Gamma Augmentation Research Articles

Bayesian Inference of Recurrent Switching Linear Dynamical Systems with Higher-Order Dependence

Many complicated dynamical events may be broken down into simpler pieces and efficiently described by a system that shifts among a variety of conditionally dynamical modes. Building on switching linear dynamical systems, we develop a new model that extends the switching linear dynamical systems for better discovering these dynamical modes. In the proposed model, the linear dynamics of latent variables can be described by a higher-order vector autoregressive process, which makes it feasible to evaluate the higher-order dependency relationships in the dynamics. In addition, the transition of switching states is determined by a stick-breaking logistic regression, overcoming the limitation of a restricted geometric state duration and recovering the symmetric dependency between the switching states and the latent variables from asymmetric relationships. Furthermore, logistic regression evidence potentials can appear as conditionally Gaussian potentials by utilizing the Pólya-gamma augmentation strategy. Filtering and smoothing algorithms and Bayesian inference for parameter learning in the proposed model are presented. The utility and versatility of the proposed model are demonstrated on synthetic data and public functional magnetic resonance imaging data. Our model improves the current methods for learning the switching linear dynamical modes, which will facilitate the identification and assessment of the dynamics of complex systems.

Different Alterations of Hippocampal and Reticulo-Thalamic GABAergic Parvalbumin-Expressing Interneurons Underlie Different States of Unconsciousness

We traced the changes in GABAergic parvalbumin (PV)-expressing interneurons of the hippocampus and reticulo-thalamic nucleus (RT) as possible underlying mechanisms of the different local cortical and hippocampal electroencephalographic (EEG) microstructures during the non-rapid-eye movement (NREM) sleep compared with anesthesia-induced unconsciousness by two anesthetics with different main mechanisms of action (ketamine/diazepam versus propofol). After 3 h of recording their sleep, the rats were divided into two experimental groups: one half received ketamine/diazepam anesthesia and the other half received propofol anesthesia. We simultaneously recorded the EEG of the motor cortex and hippocampus during sleep and during 1 h of surgical anesthesia. We performed immunohistochemistry and analyzed the PV and postsynaptic density protein 95 (PSD-95) expression. PV suppression in the hippocampus and at RT underlies the global theta amplitude attenuation and hippocampal gamma augmentation that is a unique feature of ketamine-induced versus propofol-induced unconsciousness and NREM sleep. While PV suppression resulted in an increase in hippocampal PSD-95 expression, there was no imbalance between inhibition and excitation during ketamine/diazepam anesthesia compared with propofol anesthesia in RT. This increased excitation could be a consequence of a lower GABA interneuronal activity and an additional mechanism underlying the unique local EEG microstructure in the hippocampus during ketamine/diazepam anesthesia.

Naming-related spectral responses predict neuropsychological outcome after epilepsy surgery.

This prospective study determined the use of intracranially recorded spectral responses during naming tasks in predicting neuropsychological performance following epilepsy surgery. We recruited 65 patients with drug-resistant focal epilepsy who underwent preoperative neuropsychological assessment and intracranial EEG recording. The Clinical Evaluation of Language Fundamentals evaluated the baseline and postoperative language function. During extra-operative intracranial EEG recording, we assigned patients to undergo auditory and picture naming tasks. Time-frequency analysis determined the spatiotemporal characteristics of naming-related amplitude modulations, including high gamma augmentation at 70-110 Hz. We surgically removed the presumed epileptogenic zone based on the intracranial EEG and MRI abnormalities while maximally preserving the eloquent areas defined by electrical stimulation mapping. The multivariate regression model incorporating auditory naming-related high gamma augmentation predicted the postoperative changes in Core Language Score with r2 of 0.37 and in Expressive Language Index with r2 of 0.32. Independently of the effects of epilepsy and neuroimaging profiles, higher high gamma augmentation at the resected language-dominant hemispheric area predicted a more severe postoperative decline in Core Language Score and Expressive Language Index. Conversely, the model incorporating picture naming-related high gamma augmentation predicted the change in Receptive Language Index with an r2 of 0.50. Higher high gamma augmentation independently predicted a more severe postoperative decline in Receptive Language Index. Ancillary regression analysis indicated that naming-related low gamma augmentation and alpha/beta attenuation likewise independently predicted a more severe Core Language Score decline. The machine learning-based prediction model suggested that naming-related high gamma augmentation, among all spectral responses used as predictors, most strongly contributed to the improved prediction of patients showing a >5-point Core Language Score decline (reflecting the lower 25th percentile among patients). We generated the model-based atlas visualizing sites, which, if resected, would lead to such a language decline. With a 5-fold cross-validation procedure, the auditory naming-based model predicted patients who had such a postoperative language decline with an accuracy of 0.80. The model indicated that virtual resection of an electrical stimulation mapping-defined language site would have increased the relative risk of the Core Language Score decline by 5.28 (95% confidence interval: 3.47-8.02). Especially, that of an electrical stimulation mapping-defined receptive language site would have maximized it to 15.90 (95% confidence interval: 9.59-26.33). In summary, naming-related spectral responses predict neuropsychological outcomes after epilepsy surgery. We have provided our prediction model as an open-source material, which will indicate the postoperative language function of future patients and facilitate external validation at tertiary epilepsy centres.

Neural dynamics during the vocalization of \u2018uh\u2019 or \u2018um\u2019

People occasionally use filler phrases or pauses, such as “uh”, “um”, or “y’know,” that interrupt the flow of a sentence and fill silent moments between ordinary (non-filler) phrases. It remains unknown which brain networks are engaged during the utterance of fillers. We addressed this question by quantifying event-related cortical high gamma activity at 70–110 Hz. During extraoperative electrocorticography recordings performed as part of the presurgical evaluation, patients with drug-resistant focal epilepsy were instructed to overtly explain, in a sentence, ‘what is in the image (subject)’, ‘doing what (verb)’, ‘where (location)’, and ‘when (time)’. Time–frequency analysis revealed that the utterance of fillers, compared to that of ordinary words, was associated with a greater magnitude of high gamma augmentation in association and visual cortex of either hemisphere. Our preliminary results raise the hypothesis that filler utterance would often occur when large-scale networks across the association and visual cortex are engaged in cognitive processing, including lexical retrieval as well as verbal working memory and visual scene scanning.

Human subthalamic oscillatory dynamics following somatosensory stimulation

ObjectiveElectrical median nerve somatosensory stimulation leads to a distinct modulation of cortical oscillations. Initial high frequency and gamma augmentation, as well as modulation of beta and alpha oscillations have been reported. We aimed at investigating the involvement of the subthalamic nucleus in somatosensory processing by means of local field potential recordings, since recordings during passive movements and peripheral somatosensory stimulation have suggested a prominent role. MethodsRecordings of subthalamic neuronal activity following median nerve stimulation in 11 Parkinson’s disease patients were performed. Time-frequency analysis from 1 to 500 Hz was averaged and analyzed. ResultsSeveral oscillatory components in response to somatosensory stimulation were revealed in the time-frequency analysis: (I) prolonged increase in alpha band power, followed by attenuation; (II) initial suppression of power followed by a subsequent rebound in the beta band; (III) early broad-frequency increase in gamma band power; (IV) and sustained increase of 160 Hz frequency oscillations throughout the trial. ConclusionsThese results further corroborate the involvement of the subthalamic nucleus in somatosensory processing. SignificanceThe present results not only support the notion of somatosensory processing in the subthalamic nucleus. Moreover, an improvement of somatosensory processing during subthalamic deep brain stimulation in Parkinson’s disease might be accounted for by enhancement of prevailing high frequency oscillations.

Differentiated effects of deep brain stimulation and medication on somatosensory processing in Parkinson's disease.

Deep brain stimulation (DBS) and dopaminergic medication effectively alleviate the motor symptoms in Parkinson's disease (PD) patients, but their effects on the sensory symptoms of PD are still not well understood. To explore early somatosensory processing in PD, we recorded magnetoencephalography (MEG) from thirteen DBS-treated PD patients and ten healthy controls during median nerve stimulation. PD patients were measured during DBS-treated, untreated and dopaminergic-medicated states. We focused on early cortical somatosensory processing as indexed by N20m, induced gamma augmentation (31-45Hz and 55-100Hz) and induced beta suppression (13-30Hz). PD patients' motor symptoms were assessed by UPDRS-III. Using Bayesian statistics, we found positive evidence for differentiated effects of treatments on the induced gamma augmentation (31-45Hz) with highest gamma in the dopaminergic-medicated state and lowest in the DBS-treated and untreated states. In contrast, UPDRS-III scores showed beneficial effects of both DBS and dopaminergic medication on the patients' motor symptoms. Furthermore, treatments did not affect the amplitude of N20m. Our results suggest differentiated effects of DBS and dopaminergic medication on cortical somatosensory processing in PD patients despite consistent ameliorating effects of both treatments on PD motor symptoms. The differentiated effect suggests differences in the effect mechanisms of the two treatments.

Topography of the sleep/wake states related EEG microstructure and transitions structure differentiates the functionally distinct cholinergic innervation disorders in rat

In order to identify the differences for the onset and progression of functionally distinct cholinergic innervation disorders, we investigated the effect of bilateral nucleus basalis (NB) and pedunculopontine tegmental nucleus (PPT) lesions on sleep/wake states and electroencephalographic (EEG) microstructure in rats, chronically implanted for sleep recording. Bilateral NB lesion transiently altered Wake/NREM duration within the sensorimotor cortex, and Wake/REM duration within the motor cortex, while there was no change in the sleep/wake states distributions following the bilateral PPT lesion. Bilateral PPT lesion sustainably increased the Wake/REM and REM/Wake transitions followed by inconsistent dysregulation of the NREM/REM and REM/NREM transitions in sensorimotor cortex, but oppositely by their increment throughout four weeks in motor cortex. Bilateral NB lesion sustainably decreased the NREM/REM and REM/NREM transitions during four weeks in the sensorimotor cortex, but oppositely increased them in the motor cortex. We have shown that the sustained beta and gamma augmentation within the sensorimotor and motor cortex, and across all sleep/wake states, simultaneously with Wake delta amplitude attenuation only within the sensorimotor cortex, were the underlying EEG microstructure for the sleep/wake states transitions structure disturbance following bilateral PPT lesion. In contrast, the bilateral NB lesion only augmented REM theta in sensorimotor cortex during three weeks.We have shown that the NB and PPT lesions induced differing, structure-related EEG microstructure and transition structure disturbances particularly expressed in motor cortex during NREM and REM sleep. We evidenced for the first time the different topographical expression of the functionally distinct cholinergic neuronal innervation impairment in rat.

Independent predictors of neuronal adaptation in human primary visual cortex measured with high-gamma activity

Neuronal adaptation is defined as a reduced neural response to a repeated stimulus and can be demonstrated by reduced augmentation of event-related gamma activity. Several studies reported that variance in the degree of gamma augmentation could be explained by pre-stimulus low-frequency oscillations. Here, we measured the spatio-temporal characteristics of visually-driven amplitude modulations in human primary visual cortex using intracranial electrocorticography. We determined if inter-stimulus intervals or pre-stimulus oscillations independently predicted local neuronal adaptation measured with amplitude changes of high-gamma activity at 80-150 Hz. Participants were given repetitive photic stimuli with a flash duration of 20 μs in each block; the inter-stimulus interval was set constant within each block but different (0.2, 0.5, 1.0 or 2.0s) across blocks. Stimuli elicited augmentation of high-gamma activity in the occipital cortex at about 30 to 90 ms, and high-gamma augmentation was most prominent in the medial occipital region. High-gamma augmentation was subsequently followed by lingering beta augmentation at 20-30 Hz and high-gamma attenuation. Neuronal adaptation was demonstrated as a gradual reduction of high-gamma augmentation over trials. Multivariate analysis demonstrated that a larger number of prior stimuli, shorter inter-stimulus interval, and pre-stimulus high-gamma attenuation independently predicted a reduced high-gamma augmentation in a given trial, while pre-stimulus beta amplitude or delta phase had no significant predictive value. Association between pre-stimulus high-gamma attenuation and a reduced neural response suggests that high-gamma attenuation represents a refractory period. The local effects of pre-stimulus beta augmentation and delta phase on neuronal adaptation may be modest in primary visual cortex.

Language Mapping in Multilingual Patients: Electrocorticography and Cortical Stimulation During Naming

Multilingual patients pose a unique challenge when planning epilepsy surgery near language cortex because the cortical representations of each language may be distinct. These distinctions may not be evident with routine electrocortical stimulation mapping (ESM). Electrocorticography (ECoG) has recently been used to detect task-related spectral perturbations associated with functional brain activation. We hypothesized that using broadband high gamma augmentation (HGA, 60–150 Hz) as an index of cortical activation, ECoG would complement ESM in discriminating the cortical representations of first (L1) and second (L2) languages. We studied four adult patients for whom English was a second language, in whom subdural electrodes (a total of 358) were implanted to guide epilepsy surgery. Patients underwent ECoG recordings and ESM while performing the same visual object naming task in L1 and L2. In three of four patients, ECoG found sites activated during naming in one language but not the other. These language-specific sites were not identified using ESM. In addition, ECoG HGA was observed at more sites during L2 versus L1 naming in two patients, suggesting that L2 processing required additional cortical resources compared to L1 processing in these individuals. Post-operative language deficits were identified in three patients (one in L2 only). These deficits were predicted by ECoG spectral mapping but not by ESM. These results suggest that pre-surgical mapping should include evaluation of all utilized languages to avoid post-operative functional deficits. Finally, this study suggests that ECoG spectral mapping may potentially complement the results of ESM of language.

Cortical gamma oscillations modulated by word association tasks: Intracranial recording

Recent studies have suggested that cortical activation can be measured using event-related augmentation of gamma oscillations in humans. We determined how commonly and differentially gamma oscillations (50–150 Hz) were modulated by three distinct word-association tasks during extraoperative electrocorticography monitoring in a patient with focal epilepsy who underwent epilepsy surgery. He was auditorily presented names of common foods (e.g., apple) during each task. He was instructed to overtly verbalize the color (e.g., red) of each given food during the first association task, the taste (e.g., sweet) during the second task, and the texture (e.g., crunchy) during the third task. All three word-association tasks commonly elicited significant augmentation of gamma oscillations in the superior temporal gyrus, the middle temporal gyrus, and the inferior frontal gyrus, as well as the pre- and postcentral gyri. The food–texture association task specifically elicited significant gamma augmentation in the supramarginal gyrus. This preliminary study generated the hypothesis that word-association tasks may supplement functional language mapping using electrical stimulation. Differential gamma augmentation in the supramarginal gyrus might be attributed to a larger workload required in the food–texture association task compared with the remaining two tasks.

Somatosensory-related gamma-, beta- and alpha-augmentation precedes alpha- and beta-attenuation in humans

Several human studies have demonstrated that the amplitudes of cortical oscillations are altered by various sensorimotor and cognitive tasks. Event-related augmentation of gamma oscillations and attenuation of alpha and beta oscillations have been often used as surrogate markers of cortical activation elicited by tasks especially in presurgical identification of eloquent cortices. In the present study, we addressed a question whether somatosensory-related gamma augmentation 'precedes' or 'co-occurs with' somatosensory-related attenuation of alpha-beta oscillations. We studied 10 patients who underwent intracranial electrocorticography for epilepsy surgery, and determined the temporal and spatial characteristics of median-nerve somatosensory-related amplitude changes at gamma- (30-100Hz), beta- (14-28Hz) and alpha-band (8-12Hz) oscillations. We found that somatosensory-related gamma augmentation involving the post- and pre-central gyri evolved into beta and alpha augmentation, which was subsequently followed by beta and alpha attenuation involving the post- and pre-central gyri. These observations support the hypothesis that somatosensory-related gamma augmentation but not alpha-beta attenuation represents the initial cortical processing for external somatosensory stimuli. Somatosensory-related alpha-beta attenuation appears to represent a temporally distinct stage of somatosensory processing. The present study has increased our understanding of event-related gamma augmentation and alpha-beta attenuation seen on electrocorticography.

Functional dynamics of spoken and signed word production: A case study using electrocorticographic spectral analysis

Background: Event-related changes in the EEG power spectrum have recently been used to study functional brain activation in humans. Like traditional event-related potentials, event-related spectral changes provide information about the temporal evolution of cortical activation that is difficult to obtain with fMRI or PET. These spectral changes include event-related suppression of power in the alpha band (8-13 Hz) and even-related augmentation of power in the gamma band (>30 Hz). Most studies of the gamma band have focused on frequencies in and around 40 Hz. Using electrocorticographic (ECoG) signals recorded with subdural electrodes implanted for the surgical management of epilepsy, we have also observed a broadband augmentation of power in higher gamma frequencies (>80 Hz). This index of cortical activation has compared favourably with alpha suppression and with electrical cortical stimulation mapping in studies utilising simple motor and auditory processing, but such a comparison has not been done for tasks requiring more complex language processing. Aims: We used two different spectral indices of cortical activation - alpha power suppression and gamma power augmentation, to study the spatial and temporal patterns of human cortical activation during different word production tasks. Methods: Subdural ECoG electrodes were implanted for clinical purposes in a patient with normal hearing, who had learned sign language as an adult and later developed intractable epilepsy. We measured event-related spectral changes during language tasks with different input and output modalities: Picture naming and word reading (visual inputs), and word repetition (auditory input) were performed with spoken responses (oral-articulatory output) and with signed responses (manual-gestural output). In addition we used a visually guided motor task to map tongue and hand representations independent of language. Results: Speech and signing differentially activated tongue and hand regions of sensorimotor cortex. Although posterior superior temporal gyrus was activated early during auditory word repetition, picture naming and word reading also activated this region, albeit slightly later, consistent with phonological and/or lexical-semantic processing. In contrast, basal temporal-occipital cortex was activated earlier and with greater magnitude during picture naming and word reading than during word repetition, suggesting semantic processing or object and word recognition. In all of the tasks, event-related gamma augmentation occurred in more discrete spatial and temporal patterns than event-related alpha suppression. Conclusions: Event-related alpha suppression and gamma augmentation provide complementary information about task-related cortical activation. This study demonstrates the utility of ECoG spectral analysis for studying the functional anatomy of human language with excellent temporal resolution.

Induced electrocorticographic gamma activity during auditory perception

Objective: To define the spatial, temporal, and functional characteristics of induced gamma (>30 Hz) activity during functional activation of the left superior temporal gyrus. Methods: Electrocorticographic (ECoG) recordings were made in 4 clinical subjects during auditory tone and phoneme discrimination tasks, and event-related changes in the ECoG band power were calculated. The topography and temporal sequence of event-related power changes in different gamma bands were contrasted with those of auditory evoked potentials (AEPs), and with those of event-related power changes in the alpha band (8–12 Hz). Results: Auditory stimuli induced a broadband power augmentation that included 40 Hz, as well as higher (80–100 Hz) gamma frequencies. The topography of gamma augmentation was similar, but not identical, to that of the AEP, and was more focused than that of alpha power suppression. Its temporal onset coincided with the N100, but outlasted it. Phonemes produced greater gamma augmentation than tones, while a similar difference was not observed in the N100. Conclusions: Auditory perception induces ECoG gamma activity not only at 40 Hz, but also in higher gamma frequencies. This activity appears to be an index of cortical activation that reflects task-specific processing in the human auditory cortex more closely than the AEP or alpha power suppression.

1,25-Dihydroxyvitamin D3 Antagonizes Interferon-γ-Induced Expression of Class II Major Histocompatibility Antigens on Thyroid Follicular and Testicular Leydig Cells*

Interferon-gamma (IFN gamma) induces production and expression of major histocompatibility complex class II molecules on both marrow-derived and nonbone marrow-derived cell types. 1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3], a seco-steroid derived from vitamin D3, has previously been reported to enhance such expression alone or together with IFN gamma on a number of monocyte/macrophage tumorigenic lines. In contrast, the present studies have found that 1,25-(OH)2D3 inhibited the ability of IFN gamma to induce class II antigen expression on nontransformed rat thyroid follicular epithelial cells (FRTL-5) and mouse testicular Leydig cells (TM3). Although 1,25-(OH)2D3 inhibited the induction of both IA and IE class II locus products, IFN gamma augmentation of class I major histocompatibility complex antigens was not affected. 1,24-(OH)2D3 and 24,25-(OH)2D3 also inhibited class II induction by IFN gamma. Notably, the relative inhibitory ability of these compounds paralleled the strength of their binding affinities for the 1,25-(OH)2D3 receptor, indicating that this antagonistic effect probably requires receptor-ligand interaction. Other steroid hormones, such as hydrocortisone or testosterone, had no inhibitory effect on IFN gamma-induced class II expression on Leydig cells. Additionally, the failure of indomethacin to reverse the effect of 1,25-(OH)2D3 and the finding that exogenous prostaglandin E2 did not inhibit class II induction in these cells indicated that prostaglandins are probably not responsible for this anti-IFN gamma activity. In total, these results suggest that an endocrinological mediator is capable of inhibiting class II induction on resident endocrine tissue populations and, therefore, could help to diminish local CD4+ T-cell recognition of these cells.