Gamma-band Responses Research Articles

Multiple Reference Frames in Cortical Oscillatory Activity during Tactile Remapping for Saccades

Single-unit recordings have shown that the brain uses multiple reference frames in spatial processing. The brain could use this neural architecture to implicitly create multiple modes of representation at the population level, with each reference frame weighted as a function of task demands. Using magnetoencephalography, we tested this hypothesis by studying the reference frames in rhythmic neuronal synchronization--a population measure--during tactile remapping for saccades. Human subjects fixated either to the left or right of the body midline, while a tactile stimulus was applied to an invisible fingertip, located either left or right of fixation. After a variable delay, they looked at the remembered stimulus location. Results show a transient body-centered, stimulus-induced gamma-band response (70-90 Hz) in somatosensory areas, contralateral to the stimulated hand. Concurrently, a gamma-band response occurred in posterior parietal cortex (PPC), contralateral to the gaze-centered location of the stimulus, even though the stimulus was not seen. The temporal overlap of these early representations suggests that there is a fast bottom-up sensory-induced remapping in PPC, taking into account the relative positions of eyes and hand. The gaze-centered representation in PPC was sustained in a high gamma range (85-115 Hz) and increased in power closer to the initiation of the saccade. Lower-frequency rhythms (alpha, beta) showed body-centered power modulations in somatosensory areas in anticipation of the stimulus and a mixture of reference frames in PPC after stimulus presentation. We conclude that oscillatory activity reflects the time-varying coding of information in body- and gaze-centered reference frames during tactile remapping for saccades.

Functional and structural correlates of the aging brain: Relating visual cortex (V1) gamma band responses to age‐related structural change

The gamma band response is thought to be a key neural signature of information processing in the mammalian brain, yet little is known about how age-related maturation influences the γ-band response. Recent MRI-based studies have shown that brain maturation is accompanied by clear structural changes in both gray and white matter, yet the correspondence of these changes to brain function is unclear. The objective of this study was to relate visual cortex (V1) γ-band responses to age-related structural change. We evaluated MEG measured γ-band responses to contrast gratings stimuli and structural MRIs from participants observed from two separate research centers (MEG lab at CUBRIC, Cardiff University, UK, and the Lurie Family Foundations MEG Imaging Center, (CHOP) at the Children's Hospital of Philadelphia). Pooled participant data (N = 59) ranged in age from 8.7 to 45.3 years. We assessed linear associations between age and MEG γ-band frequency and amplitude, as well as between age and MRI volumetric parameters of the occipital lobe. Our MEG findings revealed a significant negative correlation for gamma band frequency versus age. Volumetric brain analysis from the occipital lobe also revealed significant negative correlations between age and the cortical thickness of pericalcarine and cuneus areas. Our functional MEG and structural MRI findings shows regionally specific changes due to maturation and may thus be informative for understanding physiological processes of neural development, maturation, and age-related decline. In addition, this study represents (to our knowledge), the first published demonstration of multicenter data sharing across MEG centers.

Induced gamma band responses in human EEG after the control of miniature saccadic artifacts

Induced gamma band responses (iGBRs) in the human electroencephalogram (EEG) have been ascribed to the activation of cortical object representations. Recently, this claim was challenged and it was stated that iGBRs occurring in the time window between 200 and 350 ms after stimulus onset are, to a great extent, generated by an electromyogenic artifact caused by miniature saccades (MS). In the present paper we focus on the characterization of iGBRs during the activation of cortical object representations, when recordings have been controlled for saccade-related transient potentials. For this we present an algorithm for the correction of saccade-related transient potentials (COSTRAP) which identifies and notably suppresses transient spike potentials (TSPs) that are likely to be linked to MSs. Furthermore, we conducted an EEG study to demonstrate (1) the feasibility of the algorithm, (2) the cortical origin iGBRs and (3) their relation to cortical object representations. Our results revealed that (i) it is possible to isolate TSPs, (ii) the morphology of the cleansed iGBR cannot be explained by an underlying myogenic artifact and (iii) the remaining iGBRs are sensitive to object recognition. Therefore we conclude that, with saccadic artifacts being controlled, high-frequency oscillations in human EEG are reliable electrophysiological correlates of cognitive processes.

Auditory Event-Related Response in Visual Cortex Modulates Subsequent Visual Responses in Humans

Growing evidence from electrophysiological data in animal and human studies suggests that multisensory interaction is not exclusively a higher-order process, but also takes place in primary sensory cortices. Such early multisensory interaction is thought to be mediated by means of phase resetting. The presentation of a stimulus to one sensory modality resets the phase of ongoing oscillations in another modality such that processing in the latter modality is modulated. In humans, evidence for such a mechanism is still sparse. In the current study, the influence of an auditory stimulus on visual processing was investigated by measuring the electroencephalogram (EEG) and behavioral responses of humans to visual, auditory, and audiovisual stimulation with varying stimulus-onset asynchrony (SOA). We observed three distinct oscillatory EEG responses in our data. An initial gamma-band response around 50 Hz was followed by a beta-band response around 25 Hz, and a theta response around 6 Hz. The latter was enhanced in response to cross-modal stimuli as compared to either unimodal stimuli. Interestingly, the beta response to unimodal auditory stimuli was dominant in electrodes over visual areas. The SOA between auditory and visual stimuli--albeit not consciously perceived--had a modulatory impact on the multisensory evoked beta-band responses; i.e., the amplitude depended on SOA in a sinusoidal fashion, suggesting a phase reset. These findings further support the notion that parameters of brain oscillations such as amplitude and phase are essential predictors of subsequent brain responses and might be one of the mechanisms underlying multisensory integration.

The role of gamma-band activity in the representation of faces: reduced activity in the fusiform face area in congenital prosopagnosia.

BackgroundCongenital prosopagnosia (CP) describes an impairment in face processing that is presumably present from birth. The neuronal correlates of this dysfunction are still under debate. In the current paper, we investigate high-frequent oscillatory activity in response to faces in persons with CP. Such neuronal activity is thought to reflect higher-level representations for faces.MethodologySource localization of induced Gamma-Band Responses (iGBR) measured by magnetoencephalography (MEG) was used to establish the origin of oscillatory activity in response to famous and unknown faces which were presented in upright and inverted orientation. Persons suffering from congenital prosopagnosia (CP) were compared to matched controls.Principal FindingsCorroborating earlier research, both groups revealed amplified iGBR in response to upright compared to inverted faces predominately in a time interval between 170 and 330 ms and in a frequency range from 50–100 Hz. Oscillatory activity upon known faces was smaller in comparison to unknown faces, suggesting a “sharpening” effect reflecting more efficient processing for familiar stimuli. These effects were seen in a wide cortical network encompassing temporal and parietal areas involved in the disambiguation of homogenous stimuli such as faces, and in the retrieval of semantic information. Importantly, participants suffering from CP displayed a strongly reduced iGBR in the left fusiform area compared to control participants.ConclusionsIn sum, these data stress the crucial role of oscillatory activity for face representation and demonstrate the involvement of a distributed occipito-temporo-parietal network in generating iGBR. This study also provides the first evidence that persons suffering from an agnosia actually display reduced gamma band activity. Finally, the results argue strongly against the view that oscillatory activity is a mere epiphenomenon brought fourth by rapid eye-movements (micro saccades).

The genetic and environmental influences of event-related gamma oscillations on bipolar disorder

Gamma oscillations have been proposed to play an important role in neural information coding. There have been a limited number of electrophysiology studies in evoked gamma band responses (GBRs) in bipolar disorder (BPD). It is also unclear whether GBR deficits, if present, are potential endophenotypes for BPD as little is known about the heritability of GBRs. The present study aimed to examine whether GBRs derived from two auditory tasks, the oddball task and the dual-click paradigm, are potential BPD endophenotypes. A total of 308 subjects were included in this study: 198 healthy controls, 59 BPD patients (22 monozygotic BPD twins and 37 BPD patients from 31 families), and 51 unaffected relatives. The evoked gamma responses were calculated using a Morlet wavelet transformation. Structural equation modelling was applied to obtain the genetic (heritability) and environment estimates in each GBR variable and their (genetic) overlap with BPD. The heritability estimates of GBR to standard stimuli were 0.51 and 0.35 to target stimuli in the oddball task. However, neither response type was impaired in BPD patients or their unaffected relatives. The heritability estimates of GBR to S1 stimuli were 0.54 and 0.50 to S2 stimuli in the dual-click paradigm. BPD patients had reduced gamma power and suppression to S1 stimuli but their unaffected relatives did not. Evoked GBRs are heritable traits. However, GBR deficits are not observed in clinically unaffected relatives nor associated with BPD. Gamma responses do not appear to satisfy criteria for being BPD endophenotypes.

Intracranial Study of Speech-Elicited Activity on the Human Posterolateral Superior Temporal Gyrus

To clarify speech-elicited response patterns within auditory-responsive cortex of the posterolateral superior temporal (PLST) gyrus, time-frequency analyses of event-related band power in the high gamma frequency range (75-175 Hz) were performed on the electrocorticograms recorded from high-density subdural grid electrodes in 8 patients undergoing evaluation for medically intractable epilepsy. Stimuli were 6 stop consonant-vowel (CV) syllables that varied in their consonant place of articulation (POA) and voice onset time (VOT). Initial augmentation was maximal over several centimeters of PLST, lasted about 400 ms, and was often followed by suppression and a local outward expansion of activation. Maximal gamma power overlapped either the Nα or Pβ deflections of the average evoked potential (AEP). Correlations were observed between the relative magnitudes of gamma band responses elicited by unvoiced stop CV syllables (/pa/, /ka/, /ta/) and their corresponding voiced stop CV syllables (/ba/, /ga/, /da/), as well as by the VOT of the stimuli. VOT was also represented in the temporal patterns of the AEP. These findings, obtained in the passive awake state, indicate that PLST discriminates acoustic features associated with POA and VOT and serve as a benchmark upon which task-related speech activity can be compared.

Frequency-specific electrocorticographic correlates of working memory delay period fMRI activity

Electrocorticography (ECoG) and functional MRI (BOLD–fMRI) have been used previously to measure brain activity during working memory delay periods. These studies have separately reported oscillation changes in the theta (4–8Hz) band and BOLD–fMRI increases during delay periods when information is maintained in memory. However, it is not known how intracranial cortical field potential (CFP) changes relate to BOLD–fMRI responses during delay periods. To answer this question, fMRI was obtained from six epilepsy patients during a visual working memory task. Then, following subdural macroelectrode implant, continuous ECoG was used to record CFPs during the same task. Time–frequency analyses showed delay period gamma band oscillation amplitude increases on electrodes located near fMRI activity, while in the theta band changes were higher for electrodes located away from fMRI activation. The amplitude of the ECoG gamma band response was significantly positively correlated with the fMRI response, while a negative correlation was found for the theta band. The findings are consistent with previous reports of local field potential (LFP) coupling in the gamma band with BOLD–fMRI responses during visual stimulation in monkeys, but are novel in that the relationship reported here persists after the disappearance of visual stimuli while information is being maintained in memory. We conclude that there is a relationship between BOLD–fMRI increases and human working memory delay period gamma oscillation increases and theta decreases. The spectral profile change provides a basis for comparison of working memory delay period BOLD–fMRI with field potential recordings in animals and other human intracranial EEG studies.

Direct Evidence for Two Different Neural Mechanisms for Reading Familiar and Unfamiliar Words: An Intra-Cerebral EEG Study

After intensive practice, unfamiliar letter strings become familiar words and reading speed increases strikingly from a slow processing to a fast and with more global recognition of words. While this effect has been well documented at the behavioral level, its neural underpinnings are still unclear. The question is how the brain modulates the activity of the reading network according to the novelty of the items. Several models have proposed that familiar and unfamiliar words are not processed by separate networks but rather by common regions operating differently according to familiarity. This hypothesis has proved difficult to test at the neural level because the effects of familiarity and length on reading occur (a) on a millisecond scale, shorter than the resolution of fMRI and (b) in regions which cannot be isolated with non-invasive EEG or MEG. We overcame these limitations by using invasive intra-cerebral EEG recording in epileptic patients. Neural activity (gamma-band responses, between 50 and 150 Hz) was measured in three major nodes of reading network – left inferior frontal, supramarginal, and inferior temporo-occipital cortices – while patients silently read familiar (words) and unfamiliar (pseudo-words) items of two lengths (short composed of one-syllable vs. long composed of three-syllables). While all items elicited strong neural responses in the three regions, we found that the duration of the neural response increases with length only for pseudo-words, in direct relation to orthographic-to-phonological conversion. Our results validate at the neural level the hypothesis that all words are processed by a common network operating more or less efficiently depending on words’ novelty.

Disassociation between gamma power and visual evoked potential revealed in human visual cortex

Event Abstract Back to Event Disassociation between gamma power and visual evoked potential revealed in human visual cortex Eran Privman1* 1 Blavatnik School of Computer Science, Tel-Aviv University, Israel Recently scalp magnetoencephalography (MEG) studies revealed a rapid evoked response adaptation where one visual stimulus suppresses the evoked response (ERP) to the second stimulus. Here we investigated this effect using subdural intracranial recordings in humans. Our results show that the suppression of the ERP does not involve a reduction in neuronal activity - since gamma band responses remained unaffected. Rather, the ERP suppression was tightly related to the level of gamma activity preceding the event, and this effect was independent of the inter-stimulus interval. We propose that the ERP suppression is due to a desynchronization of neuronal firing resulting from recurrent neural activity in the vicinity of the freshly stimulated neurons and not an attenuation of the overall neural activity. This evoked potential suppression (EPS) effect can therefore serve as a robust marker for gamma-band activity even in non-invasive scalp EEG recordings. Due to its neuronal selectivity the EPS could provide a unique tool to study the tuning properties of human cortical neurons. Keywords: EEG, neural activity Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Symposium: Oral Presentation Topic: Symposium 7: From single neuron responses to neuronal population oscillations during vision and memory: new insights from human intracranial recordings Citation: Privman E (2011). Disassociation between gamma power and visual evoked potential revealed in human visual cortex. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00043 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: 09 Nov 2011; Published Online: 15 Nov 2011. * Correspondence: Dr. Eran Privman, Blavatnik School of Computer Science, Tel-Aviv University, Tel-Aviv, Israel, eran.privman@gmail.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 Eran Privman Google Eran Privman Google Scholar Eran Privman PubMed Eran Privman 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.

Dissociating explicit and implicit face processing in the amygdala and fusiform face area with intracranial gamma band responses

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The neural facebook": exemplar selectivity in human face-selective areas revealed through intracranial EEG recordings

Event Abstract Back to Event The neural facebook": exemplar selectivity in human face-selective areas revealed through intracranial EEG recordings Ido Davidesco1*, Stephan Bickel2, Elana Zion-Golumbic3, Michal Harel4, Charles E. Schroeder3, Ashesh D. Mehta2 and Rafael Malach4 1 Hebrew University of Jerusalem, Israel 2 Long Island Jewish Medical Center, New Hyde Park, United States 3 Columbia University College of Physicians and Surgeons & Nathan Kline Institute, United States 4 Weizmann Institute of Science, Israel Humans have a remarkable ability to distinguish between different faces, familiar and unfamiliar alike. However, fMRI studies of high-order visual cortex generally show only category selectivity (e.g. preference for faces), not selectivity for individual exemplars from the same category. Exemplar selectivity has been inferred so far only indirectly from adaptation effects. Here, we examined this issue directly, using intracranial EEG recordings (iEEG) in epilepsy patients monitored for presurgical evaluation. The patients were presented with images of faces, houses, objects and patterns. Each individual image was repeated 6 times throughout the experiment. Our results show that in addition to category selectivity, high-order visual regions, especially face-related areas (e.g. Fusiform face area, FFA), exhibit exemplar selectivity. Comparing the Gamma band responses to optimal and non-optimal stimuli from the same category showed a highly significant decline to about 30%. This effect was highly reproducible within each patient and across patients. Interestingly, the optimal face exemplars, which yielded the strongest response, were different in each electrode, even when the electrodes were adjacent. Control experiments were performed in order to verify that this effect can not be explained by low level differences between the exemplars. These results demonstrate clear exemplar selectivity in human high-order visual areas. Furthermore, the high selectivity evident in the mass local field potentials - likely reflecting activity in thousands of neurons - points to the clustering of these neurons in exemplar-selective cortical patches or columns. Such exemplar selectivity provides the neuronal substrate for individual identification in human observers. Funding: Supported by ISF, Bikura, and Mark Scher’s estate grants to RM. Keywords: EEG, Intra-cranial Electrophysiology Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Abstracts Citation: Davidesco I, Bickel S, Zion-Golumbic E, Harel M, Schroeder CE, Mehta AD and Malach R (2011). The neural facebook": exemplar selectivity in human face-selective areas revealed through intracranial EEG recordings. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00071 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: 16 Nov 2011; Published Online: 25 Nov 2011. * Correspondence: Dr. Ido Davidesco, Hebrew University of Jerusalem, Jerusalem, Israel, idd@netvision.net.il 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 Ido Davidesco Stephan Bickel Elana Zion-Golumbic Michal Harel Charles E Schroeder Ashesh D Mehta Rafael Malach Google Ido Davidesco Stephan Bickel Elana Zion-Golumbic Michal Harel Charles E Schroeder Ashesh D Mehta Rafael Malach Google Scholar Ido Davidesco Stephan Bickel Elana Zion-Golumbic Michal Harel Charles E Schroeder Ashesh D Mehta Rafael Malach PubMed Ido Davidesco Stephan Bickel Elana Zion-Golumbic Michal Harel Charles E Schroeder Ashesh D Mehta Rafael Malach 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.

Beyond the saccadic spike potential ? scalp EEG manifestation of cerebral induced gamma band responses to visual stimuli

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Transient and steady-state auditory gamma-band responses in first-degree relatives of people with autism spectrum disorder

BackgroundStimulus-related γ-band oscillations, which may be related to perceptual binding, are reduced in people with autism spectrum disorders (ASD). The purpose of this study was to examine auditory transient and steady-state γ-band findings in first-degree relatives of people with ASD to assess the potential familiality of these findings in ASD.MethodsMagnetoencephalography (MEG) recordings in 21 parents who had a child with an autism spectrum disorder (pASD) and 20 healthy adult control subjects (HC) were obtained. Gamma-band phase locking factor (PLF), and evoked and induced power to 32, 40 and 48 Hz amplitude-modulated sounds were measured for transient and steady-state responses. Participants were also tested on a number of behavioral and cognitive assessments related to the broad autism phenotype (BAP).ResultsReliable group differences were seen primarily for steady-state responses. In the left hemisphere, pASD subjects exhibited lower phase-locked steady-state power in all three conditions. Total γ-band power, including the non-phase-locked component, was also reduced in the pASD group. In addition, pASD subjects had significantly lower PLF than the HC group. Correlations were seen between MEG measures and BAP measures.ConclusionsThe reduction in steady-state γ-band responses in the pASD group is consistent with previous results for children with ASD. Steady-state responses may be more sensitive than transient responses to phase-locking errors in ASD. Together with the lower PLF and phase-locked power in first-degree relatives, correlations between γ-band measures and behavioral measures relevant to the BAP highlight the potential of γ-band deficits as a potential new autism endophenotype.

Induced Gamma-Band Activity and Fixational Eye Movements are Differentially Influenced by Low-and High-Level Factors in a Visual Object Classification Task

Until recently induced high frequency oscillatory activity (gamma-band activity; >30 Hz) was considered a neural marker of cortical object representation. However, Yuval-Greenberg et al (2008; Neuron) demonstrated that induced gamma-band activity (GBA) in the elecetroencephalogram (EEG) is susceptible to artifacts caused by miniature eye movements, which account for the major part of the signal in the crucial time window of 200-400 ms after stimulus onset. Is there an underlying cortical-induced gamma-band response that is obscured by ocular artifacts but can still be recorded with EEG? Furthermore, if object-specific modulations of induced GBA in previous studies were caused by ocular artifacts, should we instead study fixational eye movements as a response that can reflect higher-level representational processes in vision? In order to investigate this, we conducted an eye tracking experiment and an EEG experiment using the same design. Participants were asked to classify line drawings of objects or non-objects. To introduce low-level differences, their contours were defined along different directions in cardinal colour space: 1) S-cone-isolating (S), or 2) intermediate isoluminant (S and L-M), or 3) a full-colour stimulus, containing an additional achromatic component (S; L-M; L+M+S). In both experiments, behavioural performance was optimal for full-colour stimuli. In the eye tracking experiment, fixational eye movement rates 200-400 ms after stimulus onset depended on low-level factors, with no difference between objects and non-objects. In the EEG experiment, miniature eye movements were identified and removed using the saccadic filter approach. The artifact-free induced GBA exhibited a lateralised distribution, with enhancements at left and right posterior sites. Activity was higher for full-colour objects on the left, with the opposite effect observed on the right. We conclude that induced GBA can be observed in the EEG. While it showed high-level object-specific modulations, miniature eye movements were driven solely by low-level information.

On electroencephalographic (EEG)-entrainment via transcranial alternating current (tacs) and sensory stimulation

Event Abstract Back to Event On electroencephalographic (EEG)-entrainment via transcranial alternating current (tacs) and sensory stimulation Christoph S. Herrmann1* 1 Carl-von-Ossietzky Universität, Germany Neural activity can be entrained by sensory and electromagnetic stimuli if stimulation is repetitive. We have performed two entrainment experiments to demonstrate this effect. In the first experiment, 21 subjects were entrained with auditory stimuli that elicited steady-state auditory evoked potentials (SSAEPs) in the subjects’ electroencephalogram (EEG). The stimuli were amplitude-modulated sine tones whose modulation frequency ranged from 1 to 250 Hz. SSAEPs revealed amplitude maxima around 45 Hz stimulation frequency, probably reflecting a resonance frequency of auditory cortex. In addition, auditory evoked potentials (AEPs) in response to 1000 Hz tones were recorded from the same 21 subjects and AEPs were analyzed in the frequency domain. It turned out that the frequency of the evoked gamma-band response in AEPs correlated with the frequency of the maximum SSAEP. Thus, we speculate that the resonance frequencies determine the frequency spectrum of the AEP. In the second experiment, we applied transcranial alternating current stimulation (tACS) that has been introduced to directly modulate rhythmic brain activity by the application of oscillatory currents. Until now, the efficiency of tACS in modulating rhythmic brain activity has been mainly indicated by inference from the perceptual and behavioural consequences. We delivered tACS over the occipital cortex of 10 healthy participants to entrain the neuronal oscillations in their individual alpha frequency range and compared results with those from a separate group of participants receiving sham stimulation. The tACS but not the sham stimulation elevated EEG alpha power. The results demonstrate the ability of tACS to modulate oscillatory brain activity at a specific frequency. Keywords: EEG, neural activity, SSAEPs Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Symposium: Oral Presentation Topic: Symposium 10: Entraining the brain? Effects of rhythmic brain stimulation protocols on oscillatory brain activity and behavior Citation: Herrmann CS (2011). On electroencephalographic (EEG)-entrainment via transcranial alternating current (tacs) and sensory stimulation. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00527 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: 09 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Prof. Christoph S Herrmann, Carl-von-Ossietzky Universität, Oldergurg, Germany, christoph.herrmann@uni-oldenburg.de 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 Christoph S Herrmann Google Christoph S Herrmann Google Scholar Christoph S Herrmann PubMed Christoph S Herrmann 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.

Gamma in motion: Pattern reversal elicits stronger gamma-band responses than motion

Previous studies showed higher gamma-band responses (GBRs, ≈40Hz) of the electroencephalogram (EEG) for moving compared to stationary stimuli. However, it is unclear whether this modulation by motion reflects a special responsiveness of the GBR to the stimulus feature “motion,” or whether GBR enhancements of similar magnitude can be elicited also by a salient change within a static stimulus that does not include motion.Therefore, we measured the EEG of healthy subjects watching stationary square wave gratings of high contrast that either started to move or reversed their black and white pattern shortly after their onset. The strong contrast change of the pattern reversal represented a salient but motionless change within the grating that was compared to the onset of the stationary grating and the motion onset. Induced and evoked GBRs were analyzed for all three display conditions. In order to assess the influenceof fixational eye movements on the induced GBRs, we also examined the time courses of microsaccade rates during the three display conditions.Amplitudes of both evoked and induced GBRs were stronger for pattern reversal than for motion onset. There was no significant amplitude difference between the onsets of the stationary and moving gratings. However, mean frequencies of the induced GBR were ~10Hz higher in response to the onsets of moving compared to stationary gratings. Furthermore, the modulations of the induced GBR did not parallel the modulations of microsaccade rate, indicating that our induced GBRs reflect neuronal processes.These results suggest that, within the gamma-band range, the encoding of moving gratings in early visual cortex is primarily based on an upward frequency shift, whereas contrast changes within static gratings are reflected by amplitude enhancement.

An MEG investigation of the neural mechanisms subserving complex visuomotor coordination

Fifteen human participants performed a manual and ocular tracking task with a continuously and unpredictably moving visual target, while magnetoencephalography (MEG) signals were recorded. Three-dimensional source reconstructions were generated from the MEG signals, using synthetic aperture magnetometry (SAM). The SAM images indicated main effects of alpha band (8–15 Hz) and beta band (15–30 Hz) source power decreases, for manual tracking in the sensorimotor and parietal cortices, and for ocular tracking in the parietal and occipital cortices. Additionally, the manual tracking task evoked a clear, contralateral motor cortex response in the form of high gamma band (60–90 Hz) source power increases. Time-frequency spectrograms revealed the induced gamma band power increases were sustained for the duration of each ten second trial demonstrating these oscillations are not simply transients associated with movement onset. The onset of the gamma band response was characterised by higher initial onset power and frequency but no correlations were observed between oscillatory power and successful tracking performance.

Alterations of the early auditory evoked gamma-band response in first-degree relatives of patients with schizophrenia: Hints to a new intermediate phenotype

Background There is growing evidence of abnormalities of high-frequency oscillations in the gamma-range of the electroencephalography in schizophrenia. The generation of neural activity in the gamma-band was shown to be critically related to a glutamatergic and GABAergic microcircuit which is also known to be involved in the pathophysiology of schizophrenia. Recently, a reduction of the early auditory evoked gamma-band response (eGBR) in schizophrenic patients was reported. In order to investigate the possible applicability of this neurophysiological marker as an intermediate phenotype for schizophrenia, this is the main question of our investigation: Is the early eGBR decreased regarding evoked power and phase locking in first-degree relatives of patients with schizophrenia? Methods We investigated the early eGBR in 17 unaffected first-degree relatives of patients with schizophrenia and in age-, gender- and education-matched groups of schizophrenic patients and healthy controls using an auditory reaction task. Results First-degree relatives of patients with schizophrenia and schizophrenic patients showed a significant reduction of evoked power and phase locking of the early eGBR compared to healthy controls. Conclusion This study shows significantly reduced evoked power and phase locking of the early auditory eGBR in first-degree relatives of patients with schizophrenia pointing to the applicability of this marker as a heritable intermediate phenotype for schizophrenia. The findings are in line with the hypothesis of a disturbed GABAergic interneural modulation of pyramidal cells in schizophrenia and findings of different schizophrenia risk genes associated with transmission at glutamatergic and GABAergic synapses.

Intracerebral gamma modulations reveal interaction between emotional processing and action outcome evaluation in the human orbitofrontal cortex

The orbitofrontal cortex (OFC) plays a key role not only in processing emotions but also in monitoring performance outcome. Although the neuroanatomical substrates underlying each of the two processes have been extensively investigated, they have predominantly been probed separately and therefore a precise knowledge of the functional overlap within the multiple OFC sub-portions involved is still lacking. Here, we explore the neural dynamics mediating performance monitoring and emotional processing using direct intracranial EEG (iEEG) recordings from multiple OFC sites of an epileptic patient. Neural activity was recorded during two experiments. The first task required processing of emotional faces and the second investigated action outcome evaluation based on a visual feedback on the subject's performance. Task-related neural dynamics were assessed using modulations of high frequency responses in the gamma-band (50–150 Hz). Our results reveal that processing negative facial emotions as well as receiving negative feedback both elicited gamma-band responses in the lateral OFC. By contrast, the mid-OFC was selectively activated for positive feedback. Furthermore, we also found significant gamma-band deactivation in the gyrus rectus during processing of negative feedback. Our findings provide novel evidence for an intricate valence-selective interaction between the networks mediating emotion processing and performance monitoring in human OFC and support the hypothesis of a tight relationship between gamma-band activity and behavior.