Low-frequency Alpha Research Articles

Power and functional connectivity of alpha oscillations in mild cognitive impairment: A systematic review and meta‐analysis

AbstractBackgroundAlzheimer’s disease (AD) is sometimes preceded by a less severe decline in cognitive abilities called mild cognitive impairment (MCI). Having affordable and non‐invasive biomarkers of MCI would ease diagnosis, improve prognosis, and open up possibilities to delay the transition to AD. One potential biomarker is alpha oscillations measured with electroencephalography (EEG) that have been found to differ between cognitively intact older adults (OA) and people with AD. To find whether these changes can already be detected in MCI, we reviewed studies that compared alpha power and functional connectivity in people with MCI and OA, in people with MCI and people with AD, and in people with MCI who progress to AD and those who do not.MethodWe searched for records published until 24 January 2020 using search terms “mild cognitive impairment” AND (eeg OR oscillations). 65 studies were included in the review. We conducted four random effects meta‐analyses. We compared resting state power in people with MCI and OA in the full alpha band (∼ 8‐12 Hz; k=5; n=198 MCI, 258 OA), in lower alpha frequencies (∼ 8‐10 Hz; k=5; n=196 MCI, 203 OA), and in upper alpha frequencies (∼ 10‐12 Hz; k=5; n=131 MCI, OA 139). We also compared resting state power in the full alpha band in people with AD and people with MCI (k=6; n=481 AD, 499 MCI).ResultIn the full alpha band, resting state power was lower in people with AD than in people with MCI (ES=‐0.30, 95% CI=‐0.51, ‐0.10, p=0.003), and in people with MCI than in OA (ES=‐1.49, 95% CI=‐2.69, ‐0.29, p=0.02). Reviewing the literature showed that resting state alpha power is lower in people with MCI who eventually progress to AD than in those who do not. During task performance, alpha activity changed less in people with MCI than in OA. Studies that compared functional connectivity between the three groups reported inconsistent results.ConclusionLower resting state alpha power, that has been found in people with AD can, though to a lesser degree, also be detected in people with MCI, especially those who are on a trajectory towards AD.

Testing the effect of tACS over parietal cortex in modulating endogenous alpha rhythm and temporal integration windows in visual perception.

Neural oscillations in the alpha band (8–12 Hz) have been proposed as a key mechanism for the temporal resolution of visual perception. Higher alpha frequencies have been related to improved segregation of visual events over time, whereas lower alpha frequencies have been related to improved temporal integration. Similarly, also the phase of ongoing alpha has been shown to correlate with temporal integration/segregation. To test a causal relationship between alpha oscillations and perception, we here employed multi‐channel transcranial alternating current stimulation (mc‐tACS) over the right parietal cortex, whereas participants performed a visual temporal integration/segregation task that used identical stimuli with different instructions. Before and after mc‐tACS we recorded the resting‐state electroencephalogram (EEG) to extract the individual alpha frequency (IAF) and delivered electrical stimulation at slightly slower and faster frequencies (IAF±2 Hz). We hypothesized that this would not only drive endogenous alpha rhythms, but also affect temporal integration and segregation in an opposite way. However, the mc‐tACS protocol used here did not consistently increase or decrease the IAF after the stimulation and did not affect temporal integration/segregation accuracy as expected. Although we found some preliminary evidence for an influence of tACS phase on temporal integration accuracy, the ongoing phase of mc‐tACS oscillations did not reliably modulate temporal integration/segregation accuracy in a sinusoidal way as would have been predicted by an effective entrainment of brain oscillations. These findings may guide future studies using different stimulation montages for investigating the role of cortical alpha oscillations for human vision.

Associations Among Emotional State, Sleep Quality, and Resting-State EEG Spectra: A Longitudinal Study in Graduate Students

University students are routinely influenced by a variety of natural stressors and experience irregular sleep-wake cycles caused by the necessity to trade sleep for studying while dealing with academic assignments. Often these factors result in long-term issues with daytime sleepiness, emotional instability, and mental exhaustion, which may lead to difficulties in the educational process. This study introduces the Daily Sampling System (DSS) implemented as a smartphone application, which combines a set of self-assessment scales for evaluating variations in the emotional state and sleep quality throughout a full academic term. In addition to submitting the daily sampling scores, the participants regularly filled in the Depression, Anxiety, and Stress Scales (DASS) reports and took part in resting-state EEG data recording immediately after report completion. In total, this study collected 1835 daily samples and 94 combined DASS with EEG datasets from 18 university students (aged 23-27 years), with 79.3± 15.3% response ratio in submitting the daily reports during an academic semester. The results of pairwise testing and multiple regression analysis demonstrate that the daily level of self-perceived fatigue correlates positively with stress, daytime sleepiness, and negatively with alertness on awakening, self-evaluated sleep quality, and sleep duration. The spectral analysis of the EEG data reveals a significant increase in the resting-state spectral power density across the theta and low-alpha frequency bands associated with increased levels of anxiety and stress. Additionally, the state of depression was accompanied by an intensification of high-frequency EEG activity over the temporal regions. No significant differences in prefrontal alpha power asymmetry were observed under the described experimental conditions while comparing the states of calmness and emotional arousal of the participants for the three conditions of depression, anxiety, and stress.

Low frequency alpha (8–10 Hz) activity correlated with inhibitory behavior

Low frequency alpha (8–10 Hz) activity correlated with inhibitory behavior

Multivariate Analyses Reveal Biological Components Related to Neuronal Signaling and Immunity Mediating Electroencephalograms Abnormalities in Alcohol-Dependent Individuals from the Collaborative Study on the Genetics of Alcoholism Cohort.

The underlying molecular mechanisms associated with alcohol use disorder (AUD) risk have only been partially revealed using traditional approaches such as univariate genomewide association and linkage-based analyses. We therefore aimed to identify gene clusters related to Electroencephalograms (EEG) neurobiological phenotypes distinctive to individuals with AUD using a multivariate approach. The current project adopted a bimultivariate data-driven approach, parallel independent component analysis (para-ICA), to derive and explore significant genotype-phenotype associations in a case-control subset of the Collaborative Study on the Genetics of Alcoholism (COGA) dataset. Para-ICA subjects comprised N=799 self-reported European Americans (367 controls and 432 AUD cases), recruited from COGA, who had undergone resting EEG and genotyping. Both EEG and genomewide single nucleotide polymorphism (SNP) data were preprocessed prior to being subjected to para-ICA in order to derive genotype-phenotype relationships. From the data, 4 EEG frequency and 4 SNP components were estimated, with 2 significantly correlated EEG-genetic relationship pairs. The first such pair primarily represented theta activity, negatively correlated with a genetic cluster enriched for (but not limited to) ontologies/disease processes representing cell signaling, neurogenesis, transmembrane drug transportation, alcoholism, and lipid/cholesterol metabolism. The second component pair represented mainly alpha activity, positively correlated with a genetic cluster with ontologies similarly enriched as the first component. Disease-related enrichments for this component revealed heart and autoimmune disorders as top hits. Loading coefficients for both the alpha and theta components were significantly reduced in cases compared to controls. Our data suggest plausible multifactorial genetic components, primarily enriched for neuronal/synaptic signaling/transmission, immunity, and neurogenesis, mediating low-frequency alpha and theta abnormalities in alcohol addiction.

Two-Year Longitudinal Monitoring of Amnestic Mild Cognitive Impairment Patients with Prodromal Alzheimer's Disease Using Topographical Biomarkers Derived from Functional Magnetic Resonance Imaging and Electroencephalographic Activity.

Auditory "oddball" event-related potentials (aoERPs), resting state functional magnetic resonance imaging (rsfMRI) connectivity, and electroencephalographic (rsEEG) rhythms were tested as longitudinal functional biomarkers of prodromal Alzheimer's disease (AD). Data were collected at baseline and four follow-ups at 6, 12, 18, and 24 months in amnesic mild cognitive impairment (aMCI) patients classified in two groups: "positive" (i.e., "prodromal AD"; n = 81) or "negative" (n = 63) based on a diagnostic marker of AD derived from cerebrospinal samples (Aβ42/P-tau ratio). A linear mixed model design was used to test functional biomarkers for Group, Time, and Group×Time effects adjusted by nuisance covariates (only data until conversion to dementia was used). Functional biomarkers that showed significant Group effects ("positive" versus "negative", p < 0.05) regardless of Time were 1) reduced rsfMRI connectivity in both the default mode network (DMN) and the posterior cingulate cortex (PCC), both also giving significant Time effects (connectivity decay regardless of Group); 2) increased rsEEG source activity at delta (<4 Hz) and theta (4-8 Hz) rhythms and decreased source activity at low-frequency alpha (8-10.5 Hz) rhythms; and 3) reduced parietal and posterior cingulate source activities of aoERPs. Time×Group effects showed differential functional biomarker progression between groups: 1) increased rsfMRI connectivity in the left parietal cortex of the DMN nodes, consistent with compensatory effects and 2) increased limbic source activity at theta rhythms. These findings represent the first longitudinal characterization of functional biomarkers of prodromal AD relative to "negative" aMCI patients based on 5 serial recording sessions over 2 years.

The moderating effect of heart rate variability on the relationship between alpha asymmetry and depressive symptoms

Electroencephalographic (EEG) research has suggested relatively reduced brain activity in the left frontal and right posterior region trait-markers of depression. However, inconsistent results have been reported. Based on previous studies reporting the heart rate variability (HRV) as an index of emotional regulation, this study makes a novel investigation of the role of heart rate variability (HRV) as a moderator in the relationship between frontal and parietal alpha asymmetry and depression. Resting EEG (eyes open) was recorded in 38 patients with MDD and 34 healthy subjects. Frontal and parietal alpha asymmetries were calculated at total (8–12 Hz), high (10–12 Hz), and low (8–10 Hz) alpha frequency bands. Three vagally mediated HRV (vmHRV) components (LF, HF, and the LF/HF ratio) were calculated in the frequency domain. Relatively greater right parietal alpha activity significantly predicted the severity of depression only when HF was low (or the LF/HF ratio was high) at low alpha frequency band. The interaction effect of parietal alpha asymmetry and vmHRV remained significant after including anxiety score as a covariate. No moderation effect of vmHRV was found for frontal sites and other frequency bands, as well as healthy subjects. These findings suggest that vmHRV moderates the association between parietal alpha asymmetry at low frequency band and depression for MDD patients. We suggest that the interaction between parietal alpha asymmetry and vmHRV may be a biomarker of MDD.

Оценка реактивности и локализации частотных компонентов альфа-ритма ЭЭГ при выполнении и наблюдении движений

The EEG amplitude reactivity of the individually defined upper and low alpha frequency ranges was measured in 67 adults when they performed circular hand movements with a computer mouse and observed similar movements produced by another person. The upper alpha rhythm was topographically more specific and had higher amplitude reactivity under condition of self-paced movements in comparison with the low alpha rhythm. The sources for the alpha subranges were identified by means of the low-resolution brain electromagnetic tomography method (sLORETA). Comparable activation patterns for the brain structures associated with the so-called brain “mirror” system (precuneus, cingulate gyrus for the alpha1-rhythm; inferior parietal lobule, supramarginal and angular gyri, upper and middle temporal gyri, insular cortex for alpha2-rhythm) were found for the conditions of performance and observation of movements. During both conditions, there was found a significantly higher number of activated voxels in structures belonging to the right hemisphere relative to the left one. Under the condition of performing self-paced movements, this phenomenon can be the result of heightened demands to the process of visual-motor coordination (keeping the computer mouse cursor within a given screen area). Increased right hemisphere activation having a place when observing movements performed by another person can be interpreted as reflecting the social context of the task given the aspect of attributing observed movements to another person. Such results can be taken in favor of the hypothesis of the mirror neuron system and its involvement into the perception of actions performed by others. The obtained data also testify to the possibility of using a standard computer mouse as an object for instrumental movements when studying neurophysiological mechanisms underlying both movement performance and observation.

ЭЭГ активность мозга, предшествующая спонтанному восстановлению психомоторной деятельности после эпизодов микросна

In experiments with daytime sleep, according to data obtained from 23 subjects, changes in the spectral characteristics of the EEG in the period preceding the moment of awakening, which was recorded to restore the psychomotor test, were studied. During one short experiment, it can be used to investigate several consecutive episodes: the disappearance of conscious cognitive activity when falling asleep and its resumption upon spontaneous awakening. The study of the characteristics of the EEG before awakening is important for assessing the transients of the sleep-wake cycle, determining the degree of recovery of psychomotor activity upon awakening and the level of the accompanying consciousness. It is shown that the alpha activation observed upon awakening is often preceded by the appearance of K-complexes, of varying degrees of severity, on which low-frequency alpha oscillations are superimposed, which can be regarded as slow sigma spindles. This pattern most likely reflects the action of a universal thalamocortical activating mechanism, the same for both night and daytime sleep, regardless of whether it follows a short-term activation followed by sleep or further begins a cognitive activity.

Event-related neural oscillation changes following reasoning training in individuals with Mild Cognitive Impairment

Emerging evidence suggests cognitive training programs targeting higher-order reasoning may strengthen not only cognitive, but also neural functions in individuals with Mild Cognitive Impairment (MCI). However, research on direct measures of training-induced neural changes, derivable from electroencephalography (EEG), is limited. The current pilot study examined effects of Gist Reasoning training (n = 16) compared to New Learning training (n = 16) in older adults with amnestic MCI on measures of event-related neural oscillations (theta and alpha band power) corresponding to Go/NoGo tasks during basic and superordinate semantic categorization. EEG data were recorded while participants performed the Go/NoGo task pre- and post-training, and power in theta and alpha frequency bands was examined. Both groups were comparable at pre-training on all measures and both groups showed greater event-related theta synchronization post-training. Furthermore, the Gist Reasoning group had enhanced event-related desynchronization in low-frequency alpha band (8–10 Hz) on response inhibition (NoGo) trials and high-frequency alpha band (11–13 Hz) on response execution (Go) trials during superordinate categorization, relative to the New Learning group. These findings suggest that Gist Reasoning training in MCI impacted neural processing linked to strategic processing of Go and NoGo trials during the more complex superordinate categorization task. Targeting higher-order top-down cognitive processing seems to better harness residual neuroplastic potential in MCI.ClinicalTrials.gov ID: NCT02588209.

Dorsal and ventral cortices are coupled by cross-frequency interactions during working memory

Oscillatory activity in the alpha and gamma bands is considered key in shaping functional brain architecture. Power increases in the high-frequency gamma band are typically reported in parallel to decreases in the low-frequency alpha band. However, their functional significance and in particular their interactions are not well understood. The present study shows that, in the context of an N-back working memory task, alpha power decreases in the dorsal visual stream are related to gamma power increases in early visual areas. Granger causality analysis revealed directed interregional interactions from dorsal to ventral stream areas, in accordance with task demands. Present results reveal a robust, behaviorally relevant, and architectonically decisive power-to-power relationship between alpha and gamma activity. This relationship suggests that anatomically distant power fluctuations in oscillatory activity can link cerebral network dynamics on trial-by-trial basis during cognitive operations such as working memory.

Differential recruitment of brain networks in single-digit addition and multiplication: Evidence from EEG oscillations in theta and lower alpha bands

Previous neuroimaging research investigating dissociation between single-digit addition and multiplication has suggested that the former placed more reliance on the visuo-spatial processing whereas the latter on the verbal processing. However, there has been little exploration into the disassociation in spatio-temporal dynamics of the oscillatory brain activity in specific frequency bands during the two arithmetic operations. To address this issue, the electroencephalogram (EEG) data were recorded from 19 participants engaged in a delayed verification arithmetic task. By analyzing oscillatory EEG activity in theta (5–7 Hz) and lower alpha frequency (9–10 Hz) bands, we found different patterns of oscillatory brain activity between single-digit addition and multiplication during the early processing stage (0–400 ms post-operand onset). Experiment results in this study showed a larger phasic increase of theta-band power for addition than for multiplication in the midline and the right frontal and central regions during the operator and operands presentation intervals, which was extended to the right parietal and the right occipito-temporal regions during the interval immediately after the operands presentation. In contrast, during multiplication higher phase-locking in lower alpha band was evident in the centro-parietal regions during the operator presentation, which was extended to the left fronto-central and anterior regions during the operands presentation. Besides, we found stronger theta phase synchrony between the parietal areas and the right occipital areas for single-digit addition than for multiplication during operands encoding. These findings of oscillatory brain activity extend the previous observations on functional dissociation between the two arithmetic operations.

Disturbed functional connectivity within the left prefrontal cortex and sensorimotor areas predicts impaired cognitive speed in patients with first-episode schizophrenia

This study aimed at identifying abnormal cortico-cortical functional connectivity patterns that could predict cognitive slowing in patients with schizophrenia. A group of thirty-two patients with the first-episode schizophrenia and comparable healthy controls underwent resting-state qEEG and cognitive assessment. Phase Lag Index (PLI) was applied as a connectivity index and the synchronizations were analyzed in six frequencies. Pairs of electrodes were grouped to separately cover frontal, temporal, central, parietal and occipital regions. PLI was calculated for intra-regional connectivity and between-regions connectivity. Computer version processing speed tests were applied to control for possible fluctuations in cognitive efficiency during the performance of the tasks. In the group of patients, in comparison to healthy controls, significantly higher PLI values were recorded in theta frequency, especially in the posterior areas and decreased PLI in low-alpha frequency within the frontal regions. Mean PLI in gamma frequency was also lower in the patients group. Regression analysis showed that lower intra-regional PLI for left frontal cortex and higher PLI within somatosensory cortex in theta band, together with the duration of untreated psychosis, proved to be significant predictors of impaired processing speed in first-episode patients. Our investigation confirmed that disrupted cortico-cortical synchronization contributes to cognitive slowing in schizophrenia.

Aging, rule-violation checking strategies, and strategy combination: An EEG study in arithmetic

In arithmetic, rule-violation checking strategies are used while participants solve problems that violate arithmetic rules, like the five rule (i.e., products of problems including five as an operand end with either five or zero; e.g., 5×14=70) or the parity rule (i.e., when at least one of the two operands is even, the product is also even; otherwise the product is odd; e.g., 4×13=52). When problems violate both rules, participants use strategy combination and have better performance on both-rule than on one-rule violation problems (i.e., five or parity rule). Aging studies found that older adults efficiently use one-rule violation checking strategies but have difficulties to combine two strategies. To better understand these aging effects, we used EEG and found important age-related changes while participants used rule-violation checking strategies. We compared participants' performance while they verified arithmetic problems that differ in number and type of violated rule. More specifically, both-rule violation problems elicited larger negativity than one-rule violation problems between 600 and 800ms. Five-rule violation problems differed from parity-rule violation problems between 1100 and 1200ms. Moreover, rule-violation checking strategies and strategy combination involved delta, theta, and lower alpha frequencies. Age-related changes in ERPs and frequency were associated with less efficient strategy combination. Moreover, efficient use of one-rule violation checking strategies in older adults was associated with changes in ERPs and frequency. These findings contribute to further our understanding of age-related changes and invariance in arithmetic strategies, and in combination of arithmetic strategies.

Slower resting alpha frequency is associated with superior localisation of moving targets

We examined the neurophysiological underpinnings of individual differences in the ability to maintain up-to-date representations of the positions of moving objects. In two experiments similar to the multiple object tracking (MOT) task, we asked observers to monitor continuously one or several targets as they moved unpredictably for a semi-random period. After all objects disappeared, observers were immediately prompted to report the perceived final position of one queried target. Precision of these position reports declined with attentional load, and reports tended to best resemble positions occupied by the queried target between 0 and 30ms in the past. Measurement of event-related potentials showed a contralateral delay activity over occipital scalp, maximal in the right hemisphere. The peak power-spectral frequency of observers’ eyes-closed resting occipital alpha oscillations reliably predicted performance, such that lower-frequency alpha was associated with superior spatial localisation. Slower resting alpha might be associated with a cognitive style that depends less on memory-related processing and instead emphasises attention to changing stimuli.

Separability of motor imagery of the self from interpretation of motor intentions of others at the single trial level: an EEG study

BackgroundWe aimed to investigate the separability of the neural correlates of 2 types of motor imagery, self and third person (actions owned by the participant himself vs. another individual). If possible this would allow for the development of BCI interfaces to train disorders of action and intention understanding beyond simple imitation, such as autism.MethodsWe used EEG recordings from 20 healthy participants, as well as electrocorticography (ECoG) in one, based on a virtual reality setup. To test feasibility of discrimination between each type of imagery at the single trial level, time-frequency and source analysis were performed and further assessed by data-driven statistical classification using Support Vector Machines.ResultsThe main observed differences between self-other imagery conditions in topographic maps were found in Frontal and Parieto-Occipital regions, in agreement with the presence of 2 independent non μ related contributions in the low alpha frequency range. ECOG corroborated such separability. Source analysis also showed differences near the temporo-parietal junction and single-trial average classification accuracy between both types of motor imagery was 67 ± 1%, and raised above 70% when 3 trials were used. The single-trial classification accuracy was significantly above chance level for all the participants of this study (p < 0.02).ConclusionsThe observed pattern of results show that Self and Third Person MI use distinct electrophysiological mechanisms detectable at the scalp (and ECOG) at the single trial level, with separable levels of involvement of the mirror neuron system in different regions.These observations provide a promising step to develop new BCI training/rehabilitation paradigms for patients with neurodevelopmental disorders of action understanding beyond simple imitation, such as autism, who would benefit from training and anticipation of the perceived intention of others as opposed to own intentions in social contexts.

Theta and Alpha Alterations in Amnestic Mild Cognitive Impairment in Semantic Go/NoGo Tasks.

Growing evidence suggests that cognitive control processes are impaired in amnestic mild cognitive impairment (aMCI); however the nature of these alterations needs further examination. The current study examined differences in electroencephalographic theta and alpha power related to cognitive control processes involving response execution and response inhibition in 22 individuals with aMCI and 22 age-, sex-, and education-matched cognitively normal controls. Two Go/NoGo tasks involving semantic categorization were used. In the basic categorization task, Go/NoGo responses were made based on exemplars of a single car (Go) and a single dog (NoGo). In the superordinate categorization task, responses were made based on multiple exemplars of objects (Go) and animals (NoGo). Behavioral data showed that the aMCI group had more false alarms during the NoGo trials compared to controls. The EEG data revealed between group differences related to response type in theta (4–7 Hz) and low-frequency alpha (8–10 Hz) power. In particular, the aMCI group differed from controls in theta power during the NoGo trials at frontal and parietal electrodes, and in low-frequency alpha power during Go trials at parietal electrodes. These results suggest that alterations in theta power converge with behavioral deterioration in response inhibition, whereas alterations in low-frequency alpha power appear to precede behavioral changes in response execution. Both behavioral and electrophysiological correlates combined provide a more comprehensive characterization of cognitive control deficits in aMCI.

Reactivity of alpha rhythms to eyes opening (the Berger effect) during menstrual cycle phases

The impact of the menstrual cycle on the alpha EEG reactivity to eyes opening (Berger effect) was studied in relation to hormonal and EMG indices. Repeated measurements of salivary progesterone and cortisol, forehead EMG, and EEG alpha-activity indices in 76 healthy women aged 18–27 were obtained in resting eyes closed (1min) and eyes open (30s) conditions. Ten recording sessions occurred, at 2–3day intervals, during 1–2 menstrual cycles. For example, if a participant had a menstrual cycle length of 30–32days, she could finish the investigation during 1cycle, but if she had a 24day cycle, she would finish the investigation over 1 1/2cycles. 6 women extended their investigation into a second cycle. The personal points of each woman's phase data were averaged before being used in group analyses.EEG and EMG responses to eyes open showed that magnitude of α-1 amplitude suppression corresponds to increasing EMG and salivary cortisol concentration only at the Follicular phase, when low alpha frequency waves are dominant in combination with low progesterone level. The magnitude of alpha suppression in response to eyes open in the upper α-2 frequency range does not vary with the menstrual cycle. The Luteal phase corresponds to the highest level of salivary progesterone and is associated with enhancement of the α-bandwidth. The most prominent reaction of salivary cortisol level, forehead EMG, and alpha EEG power to opening of the eyes occurs in the Follicular phase. This research reveals the dependence of the EEG Berger effect on the hormonal state and EEG alpha frequency.

Cortical sources of resting state EEG rhythms are related to brain hypometabolism in subjects with Alzheimer's disease: an EEG-PET study

Cortical sources of resting state electroencephalographic (EEG) delta (2–4 Hz) and low-frequency alpha (8–10.5 Hz) rhythms show abnormal activity (i.e., current density) in patients with dementia due to Alzheimer's disease (AD). Here, we hypothesized that abnormality of this activity is related to relevant disease processes as revealed by cortical hypometabolism typically observed in AD patients by fluorodeoxyglucose positron emission tomography. Resting state eyes-closed EEG data were recorded in 19 AD patients with dementia and 40 healthy elderly (Nold) subjects. EEG frequency bands of interest were delta and low-frequency alpha. EEG sources were estimated in these bands by low-resolution brain electromagnetic tomography (LORETA). Fluorodeoxyglucose positron emission tomography images were recorded only in the AD patients, and cortical hypometabolism was indexed by the so-called Alzheimer's discrimination analysis tool (PALZ) in the frontal association, ventromedial frontal, temporoparietal association, posterior cingulate, and precuneus areas. Results showed that compared with the Nold group, the AD group pointed to higher activity of delta sources and lower activity of low-frequency alpha sources in a cortical region of interest formed by all cortical areas of the PALZ score. In the AD patients, there was a positive correlation between the PALZ score and the activity of delta sources in the cortical region of interest (p < 0.05). These results suggest a relationship between resting state cortical hypometabolism and synchronization of cortical neurons at delta rhythms in AD patients with dementia.

Phase-Amplitude Coupling Is Elevated in Deep Sleep and in the Onset Zone of Focal Epileptic Seizures.

The interactions between different EEG frequency bands have been widely investigated in normal and pathologic brain activity. Phase-amplitude coupling (PAC) is one of the important forms of this interaction where the amplitude of higher frequency oscillations is modulated by the phase of lower frequency activity. Here, we studied the dynamic variations of PAC of high (gamma and ripple) and low (delta, theta, alpha, and beta) frequency bands in patients with focal epilepsy in different sleep stages during the interictal period, in an attempt to see if coupling is different in more or less epileptogenic regions. Sharp activities were excluded to avoid their effect on the PAC. The results revealed that the coupling intensity was generally the highest in stage N3 of sleep and the lowest in rapid eye movement sleep. We also compared the coupling strength in different regions [seizure onset zone (SOZ), exclusively irritative zone, and normal zone]. PAC between high and low frequency rhythms was found to be significantly stronger in the SOZ compared to normal regions. Also, the coupling was generally more elevated in spiking channels outside the SOZ than in normal regions. We also examined how the power in the delta band correlates to the PAC, and found a mild but statistically significant correlation between slower background activity in epileptic channels and the elevated coupling in these channels. The results suggest that an elevated PAC may reflect some fundamental abnormality, even after exclusion of sharp activities and even in the interictal period. PAC may therefore contribute to understanding the underlying dynamics of epileptogenic brain regions.