Alpha Desynchronization Research Articles

Effects of subjective preference of colors on attention-related occipital theta oscillations

Human daily behaviors are often affected by subjective preferences. Studies have shown that physical responses are affected by unconscious preferences before conscious decision making. Accordingly, attention-related neural activities could be influenced by unconscious preferences. However, few neurological data exist on the relationship between visual attention and subjective preference. To address this issue, we focused on lateralization during visual attention and investigated the effects of subjective color preferences on visual attention-related brain activities. We recorded electroencephalograph (EEG) data during a preference judgment task that required 19 participants to choose their preferred color from 2 colors simultaneously presented to the right and left hemifields. In addition, to identify oscillatory activity during visual attention, we conducted a control experiment in which the participants focused on either the right or the left color without stating their preference. The EEG results showed enhanced theta (4-6 Hz) and decreased alpha (10-12 Hz) activities in the right and left occipital electrodes when the participants focused on the color in the opposite hemifield. Occipital theta synchronizations also increased contralaterally to the hemifield to which the preferred color was presented, whereas the alpha desynchronizations showed no lateralization. The contralateral occipital theta activity lasted longer than the ipsilateral occipital theta activity. Interestingly, theta lateralization was observed even when the preferred color was presented to the unattended side in the control experiment, revealing the strength of the preference-related theta-modulation effect irrespective of visual attention. These results indicate that subjective preferences modulate visual attention-related brain activities.

Differential Contribution of Right and Left Parietal Cortex to the Control of Spatial Attention: A Simultaneous EEG-rTMS Study

We have recently shown that interference with repetitive transcranial magnetic stimulation (rTMS) of right posterior intraparietal sulcus (IPS) cortex during the allocation of spatial attention leads to abnormal desynchronization of anticipatory (pretarget) electroencephalographic alpha rhythms (8-12 Hz) in occipital-parietal cortex and the detection of subsequently presented visual targets (Capotosto et al. 2009). Since lesion data suggest that lesions of the right frontoparietal cortices produce more severe and long-lasting deficits of visual spatial attention than lesions of the left hemisphere, here, we used the mentioned rTMS-electroencephalographic procedure to test if the control of anticipatory alpha rhythms by IPS is asymmetrically organized in the 2 hemispheres. Results showed that interference with either left or right IPS during covert spatial attention equally disrupted the normally lateralized anticipatory modulation of occipital visual cortex, with stronger alpha desynchronization contralaterally to the attended visual field. In contrast, only interference with right IPS induced a paradoxical pretarget synchronization of alpha rhythms and bilateral deficits of target identification. These results suggest that the control of spatial topography of anticipatory alpha rhythms in occipital-parietal cortex is shared between left and right IPS cortex, but that right IPS uniquely contributes to a bilateral prestimulus activation of occipital visual cortex.

Psychopathology and working memory‐induced activation of the prefrontal cortex in schizophrenia‐like psychosis of epilepsy: Evidence from magnetoencephalography

The aim of this study was to investigate whether magnetoencephalographic oscillations underlying working memory dysfunction in the dorsolateral prefrontal cortex (DLPFC) are related to psychopathological disturbance in patients with schizophrenia-like psychosis of epilepsy (SLPE). Twelve patients with SLPE and 14 non-psychotic epilepsy controls participated in this study. Magnetoencephalography was recorded while patients performed a visual working memory (WM) task. Psychopathology was assessed using a four-factor structure of the Brief Psychiatric Rating Scale, and regression analyses were carried out to examine the relative impact of severity of psychopathology on WM-induced activation of the DLPFC. We found that activation of the WM-compromising DLPFC, as indicated by increased alpha desynchronization in patients with SLPE compared with their non-psychotic counterparts, showed a positive linear correlation with disorganization symptom scores. This association remained significant after controlling for confounding factors, including age, task performance, IQ, and duration of psychosis. Our results indicate that abnormal activation in prefrontal areas engaged during working memory may be critical to domains of psychopathology, in particular disorganized thought-processing in patients with SLPE.

Modulation of subthalamic alpha activity to emotional stimuli correlates with depressive symptoms in Parkinson's disease1

Deep brain stimulation of the subthalamic nucleus is an effective treatment for patients with advanced Parkinson's disease. However, affective side effects following subthalamic deep brain stimulation have been reported. Here, we aim to elucidate the influence of affective state on emotional processing as indexed by local field potential activity and to identify neurophysiological markers in patients at risk of developing depressive symptoms during subthalamic deep brain stimulation. Subthalamic local field potentials were directly recorded via electrodes implanted for deep brain stimulation in 12 Parkinson's disease patients while viewing emotionally salient and neutral pictures. Parkinson's disease patients were assessed for depressive symptoms using the Beck depression inventory at the time of operation and 3 months after continuous subthalamic nucleus deep brain stimulation. We found a significant event-related desynchronization in the local alpha frequency band (8-12 Hz) for emotionally arousing but not neutral pictures. The the event-related desynchronization (ERD) in the alpha frequency band was reduced for pleasant stimuli in patients with mild to moderate depressive symptoms compared with patients without depression. The alpha-ERD to unpleasant stimuli showed the opposite pattern. Consistently, the index of event-related alpha desynchronization (alpha ERD for pleasant stimuli minus alpha ERD for unpleasant stimuli) correlated with the Beck depression inventory at the time of the recordings and at 3 months after continuous deep brain stimulation. The alpha ERD to unpleasant pictures correlated significantly with the Beck depression inventory score at 3 months after chronic deep brain stimulation. In conclusion, we found mood-congruent stimulus processing in the subthalamic nucleus of Parkinson's disease patients. Electrophysiological markers such as event-related desynchronization of subthalamic alpha activity reflect state-dependent emotional processing and may potentially be used to predict depressive mood disturbances in Parkinson's disease patients with chronic subthalamic deep brain stimulation at an early stage.

Indexing the graded allocation of visuospatial attention using anticipatory alpha oscillations

Lateralization in the desynchronization of anticipatory occipitoparietal alpha (8–12 Hz) oscillations has been implicated in the allocation of selective visuospatial attention. Previous studies have demonstrated that small changes in the lateralization of alpha-band activity are predictive of behavioral performance but have not directly investigated how flexibly alpha lateralization is linked to top-down attentional goals. To address this question, we presented participants with cues providing varying degrees of spatial certainty about the location at which a target would appear. Time-frequency analysis of EEG data demonstrated that manipulating spatial certainty led to graded changes in the extent to which alpha oscillations were lateralized over the occipitoparietal cortex during the cue-target interval. We found that individual differences in alpha desynchronization contralateral to attention predicted reaction times, event-related potential measures of perceptual processing of targets, and beta-band (15–25 Hz) activity typically associated with response preparation. These results support the hypothesis that anticipatory alpha modulation is a plausible neural mechanism underlying the allocation of visuospatial attention and is under flexible top-down control.

Aging and motor programming: differential effects according to the selection of action

There are controversial reports about the effect of aging on movement preparation, and it is unclear to which extent cognitive and/or motor related cerebral processes may be affected. This study examines the age effects on electro-cortical oscillatory patterns during various motor programming tasks, in order to assess potential differences according to the mode of action selection. Twenty elderly (EP, 60-84 years) and 20 young (YP, 20-29 years) participants with normal cognition underwent 3 pre-cued response tasks (S1-S2 paradigm). S1 carried either complete information on response side (Full; stimulus-driven motor preparation), no information (None; general motor alertness), or required free response side selection (Free; internally-driven motor preparation). Electroencephalogram (EEG) was recorded using 64 surface electrodes. Alpha (8-12 Hz) desynchronization (ERD)/synchronization (ERS) and motor-related amplitude asymmetries (MRAA) were analyzed during the S1-S2 interval. Reaction times (RTs) to S2 were slower in EP than YP, and in None than in the other 2 tasks. There was an Age x Task interaction due to increased RTs in Free compared to Full in EP only. Central bilateral and midline activation (alpha ERD) was smaller in EP than YP in None. In Full just before S2, readiness to move was reflected by posterior midline inhibition (alpha ERS) in both groups. In Free, such inhibition was present only in YP. Moreover, MRAA showed motor activity lateralization in both groups in Full, but only in YP in Free. The results indicate reduced recruitment of motor regions for motor alertness in the elderly. They further show less efficient cerebral processes subtending free selection of movement in elders, suggesting reduced capacity for internally-driven action with age.

MEG source imaging reveals robust sound induced low-frequency power decreases in the auditory cortex validated with intracerebral EEG

Event Abstract Back to Event MEG source imaging reveals robust sound induced low-frequency power decreases in the auditory cortex validated with intracerebral EEG Sarang S. Dalal1*, Nathan Weisz1, Aurélie Bidet-Caulet2, Françoise Lecaignard2, 3 and Olivier Bertrand2 1 University of Konstanz, Germany 2 INSERM U1028, CNRS UMR5292, France 3 CERMEP, France Despite some supportive data, the existence of an attention-modulated alpha-like rhythm in auditory cortex is still controversial. In order to settle this issue, we analyzed sound-induced alpha desynchronization using advanced MEG source imaging and compared the locus of the main generators with data gained from intracerebral EEG (iEEG) recordings using an identical paradigm. MEG/iEEG recordings were obtained while subjects performed an auditory discrimination task. The stimuli consisted of 50 ms tones, with frequently occurring standards (1000 Hz tone) and less frequently occurring distractors (1080 Hz) and targets (1040 Hz). A time-frequency beamformer was used to reconstruct and image spectral power modulations. In parallel to traditional evoked responses, significant beta band power decreases relative to pre-stimulus baseline were observed in bilateral auditory cortex, peaking at approximately 200 ms post-stimulus, followed by alpha band power decreases, peaking at approximately 500 ms. Frequency bands as well as source locations corresponded well with similar desynchronization effects found with iEEG. Taken together, our results strongly support the idea of ongoing alpha and beta activity in auditory cortex that is suppressed by an incoming sound. Importantly, we show that these processes can be monitored noninvasively using advanced source analysis methods. Funding: Supported by European Commission FP7 Grant PIIF-GA-2008-221097. Keywords: Cognition, MEG Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Poster Sessions: Neurophysiology of Cognition and Attention Citation: Dalal SS, Weisz N, Bidet-Caulet A, Lecaignard F and Bertrand O (2011). MEG source imaging reveals robust sound induced low-frequency power decreases in the auditory cortex validated with intracerebral EEG. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00485 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: 25 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Dr. Sarang S Dalal, University of Konstanz, Konstanz, Germany, sarang@frontiersin.org 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 Sarang S Dalal Nathan Weisz Aurélie Bidet-Caulet Françoise Lecaignard Olivier Bertrand Google Sarang S Dalal Nathan Weisz Aurélie Bidet-Caulet Françoise Lecaignard Olivier Bertrand Google Scholar Sarang S Dalal Nathan Weisz Aurélie Bidet-Caulet Françoise Lecaignard Olivier Bertrand PubMed Sarang S Dalal Nathan Weisz Aurélie Bidet-Caulet Françoise Lecaignard Olivier Bertrand 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.

Time course and specificity of sensory-motor alpha modulation during the observation of hand motor acts and gestures: a high density EEG study

The main aim of the present study was to explore, by means of high-density EEG, the intensity and the temporal pattern of event-related sensory-motor alpha desynchronization (ERD) during the observation of different types of hand motor acts and gestures. In particular, we aimed to investigate whether the sensory-motor ERD would show a specific modulation during the observation of hand behaviors differing for goal-relatedness (hand grasping of an object and meaningless hand movements) and social relevance (communicative hand gestures and grasping within a social context). Time course analysis of alpha suppression showed that all types of hand behaviors were effective in triggering sensory-motor alpha ERD, but to a different degree depending on the category of observed hand motor acts and gestures. Meaningless gestures and hand grasping were the most effective stimuli, resulting in the strongest ERD. The observation of social hand behaviors such as social grasping and communicative gestures, triggered a more dynamic time course of ERD compared to that driven by the observation of simple grasping and meaningless gestures. These findings indicate that the observation of hand motor acts and gestures evoke the activation of a motor resonance mechanism that differs on the basis of the goal-relatedness and the social relevance of the observed hand behavior.

Alpha band oscillations track temporal orienting of attention

AbstractIntroduction: Recent investigations using field-potential recordings in visual and auditory cortices have shown that oscillatory activity in neuronal ensembles become entrained to the timing of rhythmically presented stimuli according to their modality and location (Lakatos, Chen et al. 2007; Lakatos, Karmos et al. 2008; Lakatos, O'Connell et al. 2009). In spite of the evidence showing the role of brain oscillations on forming predictions about forthcoming sensory events (for a review (Engel, Fries et al. 2001), little is known about the role of such oscillations in the temporal orienting of attention (Nobre 2001; Coull and Nobre 2008). To test the effect of temporal orienting of attention on early perceptual processing, motor selection, and anticipatory low frequency oscillation (alpha waves), we analysed EEG data from healthy adults participants who were performing a visual perceptual discrimination task of targets preceded by rhythmic spatio-temporal cues. Methods: EEG was recorded continuously from 30 healthy, right-handed participants [mean age, 23.9 years (SD, 4.9 years); range, 19–32 years; 9 males], using a 34 Ag/AgCl electrodes at 1000Hz (AFZ ground, right mastoid reference) in an electrically shielded room. The task consisted of rhythmic stimuli that cued participants to the time and location that a subsequent target stimulus would occur after an occlusion (Fig. 1). At the beginning of each trial, a stimulus (ball - diameter:1.0°) appeared on the upper (50%) or lower (50%) left side of the screen and moved across the screen in a diagonal spatial trajectory of seven steps (200 ms for each step). Temporal orienting was induced by manipulating the SOA of each stimuli in three different conditions: fast (400 ms), slow (800 ms) and neutral, where the SOA within a trial was unpredictable, and varied randomly between 300-900 ms. Upon reaching an “occluder”, the ball disappeared for 600 (short occlusion) or 1400ms (long occlusion). When it reappeared on the right-hand side of the occluder, it contained an upright or tilted cross (200 ms, for which participants were required to discriminate the target, using a button-press response with either their right or left hand accordingly. The time-frequency analysis was performed in unfiltered continuous data, epoched from -700 to 1800 ms relative to the beginning of the occlusion period. Data from 12 participants had to be excluded from the analysis due to excessive artifacts in the EEG recordings or poor behavioural performance (accuracy < 60%). A multitaper time–frequency transformation was applied to all electrodes in each trial. This transformation produced an estimation of oscillatory power for each time sample and frequencies between 4 and 20 Hz. Alpha power (8 to 14 Hz) values were extracted from the epochs and submitted to a repeated-measures. All frequency analysis was done using Fieldtrip package ("http://www.ru.nl/fcdonders/fieldtrip/":http://www.ru.nl/fcdonders/fieldtrip/) for MATLAB (MatWorks). Results: To test the effect of reorienting of attention in time we analyzed alpha band oscillations during the long occlusion period. In this way we can observed the reorienting effect in the invalid (fast) trials, when participants have to shift their attention to the long occlusion given that the target did not appear after the expected cued (short) interval. This result reveals an alpha desynchronization preceding the expected target (blue dashed line). When comparing these oscillations within the same period for the slow (valid) rhythm, we observed that this desynchronization in alpha is only present when preceding by a fast, but not slow, rhythm [F(1,17) = 3.85; p = 0.029]. As can be observed in Figure 2, in the valid condition (slow rhythm) there is also a desynchronization of alpha preceding the cued late target. However, if we compare the alpha oscillations preceding the appearance of the later presented target for the valid and invalid temporal cues, no significant difference is observed [F(1,17) = 0.31; p = 0.905]. Conclusion: Our findings support the hypothesis that temporal orienting can also modulate brain oscillations, specifically in the alpha range. Importantly, we showed that in the invalid (fast) condition, in which participants were prepared for a target presentation after a short occlusion, there was also a preparation for the presentation of the later target. This indicates that participants were able to reorient their attention to the second interval given that the target fail to appear after the short (expected) occlusion.

Simultaneous EEG-fMRI in Patients with Unverricht-Lundborg Disease: Event-Related Desynchronization/Synchronization and Hemodynamic Response Analysis

We performed simultaneous acquisition of EEG-fMRI in seven patients with Unverricht-Lundborg disease (ULD) and in six healthy controls using self-paced finger extension as a motor task. The event-related desynchronization/synchronization (ERD/ERS) analysis showed a greater and more diffuse alpha desynchronization in central regions and a strongly reduced post-movement beta-ERS in patients compared with controls, suggesting a significant dysfunction of the mechanisms regulating active movement and movement end. The event-related hemodynamic response obtained from fMRI showed delayed BOLD peak latency in the contralateral primary motor area suggesting a less efficient activity of the neuronal populations driving fine movements, which are specifically impaired in ULD.

Hypnotizability-related EEG alpha and theta activities during visual and somesthetic imageries

Hypnotizability is a cognitive multidimensional trait that involves peculiar imagery characteristics. Subjects with high- (Highs) and low (Lows)-susceptibilities to hypnosis have shown different levels of skill at visual and somesthetic-guided imageries performed during upright stance. The aim of this experiment is to study the modulation of the EEG alpha and theta band amplitude during guided visual and somesthetic imageries in Highs and Lows, as these rhythms are responsive to the cognitive activities involved in mental imagery. Our results show that, at variance with standing subjects, subjects in both groups in a semi-reclined position report higher vividness and lower effort for visual than for somesthetic imagery. EEG patterns however are different between the two groups. Highs exhibit a more widespread alpha desynchronization and slightly different EEG patterns during visual and somesthetic imageries, while Lows show segregated alpha- and theta-desynchronization, without any difference between the tasks. Our results indicate that different, hypnotizability-related cognitive strategies, that are revealed by differences in EEG modulation, are responsible for the similar subjective experience associated with visual and somesthetic imageries in Highs and Lows. In addition, in both groups higher order mental representation of different sensory modalities might be subserved by a unique integrated neural network.

Frontoparietal Cortex Controls Spatial Attention through Modulation of Anticipatory Alpha Rhythms

A dorsal frontoparietal network, including regions in intraparietal sulcus (IPS) and frontal eye field (FEF), has been hypothesized to control the allocation of spatial attention to environmental stimuli. One putative mechanism of control is the desynchronization of electroencephalography (EEG) alpha rhythms (approximately 8-12 Hz) in visual cortex in anticipation of a visual target. We show that brief interference by repetitive transcranial magnetic stimulation (rTMS) with preparatory activity in right IPS or right FEF while subjects attend to a spatial location impairs identification of target visual stimuli approximately 2 s later. This behavioral effect is associated with the disruption of anticipatory (prestimulus) alpha desynchronization and its spatially selective topography in parieto-occipital cortex. Finally, the disruption of anticipatory alpha rhythms in occipital cortex after right IPS- or right FEF-rTMS correlates with deficits of visual identification. These results support the causal role of the dorsal frontoparietal network in the control of visuospatial attention, and suggest that this is partly exerted through the synchronization of occipital visual neurons.

An Analysis of Improving Memory Performance Based on EEG Alpha and Theta Oscillations

Evidence is presented that EEG oscillations in the alpha and theta band reflect memory performance in particular. Good performance is related to two types of EEG phenomena: a tonic increase in alpha but a decrease in theta power, and a large phasic decrease in alpha but increase in theta, depending on the type of memory demands. In a similar way as brain volume does, upper alpha power increases from early childhood to adulthood, whereas the opposite holds true for the late part of the lifespan. Alpha power is lowered and theta power enhanced in subjects with a variety of different neurological disorders. Furthermore, after sustained wakefulness and during the transition from waking to sleeping when the ability to respond to external stimuli ceases, upper alpha power decreases, whereas theta increases. Event-related changes indicate that the extent of upper alpha desynchronization is positively correlated with (semantic) long-term memory performance, whereas theta synchronization is positively correlated with the ability to encode new information.

Alpha Brain Oscillations and Inhibitory Control

A major challenge for developmental cognitive neuroscience is to understand how changes in cognitive functions related to aging are associated with changes in the neuronal information processing architecture. Previous studies on EEG event-related brain oscillations suggest functional changes in alpha-bands with age during sensory and memory tasks. Specifically, the topographical distribution of both single-trial lower and upper alpha magnitude and the corresponding phase coherence is altered in elderly persons. Thus, alpha oscillations, associated not only with sensory, but also with sensorimotor functions, may be altered with age. Compensatory mechanisms, possibly reflected in increased frontal alpha synchronization, may thereby be of profound relevance. The present study investigates age-related differences in the modulation of alpha oscillatory activity related to sensory and sensorimotor functions, including response preparation, execution, and inhibition. EEG was recorded while 10 young and 10 elderly persons performed a visual evoked potential (VEP), a cued stimulus response (S-R), and a cued visual Go/NoGo task. Early event-related synchronization (ERS, 0–250 ms) and late event-related desynchronization (ERD, 200–600 ms) of single-trial lower and upper alpha was analyzed using poststimulus amplitude enhancement and intertrial phase coherence measures. The results show comparable modulations of lower (8–10 Hz) and upper (10–15 Hz) alpha activity in young and elderly related to the sensory and different forms of motor response processing. Specifically, reduced early lower alpha ERS as well as late upper alpha ERD at central locations characterized response inhibition processing in both age groups. We discuss the counterintuitive hypothesis that reduced efficacy of some basal neural inhibitory mechanisms enables older observers to perform better than or comparable to younger observers on some visual tasks, and conclude that alterations in alpha oscillatory networks with age may depend on the stimuli applied.

Effects of rTMS on an Auditory Oddball Task: A Pilot Study of Cortical Plasticity and the EEG

The objective of this study was to explore the effects of 1Hz repetitive transcranial magnetic stimulation (rTMS) applied to dorsal lateral prefrontal cortex (DLPFC) on both an EEG index of cortical excitation and inhibition, event-related desynchronization/ synchronization (ERDIS) and on the P300 component of an auditory oddball-induced ERP. Eight normal participants received 15 minutes of 1Hz rTMS at 110% of the resting motor threshold to right DLPFC. ERDIS of alpha and beta bands was measured during an auditory oddball task immediately before and after stimulation. There was significantly less alpha desynchronization post-TMS, and this effect was widespread excepting posterior midline sites. No changes were found to oddball-P300 amplitudes or latencies. In conclusion, the findings of less alpha desynchronization post-TMS are compatible with notions of slow rTMS causing a decrease in cortical excitation.

Auditory processing indexed by stimulus-induced alpha desynchronization in children

By means of magnetoencephalography (MEG), we investigated event-related synchronization and desynchronization (ERS/ERD) in auditory cortex activity, recorded from twelve children aged four to six years, while they passively listened to a violin tone and a noise-burst stimulus. Time–frequency analysis using Wavelet Transform was applied to single-trials of source waveforms observed from left and right auditory cortices. Stimulus-induced changes in non-phase-locked activities were evident. ERS in the beta range (13–30 Hz) lasted only for 100 ms after stimulus onset. This was followed by prominent alpha ERD, which showed a clear dissociation between the upper (12 Hz) and lower (8 Hz) alpha range in both left and right auditory cortices for both stimuli. The time courses of the alpha ERD (onset around 300 ms, peak at 500 ms, offset after 1500 ms) were similar to those previously found for older children and adults with auditory memory related tasks. For the violin tone only, the ERD lasted longer in the upper than the lower alpha band. The findings suggest that induced alpha ERD indexes auditory stimulus processing in children without specific cognitive task requirement. The left auditory cortex showed a larger and longer-lasting upper alpha ERD than did the right auditory cortex, likely reflecting hemispheric differences in maturational stages of neural oscillatory mechanisms.

Posterior parietal cortex controls spatial attention through modulation of anticipatory alpha rhythms

AbstractA dorsal fronto-parietal network, including regions in intra-parietal sulcus (IPS) and frontal eye field (FEF), has been hypothesized to control the allocation of spatial attention to environmental stimuli. One putative mechanism of control is the de-synchronization of electroencephalography (EEG) alpha rhythms (~8-12 Hz) in parieto-occipital cortex in anticipation of a visual target. We show that brief interference by transcranial magnetic stimulation (rTMS) with preparatory activity in right IPS or right FEF while subjects attend to a spatial location impairs identification of target stimuli ~2 seconds later. Moreover, the visual deficit relates to the disruption of anticipatory (pre-stimulus) alpha desynchronization and its topography in parieto-occipital cortex. After right IPS stimulation, the degree to which alpha desynchronization is suppressed predicts the speed of visual identification. These results demonstrate the causal role of posterior parietal cortex in the control of visuo-spatial attention exerted through the synchronization of visual neurons.

Event-related alpha desynchronization on human scalp EEG during alphabetic character discrimination task

Event-related alpha desynchronization on human scalp EEG during alphabetic character discrimination task

Alpha synchronization during auditory spatial short-term memory

Recent studies have suggested an active role of cortical alpha oscillations for cognitive functions including short-term memory. We used magnetoencephalography to assess alpha activity during an auditory spatial delayed matching-to-sample task compared with a nonmemory control condition. In the memory task, participants had to memorize the lateralization angle of a noise stimulus S1 and compare it with another lateralized sound S2 presented after an 800-ms delay phase. Whereas alpha desynchronization following S1 was observed over superior temporal areas under both conditions, only the memory task was accompanied by posterior parietal alpha synchronization during the subsequent delay period. The findings are consistent with the notion of alpha activity reflecting active inhibition of interfering processes during memory maintenance of spatial sounds.

P36.39 Event-related alpha desynchronization on human scalp EEG during alphabetic character discrimination task

P36.39 Event-related alpha desynchronization on human scalp EEG during alphabetic character discrimination task