Event-related Gamma Oscillations Research Articles

Interindividual variability and individual stability of pain- and touch-related neuronal gamma oscillations.

Brief painful laser and innocuous tactile stimuli have been associated with an increase of neuronal oscillations in the gamma range. Although it is indicated that event-related gamma oscillations may be highly variable across individuals, to date no study has systematically investigated interindividual variability and individual stability of induced gamma synchronization. Here, we addressed this question using two EEG datasets. The first dataset contains two repeated sessions of tactile and painful stimulation from 22 participants. The second dataset contains a single session of painful stimulation from 48 participants. In the first dataset, we observed gamma responses in the majority of the included participants. We found a broad interindividual variety of gamma magnitudes, time-frequency (TF) response patterns, and scalp topographies. Some participants showed a gamma response with individually unique time-frequency patterns, others did not exhibit any gamma response. This was reproducible and therefore stable; subjects with a large gamma magnitude in the first session showed a large gamma magnitude and a similar response pattern in the follow-up session. The second dataset confirmed the large between-subject variability, but only a fraction of the included participants exhibited laser-induced gamma synchronization. Our results indicate that current EEG measures do not reflect the complex reality of the diverse individual response patterns to brief pain and touch experiences. The present findings question whether a similar phenomenon would be observed in other neuroscience domains. Group results may be replicable, but could be driven by a subgroup of the sample.NEW & NOTEWORTHY The interpretation of gamma activity in response to noxious and innocuous somatosensory stimuli has sparked controversy. Here, we show that participants' gamma oscillations measured through electroencephalography vary. Although some participants do not show a distinct gamma response, others exhibit stable and reliable response patterns in terms of time, frequency, and magnitude.

Ringing Decay of Gamma Oscillations and Transcranial Magnetic Stimulation Therapy in Autism Spectrum Disorder.

Research suggest that in autism spectrum disorder (ASD) a disturbance in the coordinated interactions of neurons within local networks gives rise to abnormal patterns of brainwave activity in the gamma bandwidth. Low frequency transcranial magnetic stimulation (TMS) over the dorsolateral prefrontal cortex (DLPFC) has been proven to normalize gamma oscillation abnormalities, executive functions, and repetitive behaviors in high functioning ASD individuals. In this study, gamma frequency oscillations in response to a visual classification task (Kanizsa figures) were analyzed and compared in 19 ASD (ADI-R diagnosed, 14.2 ± 3.61years old, 5 girls) and 19 (14.8 ± 3.67years old, 5 girls) age/gender matched neurotypical individuals. The ASD group was treated with low frequency TMS (1.0Hz, 90% motor threshold, 18 weekly sessions) targeting the DLPFC. In autistic subjects, as compared to neurotypicals, significant differences in event-related gamma oscillations were evident in amplitude (higher) pre-TMS. In addition, recordings after TMS treatment in our autistic subjects revealed a significant reduction in the time period to reach peak amplitude and an increase in the decay phase (settling time). The use of a novel metric for gamma oscillations. i.e., envelope analysis, and measurements of its ringing decay allowed us to characterize the impedance of the originating neuronal circuit. The ringing decay or dampening of gamma oscillations is dependent on the inhibitory tone generated by networks of interneurons. The results suggest that the ringing decay of gamma oscillations may provide a biomarker reflective of the excitatory/inhibitory balance of the cortex and a putative outcome measure for interventions in autism.

Nicotine Receptor Subtype-Specific Effects on Auditory Evoked Oscillations and Potentials

BackgroundIndividuals with schizophrenia show increased smoking rates which may be due to a beneficial effect of nicotine on cognition and information processing. Decreased amplitude of the P50 and N100 auditory event-related potentials (ERPs) is observed in patients. Both measures show normalization following administration of nicotine. Recent studies identified an association between deficits in auditory evoked gamma oscillations and impaired information processing in schizophrenia, and there is evidence that nicotine normalizes gamma oscillations. Although the role of nicotine receptor subtypes in augmentation of ERPs has received some attention, less is known about how these receptor subtypes regulate the effect of nicotine on evoked gamma activity.Methodology/Principal FindingsWe examined the effects of nicotine, the α7 nicotine receptor antagonist methyllycaconitine (MLA) the α4β4/α4β2 nicotine receptor antagonist dihydro-beta-erythroidine (DHβE), and the α4β2 agonist AZD3480 on P20 and N40 amplitude as well as baseline and event-related gamma oscillations in mice, using electrodes in hippocampal CA3. Nicotine increased P20 amplitude, while DHβE blocked nicotine-induced enhancements in P20 amplitude. Conversely, MLA did not alter P20 amplitude either when presented alone or with nicotine. Administration of the α4β2 specific agonist AZD3480 did not alter any aspect of P20 response, suggesting that DHβE blocks the effects of nicotine through a non-α4β2 receptor specific mechanism. Nicotine and AZD3480 reduced N40 amplitude, which was blocked by both DHβE and MLA. Finally, nicotine significantly increased event-related gamma, as did AZD3480, while DHβE but not MLA blocked the effect of nicotine on event-related gamma.Conclusions/SignificanceThese results support findings showing that nicotine-induced augmentation of P20 amplitude occurs via a DHβE sensitive mechanism, but suggests that this does not occur through activation of α4β2 receptors. Event-related gamma is strongly influenced by activation of α4β2, but not α7, receptor subtypes, while disruption of N40 amplitude requires the activation of multiple receptor subtypes.

Multimodality language mapping in patients with left-hemispheric language dominance on Wada test

ObjectiveWe determined the utility of electrocorticography (ECoG) and stimulation for detecting language-related sites in patients with left-hemispheric language-dominance on Wada test. MethodsWe studied 13 epileptic patients who underwent language mapping using event-related gamma-oscillations on ECoG and stimulation via subdural electrodes. Sites showing significant gamma-augmentation during an auditory-naming task were defined as language-related ECoG sites. Sites at which stimulation resulted in auditory perceptual changes, failure to verbalize a correct answer, or sensorimotor symptoms involving the mouth were defined as language-related stimulation sites. We determined how frequently these methods revealed language-related sites in the superior-temporal, inferior-frontal, dorsolateral-premotor, and inferior-Rolandic regions. ResultsLanguage-related sites in the superior-temporal and inferior-frontal gyri were detected by ECoG more frequently than stimulation (p<0.05), while those in the dorsolateral-premotor and inferior-Rolandic regions were detected by both methods equally. Stimulation of language-related ECoG sites, compared to the others, more frequently elicited language symptoms (p<0.00001). One patient developed dysphasia requiring in-patient speech therapy following resection of the dorsolateral-premotor and inferior-Rolandic regions containing language-related ECoG sites not otherwise detected by stimulation. ConclusionsLanguage-related gamma-oscillations may serve as an alternative biomarker of underlying language function in patients with left-hemispheric language-dominance. SignificanceMeasurement of language-related gamma-oscillations is warranted in presurgical evaluation of epileptic patients.

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.

Disturbance in long distance gamma coherence in bipolar disorder

The aim of this study was to investigate long distance event-related gamma (28–48 Hz) coherence in mania before and after valproate monotherapy. Gamma coherence in response to visual oddball paradigm in ten medication-free, manic patients was studied before and after six weeks of valproate monotherapy in comparison to ten controls. Inter-hemispheric F 3–F 4, C 3–C 4, T 3–T 4, T 5–T 6, P 3–P 4, O 1–O 2 and intra-hemispheric F 3–P 3, F 4–P 4, F 3–T 5, F 4–T 6, F 3–O 1, F 4–O 2, C 3–O 1, C 2–O 4 electrode pairs were included in the analysis. Repeated measures ANOVA revealed a significant difference between groups with regard to pre-treatment coherence values ( p: 0.018). The coherence to the target stimuli at the right fronto-temporal location was significantly reduced by 35.41% in the patients compared to controls ( p: 0.003). Patients showed significantly lower pre-treatment coherence values in response to non-target stimuli compared to controls at the right fronto-temporal (28.51%, p: 0.004), right fronto-occipital (23.71%, p: 0.024), and right centro-occipital (25.69%, p: 0.029) locations. After six weeks of valproate monotherapy, manic symptoms improved significantly. Post-treatment change in target and non-target coherence values was statistically non-significant. EEG coherence is a measure of functional connectivity in the brain. Event-related gamma oscillations are essential for brain electrical activity. The results show that acute mania presents right sided long distance connectivity disturbance, thus pointing to the potential importance of measuring oscillatory responses in the search for consistent neurobiological markers in such a complicated condition as bipolar disorder.

Cortical gamma-oscillations modulated by listening and overt repetition of phonemes

Both superior temporal gyrus and inferior Rolandic area have been reported to be involved in perception and production of speech in humans. Here, we determined how these cortical structures were activated by listening and subsequent overt articulation of syllables, by measuring event-related gamma-oscillations as quantitative measures of cortical activation. Fifteen subjects were presented an auditory syllable consisting of either “fee [fi:],” “faa [fα:],” “hee [hi:],” or “haa [hα:],” and were instructed to overtly repeat each given syllable. Gamma-oscillations in the superior temporal gyrus were highly augmented during syllable-presentation, least augmented at the onset of syllable-articulation, and again highly augmented following syllable-articulation. Gamma-oscillations were augmented in the inferior Rolandic area prior to and during syllable-articulation with the onset and peak occurring earlier in the left side. Subsets of the inferior Rolandic sites, more frequently on the left side, showed differential gamma-augmentation elicited by articulation of phoneme [f] more than [h] or phoneme [i:] more than [α:]. Our observations suggest that the superior temporal gyrus may be active when externally presented or articulated auditory stimuli are present, and may be minimally active when articulation is about to be initiated. Our novel observation of phoneme-specific differential gamma-augmentation in the inferior Rolandic area may be partially attributed to the mouth position during phoneme-articulation. Our observations support the hypothesis that positioning of the mouth to articulate phonemes is predominantly driven and/or monitored by the primary sensorimotor area on the left side.

Developmental event-related gamma oscillations: effects of auditory attention.

This study describes maturational changes in topographical patterns, stability, and functional reactivity of auditory gamma band (31-63 Hz) responses (GBRs) as brain electrical correlates relevant for cognitive development during childhood. GBRs of 114 healthy children from 9 to 16 years were elicited in an auditory focused attention task requiring motor responding to targets, and analyzed by means of the wavelet transform (WT). The effects of age and task variables (attended side and stimulus type relevance) were examined for GBR power and phase-locking within 120 ms after stimulation. Similar to the spontaneous gamma band power, the power and phase-synchronization of GBRs did not depend on the age. However, the functional reactivity of GBRs at specific locations changed in the course of development. In 9-12-year-old children, GBRs at frontal locations were larger and better synchronized to target than to nontarget stimulus type, and were larger over the left hemisphere (contralateral to the responding hand), thus manifesting sensitivity to external stimulus features and motor task. In 13-16-year-old adolescents, GBRs at parietal sites were enhanced by active attending to the side of stimulation, thus being associated with a maintenance of attentional focus to stimulus location. The results indicate that (i) specific aspects of task-stimulus processing engage distinct spatially localized gamma networks at functionally relevant areas, and (ii) the neuronal substrates of gamma band networks and the ability to synchronize them in relation to task-specific processes are available in all age groups from 9 to 16 years. However, the mode and efficiency with which gamma networks can be entrained depends on the age. This age-dependent reactivity of GBRs to different task variables may reflect a transition in processing strategies emerging at approximately 12-13 years in relation to the maturation of cognitive and executive brain functions.

Abnormal early stages of task stimulus processing in children with attention-deficit hyperactivity disorder – evidence from event-related gamma oscillations

Objectives: Attention-related differences in early stages of stimulus processing were assessed in healthy controls and children with attention-deficit hyperactivity disorder (ADHD) by analyzing phase-locked gamma band (31–63 Hz) responses to auditory stimuli in a selective-attention task. Methods: A total of 28 children aged 9–12 years (ADHD and matched healthy controls) pressed a button in response to each target stimulus presented at the attended side (right or left). Auditory gamma band responses (GBRs) within 0–120 ms were analyzed at 8 electrodes with wavelet transform. Effects of attended channel, stimulus type, and group were evaluated for GBR power and phase-locking. Results: For both groups, GBRs had a frontal-central distribution, were significantly larger and more strongly phase-locked to target than to non-target stimuli, and did not differentiate the attended from the unattended channel. ADHD children produced larger and more strongly phase-locked GBRs than controls only to right-side stimuli, irrespective of whether these were the attended or the ignored stimuli. Conclusions: The association between auditory GBR and motor task stimulus in children suggests that phase-locked gamma oscillations may reflect processes of sensory-motor integration. ADHD-related deviations of GBRs indicate that early mechanisms of auditory stimulus processing are altered in ADHD, presumably as a result of impaired motor inhibition.

104 Dynamical features of event-related gamma-oscillations in the EEG of cat auditory cortex during acquisition of discriminant aversive conditioning

ÁNGYÁN, L. AND J. CZOPF. Exercise-induced slow waves in the EEG of cats. PHYSIOL. BEHAV 64(3) 267–272, 1998.—The aim of the present study was to investigate the early signs of fatigue. Cats were chronically implanted with electrodes in the frontal and occipital cortical areas, and a thermocouple was inserted into the nasal orifice to record respiratory rate. After a recovery of 10 days, the animals were trained for running on treadmill. On the day before recording, a catheter was tied into one of the common carotid arteries to record arterial blood pressure. The electroencephalogram (EEG), arterial blood pressure, and respiration were recorded continuously. At the time of deceleration of running high amplitude, slow waves appeared both in the sensorimotor and occipital cortical regions. The power spectra showed a significant increase in frequencies of 1–6 Hz in the sensorimotor cortex, and of 1–10 Hz in the occipital cortex, with a great increase in the total power. During rest the pre-running, brain activity reappeared gradually. The arterial blood pressure, the heart rate, and the respiratory rate were elevated during running, but no special changes occurred at the onset of the slow waves in the EEG. The blood glucose level was somewhat higher after the first 2-min running than the pre-running level. It is concluded that the appearance of slow waves in the EEG is an early manifestation of fatigue. The cardiorespiratory changes and the blood sugar concentrations play no role in the slowing of the electrocorticogram. The present results show the involvement of brain mechanisms in the onset of tiredness.