop brain-computer interface (BCI) based on the motor imagery (MI). For the design of MI-based BCI, action observation (AO) during MI facilitates the detection of a user's motor intention. In this paper, we investigated whether or not the AO's targeted objects (the hand of a participant or another person) affects brain activity during MI. To investigate the differences in brain activity induced by the targeted objection, we recorded electroencephalography (EEG) data of 15 healthy right-handed males during three different conditions: 1) MI and AO of a participant's hand (MI + ownAO); 2) MI and AO of a non-participant's hand (MI + otherAO); and 3) MI only. The results showed that the event-related desynchronization (ERD) responses in the alpha frequency band (8-13 Hz) during MI + ownAO over the sensorimotor area (at the C3 and C4 channel locations) were stronger than those during the other two conditions. The results also showed that the difference between the participants' and non-participants' hands affected ERD responses during MI + ownAO and MI + otherAO.

The peak frequency of motor-related gamma oscillations is modulated by response competition

Movement execution generally occurs in an environment with numerous distractors, and requires the selection of a motor plan from multiple possible alternatives. However, the impact of such distractors on cortical motor function during movement remains largely unknown. Previous studies have identified two movement-related oscillatory responses that are critical to motor planning and execution, and these responses include the peri-movement beta event-related desynchronization (ERD) and the movement-related gamma synchronization (MRGS). In the current study, we investigate how visual distractors cuing alternative movements modulate the beta ERD and MRGS responses. To this end, we recorded magnetoencephalography (MEG) during an arrow-based version of the Eriksen flanker task in 42 healthy adults. All MEG data were transformed in to the time-frequency domain and the beta ERD and MRGS responses were imaged using a beamformer. Virtual sensors (voxel time series) were then extracted from the peak voxels of each response for the congruent and incongruent flanker conditions separately, and these data were examined for conditional differences during the movement. Our results indicated that participants exhibited the classic “flanker effect,” as they responded significantly slower during incongruent relative to congruent trials. Our most important MEG finding was a significant increase in the peak frequency of the MRGS in the incongruent compared to the congruent condition, with no conditional effect on response amplitude. In addition, we found significantly stronger peri-movement beta ERD responses in the ipsilateral motor cortex during incongruent compared to congruent trials, but no conditional effect on frequency. These data are the first to show that the peak frequency of the MRGS response is linked to the task parameters, and varies from trial to trial in individual participants. More globally, these data suggest that beta and gamma oscillations are modulated by visual distractors causing response competition.

Effects of light wavelength on MEG ERD/ERS during a working memory task

We investigated the effects of light wavelengths on cortical oscillatory activity associated with working memory processes. Cortical activity responses were measured using magnetoencephalography (MEG) while participants performed an auditory Sternberg memory task during exposure to light of different wavelength. Each trial of the memory task consisted of four words presented as a memory set and one word presented as a probe. All words were presented audibly. Participants were instructed to indicate whether the probe word was or was not presented within the memory set. A total of 90 trials were conducted under the light exposure. Event-related synchronization (ERS) and event-related desynchronization responses in the alpha frequency range during the task were analyzed. Results showed that, during memory encoding, ERS responses were significantly greater in the short-wavelength (blue) light condition than in the middle-wavelength (green) light condition, approximately 20–30min after the onset of light exposure. Behavioral performance was very high throughout the experiment and there was no difference between the light conditions. Although the light effects were not observed in behavior, the result of ERS suggests that 20–30min of exposure to blue light enhances cortical activity related to active memory maintenance and/or attention to auditory stimuli.

Spectral–temporal analysis of cortical oscillations during lexical processing

We investigated the oscillatory neural correlates of auditory lexical processing in healthy adults. Synthetic aperture magnetometry was used to characterize the timing of event-related desynchronization (ERD)/event-related synchronization (ERS) in superior temporal gyri following low-frequency and high-frequency words in contrast to nonwords. ERS and ERD responses were found with both word and nonword stimuli. Analysis of power revealed significantly elevated θ-α range (6-14 Hz) ERD in response to words compared with nonwords (left hemisphere: 390-945 ms poststimulus). Furthermore, a burst of ERS in the γ band (40-50 Hz, centered at 410 ms poststimulus) distinguished high-frequency and low-frequency words, and also displayed left-hemispheric enhancement following words. Results demonstrate a clear neural correlate of lexical access and provide a basis for further study of spectral-temporal brain activity during language processing.

Electrophysiological correlates of memory processing in early Finnish–Swedish bilinguals

Event-related desynchronization (ERD) and event-related synchronization (ERS) of the 1–30 EEG frequencies were studied in eight early Finnish–Swedish bilinguals during an auditory bilingual Sternberg memory task using Finnish–Swedish cognates as stimuli. Only subtle differences between languages were expected, since cognates have been assumed to have shared conceptual representations in the bilingual memory. Encoding elicited theta and alpha frequency ERS and beta frequency ERD responses in both languages. Retrieval elicited theta ERS and alpha and beta ERD responses. Some statistically significant differences between encoding and retrieval in Finnish versus Swedish emerged: greater theta and alpha ERS responses were observed during encoding in Swedish than during encoding in Finnish. During between-language retrieval, later-appearing theta ERS and alpha ERD responses were elicited as compared to within-language retrieval. These delayed oscillatory responses might reflect the involvement of central executive attentional functions in relation to language switching.

Brain oscillatory responses during the different stages of an auditory memory search task in children

We assessed brain oscillatory responses of the 4-30 Hz electroencephalographic frequency bands in children (mean age 13 years) during the different stages of an auditory memory search, namely the encoding of four words and recognition of the positive and negative probe words. In children, theta (approximately 4-6 Hz) electroencephalographic responses during recognition were of greater magnitude than those during encoding and alpha (approximately 8-12 Hz) event-related synchronization responses during encoding increased with increasing memory load. During recognition, greater magnitude alpha and beta (>12 Hz) event-related desynchronization responses were observed during the presentation of the positive probe as compared with the negative. Complex patterns of theta, alpha and beta frequency brain oscillatory responses during auditory information processing are present already in children of age approximately 13 years.

Brain oscillatory 4–30 Hz responses during a visual n-back memory task with varying memory load

Brain oscillatory responses of 4–30 Hz EEG frequencies elicited during the performance of a visual n-back task were examined in 36 adult volunteers. Event-related desynchronization (ERD) and event-related synchronization (ERS) responses were examined separately for targets and non-targets in four different memory load conditions (0-, 1-, 2- and 3-back). The presentation of all stimuli in all memory load conditions elicited long-lasting theta frequency (~ 4–6 Hz) ERS responses which were of greater magnitude for the target stimuli as compared to the non-target stimuli. Alpha frequency range (~ 8–12 Hz) ERD responses were observed in all memory load conditions for both targets and non-targets. The duration of these alpha ERD responses increased with increasing memory load and reaction time. In all memory load conditions, early appearing beta rhythm (~ 14–30 Hz) ERD responses were elicited, and with increasing memory load, these beta ERD responses became longer in duration. Additionally, beta ERS responses were observed in the 0- and 1-back memory load conditions. The current results reveal a complex interplay between brain oscillations at different frequencies during a cognitive task performance.

Event-related desynchronization/synchronization during an auditory–verbal working memory task in mild Parkinson's disease

Objective Event-related desynchronization (ERD) and synchronization (ERS) were studied during an auditory–verbal working memory task in patients suffering from Parkinson's disease (PD). Methods PD patients ( n=7, mean age 59) at a mild stage of the disease volunteered in the study. A group of healthy subjects ( n=10, mean age 61) served as control group. ERD and ERS of the 1–25 Hz EEG frequencies were studied using wavelet transforms during memory encoding and retrieval. Results Both groups performed equally well on the memory task. Statistically significant differences in ERD/ERS responses were observed in posterior electrodes during encoding of the memory set due to the fact that alpha (∼10–15 Hz) ERS was elicited in the controls, but not in the PD group. In broad frequency bands (∼6–25 Hz) ERD responses were observed in both groups during memory retrieval. A pre-stimulus alpha ERS seen in the control group was absent in the PD group. Conclusions The results of this preliminary study indicate that Parkinson's disease might affect brain oscillatory responses in the alpha frequency range in the encoding phase of auditory–verbal working memory. Significance The ERD/ERS patterns may reflect neurophysiological alterations in the processes underlying working memory deficits in PD.

Brain oscillatory 1–30 Hz EEG ERD/ERS responses during the different stages of an auditory memory search task

Event-related desynchronization (ERD) and event-related synchronization (ERS) responses of 1–30 Hz EEG frequencies during the different stages of an auditory Sternberg memory task were examined. The ERD/ERS responses were examined separately for successive memory set items (four) and for the two recognition conditions (YES/NO). The presentation of the memory set elicited ERS responses in the theta and alpha frequencies, and also beta ERD responses. These ERD/ERS responses elicited during encoding were found to evolve with successive memory set item presentation. The ERD/ERS responses elicited during the presentation of the probe dissociated significantly between the two recognition conditions (YES/NO). When the probe was included in the memory set (YES condition), recognition elicited stronger alpha and beta frequency ERD responses as compared to the NO condition. The findings from the current study verify that alpha ERD/ERS responses robustly dissociate between auditory encoding and recognition. The increasing alpha ERS responses with increasing memory set item presentation during encoding may be correlates of the functioning phonological loop, active memory maintenance and/or attention. The alpha ERD responses during recognition are undoubtedly associated with auditory memory search processes and distinguish between previously presented versus not presented verbal material. We propose that alpha ERD/ERS responses reflect explicitly auditory memory processes, discriminating between auditory encoding and recognition. Theta ERS responses may be associated with working memory processes, and possibly more specifically with the functioning of the central executive. Beta ERD/ERS responses may reflect also cognitive and/or memory processing, rather than merely the activity of the motor cortices.

Event-related desynchronization and synchronization during a memory task in children

Objective: To examine the event-related desynchronization (ERD) and synchronization (ERS) responses of several narrow electroencephalographic (EEG) frequency bands in children during an auditory memory task. Methods: ERD/ERS responses of the 4–6, 6–8, 8–10 and 10–12 Hz EEG frequency bands were studied in 12 children (mean age 12 years) while they performed an auditory memory task. Twelve adult subjects served as a control group. Results: The children's ERD/ERS responses differed from those of the adult's in the 4–6, 6–8 and 8–10 Hz EEG frequency bands, especially during retrieval from memory. The children's 4–6 Hz initial ERS responses were of lesser amplitude and of delayed latency as compared to those of the adults. In the 6–8 and 8–10 Hz frequency bands, especially during retrieval from memory, the children's ERD responses were of lesser magnitude than those of the adults. In the 10–12 Hz frequency band, no differences were observed between the ERD/ERS responses between the children and adults. Conclusions: Our results suggest that theta and alpha response systems might participate in auditory information processing already at this age, although not being fully developed. Memory systems involving retrieval may be the last to mature.

P300 and alpha event‐related desynchronization (ERD)

In the present study we evaluated the relationships between the P300 event-related potential and event-related desynchronization (ERD) of electroencephalographic alpha activity by simultaneously analyzing P300 as well as 7-10- and 10-14-Hz alpha ERD responses from auditory passive and active oddball conditions. We compared the effects of task (target vs. nontarget) and electrode (Fz, Cz, Pz) on P300 and ERD, and correlated P300 amplitude/latency with ERD maximal amplitude/latency across individuals. The major findings were that P300 as well as slow and fast alpha ERD manifested similar task and electrode effects. P300 preceded ERD and predicted individual variance of both slow and fast alpha ERD. The relationships of P300 with alpha ERD were different for the slow and fast alpha frequencies. These findings indicate that P300 and ERD are related such that slow and fast alpha ERDs are specifically guided or modified by the internal event(s) indexed by P300.

Event-related desynchronization and movement-related cortical potentials on the ECoG and EEG

Event-related desynchronization (ERD) 2.0 sec before and 1.0 sec after movement in the frequency bands of 8–10, 10–12, 12–20 and 20–30 Hz and movement-related cortical potentials (MRCPs) to self-paced movements were studied from subdural recordings over the central region in 3 patients, and from scalp-recorded EEGs in 20 normal volunteers. In direct cortical recordings, the peak ERD response and peak MRCP amplitude to self-paced finger movements were maximal over recording sites in the contralateral hand motor representations. The topography and time of onset of the ERD response to finger and foot movements suggest that the ERD responses in the 8–10 Hz and 10–12 Hz bands are more somatotopically restricted than the responses in the higher frequency bands. The power recovery and subsequent overshoot in the different frequency bands occurred in an orderly fashion with the faster frequencies recovering earlier. The ERD responses on the scalp-recorded EEGs were of lower magnitude and more widely distributed than those occurring on the subdural recordings. Across the population, there was no relation between the magnitude of the ERD response in any of the frequency bands studied and the peak amplitude of the negative slope (pNS') and the frontal peak of the motor potential (fpMP) of the MRCPs. MRCPs and ERD responses originate in similar cortical regions and share some common timing features, but the magnitude and spatial distribution of the two responses appear to be independent of each other, which suggests that the physiological mechanisms governing these two events are different and may represent different aspects of motor cortex activation. Differences in the timing and topographical features of the ERD responses in the various frequency bands also suggest a distinct functional significance for the various spectral components of the electrical activity in the motor cortex.

Event-related desynchronization and movement-related cortical potentials on the ECoG and EEG

Event-related desynchronization (ERD) 2.0 sec before and 1.0 sec after movement in the frequency bands of 8–10, 10–12, 12–20 and 20–30 Hz and movement-related cortical potentials (MRCPs) to self-paced movements were studied from subdural recordings over the central region in 3 patients, and from scalp-recorded EEGs in 20 normal volunteers. In direct cortical recordings, the peak ERD response and peak MRCP amplitude to self-paced finger movements were maximal over recording sites in the contralateral hand motor representations. The topography and time of onset of the ERD response to finger and foot movements suggest that the ERD responses in the 8–10 Hz and 10–12 Hz bands are more somatotopically restricted than the responses in the higher frequency bands. The power recovery and subsequent overshoot in the different frequency bands occurred in an orderly fashion with the faster frequencies recovering earlier. The ERD responses on the scalp-recorded EEGs were of lower magnitude and more widely distributed than those occurring on the subdural recordings. Across the population, there was no relation between the magnitude of the ERD response in any of the frequency bands studied and the peak amplitude of the negative slope (pNS') and the frontal peak of the motor potential (fpMP) of the MRCPs. MRCPs and ERD responses originate in similar cortical regions and share some common timing features, but the magnitude and spatial distribution of the two responses appear to be independent of each other, which suggests that the physiological mechanisms governing these two events are different and may represent different aspects of motor cortex activation. Differences in the timing and topographical features of the ERD responses in the various frequency bands also suggest a distinct functional significance for the various spectral components of the electrical activity in the motor cortex.