High-gamma Band Power Research Articles

The cortical neurophysiological signature of amyotrophic lateral sclerosis.

The progressive loss of motor function characteristic of amyotrophic lateral sclerosis is associated with widespread cortical pathology extending beyond primary motor regions. Increasing muscle weakness reflects a dynamic, variably compensated brain network disorder. In the quest for biomarkers to accelerate therapeutic assessment, the high temporal resolution of magnetoencephalography is uniquely able to non-invasively capture micro-magnetic fields generated by neuronal activity across the entire cortex simultaneously. This study examined task-free magnetoencephalography to characterize the cortical oscillatory signature of amyotrophic lateral sclerosis for having potential as a pharmacodynamic biomarker. Eight to ten minutes of magnetoencephalography in the task-free, eyes-open state was recorded in amyotrophic lateral sclerosis (n = 36) and healthy age-matched controls (n = 51), followed by a structural MRI scan for co-registration. Extracted magnetoencephalography metrics from the delta, theta, alpha, beta, low-gamma, high-gamma frequency bands included oscillatory power (regional activity), 1/f exponent (complexity) and amplitude envelope correlation (connectivity). Groups were compared using a permutation-based general linear model with correction for multiple comparisons and confounders. To test whether the extracted metrics could predict disease severity, a random forest regression model was trained and evaluated using nested leave-one-out cross-validation. Amyotrophic lateral sclerosis was characterized by reduced sensorimotor beta band and increased high-gamma band power. Within the premotor cortex, increased disability was associated with a reduced 1/f exponent. Increased disability was more widely associated with increased global connectivity in the delta, theta and high-gamma bands. Intra-hemispherically, increased disability scores were particularly associated with increases in temporal connectivity and inter-hemispherically with increases in frontal and occipital connectivity. The random forest model achieved a coefficient of determination (R2) of 0.24. The combined reduction in cortical sensorimotor beta and rise in gamma power is compatible with the established hypothesis of loss of inhibitory, GABAergic interneuronal circuits in pathogenesis. A lower 1/f exponent potentially reflects a more excitable cortex and a pathology unique to amyotrophic lateral sclerosis when considered with the findings published in other neurodegenerative disorders. Power and complexity changes corroborate with the results from paired-pulse transcranial magnetic stimulation. Increased magnetoencephalography connectivity in worsening disability is thought to represent compensatory responses to a failing motor system. Restoration of cortical beta and gamma band power has significant potential to be tested in an experimental medicine setting. Magnetoencephalography-based measures have potential as sensitive outcome measures of therapeutic benefit in drug trials and may have a wider diagnostic value with further study, including as predictive markers in asymptomatic carriers of disease-causing genetic variants.

Enhanced low-gamma band power in the hippocampus and prefrontal cortex in a rat model of depression is reversed by orexin-1 receptor antagonism

The hippocampal-prefrontal cortex network dynamics is reported to be involved in various cognitive functions and in different mood disturbances including depression. It has been suggested that blocking orexin-1 receptors can be beneficial in depression. The purpose of this study is to determine whether orexin-1 receptor antagonists have an impact on changes in brain oscillations in the hippocampus and prefrontal cortex in a rat model of depression. Forty-eight male Wistar rats were divided into six experimental groups: control, chronic mild stress (CMS), acute SB-334867, a selective orexin-1 receptor antagonist, treated rats (SB), chronic SB-treated (CSB), CMS+SB, and CMS+CSB. Two stainless steel recording electrodes were placed in the coordinates of the hippocampus (HPC) and the prefrontal cortex (PFC). After behavioral verification of the model, local field potentials were recorded at 1 kHz sampling frequency. The absolute power of different frequency bands was obtained using the Fast Fourier Transform (FFT) function, and the power spectral density (PSD) of each frequency band was calculated for each animal. In the CMS- treated animals, the low-gamma band power increased both in the HPC and PFC (p ≤ 0.05), which were reversed by chronic SB-334867 treatment (p ≤ 0.05). The alterations in theta, and high-gamma band power were not significant in CMS treated rats, while acute and chronic SB-334867 treatment diminished the theta and high-gamma band power (p ≤ 0.05), respectively. The hippocampal-prefrontal coherence decreased in the delta (p ≤ 0.01), theta (p ≤ 0.01), and alpha (p ≤ 0.05) band range of the CMS exposed rats. It is concluded that CMS boosts the low-gamma band power, which is reversed by CSB treatment. The low-frequency band coherence is attenuated after CMS treatment.

Neural oscillations while remembering traumatic memories in post-traumatic stress disorder

ObjectiveThe current study investigated the oscillatory brain activity of PTSD patients during directed and imaginal exposure to the traumatic memory using magnetoencephalography (MEG), in a paradigm resembling exposure therapy. MethodsBrain activity of healthy trauma-exposed controls and PTSD participants was measured with MEG as they listened to individualized trauma narratives as well as to a neutral narrative and as they imagined the narrative in detail. Source localization analysis by frequency bands was conducted in order to map neural generators of oscillatory activity. ResultsElicitation of traumatic memories resulted in a distinct neural pattern in PTSD patients compared to healthy trauma-exposed individuals. In response to trauma scripts PTSD patients showed increases in high-gamma band power in visual areas, increased frontal and temporal theta as well as prefrontal alpha and medial temporal beta power relative to neutral scripts. ConclusionsResults suggest that when recollecting and imagining traumatic memories PTSD patients attempt to engage control or inhibition mechanisms. However, these are either not successfully recruited or inefficient leading to heightened responses and recollection. SignificanceInvestigating the oscillatory neural dynamics of PTSD patients can help us better understand the processes underlying trauma re-experiencing.

Neural Mechanism of Noise Affecting Face Recognition

Face recognition is one of the most important cognitive functions for humans in social activities. The ability will be negatively affected when the face images deteriorate. However, the neural process of extracting facial information under challenging conditions is still poorly understood. Therefore, it is necessary to further understand the neurophysiological relevance of this effect. We examined patients with multiple subdural electrodes (ECoG) monitored for clinical purposes. During the experimental task, the patients were presented with face and house images with different noise levels and were asked to recognize the faces. We found a striking increase in high gamma band power (HGP; 60–160 Hz) when face images were shown. We localized the face-specific electrodes to the fusiform gyrus (FG) and surrounding cortices. For each subject, the behavioral performance and magnitudes of the HGP for the face-specific sites significantly both fit a sigmoid function and showed similar changes. Additionally, the curve profile of the average HGP magnitude across the face-specific sites was almost equal to the average behavior curve; the former could precisely track the behavioral performance. In general, these results suggest that the HGP in the FG is closely related to the performance of face image recognition.

The Effect of Transcranial Pulsed Current Stimulation at 4 and 75 Hz on Electroencephalography Theta and High Gamma Band Power: A Pilot Study.

Introduction: Transcranial pulsed current stimulation (tPCS) is an emerging noninvasive brain stimulation technique that has shown significant effects on cortical excitability. To date, electrophysiological measures of the efficiency of monophasic tPCS have not been reported. Objective: We aimed to explore the effects of monophasic anodal and cathodal-tPCS (a-tPCS/c-tPCS) at theta (4 Hz) and gamma (75 Hz) frequencies on theta and high gamma electroencephalography (EEG) oscillatory power. Methods: In a single-blind, randomized, sham-controlled crossover design, 15 healthy participants were randomly assigned into 5 experimental sessions in which they received a-PCS/c-tPCS at 4 and 75 Hz or sham stimulation over the left primary motor cortex (M1) for 15 min at an intensity of 1.5 mA. Changes in theta and high gamma oscillatory power were recorded at baseline, immediately after, and 30 min after stimulation using EEG at rest with eyes open. Results: a-tPCS at 4 Hz showed a significant increase in theta power compared with sham, whereas c-tPCS at 4 Hz had no significant effect on theta power. a-tPCS at 75 Hz produced no changes in high gamma power compared with sham. Importantly, c-tPCS at 75 Hz led to a significant reduction in high gamma power compared with baseline, as well as compared with c-tPCS at 4 Hz and sham stimulation. Conclusion: The results demonstrate the modulation of oscillatory brain activity by monophasic tPCS, and highlight the need for future studies on a larger scale to confirm these initial findings. Impact statement Transcranial pulsed current stimulation (tPCS) is a novel brain stimulation technique. Recently, tPCS has been introduced to directly modulate brain oscillations by applying pulsatile current over the target brain area. Using both anodal and cathodal monophasic tPCS at theta and gamma frequencies, we demonstrate the ability of the stimulation to modulate brain activity. The present findings are the first direct electroencephalography evidence of an interaction between tPCS and ongoing oscillatory activity in the human motor cortex. Our work recommends tPCS as a tool for investigating human brain oscillations and open more studies in this area.

Ketamine normalizes high-gamma power in the anterior cingulate cortex in a rat chronic pain model

Chronic pain alters cortical and subcortical plasticity, causing enhanced sensory and affective responses to peripheral nociceptive inputs. Previous studies have shown that ketamine had the potential to inhibit abnormally amplified affective responses of single neurons by suppressing hyperactivity in the anterior cingulate cortex (ACC). However, the mechanism of this enduring effect has yet to be understood at the network level. In this study, we recorded local field potentials from the ACC of freely moving rats. Animals were injected with complete Freund’s adjuvant (CFA) to induce persistent inflammatory pain. Mechanical stimulations were administered to the hind paw before and after CFA administration. We found a significant increase in the high-gamma band (60–100 Hz) power in response to evoked pain after CFA treatment. Ketamine, however, reduced the high-gamma band power in response to evoked pain in CFA-treated rats. In addition, ketamine had a sustained effect on the high-gamma band power lasting up to five days after a single dose administration. These results demonstrate that ketamine has the potential to alter maladaptive neural responses in the ACC induced by chronic pain.

Impact of Stress on Gamma Oscillations in the Rat Nucleus Accumbens During Spontaneous Social Interaction.

Alteration in social behavior is one of the most debilitating symptoms of major depression, a stress related mental illness. Social behavior is modulated by the reward system, and gamma oscillations in the nucleus accumbens (NAc) seem to be associated with reward processing. In this scenario, the role of gamma oscillations in depression remains unknown. We hypothesized that gamma oscillations in the rat NAc are sensitive to the effects of social distress. One group of male Sprague-Dawley rats were exposed to chronic social defeat stress (CSDS) while the other group was left undisturbed (control group). Afterward, a microelectrode array was implanted in the NAc of all animals. Local field potential (LFP) activity was acquired using a wireless recording system. Each implanted rat was placed in an open field chamber for a non-social interaction condition, followed by introducing another unfamiliar rat, creating a social interaction condition, where the implanted rat interacted freely and continuously with the unfamiliar conspecific in a natural-like manner (see Supplementary Videos). We found that the high-gamma band power in the NAc of non-stressed rats was higher during the social interaction compared to a non-social interaction condition. Conversely, we did not find significant differences at this level in the stressed rats when comparing the social interaction- and non-social interaction condition. These findings suggest that high-gamma oscillations in the NAc are involved in social behavior. Furthermore, alterations at this level could be an electrophysiological signature of the effect of chronic social stress on reward processing.

Electrocorticographic changes in field potentials following natural somatosensory percepts in humans.

Restoration of somatosensory deficits in humans requires a clear understanding of the neural representations of percepts. To characterize the cortical response to naturalistic somatosensation, we examined field potentials in the primary somatosensory cortex of humans. Four patients with intractable epilepsy were implanted with subdural electrocorticography (ECoG) electrodes over the hand area of S1. Three types of stimuli were applied, soft-repetitive touch, light touch, and deep touch. Power in the alpha (8-15Hz), beta (15-30Hz), low-gamma (30-50Hz), and high-gamma (50-125Hz) frequency bands were evaluated for significance. Seventy-seven percent of electrodes over the hand area of somatosensory cortex exhibited changes in these bands. High-gamma band power increased for all stimuli, with concurrent alpha and beta band power decreases. Earlier activity was seen in these bands in deep touch and light touch compared to soft touch. These findings are consistent with prior literature and suggest a widespread response to focal touch, and a different encoding of deeper pressure touch than soft touch.

Neural speech recognition: continuous phoneme decoding using spatiotemporal representations of human cortical activity

Objective. The superior temporal gyrus (STG) and neighboring brain regions play a key role in human language processing. Previous studies have attempted to reconstruct speech information from brain activity in the STG, but few of them incorporate the probabilistic framework and engineering methodology used in modern speech recognition systems. In this work, we describe the initial efforts toward the design of a neural speech recognition (NSR) system that performs continuous phoneme recognition on English stimuli with arbitrary vocabulary sizes using the high gamma band power of local field potentials in the STG and neighboring cortical areas obtained via electrocorticography. Approach. The system implements a Viterbi decoder that incorporates phoneme likelihood estimates from a linear discriminant analysis model and transition probabilities from an n-gram phonemic language model. Grid searches were used in an attempt to determine optimal parameterizations of the feature vectors and Viterbi decoder. Main results. The performance of the system was significantly improved by using spatiotemporal representations of the neural activity (as opposed to purely spatial representations) and by including language modeling and Viterbi decoding in the NSR system. Significance. These results emphasize the importance of modeling the temporal dynamics of neural responses when analyzing their variations with respect to varying stimuli and demonstrate that speech recognition techniques can be successfully leveraged when decoding speech from neural signals. Guided by the results detailed in this work, further development of the NSR system could have applications in the fields of automatic speech recognition and neural prosthetics.

Decoding three-dimensional reaching movements using electrocorticographic signals in humans

Objective. Electrocorticography (ECoG) signals have emerged as a potential control signal for brain–computer interface (BCI) applications due to balancing signal quality and implant invasiveness. While there have been numerous demonstrations in which ECoG signals were used to decode motor movements and to develop BCI systems, the extent of information that can be decoded has been uncertain. Therefore, we sought to determine if ECoG signals could be used to decode kinematics (speed, velocity, and position) of arm movements in 3D space. Approach. To investigate this, we designed a 3D center-out reaching task that was performed by five epileptic patients undergoing temporary placement of ECoG arrays. We used the ECoG signals within a hierarchical partial-least squares (PLS) regression model to perform offline prediction of hand speed, velocity, and position. Main Results. The hierarchical PLS regression model enabled us to predict hand speed, velocity, and position during 3D reaching movements from held-out test sets with accuracies above chance in each patient with mean correlation coefficients between 0.31 and 0.80 for speed, 0.27 and 0.54 for velocity, and 0.22 and 0.57 for position. While beta band power changes were the most significant features within the model used to classify movement and rest, the local motor potential and high gamma band power changes, were the most important features in the prediction of kinematic parameters. Significance. We believe that this study represents the first demonstration that truly three-dimensional movements can be predicted from ECoG recordings in human patients. Furthermore, this prediction underscores the potential to develop BCI systems with multiple degrees of freedom in human patients using ECoG.

Electrocorticography Reveals Enhanced Visual Cortex Responses to Visual Speech

Human speech contains both auditory and visual components, processed by their respective sensory cortices. We test a simple model in which task-relevant speech information is enhanced during cortical processing. Visual speech is most important when the auditory component is uninformative. Therefore, the model predicts that visual cortex responses should be enhanced to visual-only (V) speech compared with audiovisual (AV) speech. We recorded neuronal activity as patients perceived auditory-only (A), V, and AV speech. Visual cortex showed strong increases in high-gamma band power and strong decreases in alpha-band power to V and AV speech. Consistent with the model prediction, gamma-band increases and alpha-band decreases were stronger for V speech. The model predicts that the uninformative nature of the auditory component (not simply its absence) is the critical factor, a prediction we tested in a second experiment in which visual speech was paired with auditory white noise. As predicted, visual speech with auditory noise showed enhanced visual cortex responses relative to AV speech. An examination of the anatomical locus of the effects showed that all visual areas, including primary visual cortex, showed enhanced responses. Visual cortex responses to speech are enhanced under circumstances when visual information is most important for comprehension.

Altered oscillation patterns and connectivity during picture naming in autism

Similar behavioral deficits are shared between individuals with autism spectrum disorders (ASD) and their first-degree relatives, such as impaired face memory, object recognition, and some language aspects. Functional neuroimaging studies have reported abnormalities in ASD in at least one brain area implicated in those functions, the fusiform gyrus (FG). High frequency oscillations have also been described as abnormal in ASD in a separate line of research. The present study examined whether low- and high-frequency oscillatory power, localized in part to FG and other language-related regions, differs in ASD subjects and first-degree relatives. Twelve individuals with ASD, 16 parents of children with ASD, and 35 healthy controls participated in a picture-naming task using magnetoencephalography (MEG) to assess oscillatory power and connectivity. Relative to controls, we observed reduced evoked high-gamma activity in the right superior temporal gyrus (STG) and reduced high-beta/low-gamma evoked power in the left inferior frontal gyrus (IFG) in the ASD group. Finally, reductions in phase-locked beta-band were also seen in the ASD group relative to controls, especially in the occipital lobes (OCC). First degree relatives, in contrast, exhibited higher high-gamma band power in the left STG compared with controls, as well as increased high-beta/low-gamma evoked power in the left FG. In the left hemisphere, beta- and gamma-band functional connectivity between the IFG and FG and between STG and OCC were higher in the autism group than in controls. This suggests that, contrary to what has been previously described, reduced connectivity is not observed across all scales of observation in autism. The lack of behavioral correlation for the findings warrants some caution in interpreting the relevance of such changes for language function in ASD. Our findings in parents implicates the gamma- and beta-band ranges as potential compensatory phenomena in autism relatives.

Saccade Related Gamma-Band Activity in Intracerebral EEG: Dissociating Neural from Ocular Muscle Activity

Recent evidence suggests that transient increases in scalp electroencephalography (EEG) gamma band power (above 30 Hz) can be due to miniature eye movements. Although, these findings do not raise doubts about the widely established role of gamma range neural synchrony, it does call for caution when it comes to interpreting high frequency scalp EEG data. By contrast, gamma-band activity detected with intracerebral EEG (iEEG) is assumed to be immune to such miniature saccade artefacts. Here, we show for the first time, that while this is indeed largely the case, intracerebral recordings in the temporal pole of implanted patients can be contaminated by saccadic eye muscle artefacts resulting in typical high gamma-band power increases. By analyzing data from multiple depth electrodes, we show that this artefact is confined to the pole of the temporal lobe because of its immediate vicinity to extraocular muscles (rectus lateralis). For other brain structures, our analysis shows that the use of stereotactic EEG with a bipolar montage provides a robust and convenient tool to explore the functional role of gamma synchronization in humans with high anatomical accuracy during a wide range of cognitive processes, including oculomotor behaviour.

Auditory Cortical Plasticity in Learning to Discriminate Modulation Rate

The discrimination of temporal information in acoustic inputs is a crucial aspect of auditory perception, yet very few studies have focused on auditory perceptual learning of timing properties and associated plasticity in adult auditory cortex. Here, we trained participants on a temporal discrimination task. The main task used a base stimulus (four tones separated by intervals of 200 ms) that had to be distinguished from a target stimulus (four tones with intervals down to approximately 180 ms). We show that participants' auditory temporal sensitivity improves with a short amount of training (3 d, 1 h/d). Learning to discriminate temporal modulation rates was accompanied by a systematic amplitude increase of the early auditory evoked responses to trained stimuli, as measured by magnetoencephalography. Additionally, learning and auditory cortex plasticity partially generalized to interval discrimination but not to frequency discrimination. Auditory cortex plasticity associated with short-term perceptual learning was manifested as an enhancement of auditory cortical responses to trained acoustic features only in the trained task. Plasticity was also manifested as induced non-phase-locked high gamma-band power increases in inferior frontal cortex during performance in the trained task. Functional plasticity in auditory cortex is here interpreted as the product of bottom-up and top-down modulations.