Decrease In Beta Power Research Articles

On the neural basis of sensory weighting: Alpha, beta and gamma modulations during complex movements

Previous studies have revealed that visual and somatosensory information is processed as a function of its relevance during movement execution. We thus performed spectral decompositions of ongoing neural activities within the somatosensory and visual areas while human participants performed a complex visuomotor task. In this task, participants followed the outline of irregular polygons with a pen-controlled cursor. At unpredictable times, the motion of the cursor deviated 120° with respect to the actual pen position creating an incongruence between visual and somatosensory inputs, thus increasing the importance of visual feedback to control the movement as suggested in previous studies. We found that alpha and beta power significantly decreased in the visual cortex during sensory incongruence when compared to unperturbed conditions. This result is in line with an increased gain of visual inputs during sensory incongruence. In parallel, we also found a simultaneous decrease of gamma and beta power in sensorimotor areas which has not been reported previously. The gamma desynchronization suggests a reduced integration of somatosensory inputs for controlling movements with sensory incongruence while beta ERD could be more specifically linked to sensorimotor adaptation processes.

Automated classification of pain perception using high-density electroencephalography data.

The translation of brief, millisecond-long pain-eliciting stimuli to the subjective perception of pain is associated with changes in theta, alpha, beta, and gamma oscillations over sensorimotor cortex. However, when a pain-eliciting stimulus continues for minutes, regions beyond the sensorimotor cortex, such as the prefrontal cortex, are also engaged. Abnormalities in prefrontal cortex have been associated with chronic pain states, but conventional, millisecond-long EEG paradigms do not engage prefrontal regions. In the current study, we collected high-density EEG data during an experimental paradigm in which subjects experienced a 4-s, low- or high-intensity pain-eliciting stimulus. EEG data were analyzed using independent component analyses, EEG source localization analyses, and measure projection analyses. We report three novel findings. First, an increase in pain perception was associated with an increase in gamma and theta power in a cortical region that included medial prefrontal cortex. Second, a decrease in lower beta power was associated with an increase in pain perception in a cortical region that included the contralateral sensorimotor cortex. Third, we used machine learning for automated classification of EEG data into low- and high-pain classes. Theta and gamma power in the medial prefrontal region and lower beta power in the contralateral sensorimotor region served as features for classification. We found a leave-one-out cross-validation accuracy of 89.58%. The development of biological markers for pain states continues to gain traction in the literature, and our findings provide new information that advances this body of work.NEW & NOTEWORTHY The development of a biological marker for pain continues to gain traction in literature. Our findings show that high- and low-pain perception in human subjects can be classified with 89% accuracy using high-density EEG data from prefrontal cortex and contralateral sensorimotor cortex. Our approach represents a novel neurophysiological paradigm that advances the literature on biological markers for pain.

EP 106. Contributions of alpha and beta oscillations to bimanual sequence tapping

Objective In 1:n bi-manual tapping studies participants intuitively choose their right hand for tapping the fast frequency. This preference is expressed in faster and more accurate performance compared to the opposite frequency mapping. This could be either due to a dominant role of the left hemisphere in planning and integration of movements ( Serrien et al., 2003 ) or due to a hemispheric specialization for relative frequencies [double filtering by frequency theory ( Robertson and Ivry, 2000 )]. In this framework, which has been proposed for sensory processing, the left hemisphere is optimized in processing higher relative frequencies while the right hemisphere excels in processing lower relative frequencies of a complex stimulus. We hypothesized comparable lateralization effects relative to movement frequencies. Since the strong tendency of the left hemisphere in controlling bi-manual learned sequences [pre-defined motor programs] would overlay a right hemisphere preference for lower frequencies, we expected to disclose frequency-related lateralization effects only in untrained sequences. Methods In 1:4 tapping paradigms, participants usually tap the first tone with both hands, continue tapping to every auditory tone with the fast hand, count until four and tap again with both hands. In our paradigm, participants were asked to wait for the fourth tone for the slow hand tapping, creating an unintuitive quadruple meter. We recorded magnetoencephalography (MEG) signals in 10 healthy right-handed subjects while performing optimal (left hand slow and right hand fast tapping) and non-optimal (opposite arrangement) bi-manual tapping conditions. As a control, uni-manual fast and slow conditions were performed with each hand alone and with both hands together. We reconstructed the timing signal in the alpha and beta bands of the underlying sources with beamforming. For comparing modulation of intra- and interhemispheric connectivity at different levels of the motor cortex hierarchy in optimal and non-optimal hand arrangements we used dynamic causal modeling. Results We found that the right hand benefit disappeared in all fast tapping conditions. Additionally, a left hand benefit for slow taps was found in the optimal bi-manual condition, which supports frequency-dependent lateralization effects. Comparing power spectra of the different positions in the sequence of four tones revealed two different effects in slow conditions. First and last position coincided with reduced alpha power while successive positions seem to be coded by a decrease in beta power. Changes in alpha power were found in right sensors, changes in beta power were found contralateral to the hand used for slow tapping. Conclusion Behavioral as well as spectral results fit the double filtering by frequency hypothesis. We therefore expected to find stronger intra-hemispheric connections in optimal hand arrangement indicating a local processing of information, whereas in non-optimal hand arrangement inter-hemispheric communication should be enhanced pointing to a higher amount of information exchange between the hemispheres.

EP 60. Bicycling suppresses beta power more strongly than walking in the subthalamic nucleus of Parkinsonian patients

Introduction Walking abilities are severely affected in patients suffering from Freezing of Gait (FOG), a common phenomenon in advanced Parkinson’s disease (PD). Despite the high occurrence of the symptom in the progression of the disease, little is known about the underlying mechanisms. Remarkably, it was recently reported that patients with FOG are still able to ride a bike ( [Snijders et al., 2011] , [Snijders et al., 2012] ). While similar brain networks are involved in walking and bicycling ( [Fukuyama et al., 1997] , [Christensen et al., 2002] ), it is not understood why both types of movement are differently affected in patients with FOG. Therefore, this study aimed to investigate neural oscillations underlying bicycling and walking in PD patients. Patients and methods Seven PD patients (mean age 55.4±6.3 y) clinically selected for bilateral deep brain stimulation (DBS) therapy were included in the study. Using a portable EEG system (Porti, TMSi, Enschede, The Netherlands), local field potentials from the subthalamic nucleus (STN) were recorded using externalised leads the day after implantation of DBS electrodes. Patients were recorded while OFF any dopaminergic medication during unconstrained bicycling and walking on a stationary bicycle. The paradigm consisted of a baseline rest period, continuous movement, and an alternating sequence of rest and movement, i.e. bicycling or walking, in order to study both movement initiation and movement termination. For each STN the bipolar channel with the highest baseline beta peak power was selected for further analyses. Three of 14 STNs had to be excluded because of movement artefact contamination and a broken externalised lead in one patient. Differences were determined using cluster-based permutation tests as implemented in the FieldTrip analysis toolbox ( Oostenveld et al., 2011 ). Results Movement initiation was accompanied by power decreases in the alpha–beta range (8–35 Hz) in bicycling and walking. Contrasting both conditions revealed a stronger beta power decrease in bicycling (p 0.05). Conclusions Our finding that bicycling leads to a stronger power decrease in the beta band than walking is particularly interesting as Parkinson’s disease is generally associated with abnormally increased beta band activity in the corticobasal ganglia loop ( Oswal et al., 2013 ). The difference between oscillatory activity underlying bicycling and walking was specific to beta power suppression during movement, whereas beta rebound after movement termination was equally strong. In this sense, bicycling seems to promote the suppression of pathological oscillations in the basal ganglia, as opposed to walking. This may be due to the more continuous movement in bicycling with both legs being pushed forward permanently. In walking, stance and swing phases alternate. Therefore, one may speculate that bicycling may be less hampered in FOG because the more continuous nature of this movement promotes beta suppression and thus, facilitates movement.

Soft drink effects on sensorimotor rhythm brain computer interface performance and resting-state spectral power.

Brain-computer interface (BCI) systems allow users to directly control computers and other machines by modulating their brain waves. In the present study, we investigated the effect of soft drinks on resting state (RS) EEG signals and BCI control. Eight healthy human volunteers each participated in three sessions of BCI cursor tasks and resting state EEG. During each session, the subjects drank an unlabeled soft drink with either sugar, caffeine, or neither ingredient. A comparison of resting state spectral power shows a substantial decrease in alpha and beta power after caffeine consumption relative to control. Despite attenuation of the frequency range used for the control signal, caffeine average BCI performance was the same as control. Our work provides a useful characterization of caffeine, the world's most popular stimulant, on brain signal frequencies and their effect on BCI performance.

Timing of beta oscillatory synchronization and temporal prediction of upcoming stimuli

Modulations of beta oscillatory power serve a predictive role, in preparation of future actions. It is well known that beta amplitude decreases prior to voluntary movements and expected tactile stimuli. Paradoxically, recent studies have reported a beta amplitude increase prior to expected visual and auditory stimuli. Moreover, it has been suggested that, in isochronic stimulus series, the rising beta slope is adjusted to the duration of the interstimulus interval. We investigated the characteristics of such timing related pre-stimulus beta power increases using visual stimulus sequences that were presented at three regular rates (0.61, 0.74 and 0.95Hz). EEG was recorded from twenty participants while they attended the sequences by performing a clock reading task. Time-frequency analyses showed a consistent pattern of beta modulation: the post-stimulus beta power decrease was followed by a steep increase. Contrary to recent views, we found that the peaks of beta power, for the three presentation rates, were reached at a similar latency post-stimulus, instead of a fixed interval preceding the next stimulus. This demonstrates that, at interstimulus intervals between 1–2s, beta synchronization slopes are not modulated by timing mechanisms related to prediction of upcoming stimuli. We reconcile the discrepant results by proposing that when shorter interval durations are used, as in previous studies, beta resynchronization is interrupted by the presentation of a new stimulus, making it seem as if beta power peaks prior to upcoming stimuli. We emphasize caution with respect to the notion that the timing of beta synchronization is an expression of predictive timing.

The qEEG Signature of Selective NMDA NR2B Negative Allosteric Modulators; A Potential Translational Biomarker for Drug Development.

The antidepressant activity of the N-methyl-D-aspartate (NMDA) receptor channel blocker, ketamine, has led to the investigation of negative allosteric modulators (NAMs) selective for the NR2B receptor subtype. The clinical development of NR2B NAMs would benefit from a translational pharmacodynamic biomarker that demonstrates brain penetration and functional inhibition of NR2B receptors in preclinical species and humans. Quantitative electroencephalography (qEEG) is a translational measure that can be used to demonstrate pharmacodynamic effects across species. NMDA receptor channel blockers, such as ketamine and phencyclidine, increase the EEG gamma power band, which has been used as a pharmacodynamic biomarker in the development of NMDA receptor antagonists. However, detailed qEEG studies with ketamine or NR2B NAMs are lacking in nonhuman primates. The aim of the present study was to determine the effects on the qEEG power spectra of the NR2B NAMs traxoprodil (CP-101,606) and BMT-108908 in nonhuman primates, and to compare them to the NMDA receptor channel blockers, ketamine and lanicemine. Cynomolgus monkeys were surgically implanted with EEG radio-telemetry transmitters, and qEEG was measured after vehicle or drug administration. The relative power for a number of frequency bands was determined. Ketamine and lanicemine increased relative gamma power, whereas the NR2B NAMs traxoprodil and BMT-108908 had no effect. Robust decreases in beta power were elicited by ketamine, traxoprodil and BMT-108908; and these agents also produced decreases in alpha power and increases in delta power at the doses tested. These results suggest that measurement of power spectra in the beta and delta bands may represent a translational pharmacodynamic biomarker to demonstrate functional effects of NR2B NAMs. The results of these studies may help guide the selection of qEEG measures that can be incorporated into early clinical evaluation of NR2B NAMs in healthy humans.

Bicycling and Walking are Associated with Different Cortical Oscillatory Dynamics.

Although bicycling and walking involve similar complex coordinated movements, surprisingly Parkinson’s patients with freezing of gait typically remain able to bicycle despite severe difficulties in walking. This observation suggests functional differences in the motor networks subserving bicycling and walking. However, a direct comparison of brain activity related to bicycling and walking has never been performed, neither in healthy participants nor in patients. Such a comparison could potentially help elucidating the cortical involvement in motor control and the mechanisms through which bicycling ability may be preserved in patients with freezing of gait. The aim of this study was to contrast the cortical oscillatory dynamics involved in bicycling and walking in healthy participants. To this end, EEG and EMG data of 14 healthy participants were analyzed, who cycled on a stationary bicycle at a slow cadence of 40 revolutions per minute (rpm) and walked at 40 strides per minute (spm), respectively. Relative to walking, bicycling was associated with a stronger power decrease in the high beta band (23–35 Hz) during movement initiation and execution, followed by a stronger beta power increase after movement termination. Walking, on the other hand, was characterized by a stronger and persisting alpha power (8–12 Hz) decrease. Both bicycling and walking exhibited movement cycle-dependent power modulation in the 24–40 Hz range that was correlated with EMG activity. This modulation was significantly stronger in walking. The present findings reveal differential cortical oscillatory dynamics in motor control for two types of complex coordinated motor behavior, i.e., bicycling and walking. Bicycling was associated with a stronger sustained cortical activation as indicated by the stronger high beta power decrease during movement execution and less cortical motor control within the movement cycle. We speculate this to be due to the more continuous nature of bicycling demanding less phase-dependent sensory processing and motor planning, as opposed to walking.

Alpha and beta power decrease during enhanced cognitive effort in the basal ganglia: An intracerebral recording study

Purpose Cognitive adverse effects may accompany deep brain stimulation (DBS) treatment, as the basal ganglia have influence on widespread neocortical networks. The aim of this study was to investigate how complex motor-cognitive activities are processed in the subthalamic nucleus (STN) and internal globus pallidum (GPi). Methods Dystonia patients implanted with GPi-DBS electrodes ( n = 5), and individuals with Parkinson’s disease (PD) ( n = 4) or essential tremor ( n = 1) with STN-DBS electrodes performed two tasks involving the writing of single letters: 1. copying letters from a monitor; and 2. writing of any letter other than that appearing on the monitor. The cognitive load of the second task was increased relative to the first. Intracranial recordings of task-related oscillatory changes were assessed and compared. Results Local event-related alpha and beta desynchronization (ERD) were more expressed during the second task while the lower gamma synchronization (ERS) decreased regardless of the basal ganglia structure from which recordings were obtained or the clinical diagnosis. Task-related ERD differences recorded from the language-dominant left hemisphere correlated with a behavioural (RT) measure of cognitive effort. ERD changes declined after levodopa intake in PD patients. Conclusions The STN and Gpi participate in cognitive networks. Alpha and beta ERD seems to be essential during processing complex motor-cognitive tasks and increase with enhanced cognitive effort.

Aberrant prefrontal beta oscillations predict episodic memory encoding deficits in schizophrenia.

Verbal episodic memory is one of the core cognitive functions affected in patients with schizophrenia (SZ). Although this verbal memory impairment in SZ is a well-known finding, our understanding about its underlying neurophysiological mechanisms is rather scarce. Here we address this issue by recording brain oscillations during a memory task in a sample of healthy controls and patients with SZ. Brain oscillations represent spectral fingerprints of specific neurocognitive operations and are therefore a promising tool to identify neurocognitive mechanisms that are affected by SZ. Healthy controls showed a prominent suppression of left prefrontal beta oscillatory activity during successful memory formation, which replicates several previous oscillatory memory studies. In contrast, patients failed to exhibit such a left prefrontal beta power suppression. Utilizing a new topographical pattern similarity approach, we further demonstrate that the degree of similarity between a patient's beta power decrease to that of the controls reliably predicted memory performance. This relationship between beta power decreases and memory was such that the patients' memory performance improved as they showed a more similar topographical beta desynchronization pattern compared to that of healthy controls. Together, these findings support left prefrontal beta desynchronization as the spectral fingerprint of verbal episodic memory formation, likely indicating deep semantic processing of verbal material. These findings also demonstrate that left prefrontal beta power suppression (or lack thereof) during memory encoding are a reliable biomarker for the observed encoding impairments in SZ in verbal memory.

Deficits in low beta desynchronization reflect impaired emotional processing in schizophrenia

Empirical data from previous investigations showed that emotion processing is reflected in beta, and especially in low beta event related desynchronization (ERD) (i.e. a decrease in low beta power). While recognition of social information and emotion processing are impaired in schizophrenia, no previous study analyzed induced and evoked beta oscillations in patients with schizophrenia during emotion processing.Twenty-eight subjects with schizophrenia and twenty-seven healthy controls subjects were enrolled in the study. The two study groups did not differ in age, gender and education. Participants viewed positive, neutral and negative scenes selected from the International Affective Picture System (IAPS) while 128-channel EEG was recorded.A significantly weaker low beta ERD was detected in patients relative to controls for the negative stimulus condition in the right parieto-occipital and temporal regions. Patients with decreased beta ERD showed more prominent negative symptoms and more severe deficits in psychosocial functioning. Only in the control group stronger beta ERD was detected for the negative stimuli relative to positive and neutral stimuli in the same regions.Our major finding is that impaired emotion processing in schizophrenia is reflected in decreased low beta ERD and in the diminished differences between low beta ERD to negative and non-negative emotional stimuli. Furthermore, it was found that patients with decreased beta ERD show more prominent negative symptoms and more severe deficits in psychosocial functioning.

EEG based time and frequency dynamics analysis of visually induced motion sickness (VIMS).

3D movies are attracting the viewers as they can see the objects flying out of the screen. However, many viewers have reported various problems which are usually faced after watching 3D movies. These problems include visual fatigue, eye strain, headaches, dizziness, blurred vision or collectively may be termed as visually induced motion sickness (VIMS). This research focuses on the comparison between 3D passive technology with a conventional 2D technology to find that whether 3D is causing trouble in the viewers or not. For this purpose, an experiment was designed in which participants were randomly assigned to watch 2D or a 3D movie. The movie was specially designed to induce VIMS. The movie was shown for the duration of 10 min to every participant. The electroencephalogram (EEG) data was recorded throughout the session. At the end of the session, participants rated their feelings using simulator sickness questionnaire (SSQ). The SSQ data was analyzed and the ratings of 2D and 3D participants were compared statistically by using a two tailed t test. From the SSQ results, it was found that participants watching 3D movies reported significantly higher symptoms of VIMS (p value <0.05). EEG data was analyzed by using MATLAB and topographic plots are created from the data. A significant difference has been observed in the frontal-theta power which increases with the passage of time in 2D condition while decreases with time in 3D condition. Also, a decrease in beta power has been found in the temporal lobe of 3D group. Therefore, it is concluded that there are negative effects of 3D movies causing significant changes in the brain activity in terms of band powers. This condition leads to produce symptoms of VIMS in the viewers.

EEG Spectral Features Discriminate between Alzheimer's and Vascular Dementia.

Alzheimer’s disease (AD) and vascular dementia (VaD) present with similar clinical symptoms of cognitive decline, but the underlying pathophysiological mechanisms differ. To determine whether clinical electroencephalography (EEG) can provide information relevant to discriminate between these diagnoses, we used quantitative EEG analysis to compare the spectra between non-medicated patients with AD (n = 77) and VaD (n = 77) and healthy elderly normal controls (NC) (n = 77). We use curve-fitting with a combination of a power loss and Gaussian function to model the averaged resting-state spectra of each EEG channel extracting six parameters. We assessed the performance of our model and tested the extracted parameters for group differentiation. We performed regression analysis in a multivariate analysis of covariance with group, age, gender, and number of epochs as predictors and further explored the topographical group differences with pair-wise contrasts. Significant topographical differences between the groups were found in several of the extracted features. Both AD and VaD groups showed increased delta power when compared to NC, whereas the AD patients showed a decrease in alpha power for occipital and temporal regions when compared with NC. The VaD patients had higher alpha power than NC and AD. The AD and VaD groups showed slowing of the alpha rhythm. Variability of the alpha frequency was wider for both AD and VaD groups. There was a general decrease in beta power for both AD and VaD. The proposed model is useful to parameterize spectra, which allowed extracting relevant clinical EEG key features that move toward simple and interpretable diagnostic criteria.

40. Alpha and beta power decrease during enhanced cognitive effort in the basal ganglia: An intracerebral recording study

Cognitive adverse effects may accompany deep brain stimulation (DBS) treatment, as the basal ganglia have influence on widespread neocortical networks. The aim of this study was to investigate how complex motor-cognitive activities are processed in the subthalamic nucleus (STN) and internal globus pallidum (GPi). Dystonia patients implanted with GPi-DBS electrodes (n = 5), and individuals with Parkinson’s disease (PD) (n = 4) or essential tremor (n = 1) with STN-DBS electrodes performed two tasks involving the writing of single letters: 1. copying letters from a monitor; and 2. writing of any letter other than that appearing on the monitor. The cognitive load of the second task was increased relative to the first. Intracranial recordings of task-related oscillatory changes were assessed and compared. Local event-related alpha and beta desynchronization (ERD) were more expressed during the second task while the lower gamma synchronization (ERS) decreased regardless of the basal ganglia structure from which recordings were obtained or the clinical diagnosis. Task-related ERD differences recorded from the language-dominant left hemisphere correlated with a behavioural (RT) measure of cognitive effort. ERD changes declined after levodopa intake in PD patients. The STN and Gpi participate in cognitive networks. Alpha and beta ERD seems to be essential during processing complex motor-cognitive tasks and increase with enhanced cognitive effort.

Electroencephalography theta differences between object nouns and action verbs when identifying semantic relations

Nouns and verbs differ in their semantic properties and relationships with other words in the lexicon. This study uses electroencephalography (EEG) to investigate how word class differences influence semantic retrieval and identification of semantic relationships. Participants identified whether the final word in a triplet (noun or verb) was related to the first two words (both nouns). Time frequency analysis of the EEG revealed word class and relatedness effects in theta, beta and gamma. Decreases in beta power were found during action verbs, which may be related to motor processing. Theta exhibited a word class by relatedness interaction in which unrelated verbs elicited a greater power increase compared to other conditions. These data indicate that action verbs require more neural activity when identifying the absence of relationships than object nouns, likely due to the abstract, flexible nature of verb meanings and the shallow structure of verb organisation.

Beta oscillations, timing, and stuttering.

Beta oscillations, timing, and stuttering.

Listening to Mozart K.448 decreases electroencephalography oscillatory power associated with an increase in sympathetic tone in adults: a post-intervention study

SummaryObjectiveListening to Mozart K.448 has been demonstrated to improve spatial task scores, leading to what is known as the Mozart Effect. However, most of these reports only describe the phenomena but lack the scientific evidence needed to properly investigate the mechanism of Mozart Effect. In this study, we used electroencephalography (EEG) and heart rate variability (HRV) to evaluate the effects of Mozart K.448 on healthy volunteers to explore Mozart Effect.DesignAn EEG-based post-intervention analysis.SettingKaohsiung Medical University Hospital, Kaohsiung, Taiwan.ParticipantsTwenty-nine college students were enrolled. They received EEG and electrocardiogram examinations simultaneously before, during and after listening to the first movement of Mozart K.448.Main outcome measureEEG alpha, theta and beta power and HRV were compared in each stage.ResultsThe results showed a significant decrease in alpha, theta and beta power when they listened to Mozart K.448. In addition, the average root mean square successive difference, the proportion derived by dividing NN50 by the total number of NN intervals, standard deviations of NN intervals and standard deviations of differences between adjacent NN intervals showed a significant decrease, while the high frequency revealed a significant decrease with a significantly elevated low-frequency/high-frequency ratio.ConclusionListening to Mozart K.448 significantly decreased EEG alpha, theta and beta power and HRV. This study indicates that there is brain cortical function and sympathetic tone activation in healthy adults when listening to Mozart K.448, which may play an important role in the mechanism of Mozart Effect.

Processing Graded Feedback: Electrophysiological Correlates of Learning from Small and Large Errors

Feedback processing is important for learning and therefore may affect the consolidation of skills. Considerable research demonstrates electrophysiological differences between correct and incorrect feedback, but how we learn from small versus large errors is usually overlooked. This study investigated electrophysiological differences when processing small or large error feedback during a time estimation task. Data from high-learners and low-learners were analyzed separately. In both high- and low-learners, large error feedback was associated with higher feedback-related negativity (FRN) and small error feedback was associated with a larger P300 and increased amplitude over the motor related areas of the left hemisphere. In addition, small error feedback induced larger desynchronization in the alpha and beta bands with distinctly different topographies between the two learning groups: The high-learners showed a more localized decrease in beta power over the left frontocentral areas, and the low-learners showed a widespread reduction in the alpha power following small error feedback. Furthermore, only the high-learners showed an increase in phase synchronization between the midfrontal and left central areas. Importantly, this synchronization was correlated to how well the participants consolidated the estimation of the time interval. Thus, although large errors were associated with higher FRN, small errors were associated with larger oscillatory responses, which was more evident in the high-learners. Altogether, our results suggest an important role of the motor areas in the processing of error feedback for skill consolidation.

The effect of ((−)-2-oxa-4-aminobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (LY379268), an mGlu2/3 receptor agonist, on EEG power spectra and coherence in ketamine model of psychosis

In the present study we investigated the potential antipsychotic effects of the mGlu2/3 agonist LY379268 on changes in EEG power spectra and coherence in the ketamine model of psychosis. In order to use behaviorally active drug doses, experiments detecting changes in locomotor activity and sensorimotor gating were also conducted. In EEG experiments, adult male Wistar rats were injected with ketamine 30mg/kg i.p. and LY379268 3mg/kg i.p. Cortical EEG was recorded from twelve (2×6) electrodes placed homolaterally on each hemisphere. To avoid interference with the behavioral hyperactivity of ketamine challenge, the behavioral activity of animals was simultaneously registered at the time of recording. Subsequent power spectral and coherence analyses were assessed in epochs corresponding to behavioral inactivity. Analysis of segments with behavioral activity compared to inactivity was also performed. The effects of LY379268 3mg/kg i.p. on the deficits in sensorimotor processing and on hyperlocomotion induced by ketamine were evaluated in the test of prepulse inhibition of acoustic startle reaction (PPI ASR) and in the open field. LY379268 reversed the ketamine-induced hyperlocomotion but had no effect on ketamine-induced PPI deficits. In EEG epochs corresponding to behavioral inactivity ketamine decreased the power in the delta band, induced a power increase in the high frequency bands and globally decreased EEG coherence. Pretreatment with the LY379268 completely reversed the ketamine-induced power increase in high frequency bands and had a partial effect on EEG coherence. LY379268 alone induced a decrease of beta, high beta and low-gamma power, and an increase in coherence in high frequency bands. Additional analysis revealed that behavioral activity increases power as well as coherence in most frequency bands. In conclusion, agonism of mGlu2/3 receptors was effective in reversing most of the changes induced by ketamine, however due to the lack of effectiveness on PPI deficits its potential antipsychotic properties remain disputable.

Brain oscillatory subsequent memory effects differ in power and long-range synchronization between semantic and survival processing

Memory crucially depends on the way information is processed during encoding. Differences in processes during encoding not only lead to differences in memory performance but also rely on different brain networks. Although these assumptions are corroborated by several previous fMRI and ERP studies, little is known about how brain oscillations dissociate between different memory encoding tasks. The present study therefore compared encoding related brain oscillatory activity elicited by two very efficient encoding tasks: a typical deep semantic item feature judgment task and a more elaborative survival encoding task. Subjects were asked to judge words either for survival relevance or for animacy, as indicated by a cue presented prior to the item. This allowed dissociating pre-item activity from item-related activity for both tasks. Replicating prior studies, survival processing led to higher recognition performance than semantic processing. Successful encoding in the semantic condition was reflected by a strong decrease in alpha and beta power, whereas successful encoding in the survival condition was related to increased alpha and beta long-range phase synchrony. Moreover, a pre-item subsequent memory effect in theta power was found which did not vary with encoding condition. These results show that measures of local synchrony (power) and global long range-synchrony (phase synchronization) dissociate between memory encoding processes. Whereas semantic encoding was reflected in decreases in local synchrony, increases in global long range synchrony were related to elaborative survival encoding, presumably reflecting the involvement of a more widespread cortical network in this task.