Beta Event-related Synchronization Research Articles

Movement-related ERS and connectivity in the gamma frequency decrease with practice

Previous work showed that movements are accompanied by modulation of electroencephalographic (EEG) activity in both beta (13–30 Hz) and gamma (>30 Hz) ranges. The amplitude of beta event-related synchronization (ERS) is not linked to movement characteristics, but progressively increases with motor practice, returning to baseline after a period of rest. Conversely, movement-related gamma ERS amplitude is proportional to movement distance and velocity. Here, high-density EEG was recorded in 51 healthy subjects to investigate whether i) three-hour practice in two learning tasks, one with a motor component and one without, affects gamma ERS amplitude and connectivity during a motor reaching test, and ii) 90-minutes of either sleep or quiet rest have an effect on gamma oscillatory activity. We found that, while gamma ERS was appropriately scaled to the target extent at all testing points, its amplitude decreased after practice, independently of the type of interposed learning, and after both quiet wake and nap, with partial correlations with subjective fatigue scores. During movement execution, connectivity patterns within fronto-parieto-occipital electrodes, over areas associated with attentional networks, decreased after both practice and after 90-minute rest. While confirming the prokinetic nature of movement-related gamma ERS, these findings demonstrated the preservation of gamma ERS scaling to movement velocity with practice, despite constant amplitude reduction. We thus speculate that such decreases, differently from the practice-related increases of beta ERS, are related to reduced attention or working memory mechanisms due to fatigue or a switch of strategy toward automatization of movement execution and do not specifically reflect plasticity phenomena.

Stimulus Onset Asynchrony Affects Weighting-related Event-related Spectral Power in Self-motion Perception.

Self-motion perception relies primarily on the integration of the visual, vestibular, proprioceptive, and somatosensory systems. There is a gap in understanding how a temporal lag between visual and vestibular motion cues affects visual-vestibular weighting during self-motion perception. The beta band is an index of visual-vestibular weighting, in that robust beta event-related synchronization (ERS) is associated with visual weighting bias, and robust beta event-related desynchronization is associated with vestibular weighting bias. The present study examined modulation of event-related spectral power during a heading judgment task in which participants attended to either visual (optic flow) or physical (inertial cues stimulating the vestibular, proprioceptive and somatosensory systems) motion cues from a motion simulator mounted on a MOOG Stewart Platform. The temporal lag between the onset of visual and physical motion cues was manipulated to produce three lag conditions: simultaneous onset, visual before physical motion onset, and physical before visual motion onset. There were two main findings. First, we demonstrated that when the attended motion cue was presented before an ignored cue, the power of beta associated with the attended modality was greater than when visual-vestibular cues were presented simultaneously or when the ignored cue was presented first. This was the case for beta ERS when the visual-motion cue was attended to, and beta event-related desynchronization when the physical-motion cue was attended to. Second, we tested whether the power of feature-binding gamma ERS (demonstrated in audiovisual and visual-tactile integration studies) increased when the visual-vestibular cues were presented simultaneously versus with temporal asynchrony. We did not observe an increase in gamma ERS when cues were presented simultaneously, suggesting that electrophysiological markers of visual-vestibular binding differ from markers of audiovisual and visual-tactile integration. All event-related spectral power reported in this study were generated from dipoles projecting from the left and right motor areas, based on the results of Measure Projection Analysis.

Sustained attention to response task-related beta oscillations relate to performance and provide a functional biomarker in ALS

Objective. To characterize the cortical oscillations associated with performance of the sustained attention to response task (SART) and their disruptions in the neurodegenerative condition amyotrophic lateral sclerosis (ALS). Approach. A randomised SART was undertaken by 24 ALS patients and 33 healthy controls during 128-channel electroencephalography (EEG). Complex Morlet wavelet transform was used to quantify non-phase-locked oscillatory activity in event-related spectral perturbations associated with performing the SART. We investigated the relationships between these perturbations and task performance, and associated motor and cognitive changes in ALS. Main results. SART induced theta-band event-related synchronization (ERS) and alpha- and beta-band event-related desynchronization (ERD), followed by rebound beta ERS, in both Go and NoGo trials across the frontoparietal axis, with NoGo trials eliciting greater theta ERS and lesser beta ERS. Controls with greater Go trial beta ERS performed with greater speed and less accuracy. ALS patients exhibited increased anticipation compared to controls but similar reaction times and accuracy. Prefrontal (area under the receiver operating characteristic curve (AUROC) = 0.8, Cohen’s d = 0.97) and parietal (AUROC = 0.82, Cohen’s d = 1.12) beta-band ERD was significantly reduced in ALS but did not relate to performance, while patients with higher Edinburgh Cognitive and Behavioural ALS Screen (ECAS) ALS-specific scores demonstrated greater ERS in beta (rho = 0.72) upon successful withholding. Significance. EEG measurement of task-related oscillation changes reveals variation in cortical network engagement in relation to speed versus accuracy strategies. Such measures can also capture cognitive and motor network pathophysiology in the absence of task performance decline, which may facilitate development of more sensitive early neurodegenerative disease biomarkers.

Variability and Reliability of Paired-Pulse Depression and Cortical Oscillation Induced by Median Nerve Stimulation

Paired-pulse depression (PPD) has been widely used to investigate the functional profiles of somatosensory cortical inhibition. However, PPD induced by somatosensory stimulation is variable, and the reasons for between- and within-subject PPD variability remains unclear. Therefore, the purpose of this study was to clarify the factors influencing PPD variability induced by somatosensory stimulation. The study participants were 19 healthy volunteers. First, we investigated the relationship between the PPD ratio of each component (N20m, P35m, and P60m) of the somatosensory magnetic field, and the alpha, beta, and gamma band changes in power [event-related desynchronization (ERD) and event-related synchronization (ERS)] induced by median nerve stimulation. Second, because brain-derived neurotrophic factor (BDNF) gene polymorphisms reportedly influence the PPD ratio, we assessed whether BDNF genotype influences PPD ratio variability. Finally, we evaluated the test–retest reliability of PPD and the alpha, beta, and gamma ERD/ERS induced by somatosensory stimulation. Significant positive correlations were observed between the P60m_PPD ratio and beta power change, and the P60m_PPD ratio was significantly smaller for the beta ERD group than for the beta ERS group. P35m_PPD was found to be robust and highly reproducible; however, P60m_PPD reproducibility was poor. In addition, the ICC values for alpha, beta, and gamma ERD/ERS were 0.680, 0.760, and 0.552 respectively. These results suggest that the variability of PPD for the P60m deflection may be influenced by the ERD/ERS magnitude, which is induced by median nerve stimulation.

Decreased Event-Related Beta Synchronization During Memory Maintenance Marks Early Cognitive Decline in Mild Cognitive Impairment.

Mild cognitive impairment (MCI) refers to a measurable deficit in cognition in the absence of dementia or impairment in activities of daily living. Working memory impairment is among the earliest signs of MCI. Oscillatory analysis of working memory might be a potential tool for identifying patients at increased risk of developing dementia. Our study aimed to assess the temporospatial pattern of spectral differences during working memory maintenance between MCI patients and healthy controls and to compare the sources of oscillatory activity between the two groups. Event-related spectral perturbation of 17 MCI patients and 21 healthy control participants was studied with 128-channel EEG during the Sternberg working memory task. Source localization was performed by using the eLORETA software. Among the participants, 13 MCI and 15 control participants underwent a structural brain MRI examination. Event-related synchronization (ERS) in the alpha and beta frequency band was significantly lower in MCI patients compared to healthy control participants during retention. Both study groups showed significant memory load-related enhancement in both frequency band. In the MCI group, source localization revealed significantly attenuated beta oscillatory activity in the inferior and middle temporal gyrus, in the fusiform gyrus, and in the cuneus. Beta ERS correlated significantly with the size of the hippocampus, entorhinal cortex, and parahippocampal gyrus. During the retention period, MCI is characterized by decreased alpha and beta ERS compared to controls indicating early impairment in neural networks serving working memory maintenance. The assessment of electrophysiological changes in the beta frequency range may provide a useful diagnostic tool for the early detection of cognitive impairment.

Inhibitory transcranial direct current stimulation enhances weak beta event-related synchronization after foot motor imagery in patients with lower limb amputation.

Sensorimotor rhythm patterns in patients with lower limb amputations might be altered because of reorganization of the sensorimotor cortices. The authors evaluated the sensorimotor rhythm of motor imagery (MI) in healthy subjects and patients with lower limb amputations. In addition, the authors investigated whether transcranial direct current stimulation (tDCS) could modulate sensorimotor rhythm control. Six healthy subjects and six patients with lower limb amputations were assigned to receive anodal, cathodal, or sham tDCS over the foot motor area in a randomized order. The authors evaluated event-related desynchronization and event-related synchronization (ERS) of unilateral hand and bilateral foot MI before and after tDCS. Beta ERS of foot MI in patients with lower limb amputations was significantly lesser than that in healthy subjects. Compared with sham stimulation, cathodal tDCS enhanced beta ERS of foot MI in patients with lower limb amputations. In contrast, anodal tDCS decreased beta ERS of foot MI in healthy subjects. This is the first study to demonstrate that cathodal tDCS can enhance a weak beta ERS of foot MI in patients with lower limb amputations. These findings might contribute in improving the effectiveness of sensorimotor rhythm-based brain computer interface for gait restoration after lower limb amputation.

Event-related synchronization of delta and beta oscillations reflects developmental changes in the processing of affective pictures during adolescence

Recent research has determined that affective pictures modulate event-related delta and beta oscillations in adults. However, it is unclear whether these brain oscillations reflect developmental changes in the processing of affective information during adolescence. EEG data were collected from 51 adolescents and 18 undergraduates as they viewed a total of 90 pictures. In the range of fast wave activities, event-related synchronization (ERS) in the beta band varied with emotional valence, indicating that beta ERS is indicative of early bottom-up processing of visual emotional stimuli. Adolescents at the age of 12years exhibited more positive beta ERS amplitudes over posterior brain regions for positive versus neutral pictures compared to adolescents at the ages 14years, 16years and in young adults; however, no age-related differences were found for negative versus neutral pictures. In the range of slow wave activities, delta ERSs and late positive potential (LPP) amplitudes exhibited affective modulation and decreased over anterior brain regions from between the age of 12years and early adulthood. These slow wave activities (delta and LPPs) reflected top-down attention to the motivational relevance of the emotional stimuli. Taken together, these observations suggest that adolescents exhibit dissociable ERS patterns in the delta and beta bands during affective processing. Furthermore, adolescents undergo age-dependent changes in oscillatory brain reorganization. Our results should be useful to researchers interested in affective processing during adolescence.

Effect of Aging on Hedonic Appreciation of Pleasant and Unpleasant Odors

Does hedonic appreciation evolve differently for pleasant odors and unpleasant odors during normal aging? To answer this question we combined psychophysics and electro-encephalographic recordings in young and old adults. A first study showed that pleasant odorants (but not unpleasant ones) were rated as less pleasant by old adults. A second study validated this decrease in hedonic appreciation for agreeable odors and further showed that smelling these odorants decreased beta event-related synchronization in aged participants. In conclusion, the study offers new insights into the evolution of odor hedonic perception during normal aging, highlighting for the first time a change in processing pleasant odors.

Event-related oscillations in structural and semantic encoding of faces

Objective The ability to perceive faces is acquired through an interaction between species-specific biological mechanisms and social experience. To elucidate the mechanisms of the cognitive system underlying face recognition, we investigated cerebral oscillations related to encoding in ‘person identity nodes’. Methods EEG was measured in nine healthy adults during perception of their own face, familiar face and unfamiliar face images. Results Event-related synchronization (ERS) in theta, alpha and beta bands was initially induced in occipito-temporal areas within 0–200 ms of the presentation of facial stimuli. In addition, delta ERS over parietal and left temporal areas was greater in response to familiar faces around 0–800 ms compared with unfamiliar faces. Beta ERS over the right prefrontal area was significantly greater in response to a participant’s own face compared with a familiar face at 400–800 ms post-stimulus. Conclusions ERS within 0–200 ms reflects structural encoding of faces (i.e., N170 of the event related potential). Delta ERS within 0–800 ms suggests an association with memory retrieval. Beta ERS within 400–800 ms is consistent with the cortical areas reported to be strongly related to self-face perception in previous fMRI studies. Significance The delta and beta bands ERS might provide an index of familiarity and self-recognition, respectively.

Age- and performance related modulations in spectral event-related dynamics during a working memory task

Event Abstract Back to Event Age- and performance related modulations in spectral event-related dynamics during a working memory task Thomas Fischer1*, Alexander Strobel1 and Sergei Schapkin2 1 Technical University of Dresden, Germany 2 Federal Institute for Occupational Safety and Health, Germany Age-dependent changes in event-related spectral perturbations (ERSP) and decrements in performance have previously been reported for several cognitive paradigms. However, the relationship between ERSP modulations, performance and age has not been well documented until now. Using a 2-back working memory task, we compared ERSPs between 44 healthy younger subjects (aged 29±3 years) and 44 older subjects (aged 55±3 years). Based on the d’ scores in the 2-back condition participants of each age group were divided into high and low performers. For event-related beta synchronization (ERS; 800-1000 ms after target), the ANOVA showed significant main effects for the factor age and the factor performance in the left frontal cluster (F3, FC3). The beta ERS was significantly larger in the high-performer group (the younger and older subjects taken together) than in the low-performer group as well as larger in younger than in older adults. No interaction effects were obtained. Additionally, age differences in the alpha event-related desynchronisation (ERD; 600-800 ms after target) in the parietal cluster (P3; Pz, P4) were found: the alpha ERD increased in younger adults as compared to older adults. Moreover, alpha ERS was larger in low performers than in high performers.Our results show that working memory processes are associated with left frontal event-related beta-synchronization and suggest that frontal beta synchronization could be an informative indicator for age-related changes in neuronal processes underlying working memory. Keywords: Aging, ERSP Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Poster Sessions: Cognitive Aging Citation: Fischer T, Strobel A and Schapkin S (2011). Age- and performance related modulations in spectral event-related dynamics during a working memory task. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00547 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Dr. Thomas Fischer, Technical University of Dresden, Dresden, Germany, fischer.tho@googlemail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Thomas Fischer Alexander Strobel Sergei Schapkin Google Thomas Fischer Alexander Strobel Sergei Schapkin Google Scholar Thomas Fischer Alexander Strobel Sergei Schapkin PubMed Thomas Fischer Alexander Strobel Sergei Schapkin Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Involvement of the human pedunculopontine nucleus region in voluntary movements

The pedunculopontine nucleus region (PPNR) is being investigated as a target for deep brain stimulation (DBS) in Parkinson disease (PD), particularly for gait and postural impairment. A greater understanding of how PPNR activities and oscillations are modulated with voluntary movements is crucial to the development of neuromodulation strategies. We studied 7 patients with PD who underwent DBS electrode implantations in the PPNR. PPNR local field potential and EEG were recorded while patients performed self-paced wrist and ankle movements. Back-averaging of the PPNR recording showed movement-related potentials before electromyography onset. Frequency analysis showed 2 discrete movement-related frequency bands in the theta (6- to 10-Hz) and beta (14- to 30-Hz) ranges. The PPNR theta band showed greater event-related desynchronization with movements in the ON than in the OFF medication state and was coupled with the sensorimotor cortices in the ON state only. Beta event-related desynchronization was observed in the PPNR during the premovement and movement execution phases in the OFF state. In contrast, premovement PPNR beta event-related synchronization occurred in the ON state. Moreover, beta band coherence between the PPNR and the midline prefrontal region was observed during movement preparation in the ON but not the OFF state. Activities of PPNR change during movement preparation and execution in patients with PD. Dopaminergic medications modulate PPNR activities and promote the interactions between the cortex and PPNR. Beta oscillations may have different functions in the basal ganglia and PPNR, and may be prokinetic rather than antikinetic in the PPNR.

Extraction of single-trial cortical beta oscillatory activities in EEG signals using empirical mode decomposition

BackgroundBrain oscillatory activities are stochastic and non-linearly dynamic, due to their non-phase-locked nature and inter-trial variability. Non-phase-locked rhythmic signals can vary from trial-to-trial dependent upon variations in a subject's performance and state, which may be linked to fluctuations in expectation, attention, arousal, and task strategy. Therefore, a method that permits the extraction of the oscillatory signal on a single-trial basis is important for the study of subtle brain dynamics, which can be used as probes to study neurophysiology in normal brain and pathophysiology in the diseased.MethodsThis paper presents an empirical mode decomposition (EMD)-based spatiotemporal approach to extract neural oscillatory activities from multi-channel electroencephalograph (EEG) data. The efficacy of this approach manifests in extracting single-trial post-movement beta activities when performing a right index-finger lifting task. In each single trial, an EEG epoch recorded at the channel of interest (CI) was first separated into a number of intrinsic mode functions (IMFs). Sensorimotor-related oscillatory activities were reconstructed from sensorimotor-related IMFs chosen by a spatial map matching process. Post-movement beta activities were acquired by band-pass filtering the sensorimotor-related oscillatory activities within a trial-specific beta band. Signal envelopes of post-movement beta activities were detected using amplitude modulation (AM) method to obtain post-movement beta event-related synchronization (PM-bERS). The maximum amplitude in the PM-bERS within the post-movement period was subtracted by the mean amplitude of the reference period to find the single-trial beta rebound (BR).ResultsThe results showed single-trial BRs computed by the current method were significantly higher than those obtained from conventional average method (P < 0.01; matched-pair Wilcoxon test). The proposed method provides high signal-to-noise ratio (SNR) through an EMD-based decomposition and reconstruction process, which enables event-related oscillatory activities to be examined on a single-trial basis.ConclusionsThe EMD-based method is effective for artefact removal and extracting reliable neural features of non-phase-locked oscillatory activities in multi-channel EEG data. The high extraction rate of the proposed method enables the trial-by-trial variability of oscillatory activities can be examined, which provide a possibility for future profound study of subtle brain dynamics.

Predicting cognitive decline in Mild Cognitive Impairment

Recent studies described several changes of endogenous event related potentials (ERP) and brain rhythm synchronization during memory activation in patients with Alzheimer's disease (AD). To examine whether memoryrelated EEG parameters may predict cognitive decline in mild cognitive impairment (MCI), we assessed P200 and N200 latencies as well as beta event-related synchronization (ERS) in 16 elderly controls (EC), 29 MCI cases and 10 patients with AD during the successful performance of a pure attentional detection task as compared to a highly working memory demanding 2-back task. At one year follow-up, sixteen MCI patients showed progressive cognitive decline (PMCI) and thirteen remained stable (SMCI). Both P200 and N200 latencies in the 2-back task were longer in PMCI and AD cases compared to EC and SMCI cases. During the interval 1000 ms to 1700 ms after stimulus, beta ERS at parietal electrodes was of lower amplitude in PMCI and AD compared to EC and SMCI cases. Univariate models showed that P200, N200 and log% beta values were significantly related to the SMCI/PMCI distinction with areas under the receiver operating characteristic curve of 0.93, 0.78 and 0.72, respectively. The combination of all three EEG hallmarks was the stronger predictor of MCI deterioration with 90% of correctly classified MCI cases. Our data reveal that PMCI and clinically overt AD share the same pattern of working memoryrelated EEG activation characterized by increased P200N200 latencies and decreased beta ERS. They also show that P200 latency during the 2-back task may be a simple and promising EEG marker of rapid cognitive decline in MCI. from International Society on Brain and Behaviour: 3rd International Congress on Brain and Behaviour Thessaloniki, Greece. 28 November – 2 December 2007

Inhibition of Return Arises from Inhibition of Response Processes: An Analysis of Oscillatory Beta Activity

Abstract In the orienting of attention paradigm, inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. No consensus has yet been reached regarding the stages of information processing underlying the inhibition. We report the results of an electro-encephalogram experiment designed to examine the involvement of response inhibition in IOR. Using a cue-target design and a target-target design, we addressed the role of response inhibition in a location discrimination task. Event-related changes in beta power were measured because oscillatory beta activity has been shown to be related to motor activity. Bilaterally located sources in the primary motor cortex showed event-related beta desynchronization (ERD) both at cue and target presentation and a rebound to event-related beta synchronization (ERS) after movement execution. In both designs, IOR arose from an enhancement of beta synchrony. IOR was related to an increase of beta ERS in the target-target design and to a decrease of beta ERD in the cue-target design. These results suggest an important role of response inhibition in IOR.

Inhibition of Return Arises from Inhibition of Response Processes: An Analysis of Oscillatory Beta Activity

Abstract In the orienting of attention paradigm, inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. No consensus has yet been reached regarding the stages of information processing underlying the inhibition. We report the results of an electro-encephalogram experiment designed to examine the involvement of response inhibition in IOR. Using a cue-target design and a target-target design, we addressed the role of response inhibition in a location discrimination task. Event-related changes in beta power were measured because oscillatory beta activity has been shown to be related to motor activity. Bilaterally located sources in the primary motor cortex showed event-related beta desynchronization (ERD) both at cue and target presentation and a rebound to event-related beta synchronization (ERS) after movement execution. In both designs, IOR arose from an enhancement of beta synchrony. IOR was related to an increase of beta ERS in the target-target design and to a decrease of beta ERD in the cue-target design. These results suggest an important role of response inhibition in IOR.

Working memory load–related electroencephalographic parameters can differentiate progressive from stable mild cognitive impairment

Recent studies described several changes of endogenous event-related potentials (ERP) and brain rhythm synchronization during memory activation in patients with Alzheimer’s disease (AD). To examine whether memory-related EEG parameters may predict cognitive decline in mild cognitive impairment (MCI), we assessed P200 and N200 latencies as well as beta event-related synchronization (ERS) in 16 elderly controls (EC), 29 MCI cases and 10 patients with AD during the successful performance of a pure attentional detection task as compared with a highly working memory demanding two-back task. At 1 year follow-up, 16 MCI patients showed progressive cognitive decline (PMCI) and 13 remained stable (SMCI). Both P200 and N200 latencies in the two-back task were longer in PMCI and AD cases compared with EC and SMCI cases. During the interval 1000 ms to 1700 ms after stimulus, beta ERS at parietal electrodes was of lower amplitude in PMCI and AD compared with EC and SMCI cases. Univariate models showed that P200, N200 and log% beta values were significantly related to the SMCI/PMCI distinction with areas under the receiver operating characteristic curve of 0.93, 0.78 and 0.72, respectively. The combination of all three EEG hallmarks was the stronger predictor of MCI deterioration with 90% of correctly classified MCI cases. Our data reveal that PMCI and clinically overt AD share the same pattern of working memory-related EEG activation characterized by increased P200–N200 latencies and decreased beta ERS. They also show that P200 latency during the two-back task may be a simple and promising EEG marker of rapid cognitive decline in MCI.

Slow repetitive transcranial magnetic stimulation changes oscillatory magnetoencephalographic activity in two patients with thalamic pain

To evaluate the effects of slow repetitive transcranial magnetic stimulation (rTMS) on thalamic pain, the magnetoencephalographic (MEG) signals following eye closing and tactile stimulation were recorded before and after rTMS in two patients. After the application of rTMS, similar neuromagnetic changes were obtained in both patients. Alpha event-related synchronization (ERS) following eyes closing increased and it became more symmetric. Beta ERS following paralytic extremities stimulation, which was hardly observed before rTMS, increased. Beta ERS following non-paralytic extremities stimulation increased as well. Slow rTMS may change oscillatory MEG activity and induce brain plasticity even if the pain cannot be relieved.

Enhanced Reactivity and Delayed Recovery of Sensorimotor Cortex in the Novelty Seeking Personality

Background: The novelty seeking (NS) personality trait is hypothesized to be associated with high cortical reactivity, poor inhibitory control and/or varied dopaminergic neurotransmission in the basal ganglia. After somatosensory stimulation, electrical oscillations in alpha and beta bands generated in the sensorimotor cortex show a short duration decrease (event-related desynchronization) and a subsequent increase (event-related synchronization) that is thought to reflect cortical activation and the inhibitory/recovery process, respectively. These oscillatory changes are also believed to be affected by the status of the basal ganglia and by dopaminergic functions. In the present study, we investigated the association between the NS personality trait and somatosensory oscillatory changes after median nerve stimulation assessed by magnetoencephalography. Methods: From 48 healthy subjects, we selected 14 high scorers and 14 age- and sex-matched low scorers on the NS dimension of the Temperament and Character Inventory. Magnetic fields were recorded while subjects received electrical stimulation of either the right or left median nerve with equal probability and with a randomized interstimulus interval. Frequency analysis was performed on the alpha and beta bands. Results: Compared with the low NS group, the high NS group showed larger magnitude of beta event-related desynchronization and larger latencies of the alpha and beta event-related synchronization. Conclusion: These results suggest that individuals with high degrees of the NS trait have greater reactivity and delayed recovery of the sensorimotor cortex in response to simple somatosensory stimulation. This may be significant for the understanding of their exploratory and impulsive behavior.

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.

P36.30 Modification of event related beta synchronization induced by motor cortex electrical stimulation for control of neuropathic pain

P36.30 Modification of event related beta synchronization induced by motor cortex electrical stimulation for control of neuropathic pain