The thalamus as the generator and modulator of EEG alpha rhythm: a combined PET/EEG study with lorazepam challenge in humans

Interrogating the Relationship Between Schizotypy, the Catechol-O-Methyltransferase (COMT) Val158Met Polymorphism, and Neuronal Oscillatory Activity

The COMT Val158Met polymorphism affects the availability of synaptic dopamine in the prefrontal cortex and has been widely studied as a genetic risk factor for psychosis. Schizotypy is associated with an increased risk of psychosis, with some studies implicating similar neurobiological mechanisms to schizophrenia. The present study sought to interrogate the link between the COMT Val158Met polymorphism and schizotypy using electroencephalogram (EEG) to identify neurophysiological mechanisms underpinning psychosis risk. Neurotypical (N = 91) adults were genotyped for the COMT Val158Met polymorphism, completed the Schizotypal Personality Questionnaire (SPQ), and had eyes open resting-state EEG recorded for 4 min. SPQ suspiciousness subscale scores were higher for individuals homozygous for Val/Val and Met/Met versus Val/Met genotypes. Delta, theta, alpha-2, beta-1, and beta-2 amplitudes were lower for Val/Val than Met/Met individuals. Lower theta amplitudes were correlated with higher total SPQ scores (P = 0.050), and multiple regression revealed that higher delta, and lower theta and beta-2 amplitudes (but not COMT genotype) best predicted total SPQ scores (P = 0.014). This study demonstrates the importance of COMT genotype in determining trait suspiciousness and EEG oscillatory activity. It also highlights relationships between dopaminergic alterations, EEG and schizotypy that are dissimilar to those observed in schizophrenia.

The effects of transcranial alternating current stimulation (tACS) at individual alpha peak frequency (iAPF) on motor cortex excitability in young and elderly adults

Transcranial alternating current stimulation (tACS) can modulate brain oscillations, cortical excitability and behaviour. In aging, the decrease in EEG alpha activity (8–12 Hz) in the parieto-occipital and mu rhythm in the motor cortex are correlated with the decline in cognitive and motor functions, respectively. Increasing alpha activity using tACS might therefore improve cognitive and motor function in the elderly. The present study explored the influence of tACS on cortical excitability in young and old healthy adults. We applied tACS at individual alpha peak frequency for 10 min (1.5 mA) to the left motor cortex. Transcranial magnetic stimulation was used to assess the changes in cortical excitability as measured by motor-evoked potentials at rest, before and after stimulation. TACS increased cortical excitability in both groups. However, our results also suggest that the mechanism behind the effects was different, as we observed an increase and decrease in intracortical inhibition in the old group and young group, respectively. Our results indicate that both groups profited similarly from the stimulation. There was no indication that tACS was more effective in conditions of low alpha power, that is, in the elderly.

Reduction in Alpha Peak Frequency and Coherence on Quantitative Electroencephalography in Patients with Schizophrenia

BACKGROUND

The aim of the study was to examine the characteristics of alpha wave peak frequency, power, and coherence in patients with schizophrenia.

METHODS

Thirty-one patients with schizophrenia and age- and sex-matched subjects with no psychopathology were enrolled. All study participants underwent quantitative electroencephalography (QEEG). Alpha-related values, including peak frequency, power, and coherence, were evaluated.

RESULTS

Alpha peak frequency on the Oz area was slower in the schizophrenia group than that in the control group. However, no differences in absolute or relative power were observed between the two groups. Significant reductions in absolute and relative coherence were observed at the C3-C4 and T3-T4 nodes in the patients with schizophrenia. Relative coherence was reduced at the P3-P4 nodes.

CONCLUSION

This study focused on alpha variables detected in QEEG as intrinsic values to distinguish schizophrenia from a healthy control. The results suggest decreased alpha peak frequency of the occipital lobe and decreased coherence between the two hemispheres in patients with schizophrenia. A further study could elucidate the causal relationship and biological meaning of the variations in alpha waves in patients with schizophrenia.

Relationship Between Alpha Rhythm and the Default Mode Network: An EEG-fMRI Study

PURPOSE

Reports of the relationship between the default mode network (DMN) and alpha power are conflicting. Our goal was to assess this relationship by analyzing concurrently obtained EEG/functional MRI data using hypothesis-independent methods.

METHODS

We collected functional MRI and EEG data during eyes-closed rest in 20 participants aged 19 to 37 (10 females) and performed independent component analysis on the functional MRI data and a Hamming-windowed fast Fourier transform on the EEG data. We correlated functional MRI fluctuations in the DMN with alpha power.

RESULTS

Of the six independent components found to have significant relationships with alpha, four contained DMN-associated regions: One independent component was positively correlated with alpha power, whereas all others were negatively correlated. Furthermore, two independent components with opposite relationships with alpha had overlapping voxels in the medial prefrontal cortex and posterior cingulate cortex, suggesting that subpopulations of neurons within these classic nodes within the DMN may have different relationships to alpha power.

CONCLUSIONS

Different parts of the DMN exhibit divergent relationships to alpha power. Our results highlight the relationship between DMN activity and alpha power, indicating that networks, such as the DMN, may have subcomponents that exhibit different behaviors.

Ultra-slow mechanical stimulation of olfactory epithelium modulates consciousness by slowing cerebral rhythms in humans

The coupling between respiration and neural activity within olfactory areas and hippocampus has recently been unambiguously demonstrated, its neurophysiological basis sustained by the well-assessed mechanical sensitivity of the olfactory epithelium. We herein hypothesize that this coupling reverberates to the whole brain, possibly modulating the subject's behavior and state of consciousness. The olfactory epithelium of 12 healthy subjects was stimulated with periodical odorless air-delivery (frequency 0.05 Hz, 8 s on, 12 off). Cortical electrical activity (High Density-EEG) and perceived state of consciousness have been studied. The stimulation induced i) an enhancement of delta-theta EEG activity over the whole cortex mainly involving the Limbic System and Default Mode Network structures, ii) a reversal of the overall information flow directionality from wake-like postero-anterior to NREM sleep-like antero-posterior, iii) the perception of having experienced an Altered State of Consciousness. These findings could shed further light via a neurophenomenological approach on the links between respiration, cerebral activity and subjective experience, suggesting a plausible neurophysiological basis for interpreting altered states of consciousness induced by respiration-based meditative practices.

On the Physiological Modulation and Potential Mechanisms Underlying Parieto-Occipital Alpha Oscillations

The parieto-occipital alpha (8–13 Hz) rhythm is by far the strongest spectral fingerprint in the human brain. Almost 90 years later, its physiological origin is still far from clear. In this Research Topic I review human pharmacological studies using electroencephalography (EEG) and magnetoencephalography (MEG) that investigated the physiological mechanisms behind posterior alpha. Based on results from classical and recent experimental studies, I find a wide spectrum of drugs that modulate parieto-occipital alpha power. Alpha frequency is rarely affected, but this might be due to the range of drug dosages employed. Animal and human pharmacological findings suggest that both GABA enhancers and NMDA blockers systematically decrease posterior alpha power. Surprisingly, most of the theoretical frameworks do not seem to embrace these empirical findings and the debate on the functional role of alpha oscillations has been polarized between the inhibition vs. active poles hypotheses. Here, I speculate that the functional role of alpha might depend on physiological excitation as much as on physiological inhibition. This is supported by animal and human pharmacological work showing that GABAergic, glutamatergic, cholinergic, and serotonergic receptors in the thalamus and the cortex play a key role in the regulation of alpha power and frequency. This myriad of physiological modulations fit with the view that the alpha rhythm is a complex rhythm with multiple sources supported by both thalamo-cortical and cortico-cortical loops. Finally, I briefly discuss how future research combining experimental measurements derived from theoretical predictions based of biophysically realistic computational models will be crucial to the reconciliation of these disparate findings.

Using Positron Emission Tomography in Revealing the Mystery of General Anesthesia: Study Design Challenges and Opportunities

Functional neuroimaging with positron emission tomography (PET) is one of the cornerstones for studying the central nervous system effects of general anesthetics and anesthesia mechanisms. General anesthesia offers a unique and safe way to directly manipulate consciousness, and can thus be used as a powerful research tool to study the neurobiology of human consciousness. In this chapter, we will address the possibilities of PET imaging in revealing the mysteries of general anesthesia and anesthetic induced unconsciousness and summarize some of the recent advancements in the field. Importantly, we will discuss possible ways to separate brain activity changes associated with the changing level of consciousness from the concentration or dose-dependent direct or indirect drug effects on the brain. We will try to demonstrate how state-of-the-art clinical pharmacology, use of specific anesthetic drugs, and innovative study design solutions could be utilized.

Ketogenic Diet Suppresses Alcohol Withdrawal Syndrome in Rats

BACKGROUND

Alcohol use disorder is underdiagnosed and undertreated, and up to 50% of alcohol-abstinent patients diagnosed with alcohol dependence relapse within the first year of treatment. Current treatments for the maintenance of alcohol abstinence in patients with alcohol use disorder have limited efficacy, and there is an urgent need for novel treatment strategies. Decreased cerebral glucose metabolism and increased brain uptake of acetate were recently reported in heavy drinkers, relative to controls. Given the switch of metabolic fuel from glucose to acetate in the alcohol-dependent brain, we investigated the potential therapeutic benefit of a ketogenic diet in managing alcohol withdrawal symptoms during detoxification.

METHODS

Male Sprague Dawley rats fed either ketogenic or regular diet were administered ethanol or water orally, twice daily for 6 days while the diet conditions were maintained. Abstinence symptoms were rated 6, 24, 48, and 72 hours after the last alcohol administration.

RESULTS

Maintenance on a ketogenic diet caused a significant decrease in the alcohol withdrawal symptoms' "rigidity" and "irritability."

CONCLUSIONS

Our preclinical pilot study suggests that a ketogenic diet may be a novel approach for treating alcohol withdrawal symptoms in humans.

Real-time fMRI neurofeedback of the mediodorsal and anterior thalamus enhances correlation between thalamic BOLD activity and alpha EEG rhythm

Real-time fMRI neurofeedback (rtfMRI-nf) with simultaneous EEG allows volitional modulation of BOLD activity of target brain regions and investigation of related electrophysiological activity. We applied this approach to study correlations between thalamic BOLD activity and alpha EEG rhythm. Healthy volunteers in the experimental group (EG, n = 15) learned to upregulate BOLD activity of the target region consisting of the mediodorsal (MD) and anterior (AN) thalamic nuclei using rtfMRI-nf during retrieval of happy autobiographical memories. Healthy subjects in the control group (CG, n = 14) were provided with a sham feedback. The EG participants were able to significantly increase BOLD activities of the MD and AN. Functional connectivity between the MD and the inferior precuneus was significantly enhanced during the rtfMRI-nf task. Average individual changes in the occipital alpha EEG power significantly correlated with the average MD BOLD activity levels for the EG. Temporal correlations between the occipital alpha EEG power and BOLD activities of the MD and AN were significantly enhanced, during the rtfMRI-nf task, for the EG compared to the CG. Temporal correlations with the alpha power were also significantly enhanced for the posterior nodes of the default mode network, including the precuneus/posterior cingulate, and for the dorsal striatum. Our findings suggest that the temporal correlation between the MD BOLD activity and posterior alpha EEG power is modulated by the interaction between the MD and the inferior precuneus, reflected in their functional connectivity. Our results demonstrate the potential of the rtfMRI-nf with simultaneous EEG for noninvasive neuromodulation studies of human brain function.

Disrupted Thalamus White Matter Anatomy and Posterior Default Mode Network Effective Connectivity in Amnestic Mild Cognitive Impairment

Alzheimer’s disease (AD) and its prodromal state amnestic mild cognitive impairment (aMCI) are characterized by widespread abnormalities in inter-areal white matter fiber pathways and parallel disruption of default mode network (DMN) resting state functional and effective connectivity. In healthy subjects, DMN and task positive network interaction are modulated by the thalamus suggesting that abnormal task-based DMN deactivation in aMCI may be a consequence of impaired thalamo-cortical white matter circuitry. Thus, this article uses a multimodal approach to assess white matter integrity between thalamus and DMN components and associated effective connectivity in healthy controls (HCs) relative to aMCI patients. Twenty-six HC and 20 older adults with aMCI underwent structural, functional and diffusion MRI scanning using the high angular resolution diffusion-weighted acquisition protocol. The DMN of each subject was identified using independent component analysis (ICA) and resting state effective connectivity was calculated between thalamus and DMN nodes. White matter integrity changes between thalamus and DMN were investigated with constrained spherical deconvolution (CSD) tractography. Significant structural deficits in thalamic white matter projection fibers to posterior DMN components posterior cingulate cortex (PCC) and lateral inferior parietal lobe (IPL) were identified together with significantly reduced effective connectivity from left thalamus to left IPL. Crucially, impaired thalamo-cortical white matter circuitry correlated with memory performance. Disrupted thalamo-cortical structure was accompanied by significant reductions in IPL and PCC cortico-cortical effective connectivity. No structural deficits were found between DMN nodes. Abnormal posterior DMN activity may be driven by changes in thalamic white matter connectivity; a view supported by the close anatomical and functional association of thalamic nuclei effected by AD pathology and the posterior DMN nodes. We conclude that dysfunctional posterior DMN activity in aMCI is consistent with disrupted cortico-thalamo-cortical processing and thalamic-based dissemination of hippocampal disease agents to cortical hubs.

Simultaneous trimodal PET-MR-EEG imaging: Do EEG caps generate artefacts in PET images?

Trimodal simultaneous acquisition of positron emission tomography (PET), magnetic resonance imaging (MRI), and electroencephalography (EEG) has become feasible due to the development of hybrid PET-MR scanners. To capture the temporal dynamics of neuronal activation on a millisecond-by-millisecond basis, an EEG system is appended to the quantitative high resolution PET-MR imaging modality already established in our institute. One of the major difficulties associated with the development of simultaneous trimodal acquisition is that the components traditionally used in each modality can cause interferences in its counterpart. The mutual interferences of MRI components and PET components on PET and MR images, and the influence of EEG electrodes on functional MRI images have been studied and reported on. Building on this, this study aims to investigate the influence of the EEG cap on the quality and quantification of PET images acquired during simultaneous PET-MR measurements. A preliminary transmission scan study on the ECAT HR+ scanner, using an Iida phantom, showed visible attenuation effect due to the EEG cap. The BrainPET-MR emission images of the Iida phantom with [¹⁸F]Fluordeoxyglucose, as well as of human subjects with the EEG cap, did not show significant effects of the EEG cap, even though the applied attenuation correction did not take into account the attenuation of the EEG cap itself.

Autism, Attention, and Alpha Oscillations: An Electrophysiological Study of Attentional Capture

Background

Autism spectrum disorder (ASD) is associated with deficits in adaptively orienting attention to behaviorally-relevant information. Neural oscillatory activity plays a key role in brain function and provides a high-resolution temporal marker of attention dynamics. Alpha band (8-12 Hz) activity is associated with both selecting task-relevant stimuli and filtering task-irrelevant information.

Methods

The present study used electroencephalography (EEG) to examine alpha-band oscillatory activity associated with attentional capture in nineteen children with ASD and twenty-one age- and IQ-matched typically developing (TD) children. Participants completed a rapid serial visual presentation paradigm designed to investigate responses to behaviorally-relevant targets and contingent attention capture by task-irrelevant distractors, which either did or did not share a behaviorally-relevant feature. Participants also completed six minutes of eyes-open resting EEG.

Results

In contrast to their TD peers, children with ASD did not evidence posterior alpha desynchronization to behaviorally-relevant targets. Additionally, reduced target-related desynchronization and poorer target detection were associated with increased ASD symptomatology. TD children also showed behavioral and electrophysiological evidence of contingent attention capture, whereas children with ASD showed no behavioral facilitation or alpha desynchronization to distractors that shared a task-relevant feature. Lastly, children with ASD had significantly decreased resting alpha power, and for all participants increased resting alpha levels were associated with greater task-related alpha desynchronization.

Conclusions

These results suggest that in ASD under-responsivity and impairments in orienting to salient events within their environment are reflected by atypical EEG oscillatory neurodynamics, which may signify atypical arousal levels and/or an excitatory/inhibitory imbalance.

Galvanic Vestibular Stimulation (GVS) effects on impaired interhemispheric connectivity in Parkinson's Disease

Disrupted interhemispheric connectivity (IHC) is being increasingly recognized as a robust feature of a number of neurological diseases, including Parkinson's Disease (PD). We investigated whether or not Galvanic Vestibular Stimulation (GVS) - a proposed treatment for PD - affected IHC in 11 PD subjects (off medication). In order to avoid the confound of stimulation artifact disrupting the EEG, we investigated the immediate period (52 sec) after stimulation (72 sec) with noisy 1/f-type GVS stimuli. Partial Least Squares (PLS) regression was used to determine the subject-specific linear combination of EEG electrodes that maximized covariance between hemispheres and then computed coherence between the dominant PLS components. PD subjects had increased IHC <;~10 Hz and decreased IHC >13 Hz compared to 11 healthy, age-matched controls. After GVS in PD subjects, a significant increase in IHC was detected, especially above 30 Hz. We suggest that GVS may partially exert its beneficial effects in PD by "normalizing" impaired IHC.

Differential Modulation of Rhythmic Brain Activity in Healthy Adults by a T-Type Calcium Channel Blocker: An MEG Study

1-octanol is a therapeutic candidate for disorders involving the abnormal activation of the T-type calcium current since it blocks this current specifically. Such disorders include essential tremor and a group of neurological and psychiatric disorders resulting from thalamocortical dysrhythmia (TCD). For example, clinically, the observable phenotype in essential tremor is the tremor itself. The differential diagnostic of TCD is not based only on clinical signs and symptoms. Rather, TCD incorporates an electromagnetic biomarker, the presence of abnormal thalamocortical low frequency brain oscillations. The effect of 1-octanol on brain activity has not been tested. As a preliminary step to such a TCD study, we examined the short-term effects of a single dose of 1-octanol on resting brain activity in 32 healthy adults using magnetoencephalograpy. Visual inspection of baseline power spectra revealed that the subjects fell into those with strong low frequency activity (set 2, n = 11) and those without such activity, but dominated by an alpha peak (set 1, n = 22). Cross-validated linear discriminant analysis, using mean spectral density (MSD) in nine frequency bands as predictors, found overall that 82.5% of the subjects were classified as determined by visual inspection. The effect of 1-octanol on the MSD in narrow frequency bands differed between the two subject groups. In set 1 subjects the MSD increased in the 4.5-6.5Hz and 6.5-8.5 Hz bands. This was consistent with a widening of the alpha peak toward lower frequencies. In the set two subjects the MSD decrease in the 2.5-4.5 Hz and 4.5-6.5 Hz bands. This decreased power is consistent with the blocking effect of 1-octanol on T-type calcium channels. The subjects reported no adverse effects of the 1-octanol. Since stronger low frequency activity is characteristic of patients with TCD, 1-octanol and other T-type calcium channel blockers are good candidates for treatment of this group of disorders following a placebo-controlled study.

Exogenous Cortisol Administration; Effects on Risk Taking Behavior, Exercise Performance, and Physiological and Neurophysiological Responses

Rationale: Exogenous cortisol is a modulator of behavior related to increased motivated decision making (Putman et al., 2010), where risky choices yield potentially big reward. Making risk based judgments has been shown to be important to athletes in optimizing pacing during endurance events (Renfree et al., 2014; Micklewright et al., 2015).

Objectives: Therefore, the aims of this study were to examine the effect of 50 mg exogenous cortisol on neurophysiological responses and risk taking behavior in nine healthy men. Further to this, to examine the effect of exogenous cortisol on exercise performance.

Methods: Using a double blind counterbalanced design, cyclists completed a placebo (PLA), and a cortisol (COR) trial (50 mg cortisol), with drug ingestion at 0 min. Each trial consisted of a rest period from 0 to 60 min, followed by a risk taking behavior task, a 30 min time trial (TT) with 5 × 30 s sprints at the following time intervals; 5, 11, 17, 23, and 29 min. Salivary cortisol (SaCOR), Electroencephalography (EEG) and Near Infrared Spectroscopy (NIRs) were measured at 15, 30, 45, and 60 min post-ingestion. Glucose and lactate samples were taken at 0 and 60 min post-ingestion. During exercise, power output (PO), heart rate (HR), EEG, and NIRS were measured. SaCOR was measured 10 min post-exercise.

Results: Cortisol increased risk taking behavior from baseline testing. This was in line with significant neurophysiological changes at rest and during exercise. At rest, SaCOR levels were higher (P < 0.01) in COR compared to PLA (29.7 ± 22.7 and 3.27 ± 0.7 nmol/l, respectively). At 60 min alpha slow EEG response was higher in COR than PLA in the PFC (5.5 ± 6.4 vs. −0.02 ± 8.7% change; P < 0.01). During the TT there was no difference in total km, average power or average sprint power, although Peak power (PP) achieved was lower in COR than PLA (465.3 ± 83.4 and 499.8 ± 104.3; P < 0.05) and cerebral oxygenation was lower in COR (P < 0.05).

Conclusion: This is the first study to examine the effect of exogenous cortisol on exercise performance. These results are in line with previous research showing altered risk taking behavior following exogenous cortisol, however the altered behavior did not translate into changes in exercise performance.

Characterization of Glutamatergic and GABAA-Mediated Neurotransmission in Motor and Dorsolateral Prefrontal Cortex Using Paired-Pulse TMS-EEG

Short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) are noninvasive transcranial magnetic stimulation (TMS) measures of GABA_A receptor-mediated inhibition and glutamatergic excitatory transmission, respectively. Conventionally these measures have been restricted to the motor cortex. We investigated whether SICI and ICF could be recorded from the dorsolateral prefrontal cortex (DLPFC) using combined TMS and electroencephalography (TMS-EEG). We first characterized the neural signature of SICI and ICF in M1 in terms of TMS-evoked potentials (TEPs) and spectral power modulation. Subsequently, these paradigms were applied in the DLPFC to determine whether similar neural signatures were evident. With TMS at M1, SICI and ICF led to bidirectional modulation (inhibition and facilitation, respectively) of P30 and P60 TEP amplitude, which correlated with MEP amplitude changes. With DLPFC stimulation, P60 was bidirectionally modulated by SICI and ICF in the same manner as for M1 stimulation, whereas P30 was absent. The sole modulation of early TEP components is in contradistinction to other measures such as long-interval intracortical inhibition and may reflect modulation of short latency excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs). Overall, the data suggest that SICI and ICF can be recorded using TMS-EEG in DLPFC providing noninvasive measures of glutamatergic and GABA_A receptor-mediated neurotransmission. This may facilitate future research attempting to ascertain the role of these neurotransmitters in the pathophysiology and treatment of neurological and psychiatric disorders.

Time-course of coherence in the human basal ganglia during voluntary movements

We are interested in characterizing how brain networks interact and communicate with each other during voluntary movements. We recorded electrical activities from the globus pallidus pars interna (GPi), subthalamic nucleus (STN) and the motor cortex during voluntary wrist movements. Seven patients with dystonia and six patients with Parkinson’s disease underwent bilateral deep brain stimulation (DBS) electrode placement. Local field potentials from the DBS electrodes and scalp EEG from the electrodes placed over the motor cortices were recorded while the patients performed externally triggered and self-initiated movements. The coherence calculated between the motor cortex and STN or GPi was found to be coupled to its power in both the beta and the gamma bands. The association of coherence with power suggests that a coupling in neural activity between the basal ganglia and the motor cortex is required for the execution of voluntary movements. Finally, we propose a mathematical model involving coupled neural oscillators which provides a possible explanation for how inter-regional coupling takes place.

Neuronal Oscillations with Non-sinusoidal Morphology Produce Spurious Phase-to-Amplitude Coupling and Directionality

Neuronal oscillations support cognitive processing. Modern views suggest that neuronal oscillations do not only reflect coordinated activity in spatially distributed networks, but also that there is interaction between the oscillations at different frequencies. For example, invasive recordings in animals and humans have found that the amplitude of fast oscillations (>40 Hz) occur non-uniformly within the phase of slower oscillations, forming the so-called cross-frequency coupling (CFC). However, the CFC patterns might be influenced by features in the signal that do not relate to underlying physiological interactions. For example, CFC estimates may be sensitive to spectral correlations due to non-sinusoidal properties of the alpha band wave morphology. To investigate this issue, we performed CFC analysis using experimental and synthetic data. The former consisted in a double-blind magnetoencephalography pharmacological study in which participants received either placebo, 0.5 or 1.5 mg of lorazepam (LZP; GABAergic enhancer) in different experimental sessions. By recording oscillatory brain activity with during rest and working memory (WM), we were able to demonstrate that posterior alpha (8-12 Hz) phase was coupled to beta-low gamma band (20-45 Hz) amplitude envelope during all sessions. Importantly, bicoherence values around the harmonics of the alpha frequency were similar both in magnitude and topographic distribution to the cross-frequency coherence (CFCoh) values observed in the alpha-phase to beta-low gamma coupling. In addition, despite the large CFCoh we found no significant cross-frequency directionality (CFD). Critically, simulations demonstrated that a sizable part of our empirical CFCoh between alpha and beta-low gamma coupling and the lack of CFD could be explained by two-three harmonics aligned in zero phase-lag produced by the physiologically characteristic alpha asymmetry in the amplitude of the peaks relative to the troughs. Furthermore, we showed that periodic signals whose waveform deviate from pure sine waves produce non-zero CFCoh with predictable CFD. Our results reveal the important role of the non-sinusoidal wave morphology on state of the art CFC metrics and we recommend caution with strong physiological interpretations of CFC and suggest basic data quality checks to enhance the mechanistic understanding of CFC.

Peripheral Attentional Targets under Covert Attention Lead to Paradoxically Enhanced Alpha Desynchronization in Neurofibromatosis Type 1

The limited capacity of the human brain to process the full extent of visual information reaching the visual cortex requires the recruitment of mechanisms of information selection through attention. Neurofibromatosis type-1 (NF1) is a neurodevelopmental disease often exhibiting attentional deficits and learning disabilities, and is considered to model similar impairments common in other neurodevelopmental disorders such as autism. In a previous study, we found that patients with NF1 are more prone to miss targets under overt attention conditions. This finding was interpreted as a result of increased occipito-parietal alpha oscillations. In the present study, we used electroencephalography (EEG) to study alpha power modulations and the performance of patients with NF1 in a covert attention task. Covert attention was required in order to perceive changes (target offset) of a peripherally presented stimulus. Interestingly, alpha oscillations were found to undergo greater desynchronization under this task in the NF1 group compared with control subjects. A similar pattern of desynchronization was found for beta frequencies while no changes in gamma oscillations could be identified. These results are consistent with the notion that different attentional states and task demands generate different patterns of abnormal modulation of alpha oscillatory processes in NF1. Under covert attention conditions and while target offset was reported with relatively high accuracy (over 90% correct responses), excessive desynchronization was found. These findings suggest an abnormal modulation of oscillatory activity and attentional processes in NF1. Given the known role of alpha in modulating attention, we suggest that alpha patterns can show both abnormal increases and decreases that are task and performance dependent, in a way that enhanced alpha desynchronization may reflect a compensatory mechanism to keep performance at normal levels. These results suggest that dysregulation of alpha oscillations may occur in NF1 both in terms of excessive or diminished activation patterns.

Spatial-temporal patterns of electrocorticographic spectral changes during midazolam sedation

OBJECTIVE

To better understand 'when' and 'where' wideband electrophysiological signals are altered by sedation.

METHODS

We generated animation movies showing electrocorticography (ECoG) amplitudes at eight spectral frequency bands across 1.0-116 Hz, every 0.1s, on three-dimensional surface images of 10 children who underwent epilepsy surgery. We measured the onset, intensity, and variance of each band amplitude change at given nonepileptic regions separately from those at affected regions. We also determined the presence of differential ECoG changes depending on the brain anatomy.

RESULTS

Within 20s following injection of midazolam, beta (16-31.5 Hz) and sigma (12-15.5 Hz) activities began to be multifocally augmented with increased variance in amplitude at each site. Beta-sigma augmentation was most prominent within the association neocortex. Augmentation of low-delta activity (1.0-1.5 Hz) was relatively modest and confined to the somatosensory-motor region. Conversely, injection of midazolam induced attenuation of theta (4.0-7.5 Hz) and high-gamma (64-116 Hz) activities.

CONCLUSIONS

Our observations support the notion that augmentation beta-sigma and delta activities reflects cortical deactivation or inactivation, whereas theta and high-gamma activities contribute to maintenance of consciousness. The effects of midazolam on the dynamics of cortical oscillations differed across regions.

SIGNIFICANCE

Sedation, at least partially, reflects a multi-local phenomenon at the cortical level rather than global brain alteration homogeneously driven by the common central control structure.

Aroused with heart: Modulation of heartbeat evoked potential by arousal induction and its oscillatory correlates

Recent studies showed that the visceral information is constantly processed by the brain, thereby potentially influencing cognition. One index of such process is the heartbeat evoked potential (HEP), an ERP component related to the cortical processing of the heartbeat. The HEP is sensitive to a number of factors such as motivation, attention, pain, which are associated with higher levels of arousal. However, the role of arousal and its associated brain oscillations on the HEP has not been characterized, yet it could underlie the previous findings. Here we analysed the effects of high- (HA) and low-arousal (LA) induction on the HEP. Further, we investigated the brain oscillations and their role in the HEP in response to HA and LA inductions. As compared to LA, HA was associated with a higher HEP and lower alpha oscillations. Interestingly, individual differences in the HEP modulation by arousal induction were correlated with alpha oscillations. In particular, participants with higher alpha power during the arousal inductions showed a larger HEP in response to HA compared to LA. In summary, we demonstrated that arousal induction affects the cortical processing of heartbeats; and that the alpha oscillations may modulate this effect.

Characteristics of thalamic local field potentials in patients with disorders of consciousness

A functioning thalamus is essential for treatment of patients with disorders of consciousness (DOC) using deep brain stimulation (DBS). This work aims to identify the potential biomarkers related to consciousness from the thalamic deep brain local field potentials (LFPs) in DOC patients. The frequency features of central thalamic LFPs were characterized with spectral analysis. The features were further compared to those of LFPs from the ventroposterior lateral nucleus of the thalamus (VPL) in patients with pain. There are several distinct characteristics of thalamic LFPs found in patients with DOC. The most important feature is the oscillation around 10Hz which could be relevant to the existence of residual consciousness, whereas high power below 8Hz seemed to be associated with loss of consciousness. The invasive deep brain recording tool opens a unique way to explore the brain function in consciousness, awareness and alertness and clarify the potential mechanisms of thalamic stimulation in DOC.

Mean-field thalamocortical modeling of longitudinal EEG acquired during intensive meditation training

Meditation training has been shown to enhance attention and improve emotion regulation. However, the brain processes associated with such training are poorly understood and a computational modeling framework is lacking. Modeling approaches that can realistically simulate neurophysiological data while conforming to basic anatomical and physiological constraints can provide a unique opportunity to generate concrete and testable hypotheses about the mechanisms supporting complex cognitive tasks such as meditation. Here we applied the mean-field computational modeling approach using the scalp-recorded electroencephalogram (EEG) collected at three assessment points from meditating participants during two separate 3-month-long shamatha meditation retreats. We modeled cortical, corticothalamic, and intrathalamic interactions to generate a simulation of EEG signals recorded across the scalp. We also present two novel extensions to the mean-field approach that allow for: (a) non-parametric analysis of changes in model parameter values across all channels and assessments; and (b) examination of variation in modeled thalamic reticular nucleus (TRN) connectivity over the retreat period. After successfully fitting whole-brain EEG data across three assessment points within each retreat, two model parameters were found to replicably change across both meditation retreats. First, after training, we observed an increased temporal delay between modeled cortical and thalamic cells. This increase provides a putative neural mechanism for a previously observed reduction in individual alpha frequency in these same participants. Second, we found decreased inhibitory connection strength between the TRN and secondary relay nuclei (SRN) of the modeled thalamus after training. This reduction in inhibitory strength was found to be associated with increased dynamical stability of the model. Altogether, this paper presents the first computational approach, taking core aspects of physiology and anatomy into account, to formally model brain processes associated with intensive meditation training. The observed changes in model parameters inform theoretical accounts of attention training through meditation, and may motivate future study on the use of meditation in a variety of clinical populations.

Resting-state alpha in autism spectrum disorder and alpha associations with thalamic volume

Alpha circuits (8-12 Hz), necessary for basic and complex brain processes, are abnormal in autism spectrum disorder (ASD). The present study obtained estimates of resting-state (RS) alpha activity in children with ASD and examined associations between alpha activity, age, and clinical symptoms. Given that the thalamus modulates cortical RS alpha rhythms, associations between thalamic structure and alpha activity were examined. RS magnetoencephalography was obtained from 47 typically-developing children (TDC) and 41 children with ASD. RS alpha activity was measured using distributed source localization. Left and right thalamic volume measurements were also obtained. In both groups, the strongest alpha activity was observed in Calcarine Sulcus regions. In Calcarine regions, only TDC showed the expected association between age and alpha peak frequency. ASD had more alpha activity than TDC in regions bordering the Central Sulcus as well as parietal association cortices. In ASD, whereas greater left Central Sulcus relative alpha activity was associated with higher Social Responsiveness Scale (SRS) scores, greater Calcarine region relative alpha activity was associated with lower SRS scores. Although thalamic volume group differences were not observed, relationships between thalamic volume and Calcarine alpha power were unique to TDC. The present study also identified a failure to shift peak alpha frequency as a function of age in primary alpha-generating areas in children with ASD. Findings suggested that increased RS alpha activity in primary motor and somatosensory as well as parietal multimodal areas-with increased alpha thought to reflect greater inhibition-might impair the ability to identify or interpret social cues. Finally, to our knowledge, this is the first study to report associations between thalamic volume and alpha power, an association observed only in TDC. The lack of thalamic and alpha associations in ASD suggests thalamic contributions to RS alpha abnormalities in ASD.

GABAergic modulation of visual gamma and alpha oscillations and its consequences for working memory performance

BACKGROUND

Impressive in vitro research in rodents and computational modeling has uncovered the core mechanisms responsible for generating neuronal oscillations. In particular, GABAergic interneurons play a crucial role for synchronizing neural populations. Do these mechanistic principles apply to human oscillations associated with function? To address this, we recorded ongoing brain activity using magnetoencephalography (MEG) in healthy human subjects participating in a double-blind pharmacological study receiving placebo, 0.5 mg and 1.5 mg of lorazepam (LZP; a benzodiazepine upregulating GABAergic conductance). Participants performed a demanding visuospatial working memory (WM) task.

RESULTS

We found that occipital gamma power associated with WM recognition increased with LZP dosage. Importantly, the frequency of the gamma activity decreased with dosage, as predicted by models derived from the rat hippocampus. A regionally specific gamma increase correlated with the drug-related performance decrease. Despite the system-wide pharmacological intervention, gamma power drug modulations were specific to visual cortex: sensorimotor gamma power and frequency during button presses remained unaffected. In contrast, occipital alpha power modulations during the delay interval decreased parametrically with drug dosage, predicting performance impairment. Consistent with alpha oscillations reflecting functional inhibition, LZP affected alpha power strongly in early visual regions not required for the task demonstrating a regional specific occipital impairment.

CONCLUSIONS

GABAergic interneurons are strongly implicated in the generation of gamma and alpha oscillations in human occipital cortex where drug-induced power modulations predicted WM performance. Our findings bring us an important step closer to linking neuronal dynamics to behavior by embracing established animal models.

Cerebral and blood correlates of reduced functional connectivity in mild cognitive impairment

Growing evidence suggests that decreased functional connectivity in cortical networks precedes clinical stages of Alzheimer's disease (AD), although our knowledge about cerebral and biological correlates of this phenomenon is limited. To shed light on this issue, we have investigated whether resting-state oscillatory connectivity patterns in healthy older (HO) and amnestic mild cognitive impairment (aMCI) subjects are related to anatomical grey matter (GM) and functional (2-[18F]fluoro-2-deoxy-D-glucose (FDG)-PET) changes of neuroelectric sources of alpha rhythms, and/or to changes in plasma amyloid-beta (Aβ) and serum lipid levels, blood markers tied to AD pathogenesis and aging-related cognitive decline. We found that aMCI subjects showed decreased levels of cortical connectivity, reduced FDG-PET intake of the precuneus, and GM atrophy of the thalamus, together with higher levels of Aβ and apolipoprotein B (ApoB) compared to HO. Interestingly, levels of high-density lipoprotein (HDL) cholesterol were positively correlated with the strength of neural-phase coupling in aMCI subjects, and increased triglycerides accompanied bilateral GM loss in the precuneus of aMCI subjects. Together, these findings provide peripheral blood correlates of reduced resting-state cortical connectivity in aMCI, supported by anatomo-functional changes in cerebral sources of alpha rhythms. This framework constitutes an integrated approach to assess functional changes in cortical networks through neuroimaging and peripheral blood markers during early stages of neurodegeneration.

Neural dynamics necessary and sufficient for transition into pre-sleep induced by EEG neurofeedback

The transition from being fully awake to pre-sleep occurs daily just before falling asleep; thus its disturbance might be detrimental. Yet, the neuronal correlates of the transition remain unclear, mainly due to the difficulty in capturing its inherent dynamics. We used an EEG theta/alpha neurofeedback to rapidly induce the transition into pre-sleep and simultaneous fMRI to reveal state-dependent neural activity. The relaxed mental state was verified by the corresponding enhancement in the parasympathetic response. Neurofeedback sessions were categorized as successful or unsuccessful, based on the known EEG signature of theta power increases over alpha, temporally marked as a distinct "crossover" point. The fMRI activation was considered before and after this point. During successful transition into pre-sleep the period before the crossover was signified by alpha modulation that corresponded to decreased fMRI activity mainly in sensory gating related regions (e.g. medial thalamus). In parallel, although not sufficient for the transition, theta modulation corresponded with increased activity in limbic and autonomic control regions (e.g. hippocampus, cerebellum vermis, respectively). The post-crossover period was designated by alpha modulation further corresponding to reduced fMRI activity within the anterior salience network (e.g. anterior cingulate cortex, anterior insula), and in contrast theta modulation corresponded to the increased variance in the posterior salience network (e.g. posterior insula, posterior cingulate cortex). Our findings portray multi-level neural dynamics underlying the mental transition from awake to pre-sleep. To initiate the transition, decreased activity was required in external monitoring regions, and to sustain the transition, opposition between the anterior and posterior parts of the salience network was needed, reflecting shifting from extra- to intrapersonal based processing, respectively.

Characterization of thalamo-cortical association using amplitude and connectivity of functional MRI in mild traumatic brain injury

PURPOSE

To examine thalamic and cortical injuries using fractional amplitude of low-frequency fluctuations (fALFFs) and functional connectivity MRI (fcMRI) based on resting state (RS) and task-related fMRI in patients with mild traumatic brain injury (MTBI).

MATERIALS AND METHODS

Twenty-seven patients and 27 age-matched controls were recruited. The 3 Tesla fMRI at RS and finger tapping task were used to assess fALFF and fcMRI patterns. fALFFs were computed with filtering (0.01-0.08 Hz) and scaling after preprocessing. fcMRI was performed using a standard seed-based correlation method, and delayed fcMRI (coherence) in frequency domain were also performed between thalamus and cortex.

RESULTS

In comparison with controls, MTBI patients exhibited significantly decreased fALFFs in the thalamus (and frontal/temporal subsegments) and cortical frontal and temporal lobes; as well as decreased thalamo-thalamo and thalamo-frontal/ thalamo-temporal fcMRI at rest based on RS-fMRI (corrected P < 0.05). This thalamic and cortical disruption also existed at task-related condition in patients.

CONCLUSION

The decreased fALFFs (i.e., lower neuronal activity) in the thalamus and its segments provide additional evidence of thalamic injury in patients with MTBI. Our findings of fALFFs and fcMRI changes during motor task and resting state may offer insights into the underlying cause and primary location of disrupted thalamo-cortical networks after MTBI.

Median nerve stimulation modulates extracellular signals in the primary motor area of a macaque monkey

Aiming to better define the functional influence of somatosensory stimuli on the primary motor cortex (M1) of primates, we investigated changes in extracellular neural activity induced by repetitive median nerve stimulation (MNS). We described neural adaptation and signal integration in both the multiunit activity (MUA) and the local field potential (LFP). To identify integration of initial M1 activity in the MNS response, we tested the correlation between peak amplitude responses and band energy preceding the peaks. Most of the sites studied in the M1 resulted responsive to MNS. MUA response peak amplitude decreased significantly in time in all sites during repetitive MNS, LFP response peak amplitude instead resulted more variable. Similarly, correlation analysis with the initial activity revealed a significant influence when tested using MUA peak amplitude modulation and a less significant correlation when tested using LFP peak amplitude. Our findings improve current knowledge on mechanisms underlying early M1 changes consequent to afferent somatosensory stimuli.

Phenotypic spectrum of glucose transporter type 1 deficiency syndrome (Glut1 DS)

Glut1 deficiency syndrome (Glut1 DS) was originally described in 1991 as a developmental encephalopathy characterized by infantile onset refractory epilepsy, cognitive impairment, and mixed motor abnormalities including spasticity, ataxia, and dystonia. The clinical condition is caused by impaired glucose transport across the blood brain barrier. The past 5 years have seen a dramatic expansion in the range of clinical syndromes that are recognized to occur with Glut1 DS. In particular, there has been greater recognition of milder phenotypes. Absence epilepsy and other idiopathic generalized epilepsy syndromes may occur with seizure onset in childhood or adulthood. A number of patients present predominantly with movement disorders, sometimes without any accompanying seizures. In particular, paroxysmal exertional dyskinesia is now a well-documented clinical feature that occurs in individuals with Glut1 DS. A clue to the diagnosis in patients with paroxysmal symptoms may be the triggering of episodes during fasting or exercise. Intellectual impairment may range from severe to very mild. Awareness of the broad range of potential clinical phenotypes associated with Glut1 DS will facilitate earlier diagnosis of this treatable neurologic condition. The ketogenic diet is the mainstay of treatment and nourishes the starving symptomatic brain during development.

Spontaneous Slow Fluctuation of EEG Alpha Rhythm Reflects Activity in Deep-Brain Structures: A Simultaneous EEG-fMRI Study

The emergence of the occipital alpha rhythm on brain electroencephalogram (EEG) is associated with brain activity in the cerebral neocortex and deep brain structures. To further understand the mechanisms of alpha rhythm power fluctuation, we performed simultaneous EEGs and functional magnetic resonance imaging recordings in human subjects during a resting state and explored the dynamic relationship between alpha power fluctuation and blood oxygenation level-dependent (BOLD) signals of the brain. Based on the frequency characteristics of the alpha power time series (APTS) during 20-minute EEG recordings, we divided the APTS into two components: fast fluctuation (0.04–0.167 Hz) and slow fluctuation (0–0.04 Hz). Analysis of the correlation between the MRI signal and each component revealed that the slow fluctuation component of alpha power was positively correlated with BOLD signal changes in the brain stem and the medial part of the thalamus and anterior cingulate cortex, while the fast fluctuation component was correlated with the lateral part of the thalamus and the anterior cingulate cortex, but not the brain stem. In summary, these data suggest that different subcortical structures contribute to slow and fast modulations of alpha spectra on brain EEG.

The effect of resting condition on resting-state fMRI reliability and consistency: a comparison between resting with eyes open, closed, and fixated

Resting-state fMRI (rs-fMRI) has been demonstrated to have moderate to high reliability and produces consistent patterns of connectivity across a wide variety of subjects, sites, and scanners. However, there is no one agreed upon method to acquire rs-fMRI data. Some sites instruct their subjects, or patients, to lie still with their eyes closed, while other sites instruct their subjects to keep their eyes open or even fixating on a cross during scanning. Several studies have compared those three resting conditions based on connectivity strength. In our study, we assess differences in metrics of test-retest reliability (using an intraclass correlation coefficient), and consistency of the rank-order of connections within a subject and the ranks of subjects for a particular connection from one session to another (using Kendall's W tests). Twenty-five healthy subjects were scanned at three different time points for each resting condition, twice the same day and another time two to three months later. Resting-state functional connectivity measures were evaluated in motor, visual, auditory, attention, and default-mode networks, and compared between the different resting conditions. Of the networks examined, only the auditory network resulted in significantly higher connectivity in the eyes closed condition compared to the other two conditions. No significant between-condition differences in connectivity strength were found in default mode, attention, visual, and motor networks. Overall, the differences in reliability and consistency between different resting conditions were relatively small in effect size but results were found to be significant. Across all within-network connections, and within default-mode, attention, and auditory networks statistically significant greater reliability was found when the subjects were lying with their eyes fixated on a cross. In contrast, primary visual network connectivity was most reliable when subjects had their eyes open (and not fixating on a cross).

Volitional eyes opening perturbs brain dynamics and functional connectivity regardless of light input

The act of opening (or closing) one's eyes has long been demonstrated to impact on brain function. However, the eyes open condition is usually accompanied by visual input, and this effect may have been a significant confounding factor in previous studies. To clarify this situation, we extended the traditional eyes open/closed study to a two-factor balanced, repeated measures resting state fMRI (rs-fMRI) experiment, in which light on/off was also included as a factor. In 16 healthy participants, we estimated the univariate properties of the BOLD signal, as well as a bivariate measure of functional connectivity and multivariate network topology measures. Across all these measures, we demonstrate that human brain adopts a distinctive configuration when eyes are open (compared to when eyes are closed) independently of exogenous light input: (i) the eyes open states were associated with decreased BOLD signal variance (P-value=0.0004), decreased fractional amplitude of low frequency fluctuation (fALFF. P-value=0.0061), and decreased Hurst exponent (H. P-value=0.0321) mainly in the primary and secondary sensory cortical areas, the insula, and the thalamus. (ii) The strength of functional connectivity (FC) between the posterior cingulate cortex (PCC), a major component of the default mode network (DMN), and the bilateral perisylvian and perirolandic regions was also significantly decreased during eyes open states. (iii) On the other hand, the average network connection distance increased during eyes open states (P-value=0.0139). Additionally, the metrics of univariate, bivariate, and multivariate analyses in this study are significantly correlated. In short, we have shown that the marked effects on the dynamics and connectivity of fMRI time series brought by volitional eyes open or closed are simply endogenous and irrespective of exogenous visual stimulus. The state of eyes open (or closed) may thus be an important factor to control in design of rs-fMRI and even other cognitive block or event-related experiments.

Thalamo-cortical mechanisms underlying changes in amplitude and frequency of human alpha oscillations

Although a large number of studies have been devoted to establishing correlations between changes in amplitude and frequency of EEG alpha oscillations and cognitive processes, it is currently unclear through which physiological mechanisms such changes are brought about. In this study we use a biophysical model of EEG generation to gain a fundamental understanding of the functional changes within the thalamo-cortical system that might underly such alpha responses. The main result of this study is that, although the physiology of the thalamo-cortical system is characterized by a large number of parameters, alpha responses effectively depend on only three variables. Physiologically, these variables determine the resonance properties of feedforward, cortico-thalamo-cortical, and intra-cortical circuits. By examining the effect of modulations of these resonances on the amplitude and frequency of EEG alpha oscillations, it is established that the model can reproduce the variety of experimentally observed alpha responses, as well as the experimental finding that changes in alpha amplitude are typically an order of magnitude larger than changes in alpha frequency. The modeling results are also in line with the fact that alpha responses often correlate linearly with indices characterizing cognitive processes. By investigating the effect of synaptic and intrinsic neuronal parameters, we find that alpha responses reflect changes in cortical activation, which is consistent with the hypothesis that alpha activity serves to selectively inhibit cortical regions during cognitive processing demands. As an example of how these analyses can be applied to specific experimental protocols, we reproduce benzodiazepine-induced alpha responses and clarify the putative underlying thalamo-cortical mechanisms. The findings reported in this study provide a fundamental physiological framework within which alpha responses observed in specific experimental protocols can be understood.

Alpha activity in the insula accompanies the urge to neutralize in sub-clinical obsessive-compulsive participants

Background and aims The behavioural addiction model of obsessive-compulsive disorder (OCD) proposes that as compulsions successfully reduce obsession-provoked anxiety in the early stages of the disorder, their performance is rewarding and therefore potentially addictive. According to this theory, the urge to perform a compulsion or neutralization resembles craving in addiction, and ventral fronto-striatal reward circuitry is activated during compulsive or neutralizing behaviour, resembling substance addiction disorders. The current study used EEG source localisation to test this hypothesis by examining brain activity accompanying the urge to neutralize and covert neutralization. Methods Two groups of non-clinical participants (15 Low-OC, 15 High-OC) performed a task in which the urge to neutralize was induced by supplying participants with an obsessive-compulsive-like thought. Source localised EEG activity was compared between a negative condition with high urge to neutralize, and a positive condition with low urge to neutralize, and correlations between brain activity and self-reported urge to neutralize were examined. Results High-OC participants reported a significantly greater urge to neutralize than Low-OC participants, and the majority of participants reported performing covert neutralization during the experiment. Between-condition comparisons in the High-OC group revealed significantly greater alpha activity in the insula and vlPFC in the negative than the positive condition, which was significantly correlated with both urge to neutralize and later decrease in negative affect. Conclusions The current results support the proposal that the urge to neutralize in OCD is neurally similar to craving in substance addiction, in agreement with the behavioural addiction model of OCD.

Long-term high frequency deep brain stimulation of the nucleus accumbens drives time-dependent changes in functional connectivity in the rodent limbic system

Deep brain stimulation of the ventral striatum is an effective treatment for a variety of treatment refractory psychiatric disorders yet the mechanism of action remains elusive. We examined how five days of stimulation affected rhythmic brain activity in freely moving rats in terms of oscillatory power within, and coherence between, selected limbic regions bilaterally. Custom made bipolar stimulating/recording electrodes were implanted, bilaterally, in the nucleus accumbens core. Local field potential (LFP) recording electrodes were implanted, bilaterally in the prelimbic and orbitofrontal cortices and mediodorsal thalamic nucleus. Stimulation was delivered bilaterally with 100 μs duration constant current pulses at a frequency of 130 Hz delivered at an amplitude of 100 μA using a custom-made stimulation device. Synchronized video and LFP data were collected from animals in their home cages before, during and after stimulation. Signals were processed to remove movement and stimulation artifacts, and analyzed to determine changes in spectral power within, and coherence between regions. Five days stimulation of the nucleus accumbens core yielded temporally dynamic modulation of LFP power in multiple bandwidths across multiple brain regions. Coherence was seen to decrease in the alpha band between the mediodorsal thalamic nucleus and core of the nucleus accumbens. Coherence between each core of the nucleus accumbens bilaterally showed rich temporal dynamics throughout the five day stimulation period. Stimulation cessation revealed significant "rebound" effects in both power and coherence in multiple brain regions. Overall, the initial changes in power observed with short-term stimulation are replaced by altered coherence, which may reflect the functional action of DBS.

Moderating effects of music on resting state networks

Resting state networks (RSNs) are spontaneous, synchronous, low-frequency oscillations observed in the brains of subjects who are awake but at rest. A particular RSN called the default mode network (DMN) has been shown to exhibit changes associated with neurological disorders such as temporal lobe epilepsy or Alzheimer's disease. Previous studies have also found that differing experimental conditions such as eyes-open versus eyes-closed can produce measurable changes in the DMN. These condition-associated changes have the potential of confounding the measurements of changes in RSNs related to or caused by disease state(s). In this study, we use fMRI measurements of resting-state connectivity paired with EEG measurements of alpha rhythm and employ independent component analysis, undirected graphs of partial spectral coherence, and spatiotemporal regression to investigate the effect of music-listening on RSNs and the DMN in particular. We observed similar patterns of DMN connectivity in subjects who were listening to music compared with those who were not, with a trend toward a more introspective pattern of resting-state connectivity during music-listening. We conclude that music-listening is a valid condition under which the DMN can be studied.

Brain state regulation during normal development: Intrinsic activity fluctuations in simultaneous EEG-fMRI

Brain maturation in adolescence is mirrored by the EEG as a pronounced decrease in low frequency activity. This EEG power attenuation parallels reductions of structural and metabolic markers of neuronal maturation (i.e., gray matter loss and decrease of absolute cerebral glucose utilization). However, it is largely unknown what causes these electrophysiological changes, and how this functional reorganization relates to other functional measures such as the fMRI BOLD signal. In this study, we used simultaneously recorded EEG and fMRI to localize hemodynamic correlates of fluctuating EEG oscillations and to study the development of this EEG-BOLD coupling. Furthermore, the maturational EEG power attenuation was directly compared to BOLD signal power maturation. Both analyses were novel in their developmental perspective and aimed at providing a functional lead to EEG maturation. Data from 19 children, 18 adolescents and 18 young adults were acquired in 10 min eyes-open/eyes-closed resting states. Our results revealed that both EEG and BOLD amplitudes strongly decrease between childhood and adulthood, but their functional coupling remains largely unchanged. The global reduction of absolute amplitude of spontaneous slow BOLD signal fluctuation is a novel marker for brain maturation, and parallels the globally decreasing trajectories of EEG amplitudes, gray matter and glucose metabolism during adolescence. Further, the absence of thalamocortical EEG-BOLD coupling in children together with age-related normalized thalamic BOLD power increase indicated maturational changes in brain state regulation.

Attention to painful cutaneous laser stimuli evokes directed functional connectivity between activity recorded directly from human pain-related cortical structures

Our previous studies show that attention to painful cutaneous laser stimuli is associated with functional connectivity between human primary somatosensory cortex (SI), parasylvian cortex (PS), and medial frontal cortex (MF), which may constitute a pain network. However, the direction of functional connections within this network is unknown. We now test the hypothesis that activity recorded from the SI has a driver role, and a causal influence, with respect to activity recorded from PS and MF during attention to a laser. Local field potentials (LFP) were recorded from subdural grid electrodes implanted for the treatment of epilepsy. We estimated causal influences by using the Granger causality (GRC), which was computed while subjects performed either an attention task (counting laser stimuli) or a distraction task (reading for comprehension). Before the laser stimuli, directed attention to the painful stimulus (counting) consistently increased the number of GRC pairs both within the SI cortex and from SI upon PS (SI>PS). After the laser stimulus, attention to a painful stimulus increased the number of GRC pairs from SI>PS, and SI>MF, and within the SI area. LFP at some electrode sites (critical sites) exerted GRC influences upon signals at multiple widespread electrodes, both in other cortical areas and within the area where the critical site was located. Critical sites may bind these areas together into a pain network, and disruption of that network by stimulation at critical sites might be used to treat pain. Electrical activity recorded from the somatosensory cortex drives activity recorded elsewhere in the pain network and may bind the network together; disruption of that network by stimulation at critical sites might be used to treat pain.

Alpha and theta rhythm abnormality in Alzheimer's Disease: a study using a computational model

Electroencephalography (EEG) studies in Alzheimer's Disease (AD) patients show an attenuation of average power within the alpha band (7.5-13 Hz) and an increase of power in the theta band (4-7 Hz). Significant body of evidence suggest that thalamocortical circuitry underpin the generation and modulation of alpha and theta rhythms. The research presented in this chapter is aimed at gaining a better understanding of the neuronal mechanisms underlying EEG band power changes in AD which may in the future provide useful biomarkers towards early detection of the disease and for neuropharmaceutical investigations. The study is based on a classic computational model of the thalamocortical circuitry which exhibits oscillation within the theta and the alpha bands. We are interested in the change in model oscillatory behaviour corresponding with changes in the connectivity parameters in the thalamocortical as well as sensory input pathways. The synaptic organisation as well as the connectivity parameter values in the model are modified based on recent experimental data from the cat thalamus. We observe that the inhibitory population in the model plays a crucial role in mediating the oscillatory behaviour of the model output. Further, increase in connectivity parameters in the afferent and efferent pathways of the inhibitory population induces a slowing of the output power spectra. These observations may have implications for extending the model for further AD research.

Pharmacodynamic differentiation of lorazepam sleepiness and dizziness using an ordered categorical measure

Categorical measures of lorazepam sleepiness and dizziness were modeled to identify differences in pharmacodynamic (PD) parameters between these adverse events (AEs). Differences in data-derived PD parameters were compared with relative incidence rates in the drug label (15.7% and 6.9%, respectively). Healthy volunteers (n = 20) received single oral doses of 2 mg lorazepam or placebo in a randomized, double-blind, cross-over fashion. A seven-point categorical scale measuring the intensity of AEs was serially administered over 24 h. The maximum score (MaxS), and area under the effect curve (AUEC) were determined by noncompartmental methods and compared using a paired t-test. Individual scores were modeled using a logistic function implemented in NONMEM. AUEC and MaxS for sleepiness were significantly higher than dizziness (20.35 vs. 9.76, p < 0.01) and (2.35 vs. 1.45, p < 0.01). Model slope estimates were similar for sleepiness and dizziness (0.21 logits x mL/ng vs. 0.19 logits x mL/ng), but baseline logits were significantly higher for sleepiness (-2.81 vs. -4.34 logits). Data-derived PD parameters were in concordance with label incidence rates. The higher intensity of sleepiness may be directly related to baseline (no drug present) while the increase in intensity as a result of drug was relatively similar for both AEs.

Lost in thoughts: neural markers of low alertness during mind wandering

During concentration tasks, spontaneous attention shifts occurs towards self-centered matters. Little is known about the brain oscillatory activity underlying these mental phenomena. We recorded 128-channels electroencephalographic activity from 12 subjects performing a breath-counting task. Subjects were instructed to press a button whenever, based on their introspective experience, they realized their attention had drifted away from the task. Theta (4-7 Hz) and delta (2-3.5 Hz) EEG activity increased during mind wandering whereas alpha (9-11 Hz) and beta (15-30 Hz) decreased. A passive auditory oddball protocol was presented to the subjects to test brain-evoked responses to perceptual stimuli during mind wandering. Mismatch negativity evoked at 100 ms after oddball stimuli onset decreased during mind wandering whereas the brain-evoked responses at 200 ms after stimuli onset increased. Spectral analyses and evoked related potential results suggest decreased alertness and sensory processing during mind wandering. To our knowledge, our experiment is one of the first neuro-imaging studies that relies purely on subjects' introspective judgment, and shows that such judgment may be used to contrast different brain activity patterns.

Reactivity of hemodynamic responses and functional connectivity to different states of alpha synchrony: a concurrent EEG-fMRI study

Concurrent EEG-fMRI studies have provided increasing details of the dynamics of intrinsic brain activity during the resting state. Here, we investigate a prominent effect in EEG during relaxed resting, i.e. the increase of the alpha power when the eyes are closed compared to when the eyes are open. This phenomenon is related to changes in thalamo-cortical and cortico-cortical synchronization. In order to investigate possible changes to EEG-fMRI coupling and fMRI functional connectivity during the two states we adopted a data-driven approach that fuses the multimodal data on the basis of parallel ICA decompositions of the fMRI data in the spatial domain and of the EEG data in the spectral domain. The power variation of a posterior alpha component was used as a reference function to deconvolve the hemodynamic responses from occipital, frontal, temporal, and subcortical fMRI components. Additionally, we computed the functional connectivity between these components. The results showed widespread alpha hemodynamic responses and high functional connectivity during eyes-closed (EC) rest, while eyes open (EO) resting abolished many of the hemodynamic responses and markedly decreased functional connectivity. These data suggest that generation of local hemodynamic responses is highly sensitive to state changes that do not involve changes of mental effort or awareness. They also indicate the localized power differences in posterior alpha between EO and EC in resting state data are accompanied by spatially widespread amplitude changes in hemodynamic responses and inter-regional functional connectivity, i.e. low frequency hemodynamic signals display an equivalent of alpha reactivity.

ADHD familial loading and abnormal EEG alpha asymmetry in children with ADHD

OBJECTIVE

Abnormal brain laterality (ABL) is indicated in ADHD. ADHD and brain laterality are heritable. Genetic factors contributing to lateralization of brain function may contribute to ADHD. If so, increased ADHD family loading should be associated with greater ABL. Previous studies have shown increased rightward alpha asymmetry in ADHD. We tested whether this was more pronounced in ADHD children with increased ADHD family loading.

METHODS

We compared EEG alpha asymmetry at rest and during the Conner's Continuous Performance Test (CPT) in ADHD children with and without ADHD affected parents, and replicated our findings in a second larger sample. The replication study additionally stratified the parent-affected sample by parental persistent versus non-persistent ADHD status, increased spatial resolution of EEG measures, and assessed low versus high-alpha.

RESULTS

Study-1: the parent-affected group showed increased rightward asymmetry across frontal and central regions and reduced rightward parietal asymmetry during an eyes closed (EC) condition, as well as increasing rightward parietal asymmetry with advancing age during the CPT. Study-2 replicated these findings and further delineated influences of low versus high-alpha, recording site, and effects of parental persistent versus non-persistent ADHD status.

CONCLUSION

Increased ADHD familial loading was associated with increased rightward frontal asymmetry. In contrast, increased rightward parietal asymmetry was associated with reduced ADHD family loading. Frontal results are consistent with an ADHD endophenotype. Parietal results suggest an ADHD adaptive trait prevalent with less ADHD family loading. Age effects indicate a unique developmental course among ADHD children whose parents have non-persistent ADHD.