Rhythmic EEG Activity Research Articles

Cefepime-induced encephalopathy

Cefepime is a fourth-generation cephalosporin antibiotic widely used in clinical practice for various organ systems pathology treatment. The article describes the clinical observation of a patient who, 3 days after cefepime administration, had a decrease in the level of consciousness, regarded as encephalopathy. Cefepime-induced neurotoxicity is characterized by toxic encephalopathy, which manifests 2–6 days after the start of the treatment with this drug and disappears 1–3 days after its withdrawal. Electroencephalography (EEG) abnormalities include generalized periodic discharges (GPR) of triphasic morphology or a pattern corresponding to the criteria for non-convulsive status epilepticus (BSES). In our observation, the EEG recorded stimulus-induced GPRs of triphasic morphology with a frequency of 1.5 Hz; a test with intravenous administration of an antiepileptic drug (levetiracetam) was negative. A day after the withdrawal of cefepime, the patient’s level of consciousness returned to the initial level, and on the EEG periodic discharges completely regressed. Thus, cefepime may cause encephalopathy in patients with rhythmic or intermittent EEG activity, especially in the presence of a stimulus-induced component. In some cases, the use of cefepime may develop epileptic seizures and BSES.

Clinical and Electrophysiological Features Predicting Response to Antiseizure Medications in Juvenile Absence Epilepsy.

We aimed to evaluate the clinical findings and electroencephalographic (EEG) characteristics of patients with juvenile absence epilepsy (JAE) and to determine the factors that predict response to antiseizure medications (ASMs) in JAE. We reviewed the medical records of 29 patients with JAE. The patients who were seizure-free during the last 12 months of their follow-up and who did not have generalized spike waves on their last EEG were considered as the treatment-responsive group, and the patients whose clinical seizures persisted during the last 12 months of their follow-up or who had generalized spike waves on their follow-up EEGs were considered as patients who did not respond to ASMs. There were 29 patients, 20 girls and nine boys, with a mean age of 13.34 ± 2.17 years and a follow-up time of 32.1 ± 11.9 months. Twenty-two cases (75.8%) were evaluated as responsive to treatment. Generalized tonic-clonic seizures (GTCS) were statistically more common in patients who did not respond to ASM. Epileptic seizures began at a younger age in the group that responded to medication. Occipital intermittent rhythmic delta activity (OIRDA) in EEG was significantly higher in the group that responded to the medication. Our study shows that concomitant GTCS may predict poorer response to ASMs in JAE. Younger age at diagnosis and OIRDA on EEG may be associated with better response to treatment. Our findings need to be confirmed by further prospective and long-term studies.

Exploring EEG spectral and temporal dynamics underlying a hand grasp movement.

For brain-computer interfaces, resolving the differences between pre-movement and movement requires decoding neural ensemble activity in the motor cortex's functional regions and behavioural patterns. Here, we explored the underlying neural activity and mechanisms concerning a grasped motor task by recording electroencephalography (EEG) signals during the execution of hand movements in healthy subjects. The grasped movement included different tasks; reaching the target, grasping the target, lifting the object upwards, and moving the object in the left or right directions. 163 trials of EEG data were acquired from 30 healthy participants who performed the grasped movement tasks. Rhythmic EEG activity was analysed during the premovement (alert task) condition and compared against grasped movement tasks while the arm was moved towards the left or right directions. The short positive to negative deflection that initiated around -0.5ms as a wave before the onset of movement cue can be used as a potential biomarker to differentiate movement initiation and movement. A rebound increment of 14% of beta oscillations and 26% gamma oscillations in the central regions was observed and could be used to distinguish pre-movement and grasped movement tasks. Comparing movement initiation to grasp showed a decrease of 10% in beta oscillations and 13% in gamma oscillations, and there was a rebound increment 4% beta and 3% gamma from grasp to grasped movement. We also investigated the combination MRCPs and spectral estimates of α, β, and γ oscillations as features for machine learning classifiers that could categorize movement conditions. Support vector machines with 3rd order polynomial kernel yielded 70% accuracy. Pruning the ranked features to 5 leaf nodes reduced the error rate by 16%. For decoding grasped movement and in the context of BCI applications, this study identifies potential biomarkers, including the spatio-temporal characteristics of MRCPs, spectral information, and choice of classifiers for optimally distinguishing initiation and grasped movement.

Changes of oxygen saturation in patients with pure temporal lobe epilepsy

PurposeIctal hypoxemia is accepted as one of the mechanisms underlying sudden unexpected death in epilepsy (SUDEP). Although ictal hypoxemia is more common in generalized seizures, it also occurs in focal seizures with or without generalization. In this study, we aimed to show the relationship between clinical and electroencephalographic findings of seizures in patients with temporal lobe epilepsy (TLE) with periictal oxygen saturation. MethodsThe data of 55 adult patients who were hospitalized in the Video EEG Monitoring Unit (VEMU) and operated on for drug-resistant TLE between January 2017 and December 2020 were examined. Forty-five seizures from 21 patients with ictal peripheral arterial saturation information and that were seizure-free for at least a year during the follow-up were included in the study. ResultsThe median patient age was 28 (IQR 25–39.5) years (women: 9, men: 12). Age at epilepsy onset was negatively correlated with saturation at seizure onset. Moreover, the age at VEMU admission was also negatively correlated with saturation at seizure onset and the lowest levels of saturation. The saturation at the end of the seizures and the lowest saturation measured in the periictal period with generalization of EEG were significantly lower than those without generalization.The onset of ictal EEG with the rhythmic theta pattern was significantly associated with the lowest level of saturation (<90%), postictal generalized electroencephalographic suppression (PGES), and the presence of generalization. ConclusionAccording to the study, rhythmic ictal theta activity, older age, nocturnal seizure, and generalization in ictal EEG might increase the potential risk of SUDEP. Further studies including a greater number of subjects and different epilepsy syndromes may provide more comprehensive information about potential biomarkers for SUDEP.

Science, Medicine, and the Anesthesiologist

Science, Medicine, and the Anesthesiologist

Treating Rhythmic and Periodic EEG Patterns in Comatose Survivors of Cardiac Arrest

BackgroundWhether the treatment of rhythmic and periodic electroencephalographic (EEG) patterns in comatose survivors of cardiac arrest improves outcomes is uncertain.MethodsWe conducted an open-label trial of suppressing rhythmic and periodic EEG patterns detected on continuous EEG monitoring in comatose survivors of cardiac arrest. Patients were randomly assigned in a 1:1 ratio to a stepwise strategy of antiseizure medications to suppress this activity for at least 48 consecutive hours plus standard care (antiseizure-treatment group) or to standard care alone (control group); standard care included targeted temperature management in both groups. The primary outcome was neurologic outcome according to the score on the Cerebral Performance Category (CPC) scale at 3 months, dichotomized as a good outcome (CPC score indicating no, mild, or moderate disability) or a poor outcome (CPC score indicating severe disability, coma, or death). Secondary outcomes were mortality, length of stay in the intensive care unit (ICU), and duration of mechanical ventilation.ResultsWe enrolled 172 patients, with 88 assigned to the antiseizure-treatment group and 84 to the control group. Rhythmic or periodic EEG activity was detected a median of 35 hours after cardiac arrest; 98 of 157 patients (62%) with available data had myoclonus. Complete suppression of rhythmic and periodic EEG activity for 48 consecutive hours occurred in 49 of 88 patients (56%) in the antiseizure-treatment group and in 2 of 83 patients (2%) in the control group. At 3 months, 79 of 88 patients (90%) in the antiseizure-treatment group and 77 of 84 patients (92%) in the control group had a poor outcome (difference, 2 percentage points; 95% confidence interval, −7 to 11; P=0.68). Mortality at 3 months was 80% in the antiseizure-treatment group and 82% in the control group. The mean length of stay in the ICU and mean duration of mechanical ventilation were slightly longer in the antiseizure-treatment group than in the control group.ConclusionsIn comatose survivors of cardiac arrest, the incidence of a poor neurologic outcome at 3 months did not differ significantly between a strategy of suppressing rhythmic and periodic EEG activity with the use of antiseizure medication for at least 48 hours plus standard care and standard care alone. (Funded by the Dutch Epilepsy Foundation; TELSTAR ClinicalTrials.gov number, NCT02056236.)

The Influence of Auditory Attention on Rhythmic Speech Tracking: Implications for Studies of Unresponsive Patients.

Language comprehension relies on integrating words into progressively more complex structures, like phrases and sentences. This hierarchical structure-building is reflected in rhythmic neural activity across multiple timescales in E/MEG in healthy, awake participants. However, recent studies have shown evidence for this “cortical tracking” of higher-level linguistic structures also in a proportion of unresponsive patients. What does this tell us about these patients’ residual levels of cognition and consciousness? Must the listener direct their attention toward higher level speech structures to exhibit cortical tracking, and would selective attention across levels of the hierarchy influence the expression of these rhythms? We investigated these questions in an EEG study of 72 healthy human volunteers listening to streams of monosyllabic isochronous English words that were either unrelated (scrambled condition) or composed of four-word-sequences building meaningful sentences (sentential condition). Importantly, there were no physical cues between four-word-sentences. Rather, boundaries were marked by syntactic structure and thematic role assignment. Participants were divided into three attention groups: from passive listening (passive group) to attending to individual words (word group) or sentences (sentence group). The passive and word groups were initially naïve to the sentential stimulus structure, while the sentence group was not. We found significant tracking at word- and sentence rate across all three groups, with sentence tracking linked to left middle temporal gyrus and right superior temporal gyrus. Goal-directed attention to words did not enhance word-rate-tracking, suggesting that word tracking here reflects largely automatic mechanisms, as was shown for tracking at the syllable-rate before. Importantly, goal-directed attention to sentences relative to words significantly increased sentence-rate-tracking over left inferior frontal gyrus. This attentional modulation of rhythmic EEG activity at the sentential rate highlights the role of attention in integrating individual words into complex linguistic structures. Nevertheless, given the presence of high-level cortical tracking under conditions of lower attentional effort, our findings underline the suitability of the paradigm in its clinical application in patients after brain injury. The neural dissociation between passive tracking of sentences and directed attention to sentences provides a potential means to further characterise the cognitive state of each unresponsive patient.

Beta-Band Activity Is a Signature of Statistical Learning.

Through statistical learning (SL), cognitive systems may discover the underlying regularities in the environment. Testing human adults (n = 35, 21 females), we document, in the context of a classical visual SL task, divergent rhythmic EEG activity in the interstimulus delay periods within patterns versus between patterns (i.e., pattern transitions). Our findings reveal increased oscillatory activity in the beta band (∼20 Hz) at triplet transitions that indexes learning: it emerges with increased pattern repetitions; and importantly, it is highly correlated with behavioral learning outcomes. These findings hold the promise of converging on an online measure of learning regularities and provide important theoretical insights regarding the mechanisms of SL and prediction.SIGNIFICANCE STATEMENT Statistical learning has become a major theoretical construct in cognitive science, providing the primary means by which organisms learn about regularities in the environment. As such, it is a critical building block for basic and higher-order cognitive functions. Here we identify, for the first time, a spectral neural index in the time window before stimulus presentation, which evolves with increased pattern exposure, and is predictive of learning performance. The manifestation of learning that is revealed, not in stimulus processing but in the blank interval between stimuli, makes a direct link between the fields of statistical learning on the one hand and either prediction or consolidation on the other hand, suggesting a possible mechanistic account of visual statistical learning.

Decoding hierarchical control of sequential behavior in oscillatory EEG activity.

Despite strong theoretical reasons for assuming that abstract representations organize complex action sequences in terms of subplans (chunks) and sequential positions, we lack methods to directly track such content-independent, hierarchical representations in humans. We applied time-resolved, multivariate decoding analysis to the pattern of rhythmic EEG activity that was registered while participants planned and executed individual elements from pre-learned, structured sequences. Across three experiments, the theta and alpha-band activity coded basic elements and abstract control representations, in particular, the ordinal position of basic elements, but also the identity and position of chunks. Further, a robust representation of higher level, chunk identity information was only found in individuals with above-median working memory capacity, potentially providing a neural-level explanation for working-memory differences in sequential performance. Our results suggest that by decoding oscillatory activity we can track how the cognitive system traverses through the states of a hierarchical control structure.

Ictal source imaging and electroclinical correlation in self-limited epilepsy with centrotemporal spikes

PurposeTo elucidate the localization of ictal EEG activity, and correlate it to semiological features in self-limited epilepsy with centrotemporal spikes (formerly called “benign epilepsy with centrotemporal spikes”). MethodsWe have performed ictal electric source imaging, and we analysed electroclinical correlations in three patients with self-limited epilepsy with centrotemporal spikes. ResultsThe source of the evolving rhythmic ictal activity (9.7-13.5Hz) localized to the operculo-insular area. The rhythmic EEG activity was time-locked to the contralateral focal motor seizure manifestation: facial rhythmic myoclonic jerks, with the same frequency as the analysed ictal rhythm. In all three patients, the seizures had fluctuating course with pauses of clinical and electrographic seizure activity, ranging from 0.4 to 7s. ConclusionSource imaging of ictal EEG activity in patients with self-limited epilepsy with centrotemporal spikes showed activation of the operculo-insular area, time-locked to the contralateral focal myoclonic jerks. Fragmented seizure dynamics, with fluctuating course, previously described as a hallmark in patients with psychogenic non-epileptic seizures, can occur in rolandic seizures.

Rhythmic activity in EEG and sleep in rats with absence epilepsy.

This study examines the hypothesis that absence epilepsy is accompanied by disturbances of rhythmic activity in EEG during sleep. Sleep-wake architecture and time-frequency parameters of EEG were analyzed during drowsiness and sleep in WAG/Rij rats with genetic predisposition to absence epilepsy. The incidence of seizures varied in a group of 10 rats, in which 5 individuals did not develop epileptic discharges in their EEG (asymptomatic rats). In contrast to asymptomatic, symptomatic subjects (1) displayed less percentage of wakefulness EEG pattern and more non-REM sleep, (2) showed higher beta and less delta EEG power in frontal cortex during non-REM sleep. Mid-frequency oscillations, such as sleep spindles and 5-9 Hz oscillations, were detected in EEG automatically and underwent time-frequency analysis by means of skeletons of wavelet surfaces. Some mid-frequency oscillations showed "complex" frequency structure, consisting of the dominant and subdominant components. "Complex" sleep spindles more frequently appeared in asymptomatic rats than in symptomatic, whereas the dominant frequency of these spindles in symptomatic rats was higher than in asymptomatic (12.7 vs 11.9 Hz). In general, low-frequency components were readily integrated in sleep spindles in asymptomatic WAG/Rij rats, and decrease in number of "complex" sleep spindles may be associated with epileptic phenotype.

Thalamic hypoperfusion on SPECT in epilepsy with bilateral synchronous discharge

Various childhood epileptic syndromes have been reported to reveal generalized symmetrical spike-wave patterns preceded by unilateral focal discharges. The thalamic rhythmogenic mechanisms responsible for spike-wave discharges have been intensively investigated leading to a better understanding of their anatomo-physiological substrate. We investigated the role of the thalamus in secondary bilateral synchrony on electroencephalography (EEG) in three patients with intractable localization-related epilepsy by performing synchronous single photon emission computed tomography (SPECT) and EEG analysis. The brain scan examination was carried out after injection 18.5 MBq/kg of Tc99m-hexamethyl-propyleneamine oxime at the same time of revealing bilateral synchronous discharges on EEG. The SPECT revealed thalamic hypoperfusion in all cases. In addition, the SPECT revealed hypoperfusion in the left cortical regions and ipsilateral thalami, corresponding to the EEG abnormalities in the cortical regions. These findings in this study suggested that the thalamus may play a role of secondary bilateral synchronization on EEG. Specific thalamic nuclei fire concurrent with cortical epileptiform discharges and are hypothesized to play a role in seizure propagation. Our findings demonstrated thalamo-cortical coupling by SPECT. In conclusion, the thalamus may play a crucial role as a pacemaker of rhythmic EEG activities such as secondary bilateral synchronous discharges.

Electroencephalographic recordings of physiological activity of the sheep cerebral cortex.

This paper presents the physiological activity of the cerebral cortex in sheep in electroencephalo- graphic findings. The study was performed to evaluate and improve understanding of brain monitor- ing methods in freely moving animals without the use of any anaesthetic methods during the acquisi- tion stage. The aim of the study was to determine the physiological activity of the cerebral cortex in animals in a sheep model (using clinically healthy Polish Merino rams, aged 1 yr.) to determine its clinical EEG protocol. The EEG was registered using an in-lab EEG device as well as ambulatory systems (Holter EEG). The bioelectrical activity of the sheep cerebral cortex was recorded using gold disc and needle electrodes placed on experimentally determined locations on the scalp. The main finding of this study was the rhythmic EEG activity of the sheep brain in wakeful and conscious states (eyes open). The rhythm was bilaterally synchronous and determined a basic pattern in the registra- tion of physiological activity of the cerebral cortex. The acquired rhythm may correspond to the theta rhythm in humans, which is a normal activity controlled by the hippocampus. This background activity comprised intermittent episodic slow waves and synchronous beta waves.

Source localization of rhythmic ictal EEG activity: A study of diagnostic accuracy following STARD criteria

Although precise identification of the seizure-onset zone is an essential element of presurgical evaluation, source localization of ictal electroencephalography (EEG) signals has received little attention. The aim of our study was to estimate the accuracy of source localization of rhythmic ictal EEG activity using a distributed source model. Source localization of rhythmic ictal scalp EEG activity was performed in 42 consecutive cases fulfilling inclusion criteria. The study was designed according to recommendations for studies on diagnostic accuracy (STARD). The initial ictal EEG signals were selected using a standardized method, based on frequency analysis and voltage distribution of the ictal activity. A distributed source model-local autoregressive average (LAURA)-was used for the source localization. Sensitivity, specificity, and measurement of agreement (kappa) were determined based on the reference standard-the consensus conclusion of the multidisciplinary epilepsy surgery team. Predictive values were calculated from the surgical outcome of the operated patients. To estimate the clinical value of the ictal source analysis, we compared the likelihood ratios of concordant and discordant results. Source localization was performed blinded to the clinical data, and before the surgical decision. Reference standard was available for 33 patients. The ictal source localization had a sensitivity of 70% and a specificity of 76%. The mean measurement of agreement (kappa) was 0.61, corresponding to substantial agreement (95% confidence interval (CI) 0.38-0.84). Twenty patients underwent resective surgery. The positive predictive value (PPV) for seizure freedom was 92% and the negative predictive value (NPV) was 43%. The likelihood ratio was nine times higher for the concordant results, as compared with the discordant ones. Source localization of rhythmic ictal activity using a distributed source model (LAURA) for the ictal EEG signals selected with a standardized method is feasible in clinical practice and has a good diagnostic accuracy. Our findings encourage clinical neurophysiologists assessing ictal EEGs to include this method in their armamentarium.

Increased susceptibility to pentetrazol-induced seizures in developing rats after cortical photothrombotic ischemic stroke at P7

Perinatal stroke is a common cerebrovascular disorder affecting 1 in every 4000 births; typically associated with epilepsy. We sought to determine seizure susceptibility to pentylentetrazol (PTZ)-induced seizures in developing rats with a history of photothrombotic lesion of sensorimotor cortex induced at postnatal day 7. Lesioned animals were tested at P12 or P25 and compared with sham-operated controls. Three models of epileptic seizures were elicited by PTZ: episodes of spike-and-wave rhythm, minimal clonic seizures and generalized tonic–clonic seizures. PTZ (60 and 100mg/kg) was administered subcutaneously to assess seizure occurrence, latency and severity. In addition, episodes of rhythmic EEG activity were analyzed at P25 following successive interperitoneal 20 and 40mg/kg PTZ administration. There was only one significant change in convulsive seizures—decreased latency of generalized seizures in lesioned 12-day-old animals. EEG study demonstrated marked difference between lesioned and control rats. Lesioned rats had longer latencies and longer durations of the first rhythmic episode (following 20mg/kg PTZ) as compared to controls. After 40mg/kg of PTZ, 7 in 8 leisioned and 1 in 8 control rats exhibited clonic seizures. Cortical ischemic lesion during early development affected differently the susceptibility of rat's brain to three types of PTZ-induced seizures 5 and 18 days post photothrombotic insults.

EEG Pattern Analysis for Physiological Indicators of Mental Fatigue in Simulated Air Traffic Control Tasks

Objective: This study was designed to identify potential neurophysiologic markers and patterns of mental fatigue among air traffic controllers in their work environment.Background: The monitoring of mental fatigue in air traffic controllers has been of interest as their tasks involve high cognitive workload and are also critical to the safety of the public.Method: High-density electroencephalogram (EEG) was used to record 2-hour long air traffic control studies in eleven participants. Participants were asked to perform realistic tasks in a simulation, to operate a virtual air traffic control system. Fourier Transforms were used to estimate EEG power spectrum, statistical tests were implemented to reveal EEG spatial pattern changes caused by the time-on-task. The concept of mental state transition was introduced to study the development of certain mental states which are related to the mental fatigue. Results: The observation of EEG spectral data over a period of time revealed statistically significant changes spatially localized to central and parietal cortices. Rhythmic EEG activity within theta, alpha, and beta bands indicates transitions among mental states, which appear to be promising indicators for the development of mental fatigue. Mental fatigue indicated by the transition of mental states was estimated to approximately 70 minutes after the time on task. Application: This study can build the foundation to develop promising technologies for real time monitoring of mental fatigue, which will increase public safety and proper human resource planning.

Complete brain‐type creatine kinase deficiency in mice blocks seizure activity and affects intracellular calcium kinetics

Brain-type creatine kinase (CK-B) and ubiquitous mitochondrial creatine kinase (UbCKmit) act as components of local phosphocreatine ATP shuttles that help in the compartmentalization and maintenance of pools of high-energy phosphate molecules in both neurons and glial cells. We investigated the role of these brain-type creatine kinases during extreme energy-demanding conditions in vivo (generalized tonic-clonic seizures) and in vitro. The physiologic response of wild-types and mice lacking both CK-B and UbCKmit (CK--/--mice) to pentylenetetrazole (PTZ)-induced seizures was measured using electroencephalography (EEG) recordings and behavioral monitoring. In vitro intracellular Ca(2+) kinetics in hippocampal granule neurons were monitored upon single and repetitive depolarizations. PTZ induced in only a few CK--/-- mice PTZ seizure-like behavior, but in all wild-types a full-blown seizure. EEG analysis showed that preseizure jerking was associated with high-amplitude discharges. Wild-type EEG recordings showed continuous runs of rhythmic 4-6 Hz activity, whereas no rhythmic EEG activities were observed in the few CK--/-- mice that developed a behavioral seizure. All other CK--/-- mice displayed a sudden postictal depression without any development of a generalized seizure. Hippocampal granule neurons of CK--/-- mice displayed a higher Ca(2+) removal speed following repetitive KCl-induced depolarizations. Deficiency for creatine kinase is affecting brain energy metabolism and will likely contribute to the disturbance of seizure development. Because CK--/-- hippocampal neurons exhibited an increase in Ca(2+) removal rate of elevated intracellular levels, we conclude that altered Ca(2+) clearance in CK--/-- neurons could play a role in the abnormal EEG and seizure activity.

低酸素脳症患者における律動性EMG-EEG活動

A patient with posthypoxic cortical action myoclonus was studied using polygraphic EEG-EMG recording techniques and transcranial magnetic stimulation. The myoclonic jerks were not stimulus-sensitive, and were not associated with enhancement of the somatosensory evoked potential (SEP). The most prominent electrophysiological finding was that rhythmic EMG activity was produced when the patient attempted rapid voluntary movement. EEG-EMG polygraph indicated that the rhythmic EMG activity was preceded by rhythmic activity in the EEG recorded overlying the contralateral central region. The frequency of both EEG and EMG activity was the same (approximately 50 Hz). Treatment using a combination of clonazepam, carbamazepine and primidone diminished the action myoclonus, concomitant with the disappearance of the rhythmic EEG and EMG activity. In the sensorimotor cortex of the normal monkey and humans, oscillatory activity ranging between 20-50 Hz has been recorded in the local field potential. Our findings suggest that cortical hyperoscillation may produce this characteristic rhythmic EEG and EMG activity and may, in turn, be related to cortical action myoclonus.

Aspects du sommeil normal

Three types of sleep and wakefulness are distinguishable: wakefulness, NREM (non-rapid eye movement) sleep and REM sleep. Analysis of vigilance states is based on the polysomnography, a technique derived from electroencephalography (EEG), that need to record several variables including the EEG, the electromyogram, the electro-oculogram and other autonomic variables. Most laboratories adhere to the guidelines published by Rechtschaffen and Kales (1968) to score sleep through visual analysis, however the amplitude and frequency of rhythmic EEG activity could be well-quantified using spectral analysis algorithms. The regulation of main physiological functions - ventilatory, cardio-vascular, endocrine, digestive functions and thermoregulation - differs, depending on the states of sleep and wakefulness. Improved knowledge of these interactions and thus of sleep physiology has been helpful in the development of sleep medicine. Human sleep is regulated by three different processes: the circadian process that determines sleep timing, the homeostatic one that determines its need, and the ultradian process. Basic research (especially molecular genetics) on circadian rhythms is one of the most advanced in biology. Mental activities during sleep involve hypnagogic and hypnopompic hallucinations, mental activities collected by experimental awakenings during REM sleep periods, dreams and reflexive activity during slow wave sleep closed to mental activities during wakefulness. The mechanisms of mental activity generation remain obscure, in particular, it is still unknown whether one or two generators are responsible for dream and reflexive activity generation.

BOLD-contrast functional MRI signal changes related to intermittent rhythmic delta activity in EEG during voluntary hyperventilation—simultaneous EEG and fMRI study

Differences in the blood oxygen level dependent (BOLD) signal changes were studied during voluntary hyperventilation (HV) between young healthy volunteer groups, (1) with intermittent rhythmic delta activity (IRDA) ( N = 4) and (2) controls ( N = 4) with only diffuse arrhythmic slowing in EEG (normal response). Subjects hyperventilated (3 min) during an 8-min functional MRI in a 1.5-T scanner, with simultaneous recording of EEG (successful with N = 3 in both groups) and physiological parameters. IRDA power and average BOLD signal intensities (of selected brain regions) were calculated. Hypocapnia showed a tendency to be slightly lighter in the controls than in the IRDA group. IRDA power increased during the last minute of HV and ended 10–15 s after HV. The BOLD signal decreased in white and gray matter after the onset of HV and returned to the baseline within 2 min after HV. The BOLD signal in gray matter decreased approximately 30% more in subjects with IRDA than in controls, during the first 2 min of HV. This difference disappeared (in three subjects out of four) during IRDA in EEG. BOLD signal changes seem to depict changes, which precede IRDA. IRDA due to HV in healthy volunteers represent a model with a clearly defined EEG pattern and an observable BOLD signal change.