Theta Ratio Research Articles

Role of visual brainwave entrainment on the resting state brainwaves of children with and without attention-deficit/hyperactivity disorder

The relationship between brainwave oscillations and Attention-Deficit/Hyperactivity Disorder (ADHD)-related cognitive challenges is a trending proposition in the field of Cognitive Neuroscience. Studies suggest the role of brainwave oscillations in the symptom expressions of ADHD-diagnosed children. Intervention studies have further suggested the scope of brain stimulation techniques in improving cognition. The current manuscript explored the effect of changes in the brainwaves post-sensory entrainment on cognitive performance of children. We calculated each participant’s brainwave difference and ratios of theta, alpha, and beta power after the entrainment sessions. Further, we explored possible correlations between these values and the psychometric scores. The beta resting state showed the strongest association with selective attention performance of all participants. Theta-beta ratio (TBR) showed an inverse correlation with selective attention and working memory performances. The theta frequency was associated with decreased working performance in children without ADHD. Our findings also suggest a predominant role of TBR than the theta-alpha ratio in determining the cognitive performance of children with ADHD. The individual differences in the entrainment reception were attributed to the participant’s age, IQ, and their innate baseline frequencies. The implications of our findings can initiate substantiating brainwave-based entrainment sessions as a therapeutic modality to improve cognition among children.

Automating Stimulation Frequency Selection for SSVEP-Based Brain-Computer Interfaces

Brain–computer interfaces (BCIs) based on steady-state visually evoked potentials (SSVEPs) are inexpensive and do not require user training. However, the highly personalized reaction to visual stimulation is an obstacle to the wider application of this technique, as it can be ineffective, tiring, or even harmful at certain frequencies. In our experimental study, we proposed a new approach to the selection of optimal frequencies of photostimulation. By using a custom photostimulation device, we covered a frequency range from 5 to 25 Hz with 1 Hz increments, recording the subjects’ brainwave activity (EEG) and analyzing the signal-to-noise ratio (SNR) changes at the corresponding frequencies. The proposed set of SNR-based coefficients and the discomfort index, determined by the ratio of theta and beta rhythms in the EEG signal, enables the automation of obtaining the recommended stimulation frequencies for use in SSVEP-based BCIs.

Asymmetries in the theta/beta ratio distinguish cognitively normal elderly from those with mild cognitive impairment

AbstractBackgroundThe search for psychophysiological markers that distinguish normal from abnormal aging has produced many candidate EEG dynamics, but relatively little research has been done (or at least reported) on the theta/beta ratio or brain wave asymmetries.MethodsWe previously reported frontal asymmetries (frontal alpha and frontal beta asymmetry) originally investigated in the context of anxiety and approach‐avoidance motivation that distinguish MCI from healthy, cognitively normal persons (HC). Another potentially more cognitively‐involved marker, the ratio of theta to beta frequencies (TBR), originally investigated as a marker of attention deficits, might also usefully distinguish cognitive HC from MCI. We took advantage of a previously collected data set to conduct an exploratory analysis of the pattern of TBR in HC and MCI participants. Resting state EEG (rsEEG) was measured before and after a simple motion direction discrimination task. We investigated the standard frontal TBR as measured at frontal electrode FZ. We estimated power spectral density in the resting state (eyes closed) for both pre‐ and post‐task, extracting estimates of TBR at electrode Fz.ResultsWe found that MCI had significantly higher TBR than cognitively normal elderly, F(1,95)=4.98, p=0.028, with no effect of timepoint and no interaction. We then explored the possibility that TBR itself has meaningful asymmetries, calculating the TBR asymmetry at the following electrode pairs: F3‐F4, C3‐C4, CP3‐CP4, P3‐P4, PO3‐PO4. This analysis revealed an interesting pattern, with group (HC vs. MCI) interacting with location, F(4,380)=5.25, p<0.001. Relative to HC, MCI participants had higher TBR on the right (positive TBR asymmetry) in frontal electrodes (F3‐F4), but higher TBR on the left (negative TBR asymmetry) over parietal‐occipital sites (P3‐P4 and PO3‐PO4). The parietal asymmetry may reflect the early spread of lesions from inferior temporal regions to areas subserving language and visuospatial processing, but the frontal asymmetry is less obviously tied to known progression of brain lesions, and may reflect heterogeneity in the underlying pathogenesis of this sample of people with MCI.ConclusionTBR asymmetries obtained in rsEEG can contribute significantly to successful discrimination of older persons with MCI from those with normal cognitive functioning.

Brain activity during dual-task standing in older adults

BackgroundIn older adults, the extent to which performing a cognitive task when standing diminishes postural control is predictive of future falls and cognitive decline. The neurophysiology of such “dual-tasking” and its effect on postural control (i.e., dual-task cost) in older adults are poorly understood. The purpose of this study was to use electroencephalography (EEG) to examine the effects of dual-tasking when standing on brain activity in older adults. We hypothesized that compared to single-task “quiet” standing, dual-task standing would decrease alpha power, which has been linked to decreased motor inhibition, as well as increase the ratio of theta to beta power, which has been linked to increased attentional control.MethodsThirty older adults without overt disease completed four separate visits. Postural sway together with EEG (32-channels) were recorded during trials of standing with and without a concurrent verbalized serial subtraction dual-task. Postural control was measured by average sway area, velocity, and path length. EEG metrics included absolute alpha-, theta-, and beta-band powers as well as theta/beta power ratio, within six demarcated regions-of-interest: the left and right anterior, central, and posterior regions of the brain.ResultsMost EEG metrics demonstrated moderate-to-high between-day test–retest reliability (intra-class correlation coefficients > 0.70). Compared with quiet standing, dual-tasking decreased alpha-band power particularly in the central regions bilaterally (p = 0.002) and increased theta/beta power ratio in the anterior regions bilaterally (p < 0.001). A greater increase in theta/beta ratio from quiet standing to dual-tasking in numerous demarcated brain regions correlated with greater dual-task cost (i.e., absolute increase, indicative of worse performance) to postural sway metrics (r = 0.45–0.56, p < 0.01). Lastly, participants who exhibited greater alpha power during dual-tasking in the anterior-right (r = 0.52, p < 0.01) and central-right (r = 0.48, p < 0.01) regions had greater postural sway velocity during dual-tasking.ConclusionIn healthy older adults, alpha power and theta/beta power ratio change with dual-task standing. The change in theta/beta power ratio in particular may be related to the ability to regulate standing postural control when simultaneously performing unrelated, attention-demanding cognitive tasks. Modulation of brain oscillatory activity might therefore be a novel target to minimize dual-task cost in older adults.

Use of EEG signals, cortisol secretion, and task performance to evaluate the effects of different lighting environments on concentration level in a sustained attention task

Previous research has indicated that lighting can affect people's concentration levels and working performance. However, it is unknown whether the same effect is also achieved when the lighting source is focused on the target to be identified. Thus, the objective of this study was to apply different lighting environments to evaluate the concentration level during a sustained attention task. To this end, 60 college students were recruited as participants (33 males and 27 females), and two lighting environments (focused and general lighting environments) with two sustained attention task times (15 and 30 min, respectively) were utilized. The task performance, electroencephalogram (EEG) signal, and cortisol secretion were employed to evaluate the concentration levels of the participants during the sustained attention task. The results show that the concentration level is affected by the lighting environment, and the participants performed better on task performance and cortisol secretion were activated in the focused lighting environment with the 15 min task time. However, there were no significant differences in task performance or cortisol secretion between the focused and general lighting environments with the 30 min task time. According to the EEG results, with either the 15 or 30 min task time, the ratio of theta to beta waves in the focused lighting environment was relatively stable, which indicates that the participants could concentrate more steadily when they worked in the focused lighting environment. In conclusion, the findings of this study could be applied to cognitive-related workplace lighting design and lighting-related research in the future. Relevance to industryThis study's results on task performance, EEG, and cortisol secretion show that the participants in a focused lighting environment can concentrate more easily. These findings could serve as a reference for the lighting environment design of cognitive-related workplaces.

Periodic and aperiodic contributions to theta-beta ratios across adulthood.

The ratio of fronto-central theta (4-7 Hz) to beta oscillations (13-30 Hz), known as the theta-beta ratio, is negatively correlated with attentional control, reinforcement learning, executive function, and age. Although theta-beta ratios have been found to decrease with age in adolescents and young adults, theta has been found to increase with age in older adults. Moreover, age-related decrease in individual alpha peak frequency and flattening of the 1/f aperiodic component may artifactually inflate the association between theta-beta ratio and age. These factors lead to an incomplete understanding of how theta-beta ratio varies across the lifespan and the extent to which variation is due to a conflation of aperiodic and periodic activity. We conducted a partially preregistered analysis examining the cross-sectional associations between age and resting canonical fronto-central theta-beta ratio, individual alpha peak frequency, and aperiodic component (n=268; age 36-84, M=55.8, SD=11.0). Age was negatively associated with theta-beta ratios, individual peak alpha frequencies, and the aperiodic exponent. The correlation between theta-beta ratios and age remained after controlling for individual peak alpha frequencies, but was nonsignificant when controlling for the aperiodic exponent. Aperiodic exponent fully mediated the relationship between theta-beta ratio and age, although beta remained significantly associated with age after controlling for theta, individual peak alpha, and aperiodic exponent. Results replicate previous observations and show age-related decreases in theta-beta ratios are not due to age-related decrease in individual peak alpha frequencies but primarily explained by flattening of the aperiodic component with age.

Features of quantitative EEG in children with hyperkinetic disorder

At the basis of numerous mental disorders lies a synaptic transmission impairment that causes metabolic and ionic changes and affects the current functional state of the brain, the reflection of which we find in electroencephalographic examination.Objective of the study: identification of electroencephalographic features in children under conditions of biochemical heterogeneity of hyperkinetic disorder (HD).Material and methods. 404 children aged 6-8 years with HD were divided into three subgroups according to the state of monoamine activity: the 1-st subgroup with a combination of hypofunction of the dopaminergic and hyperfunction of the noradrenergic systems — 120 children, the 2-nd subgroup with a combination of hyperfunction of the noradrenergic system with relative balance dopamine — 136 children, and the 3-d with a combination of hyperfunction of the dopamine and hypofunction of the noradrenergic systems — 148 children. In the selected groups, the serotonin system plays an inhibitory and modulating role in relation to the catecholamine metabolism systems. The control group consisted of 90 children (54 boys and 36 girls). An electroencephalographic study was carried out, where the following ranges and subranges were differentiated: theta rhythm (4–8 Hz) and beta1 rhythm (14–20 Hz). The power ratios of theta — and — beta1 rhythms (theta/beta1) were calculated.Results. It was the serotonin system that turned out to be the determining factor in the neurophysiological characteristics of HD. Moreover, the division into subgroups, based on the biochemical characteristics of children with HD, did not allow us to obtain significant differences. The only feature that globally distinguishes the subgroups from each other was the increase in the theta/beta1 activity index, corresponding to an increase in the tension and activity of the serotonin system from subgroup 1 to 3. The data obtained allow us to assert that the electroencephalographic index theta / beta1 can serve as a marker of inattention in children with hyperkinetic disorder and reflects the established state of imbalance of all monoamine systems, but better characterizes the behavior of the tryptophan system.Conclusion. The data on the relationship between the power of theta/beta1 rhythms in the EEG may indicate the nature of the activity of the serotonin system in prospective studies, providing a personalized approach to the selection of drug therapy in children with HD.

Electroencephalography in Evaluating Mental Workload of Gaming.

The feasibility of electroencephalography (EEG) analysis in evaluating mental workload of gaming was studied by carrying out a proof-of-concept type experiment on a set of EEG recordings, with a bespoke tool developed for the purpose. The EEG recordings (20 recordings in total) that were used in the experiment had been acquired by groups of students and staff of Tampere University during n-back gaming sessions, as part of course projects. The ratio of theta and alpha power, calculated over the EEG signal segments that were time-locked to game events, was selected as EEG metrics for mental load evaluation. Also, Phase Locking Value (PLV) was calculated for all pairs of EEG channels to assess the change in phase synchronization with the increasing difficulty level of the game. Wilcoxon rank-sum test was used to compare the metrics between the levels of the game (from 1-back to 4-back). The rank-sum test results revealed that the theta-alpha power ratio calculated from the frontal derivations Fp1 and Fp2 performed as a confident indicator for the evaluation and comparison of mental load. Also, phase locking between EEG derivations was found to become stronger with the increasing difficulty level of the game, especially in the case of channel pairs where the electrodes were located at opposite hemispheres.

Psychophysiological Characteristics of Aggression Associated with Depression before and after Successful Treatment with Sertraline: A Clinical Trial Study

Background: Depression associated with aggression can lead to violent behaviors. The present study was aimed to determine how sertraline, a standard medication for depression treatment, can efficiently decrease aggression and affect psychophysiological parameters in patients with depression. Methods: Patients with depression and aggression were included in a six-week trial with sertraline (50 100 mg/day). Depression diagnosis was confirmed by the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, Text Revision (DSM-IV-TR). Depression severity before and after treatment was assessed using Beck Depression Inventory (BDI). Aggression was evaluated by Spielberger’s State-Trait Anger Expression Inventory-2 (STAXIII). The BDI and STAXI-II were finally applied to evaluate the effectiveness of treatment. For each patient, peripheral and central psychophysiological parameters were recorded using peripheral biofeedback apparatus and electroencephalogram in the initial and final stages of treatment. These recordings were attempted to assess variations of the autonomic nervous system and electrocortical activity in response to treatment. Results: Depressive and aggressive symptoms decreased significantly over the six-week treatment period, as measured by BDI and STAXI-II. Significant changes in some of the peripheral and central psychophysiological variables were observed. Sensorimotor rhythm (SMR)/theta ratio (p=0.01) have decreased during a task, delta (p=0.02) and theta (p=0.008) wave activity and theta/alpha ratio (p=0.01) have increased during task, and theta/beta ratio has increased during both rest and task (p=0.02 for both). Among peripheral psychophysiological variables, skin conductance during task decreased significantly (p=0.03). Conclusion: Several numbers of psychophysiological parameters were influenced significantly after successful pharmacotherapy of aggressiveness in patients with depression.

Normobaric Oxygen May Ameliorate Cerebral Venous Outflow Disturbance-Related Neurological Symptoms.

Cerebral venous outflow disturbance (CVOD) has begun to garner the attention of researches owing to a series of clinical symptoms that impose a significant impact on people's quality of life. Herein, we aimed to investigate whether normobaric oxygen (NBO) can ameliorate CVOD-induced neurological symptoms. This was one part of the prospective trial registered in ClinicalTrials.gov (NCT03373292). A total of 37 CVOD patients were divided into the NBO group (5–8 L/min of oxygen inhalation, 1 h per time, 3 times daily, n = 19) and the control group (without oxygen inhalation, n = 18) randomly. The assessments were performed at admission, 1-week hospitalization, and 6-month follow-up. Quantitative electroencephalogram (qEEG) data were recorded prior to and post 1 h of NBO in some patients. R software was used for data analysis. No NBO-related adverse events were observed during the whole NBO intervention process. The 1-week Patient Global Impression of Change (PGIC) scale showed that the symptom improvement occurred in nine patients in the NBO group (47.4%) while none in the control group (p = 0.001). NBO could improve headache evaluated with visual analog scale (pre-NBO vs. post-NBO: 4.70 ± 2.16 vs. 2.90 ± 2.03, p = 0.024) and Headache Impact Test-6 (53.40 ± 12.15 vs. 50.30 ± 13.04, p = 0.041). As for 6-month PGIC follow-up, eight out of 14 cases (57.1%) in the NBO group reported improvement, while only one out of 12 patients in the control group replied mild improvement (p = 0.014). The qEEG revealed that NBO reduced the ratio of theta to alpha power (0.65 ± 0.38 vs. 0.56 ± 0.35, p = 0.030) over the fronto-central electrodes. To sum up, NBO may be a safe and effective approach to attenuate CVOD-related symptoms (especially for headache) by brain functional improvement resulting from increasing oxygen supply to the brain tissues.

Different Spectral Analysis Methods for the Theta/Beta Ratio Calculate Different Ratios But Do Not Distinguish ADHD from Controls

There has been ongoing research on the ratio of theta to beta power (Theta/Beta Ratio, TBR) as an EEG-based test in the diagnosis of ADHD. Earlier studies reported significant TBR differences between patients with ADHD and controls. However, a recent meta-analysis revealed a marked decline of effect size for the difference in TBR between ADHD and controls for studies published in the past decade. Here, we test if differences in EEG processing explain the heterogeneity of findings. We analyzed EEG data from two multi-center clinical studies. Five different EEG signal processing algorithms were applied to calculate the TBR. Differences between resulting TBRs were subsequently assessed for clinical usability in the iSPOT-A dataset. Although there were significant differences in the resulting TBRs, none distinguished between children with and without ADHD, and no consistent associations with ADHD symptoms arose. Different methods for EEG signal processing result in significantly different TBRs. However, none of the methods significantly distinguished between ADHD and healthy controls in our sample. The secular effect size decline for the TBR is most likely explained by factors other than differences in EEG signal processing, e.g. fewer hours of sleep in participants and differences in inclusion criteria for healthy controls.

VR motion sickness recognition by using EEG rhythm energy ratio based on wavelet packet transform

Background and objectivesVirtual reality motion sickness (VRMS) is one of the main factors hindering the development of VR technology. At present, the VRMS recognition methods using electroencephalogram (EEG) signals have poor applicability to multiple subjects. MethodsAiming at this dilemma, the wavelet packet transform (WPT), was used to propose a feature extraction method for EEG rhythm energy ratios of delta (δ), theta (θ), alpha (α), and beta (β) in this research. Moreover, VRMS was recognized by combining k-Nearest Neighbor classifier (k-NN), support vector machine (SVM) with polynomial kernel (polynomial-SVM) and radial basis function kernel (RBF-SVM), respectively. The method is that the raw EEG signals were de-noised by an elliptical band-pass filter and segmented by a fixed window, 7-level db4 WPT was performed on each EEG segment, and the wavelet packet energy ratios of delta, theta, alpha and beta rhythms from FP1, FP2, C3, C4, P3, P4, O1 and O2 channels were calculated and combined to form feature vectors for recognizing VRMS. ResultsUnder the condition of 4-s window size, the average VRMS recognition accuracy of polynomial-SVM for the single subject was 92.85%, and the VRMS recognition accuracy of 18 subjects was about 79.25%. ConclusionsCompared with other VRMS recognition methods, this method does not only have a higher recognition accuracy to a single subject, but also have better applicability to multiple subjects. Meanwhile, when using the EEG four rhythm energy ratios of FP1, FP2, C3, C4, P3, P4, O1 and O2 channels as feature vectors, the polynomial-SVM achieved better VRMS recognition performance than the k-NN and RBF-SVM.

Differentiating Active and Passive Fatigue with the use of Electroencephalography

Desmond and Hancock (2001) proposed that two types of cognitive fatigue can arise depending on the nature of a task: active or passive. The purpose of this study was to use electroencephalographic indices of task engagement and a candidate marker of strain to differentiate these two fatigue states. Participants ( N = 84) performed a generalized flight simulation task for 62 min under either active, passive, or control conditions. Passive fatigue was characterized by reduced EEG engagement and initially elevated and stable ratios of Fz theta to POz alpha power compared to active fatigue. No performance differences were found between the fatigue conditions; however, an overall speed-accuracy trade-off was observed from pre to post fatigue induction. These results support theoretical and empirical distinctions between active and passive fatigue and have potential applications for developing augmented cognition technologies to deliver appropriate fatigue countermeasures in automated operational environments.

EEG power spectral slope differs by ADHD status and stimulant medication exposure in early childhood.

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by hyperactivity/impulsivity and inattentiveness. Efforts toward the development of a biologically based diagnostic test have identified differences in the EEG power spectrum; most consistently reported is an increased ratio of theta to beta power during resting state in those with the disorder, compared with controls. Current approaches calculate theta/beta ratio using fixed frequency bands, but the observed differences may be confounded by other relevant features of the power spectrum, including shifts in peak oscillation frequency and altered slope or offset of the aperiodic 1/f-like component of the power spectrum. In the present study, we quantify the spectral slope and offset, peak alpha frequency, and band-limited and band-ratio oscillatory power in the resting-state EEG of 3- to 7-yr-old children with and without ADHD. We found that medication-naive children with ADHD had higher alpha power, greater offsets, and steeper slopes compared with typically developing children. Children with ADHD who were treated with stimulants had comparable slopes and offsets to the typically developing group despite a 24-h medication-washout period. We further show that spectral slope correlates with traditional measures of theta/beta ratio, suggesting the utility of slope as a neural marker over and above traditional approaches. Taken with past research demonstrating that spectral slope is associated with executive functioning and excitatory/inhibitory balance, these results suggest that altered slope of the power spectrum may reflect pathology in ADHD.NEW & NOTEWORTHY This article highlights the clinical utility of comprehensively quantifying features of the EEG power spectrum. Using this approach, we identify, for the first time, differences in the aperiodic components of the EEG power spectrum in children with attention-deficit/hyperactivity disorder (ADHD) and provide evidence that spectral slope is a robust indictor of an increase in low- relative to high-frequency power in ADHD.

The effects of visual distractors on cognitive load in a motor imagery brain-computer interface

A brain-computer interface (BCI) is a system that translates neural activity into a practical output. Its functionality, therefore, depends not only on the computer itself, but also on the cognitive system of the user. Distractors have the potential to capture attention, increase cognitive load, and may therefore impact BCI use. The purpose of the current study is to determine the effects of small visual distractors on the cognitive load of users of a motor imagery-BCI, and to examine whether these distractor-mediated effects can be improved by modifying the task interface. Sixteen typically-developed participants completed two sessions of online motor imagery to control an EEG-BCI, under conditions of no distractors, visual distractors, and cognitive strategies (intended to mitigate cognitive load) amid distractors. Cognitive load for each session was assessed through both a ratio of theta to alpha power and the NASA-Task Load Index (NASA-TLX). Task-irrelevant visual stimuli were found to significantly increase the objective measure of cognitive load, particularly for parietal channels. Subjective cognitive load as indexed by the NASA-TLX was predictive of a decrease in BCI performance for participants with below 0.75 classification accuracy (R2 = 0.32, p < 0.001), which may indicate a differential susceptibility to changes in workload for “low”-performing participants. Quantifying and addressing the increased cognitive load imparted by distractors on BCI users can aid in the future applicability of the technology in real-world settings.

Sniffing behaviour‐related changes in cardiac and cortical activity in rats

High-frequency (HF) sniffing represents active odour sampling and an increase in the animal's motivation. We examined how HF sniffing affects the physiological activity of the brain-body system. During HF sniffing, heart rates and the ratio of theta to delta critical local field potential power were comparable to those observed during motion periods. Vagus nerve spike rates did not vary depending on HF sniffing. Our results suggest that physiological factors in the central nervous system and the periphery are not simply determined by locomotion but are crucially associated with HF sniffing. Sniffing is a fundamental behaviour for odour sampling, and high-frequency (HF) sniffing, generally at a sniff frequency of more than 6Hz, is considered to represent an animal's increased motivation to explore external environments. Here, we examined how HF sniffing is associated with changes in physiological signals from the central and peripheral organs in rats. During HF sniffing while the rats were stationary, heart rates, the magnitude of dorsal neck muscle contraction, and the ratio of theta to delta local field potential power in the motor cortex were comparable to those observed during motion periods and were significantly higher than those observed during resting respiration periods. No pronounced changes in vagus nerve spike rates were detected in relation to HF sniffing. These results demonstrate that central and peripheral physiological factors are crucially associated with the emergence of HF sniffing, especially during quiescent periods. Behavioural data might be improved to more accurately evaluate an animal's internal psychological state if they are combined with a sniffing pattern as a physiological marker.

Relación entre el ratio SMR/THETA, simulación de síntomas y la calidad de vida en pacientes con fibromialgia

En el presente trabajo encontramos un estudio sobre la relación entre el ratio SMR/Theta, lasimulación de síntomas y la calidad de vida en pacientes con fibromialgia. La enfermedad de fibromialgia es un síndrome generalizado asociado con múltiples síntomas que abarcan desde problemas del sueño, fatiga o cansancio crónico y alteraciones en la cognición. El estudio se realizó con una muestra de 40 pacientes con fibromialgia bajo los criterios de la Asociación Americana de Reumatología. Los instrumentos utilizados fueron, el Inventario Estructurado de Simulación de síntomas y cuestionario autogestionado de Salud SF-36. Los resultados expuestos muestran que existen relación entre la calidad de vida y el ratio SMR/Theta pero no con la simulación de síntomas, por lo que podemos concluir que las personas con el ratio SMR/theta más bajos presentan peor puntuación en el test de calidad de vida.

Changes in Theta but not Alpha Modulation Are Associated with Impairment in Working Memory in Alzheimer's Disease and Mild Cognitive Impairment.

While several studies have found that neural oscillations play a key role in the functioning of working memory, the nature of aberrant oscillatory activity underlying working memory impairments in Alzheimer's disease (AD) and mild cognitive impairment (MCI) remains largely unexplored. These individuals often display structural alterations in brain regions and pathways involved in working memory processes and therefore may also display altered oscillatory activity during memory activation. Electroencephalographic (EEG) activity was recorded during the N-back working memory task in three groups: AD (n = 29), MCI (n = 100), and healthy controls (HCs; n = 40). Theta (4-7 Hz) and alpha (7.5-12 Hz) modulation was measured in response to the stimulus presentation during correct and incorrect responses. This modulation represents the change in EEG activity associated with the stimulus onset and was measured as a ratio of post stimulus power to pre stimulus power. We also assessed the relationship between change in oscillatory power and working memory performance. Compared to HCs, the AD group demonstrated the lowest working memory accuracy and a smaller theta ratio for correct responses on the 2-back condition; the MCI group demonstrated a smaller theta ratio for correct responses on the 3-back condition. Finally, we observed that the theta ratio, but not the alpha ratio, was a significant predictor of working memory performance in the three groups for all conditions. Taken together, these behavioral and electrophysiological results suggest that in addition to impairments in working memory performance, modulation of theta, but not alpha power, may be impaired in MCI and AD.

T19. MULTIMODAL IMAGING IN FIRST EPISODE PSYCHOSIS: MAGNETOENCEPHALOGRAPHY, 7T FMRI STROOP, AND 7T MRS SPECTROSCOPY

BackgroundSchizophrenia (SZ) is an illness whose heterogeneity has impeded understanding the underlying pathophysiology. In order to better understand this heterogeneity, here we used magnetoencephalography (MEG), 7T Magnetic Resonance Spectroscopy (MRS), and 7T fMRI during the Stroop task, on the same set of patients with first episode psychosis (SZ).Methods22 minimally treated first episode SZ and 24 healthy controls (HC) matched for age, gender, and family socio-economic status were recruited. Neurometabolite levels were obtained from the bilateral anterior cingulate cortex using 7T proton MRS with an ultra-short echo time (5 ms) STEAM sequence, and referenced to water. MEG was performed in a 4D systems 148 channel magnetometer, and both the auditory evoked potential to 40 Hz tone clicks, and the resting state (eyes closed) were recorded. The fMRI BOLD response to the Stroop task was also recorded in a 7T scanner.ResultsThe magnitude of the audio-evoked MEG responses to 40 Hz tone clicks was not significantly different between SZ and HC. However, many SZ showed high levels of theta-band activity during the resting state. The ratio of theta to alpha band activity in the anterior MEG sensors significantly differentiated SZ from HC, P<0.05 by t-test. MRS levels of glutamate and total NAA (tNAA), also separated HC from SZ, P<0.05, t-test. An across-groups whole brain analysis of the Stroop fMRI BOLD response to incongruent trials relative to congruent trials was performed (p < .01, FDR-corrected). The strongest signal came from a region in the left parietal (MNI, -30, -58.5, 48), and between-group analysis of the BOLD signal from a 4mm sphere surrounding this location revealed that the activation was greater for SZ than HC by t-test, P<0.05. The MEG theta/alpha ratio, and the left parietal fMRI Stroop effect, were significantly correlated, r=0.45, P=0.005. However, the fMRI Stroop was uncorrelated with the MRS tNAA (r = -0.11, P=0.491) and also uncorrelated with the MRS glutamate levels (r = -0.16, P=0.334).DiscussionWe speculate that the MEG and fMRI data, and the MRS neurometabolite levels, may reflect two relatively independent underlying pathological mechanisms in SZ. Possibly the MEG and fMRI results are indicative of dysfunction in long-range cortical-cortical networks, while the MRS data is more indicative of local neurometabolic dysfunction. Further exploration of SZ using multiple imaging modalities on the same subjects may help to untangle the underlying pathophysiological basis of the heterogeneity of this disorder.

Individual working memory capacity traced from multivariate pattern classification of EEG spectral power.

Working Memory (WM) processing is central for human cognitive behavior. Using neurofeedback training to enhance the individual WM capacity is a promising technique but requires careful consideration when choosing the feedback signal. Feedback in terms of univariate spectral power (specifically theta and alpha power) has yielded questionable behavioral effects. However, a promising new direction for WM neurofeedback training is by using a measure of WM that is extracted by multivariate pattern classification. This study recorded EEG oscillatory activity from 15 healthy participants while they were engaged in the n-back task, n∈[1,2]. Univariate measures of the theta, alpha, and theta-over-alpha power ratio and a measure of WM extracted from multivariate pattern classification (of n-back task load conditions) was compared in relation to individual n-back task performance. Results show that classification performance is positively correlated to individual 2-back task performance while theta, alpha and thetaover-alpha power ratio is not. These results suggest that the discriminability of multivariate EEG oscillatory patterns between two WM load conditions reflects individual WM capacity.