High-frequency EEG Activity Research Articles

Hyperarousal dynamics reveal an overnight increase boosted by insomnia

Hyperarousal is a key symptom of anxiety, stress-related disorders, and insomnia. However, it has been conceptualized in many different ways, ranging from various physiological markers (e.g. cortisol levels, high-frequency EEG activity) to personality traits, or state assessments of subjective anxiety and tension. This approach resulted in partly inconsistent evidence, complicating unified interpretations. Crucially, no previous studies addressed the likely variability of hyperarousal within and across days, nor the relationship of such variability in hyperarousal with the night-by-night variability in sleep quality characteristic of insomnia.Here, we present a novel data-driven approach to understanding dynamics of state hyperarousal in insomnia. Using ecological momentary assessment, we tracked fluctuations in a wide range of emotions across 9 days in 169 people with insomnia disorders and 38 controls without sleep problems. Exploratory factor analysis identified a hyperarousal factor, comprised of items describing tension and distress. People with insomnia scored significantly higher on this factor than controls at all timepoints. In both groups, the hyperarousal factor score peaked in the morning and waned throughout the day, pointing to a potential contributing role of sleep or other circadian processes. Importantly, the overnight increase in hyperarousal was stronger in people with in insomnia than in controls. Subsequent adaptive LASSO regression analysis revealed a stronger overnight increase in hyperarousal across nights of worse subjective sleep quality.These findings demonstrate the relationship between subjective sleep quality and overnight modulations of hyperarousal. Disorders in which hyperarousal is a predominant complaint might therefore benefit from interventions focused on improving sleep quality.

The impact of isoflurane anesthesia on brain metabolism in mice: An MRI and electroencephalography study.

Isoflurane is one of the most widely used anesthetic agents in rodent imaging studies. However, the impact of isoflurane on brain metabolism has not been fully characterized to date, primarily due to a scarcity of noninvasive technologies to quantitatively measure the brain's metabolic rate in vivo. In this study, using noncontrast MRI techniques, we dynamically measured cerebral metabolic rate of oxygen (CMRO2) under varying doses of isoflurane anesthesia in mice. Concurrently, systemic parameters of heart and respiration rates were recorded alongside CMRO2. Additionally, electroencephalogram (EEG) recording was used to identify changes in neuronal activities under the same anesthetic regimen employed in the MRI experiments. We found suppression of the CMRO2 by isoflurane in a dose-dependent manner, concomitant with a diminished high-frequency EEG activity. The degree of metabolic suppression by isoflurane was strongly correlated with the respiration rate, which offers a potential approach to calibrate CMRO2 measurements. Furthermore, the metabolic level associated with neural responses of the somatosensory and motor cortices in mice was estimated as 308.2μmol/100 g/min. These findings may facilitate the integration of metabolic parameters into future studies involving animal disease models and anesthesia usage.

Cortical hyperarousal in individuals with frequent nightmares.

Nightmares are common among the general population and psychiatric patients and have been associated with signs of nocturnal arousal such as increased heart rate or increased high-frequency electroencephalographic (EEG) activity. However, it is still unclear, whether these characteristics are more of a trait occurring in people with frequent nightmares or rather indicators of the nightmare state. We compared participants with frequent nightmares (NM group; n = 30) and healthy controls (controls; n = 27) who spent 4 nights in the sleep laboratory over the course of 8 weeks. The NM group received six sessions of imagery rehearsal therapy (IRT), the 'gold standard' of cognitive-behavioural therapy for nightmares, between the second and the third night. Sleep architecture and spectral power were compared between groups, and between nights of nightmare occurrence and nights without nightmare occurrence in the NM group. Additionally, changes before and after therapy were recorded. The NM group showed increased beta (16.25-31 Hz) and low gamma (31.25-35 Hz) power during the entire night compared to the controls, but not when comparing nights of nightmare occurrence to those without. Moreover, low gamma activity in rapid eye movement sleep was reduced after therapy in the NM group. Our findings indicate, cortical hyperarousal is more of a trait in people with frequent nightmares within a network of other symptoms, but also malleable by therapy. This is not only a new finding for IRT but could also lead to improved treatment options in the future that directly target high-frequency EEG activity.

0422 The relationship between EEG spectral analysis and pre-sleep cognitive arousal in insomnia disorder

Abstract Introduction The hyperarousal model suggests that insomnia is characterized by increased cortical, cognitive, and physiological arousal. However, the relationship between these domains of arousal remains insufficiently studied. The aim of the current observational study was to investigate pre-sleep cognitive arousal, cortical arousal during the night, and the relationship between these domains. Methods 109 patients with insomnia disorder (ID) and 109 age-and gender matched healthy controls (GSC) were investigated on two sleep laboratory nights. As a measure of cortical arousal, EEG spectral power was analyzed during NREM and REM sleep. In addition, participants completed the Pre-Sleep Arousal Scale (PSAS), which consists of a subscale for cognitive arousal (PSAS-CA) and another subscale for self-reported somatic arousal (PSAS-SA). The relationship between the subscale scores and EEG spectral power was calculated by multivariate and univariate analyses of variance. Results The total sample consisted of 218 participants. ID patients had a mean age of 44.7 years (± 10.6 years) and GSC had a mean age of 44.4 years (± 12.6 years). Both groups consisted of 78 women and 31 men.During NREM and REM sleep, patients with ID showed significantly increased spectral power in the EEG gamma band (NREM: p < .001; REM: p = .002). In addition, patients with ID showed significantly increased scores on the PSAS-SA (ID: M = 12.4, SD = 4.4; GSC: M = 10.7, SD = 3.3; t(216) = 3.34, p = .001, d = 0.45) and the PSAS-CA (ID: M = 18.3, SD = 7.2; GSC: M = 10.6, SD = 2.9; t(216) = 10.33, p < .001, d = 1.40). The PSAS-CA score was significantly associated with increased NREM (p = .001) and REM gamma power (p = .004), whereas PSAS-SA was associated with significant decreases in NREM (p < .001) and REM gamma power (p = .001). Conclusion In line with our hypothesis, patients with ID showed increased cortical and cognitive arousal. Moreover, there was a relationship between pre-sleep cognitive arousal and high-frequency EEG activity during the night. This might suggest that the latter is caused (at least in part) by pre-sleep worry and rumination. Support (if any)

0371 Acute effects of cannabinoids in insomnia disorder: a randomised, placebo-controlled trial using high-density EEG

Abstract Introduction Medicinal cannabis is often cited as a popular alternative to common sleep aids; however, there are limited studies using complex sleep EEG methods examining its’ effects in insomnia disorder. Methods Twenty participants (16 female; mean [SD] age, 47.1 [8.7] years) with insomnia disorder (mean ISI=20.8) completed two 24-hour in-laboratory visits during which they received a single oral dose of ‘CBD/THC’ containing 200 mg cannabidiol (CBD) and 10 mg Δ9-tetrahydrocannabinol (THC) or matched placebo. Co-primary outcomes were total sleep time (TST) and wake after sleep onset (WASO). Secondary outcomes included next-day neurobehavioural function and sleep architecture metrics determined using overnight polysomnography with high-density EEG. Trial registration: ACTRN12619000714189. Results Compared to placebo, CBD/THC significantly decreased TST (-24.5 min, p=0.047) with no significant change to WASO (+10.7 min, p=0.422). CBD/THC significantly decreased time spent in REM sleep (-8.1%, p< 0.001) and increased REM sleep latency (+65.6 min, p=0.008). High-density EEG analysis revealed a significant reduction in high-frequency EEG activity overlying the posterior and frontal cortex during N2 sleep with CBD/THC treatment compared to placebo. CBD/THC treatment also reduced delta activity in the posterior region of the brain during N3 sleep and increased alpha and beta activity during REM sleep in the posterior regions of the brain relative to placebo (all p’s< 0.05). CBD/THC did not impair next-day (+12 h post-treatment) cognitive performance, alertness, or simulated driving performance (all p’s>0.05). Eighty-five mild, non-serious, adverse events were reported (55 during ETC120; most common dry mouth, drowsiness, and fatigue). Conclusion An acute dose of combined 200 mg CBD and 10 mg THC reduced TST with a clear effect of REM sleep suppression. However, no next-day residual impairment on cognitive function, alertness or simulated driving performance were observed. Further research is required to determine the impact of chronic cannabinoid dosing on REM sleep and other objective sleep outcomes in insomnia disorder. Support (if any) The study was funded by the Lambert Initiative for Cannabinoid Therapeutics, a philanthropically funded centre for cannabinoid research at the University of Sydney, Australia.

Compensatory mechanisms of reduced interhemispheric EEG connectivity during sleep in patients with apnea

We performed a mathematical analysis of functional connectivity in electroencephalography (EEG) of patients with obstructive sleep apnea (OSA) (N = 10; age: 52.8 ± 13 years; median age: 49 years; male/female ratio: 7/3), compared with a group of apparently healthy participants (N = 15; age: 51.5 ± 29.5 years; median age: 42 years; male/female ratio: 8/7), based on the calculation of wavelet bicoherence from nighttime polysomnograms. Having observed the previously known phenomenon of interhemispheric synchronization deterioration, we demonstrated a compensatory increase in intrahemispheric connectivity, as well as a slight increase in the connectivity of the central and occipital areas for high-frequency EEG activity. Significant changes in functional connectivity were extremely stable in groups of apparently healthy participants and OSA patients, maintaining the overall pattern when comparing different recording nights and various sleep stages. The maximum variability of the connectivity was observed at fast oscillatory processes during REM sleep. The possibility of observing some changes in functional connectivity of brain activity in OSA patients in a state of passive wakefulness opens up prospects for further research. Developing the methods of hypnogram evaluation that are independent of functional connectivity may be useful for implementing a medical decision support system.

Progressive inflammation reduces high-frequency EEG activity and cortical dendritic arborisation in late gestation fetal sheep

BackgroundAntenatal infection/inflammation is associated with disturbances in neuronal connectivity, impaired cortical growth and poor neurodevelopmental outcomes. The pathophysiological substrate that underpins these changes is poorly understood. We tested the hypothesis that progressive inflammation in late gestation fetal sheep would alter cortical neuronal microstructure and neural function assessed using electroencephalogram band power analysis.MethodsFetal sheep (0.85 of gestation) were surgically instrumented for continuous electroencephalogram (EEG) recording and randomly assigned to repeated saline (control; n = 9) or LPS (0 h = 300 ng, 24 h = 600 ng, 48 h = 1200 ng; n = 8) infusions to induce inflammation. Sheep were euthanised 4 days after the first LPS infusion for assessment of inflammatory gene expression, histopathology and neuronal dendritic morphology in the somatosensory cortex.ResultsLPS infusions increased delta power between 8 and 50 h, with reduced beta power from 18 to 96 h (P < 0.05 vs. control). Basal dendritic length, numbers of dendritic terminals, dendritic arborisation and numbers of dendritic spines were reduced in LPS-exposed fetuses (P < 0.05 vs. control) within the somatosensory cortex. Numbers of microglia and interleukin (IL)-1β immunoreactivity were increased in LPS-exposed fetuses compared with controls (P < 0.05). There were no differences in total numbers of cortical NeuN + neurons or cortical area between the groups.ConclusionsExposure to antenatal infection/inflammation was associated with impaired dendritic arborisation, spine number and loss of high-frequency EEG activity, despite normal numbers of neurons, that may contribute to disturbed cortical development and connectivity.

Use of electroencephalogram, gait, and their combined signals for classifying cognitive impairment and normal cognition.

BackgroundEarly identification of people at risk for cognitive decline is an important step in delaying the occurrence of cognitive impairment. This study investigated whether multimodal signals assessed using electroencephalogram (EEG) and gait kinematic parameters could be used to identify individuals at risk of cognitive impairment.MethodsThe survey was conducted at the Veterans Medical Research Institute in the Veterans Health Service Medical Center. A total of 220 individuals volunteered for this study and provided informed consent at enrollment. A cap-type wireless EEG device was used for EEG recording, with a linked-ear references based on a standard international 10/20 system. Three-dimensional motion capture equipment was used to collect kinematic gait parameters. Mild cognitive impairment (MCI) was evaluated by Seoul Neuropsychological Screening Battery-Core (SNSB-C).ResultsThe mean age of the study participants was 73.5 years, and 54.7% were male. We found that specific EEG and gait parameters were significantly associated with cognitive status. Individuals with decreases in high-frequency EEG activity in high beta (25–30 Hz) and gamma (30–40 Hz) bands increased the odds ratio of MCI. There was an association between the pelvic obliquity angle and cognitive status, assessed by MCI or SNSB-C scores. Results from the ROC analysis revealed that multimodal signals combining high beta or gamma and pelvic obliquity improved the ability to discriminate MCI individuals from normal controls.ConclusionThese findings support prior work on the association between cognitive status and EEG or gait, and offer new insights into the applicability of multimodal signals to distinguish cognitive impairment.

Progressive increase of high-frequency EEG oscillations during meditation is associated with its trait effects on heart rate and proteomics: a study on the Tibetan Buddhist.

Meditation has been a spiritual and healing practice in the East for thousands of years. However, the neurophysiologic mechanisms underlying its traditional form remain unclear. In this study, we recruited a large sample of monks (n = 73) who practice Tibetan Buddhist meditation and compared with meditation-naive local controls (n = 30). Their electroencephalography (EEG) and electrocardiogram signals were simultaneously recorded and blood samples were collected to investigate the integrative effects of Tibetan Buddhist on brain, heart, and proteomics. We found that the EEG activities in monks shifted to a higher frequency from resting to meditation. Meditation starts with decrease of the (pre)frontal delta activity and increase of the (pre)frontal high beta and gamma activity; while at the deep meditative state, the posterior high-frequency activity was also increased, and could be specified as a biomarker for the deep meditation. The state increase of posterior high-frequency EEG activity was significantly correlated with the trait effects on heart rate and nueropilin-1 in monks, with the source of brain-heart correlation mainly locating in the attention and emotion networks. Our study revealed that the effects of Tibetan Buddhist meditation on brain, heart, and proteomics were highly correlated, demonstrating meditation as an integrative body-mind training.

Conscious experiences and high-density EEG patterns predicting subjective sleep depth

What accounts for feeling deeply asleep? Standard sleep recordings only incompletely reflect subjective aspects of sleep and some individuals with so-called sleep misperception frequently feel awake although sleep recordings indicate clear-cut sleep. To identify the determinants of sleep perception, we performed 787 awakenings in 20 good sleepers and 10 individuals with sleep misperception and interviewed them about their subjective sleep depth while they underwent high-density EEG sleep recordings. Surprisingly, in good sleepers, sleep was subjectively lightest in the first 2h of non-rapid eye movement (NREM) sleep, generally considered the deepest sleep, and deepest in rapid eye movement (REM) sleep. Compared to good sleepers, sleep misperceptors felt more frequently awake during sleep and reported lighter REM sleep. At the EEG level, spatially widespread high-frequency power was inversely related to subjective sleep depth in NREM sleep in both groups and in REM sleep in misperceptors. Subjective sleep depth positively correlated with dream-like qualities of reports of mental activity. These findings challenge the widely held notion that slow wave sleep best accounts for feeling deeply asleep. Instead, they indicate that subjective sleep depth is inversely related to a neurophysiological process that predominates in early NREM sleep, becomes quiescent in REM sleep, and is reflected in high-frequency EEG activity. In sleep misperceptors, this process is more frequently active, more spatially widespread, and abnormally persists into REM sleep. These findings help identify the neuromodulatory systems involved in subjective sleep depth and are relevant for studies aiming to improve subjective sleep quality.

Electrical Activity During Slow-Wave Sleep and the Relationship With Enlarged Perivascular Spaces in Arteriosclerotic Cerebral Small Vessel Disease.

We sought to analyze EEG spectral power during slow-wave sleep among patients with arteriosclerotic cerebral small vessel disease (CSVD) compared with community-dwelling individuals. We also sought to determine the relationship between EEG activity and the severity of enlarged perivascular spaces (EPVSs). Consecutive subjects with arteriosclerotic CSVD ( n = 36) and community-dwelling individuals ( n = 26) between 50 and 80 years of age were included. Nocturnal polysomnography was performed, and EEG spectral analysis was conducted during slow-wave sleep using the F4/M1 and C4/M1 channel. Regionalized EPVSs in the basal ganglia and centrum semiovale were assessed on a validated 4-point visual rating scale (0 = none, 1 = 1-10, 2 = 11-20, 3 = 21-40, and 4 = >40) using MRI. CSVD group showed lower delta:beta ratios in the frontal ( P = 0.017) and central ( P = 0.038) regions after adjusting for age, sex, mini-mental state examination score, and arousal index. The significance still remained in the frontal region when including age, sex, mini-mental state examination, and apnea-hypopnea index as covariates ( P = 0.037). Among patients with arteriosclerotic CSVD, decreased delta power ( P = 0.031) and theta power ( P = 0.034) in the frontal region were associated with a higher degree of EPVSs in the centrum semiovale rather than in the basal ganglia. Delta power in the central region showed an extremely weak association with EPVSs in the centrum semiovale ( P = 0.047). Among patients with arteriosclerotic CSVD, the intrusion of high-frequency EEG activity into slow-wave sleep was identified, and slow-wave activity during slow-wave sleep might be negatively associated with the severity of EPVSs in the centrum semiovale. Further studies are required to corroborate the conclusions.

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.

Increased high-frequency EEG activity during nerm sleep mediates the association between subjective daytime sleepiness and sustained attention in sleep apnea patients

Increased high-frequency EEG activity during nerm sleep mediates the association between subjective daytime sleepiness and sustained attention in sleep apnea patients

Decision Support System for Seizure Onset Zone Localization Based on Channel Ranking and High-Frequency EEG Activity.

Interictal high-frequency oscillations (HFO) are a promising biomarker that can help define the seizure onset zone (SOZ) and predict the surgical outcome after the epilepsy surgery. The utility of HFO in planning the surgery, though, is unclear. Reasons include the variability of the HFO across patients and brain regions and the influence of the sleep-wake cycle, which causes large fluctuations in the ratio between the HFO observed in SOZ and non-SOZ regions. To cope with these limitations, a rank-based solution is proposed to identify the SOZ by using the HFO in multichannel intracranial EEG. A time-varying index of the epileptic susceptibility of the different brain areas is derived from the HFO rate and a support vector machine is applied on this index to identify the SOZ. The solution is trained and tested on separate groups of patients to avoid the use of patient-specific information and provides optimal SOZ prediction using as little as 30 min of recordings per channel (window). Tested on 14 patients with various combinations of seizure type, epilepsy etiology, and SOZ arrangement (172.7 ± 90.1 h/channel per patient and 75.6 ± 23.5 channels/patient, mean ± S.D.), our solution identified the SOZ with 0.92 ± 0.03 accuracy and 0.91 ± 0.03 area under the ROC curve (mean ± S.D.) across patients. For each patient, the window onset time was varied over 72 continuous hours and the prediction of the SOZ remained insensitive to the onset time, thus showing potential for surgery planning.

Childhood high-frequency EEG activity during sleep is associated with incident insomnia symptoms in adolescence.

Insomnia has been associated in cross-sectional studies with increased beta (15-35Hz) electroencephalogram (EEG) power during nonrapid eye movement (NREM) sleep, an index of cortical hyperarousal. However, it is unknown whether this cortical hyperarousal is present before individuals with insomnia develop the disorder. To fill this gap, we examined the association of childhood sleep high-frequency EEG activity with incident insomnia symptoms (i.e., absence of insomnia symptoms in childhood but presence in adolescence). We studied a case-control subsample of 45 children (6-11years) from the Penn State Child Cohort, a population-based random sample of 421 children, who were followed up after 8years as adolescents (13-20years). We examined low-beta (15-25Hz) and high-beta (25-35Hz) relative power at central EEG derivations during NREM sleep and, in secondary analyses, during sleep onset latency, sleep onset, and REM sleep. Incident insomnia symptoms were defined as the absence of parent-reported difficulty falling and/or staying asleep during childhood and a self-report of these insomnia symptoms during adolescence. Childhood high-beta power during NREM sleep was significantly increased in children who developed insomnia symptoms in adolescence (n=25) as compared to normal sleeping controls (n=20; p=.03). Multivariable-adjusted logistic regression models showed that increased childhood high-beta EEG power during NREM sleep was associated with a threefold increased odds (95% CI=1.12-7.98) of incident insomnia symptoms in adolescence. No other significant relationships were observed for other sleep/wake states or EEG frequency bands. Increased childhood high-frequency EEG power during NREM sleep is associated with incident insomnia symptoms in adolescence. This study indicates that cortical hyperarousal during sleep may be a premorbid neurophysiological sign of insomnia, which may mediate the increased risk of psychiatric disorders associated with insomnia.

EEG Reflection of Clinical Effects Dynamics during Botulinum Toxin Therapy of Movement Disorders under Long-Term Consciousness Disorders

When studying the dynamics of brain electric activity (BEA) in the course of botulinum toxin (Incobotulinumtoxin A) injections into all hypertonic muscles of 16 patients suffering from post-coma longterm consciousness disorders, BEA changes were observed to start within the first minutes after the first intramuscular injection of botulinum toxin, while not being associated with any pain stimulus response. Despite the diversity of brain lesions in these patients, the dynamics of BEA reorganisation during botulinum toxin therapy showed the presence of pathological sensorimotor integration involving the whole brain in case of long-term consciousness disorders. In our opinion, it is expressed in a pathological state developing in the brain, which affects the polyfunctional capabilities of neurons. This state is unbalanced due to destabilizing effect at the beginning of the reduction by pathological hyperafferentation from muscles and, in principle, can be disrupted at a complete reduction. It is, however, maintained by memory matrix, which manifests itself in the shape of oscillation process during its disruption when the newly build-up BEA is occasionally displaced by the previous one. During the reduction of sensory hyperafferentation, BEA reorganisation initially involved the motor cortex (in 15 out of 16 patients) and then spread to other brain areas, including those responsible for the higher mental functions, vision, and hearing. The first transiently decreased muscle tone (in all patients) and improvement of neurological signs of awareness (in some patients) were observed immediately after injecting all hypertonic muscles with widespread BEA changes. The appearance of high-frequency EEG activity in the frontal areas was considered as a universal marker of an improved functional state of the brain during the disruption of pathological sensorimotor integration even before clinical signs, suggesting neuronal readiness to maintain various activities. In view of data obtained, the first-stage clinical measures in patients with disorders of consciousness should focus on disrupting pathological sensorimotor integration, opening a way for restoring neuronal functional activity, provided that all “pathological afferents” are reduced.

Effects of Social Defeat Stress on Sleep in Mice.

Stress plays a key role in the development of psychiatric disorders and has a negative impact on sleep integrity. In mice, chronic social defeat stress (CSDS) is an ethologically valid model of stress-related disorders but little is known about its effects on sleep regulation. Here, we investigated the immediate and long-term effects of 10 consecutive days of social defeat (SD) on vigilance states in C57Bl/6J male mice. Social behavior was assessed to identify susceptible mice, i.e., mice that develop long-lasting social avoidance, and unsusceptible mice. Sleep-wake stages in mice of both groups were analyzed by means of polysomnographic recordings at baseline, after the first, third, and tenth stress sessions and on the 5th recovery day (R5) following the 10-day CSDS. In susceptible mice, each SD session produced biphasic changes in sleep-wake states that were preserved all along 10-day CSDS. These sessions elicited a short-term enhancement of wake time while rapid eye-movement (REM) sleep was strongly inhibited. Concomitantly, delta power was increased during non REM (NREM) sleep. During the following dark period, an increase in total sleep time, as well as wake fragmentation, were observed after each analyzed SD session. Similar changes were observed in unsusceptible mice. At R5, elevated high-frequency EEG activity, as observed in insomniacs, emerged during NREM sleep in both susceptible and unsusceptible groups suggesting that CSDS impaired sleep quality. Furthermore, susceptible but not unsusceptible mice displayed stress-anticipatory arousal during recovery, a common feature of anxiety disorders. Altogether, our findings show that CSDS has profound impacts on vigilance states and further support that sleep is tightly regulated by exposure to stressful events. They also revealed that susceptibility to chronic psychological stress is associated with heightened arousal, a physiological feature of stress vulnerability.

O81 High frequency EEG activity is associated with preserved cerebral function in critical illness

Objectives To assess the value of continuous electroencephalography (cEEG) in detecting delirium in a medical intensive care unit (ICU), applying a visual, qualitative analysis in accordance with The American Clinical Neurophysiology Society’s Standardized Critical Care Terminology. Methods Single-center prospective observational study including 102 patients with sepsis or septic shock. Full scalp cEEG was recorded continuously after admission.Delirium screening was applied six times daily using the Confusion Assessment Method for the ICU (CAM-ICU). Results Sixty-six patients (65%) had at least one episode of delirium during their ICU stay; thirty (29%) remained delirium-free; six patients (6%) remained comatose and unassessable. In total, 6723 h of EEG-recordings were visually analyzed. Preserved beta activity (>13 Hz) was independently associated with staying delirium-free ( p 10 - 7 ) along with preserved EEG reactivity ( p 0.001 ). Reduced beta activity emerged as the stronger predictor for delirium, eliminating theta and delta electrographic band power. Time-dependent Cox regression associated burst suppression with reduced mortality. Sporadic periodic discharges occurred in fifteen patients of whom 87% were delirious. Treatment-requiring epileptic or non-convulsive EEG activity was not observed. Discussion Neuronal desynchronization expressed as loss of high frequency EEG activity could be a potential biomarker for delirium. Whether this is superior to bedside clinical screening with validated tests such as the CAM-ICU remains to be further examined. Conclusions Beta activity was the strongest predictor of preserved cerebral function in septic patients and superior to the previously described association between delirium and low frequency delta activity. Non-convulsive activity was not observed. Significance Early detection of cerebral deterioration by cEEG may provide a window for intervention to improve outcome.

Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations.

Although episodic and semantic memory share overlapping neural mechanisms, it remains unclear how our pre-existing semantic associations modulate the formation of new, episodic associations. When freely recalling recently studied words, people rely on both episodic and semantic associations, shown through temporal and semantic clustering of responses. We asked whether orienting participants toward semantic associations interferes with or facilitates the formation of episodic associations. We compared electroencephalographic (EEG) activity recorded during the encoding of subsequently recalled words that were either temporally or semantically clustered. Participants studied words with or without a concurrent semantic orienting task. We identified a neural signature of successful episodic association formation whereby high-frequency EEG activity (HFA, 44-100 Hz) overlying left prefrontal regions increased for subsequently temporally clustered words, but only for those words studied without a concurrent semantic orienting task. To confirm that this disruption in the formation of episodic associations was driven by increased semantic processing, we measured the neural correlates of subsequent semantic clustering. We found that HFA increased for subsequently semantically clustered words only for lists with a concurrent semantic orienting task. This dissociation suggests that increased semantic processing of studied items interferes with the neural processes that support the formation of novel episodic associations. (PsycINFO Database Record

EEG-fMRI Gradient Artifact Correction by Multiple Motion-Related Templates.

In simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), artifacts on the EEG arise from the switching of magnetic field gradients in the MR scanner. These artifacts depend on head position, and are, therefore, difficult to remove in the presence of subject motion. In this study, gradient artifacts are modeled by multiple templates extracted from externally recorded motion information. Gradient artifact correction was performed in EEG-fMRI recordings by estimating artifactual templates modulated by slowly varying splines, as well as head position information. The EEG signal quality was then compared following two common methods: averaged artifact subtraction (AAS) and optimal basis sets (OBS). Artifact correction using multiple templates estimated from splines or motion time courses outperformed the existing AAS and OBS approaches, as quantified by root-mean-square power across gradient epochs. Improvements were mostly seen in posterior EEG channels, where most of the residual artifacts are seen following the AAS and OBS methods. Residual spectral power was comparable to that of EEG signals recorded without fMRI scanning. Gradient artifacts can be well modeled by multiple templates estimated from head position information, resulting in an effective artifact removal. This method can facilitate EEG-fMRI of uncooperative subjects in whom motion is inevitable, for example, to investigate high-frequency EEG activity in which gradient artifacts are particularly prominent.