Continuous EEG monitoring in the intensive care unit: an overview.

Due to technological advances, it is now feasible to record continuous digital EEG (CEEG), with or without video, in critically ill patients and review recordings remotely. Nonconvulsive seizures (NCSzs) are more common than previously recognized and are associated with worse outcome. The majority of seizures in ICU patients are nonconvulsive and will be missed without CEEG. Factors associated with an increased risk for NCSzs include coma, prior clinical seizures, CNS infection, brain tumor, recent neurosurgery, and periodic epileptiform discharges. In addition to detecting seizures, CEEG is also useful for characterizing paroxysmal spells such as posturing or autonomic changes, detecting ischemia, assessing level of sedation, following long-term EEG trends, and prognosticating. Most NCSzs will be detected in the first 24 hours of CEEG in noncomatose patients, but longer recording periods may be required in comatose patients or in those with periodic epileptiform discharges. EEG patterns in encephalopathic or comatose patients are often equivocal. How aggressively to treat NCSzs and equivocal EEG patterns in these patients is unclear and requires further research. Real-time detection of ischemia at a reversible stage is technologically feasible with CEEG and should be developed into a practical form for prevention of in-hospital infarction in the near future.     

Cortical motor reorganization after paraplegia: an EEG study.

OBJECTIVE: To determine whether a previously identified posterior reorganization of the cortical motor network after spinal cord injury (SCI) is correlated with prognosis and outcome. METHODS: We applied the techniques of high-resolution EEG and dipole source analysis to record and map the motor potentials (MPs) of the movement-related cortical potentials in 44 patients after SCI. Twenty normal controls were also tested. Results were analyzed using a distance metric to compare MP locations. EEG was coregistered with individual specific MR images and a boundary element model created for dipole source analysis. RESULTS: MPs with finger movements were mapped to a posterior location in 20 of 24 tetraplegics compared with normal controls. Two patients, one studied 4 and one 6 weeks after injury, initially had posterior MPs that, on serial testing, moved to an anterior position with recovery. Dipole source localization of the MP generators confirmed these results. Nine of 20 paraplegics had a posterior MP location with actual or attempted toe movements. All 5 patients who could move their toes had posterior MPs. The MP was posterior in 4 of the 15 paralyzed patients. This is a significant difference in proportions. The only patient with paraparesis whose testing was repeated had an MP that moved to an anterior position with recovery. CONCLUSIONS: Posterior reorganization has a significant relationship to prognosis in paraplegia and is reversed in some SCI patients who recover function. Posterior reorganization may result from a preferential survival of axons that originate in somatosensory cortex and contribute to the corticospinal tract. These preliminary results should be verified by a larger prospective study.     

Non-epileptiform EEG abnormalities: an overview

More than 80 years after its introduction by Hans Berger, the electroencephalogram (EEG) remains as an important supplementary examination in the investigation of neurological disorders and gives valuable and accurate information about cerebral function. Abnormal EEG findings may include ictal patterns, interictal epileptiform activity and non-epileptiform abnormalities. The aim of this study is to make an overview on the main non-epileptiform EEG abnormalities, emphasizing the pathologic findings and the importance of their recognition, excluding periodic patterns and EEG physiologic changes. Scientific articles were selected from MEDLINE and PubMed database. The presence of non-epileptiform EEG abnormalities provide evidence of brain dysfunction that are not specific to a particular etiology and may be related to a number of disorders affecting the brain. Although these abnormalities are not specific, they can direct attention to the diagnostic possibilities and guide the best treatment choice.     

Full-band EEG (FbEEG): an emerging standard in electroencephalography.

While enormous resources have been recently invested into the development of a variety of neuroimaging techniques, the bandwidth of the clinical EEG, originally set by trivial technical limitations, has remained practically unaltered for over 50 years. An increasing amount of evidence shows that salient EEG signals are observed beyond the bandwidth of the routine clinical EEG, which is typically around 0.5-50 Hz. Physiological and pathological EEG activity ranges at least from 0.01 Hz to several hundred Hz, as demonstrated in recordings of spontaneous activity in the immature human brain, as well as during epileptic seizures, or various kinds of cognitive tasks and states in the adult brain. In the present paper, we will review several arguments leading to the conclusion that elimination of the lower (infraslow) or higher (ultrafast) bands of the EEG frequency spectrum in routine EEG leads to situations where salient and physiologically meaningful features of brain activity are ignored. Recording the full, physiologically relevant range of frequencies is readily attained with commercially available direct-current (DC) coupled amplifiers, which have a wide dynamic range and a high sampling rate. Such amplifiers, combined with appropriate DC-stable electrode-skin interface, provide a genuine full-band EEG (FbEEG). FbEEG is mandatory for a faithful, non-distorted and non-attenuated recording, and it does not have trade-offs that would favor any frequency band at the expense of another. With the currently available electrode, amplifier and data acquisition technology, FbEEG is likely to become the standard approach for a wide range of applications in both basic science and in the clinic.     

Role of cerebral cortex in human postural control: an EEG study.

OBJECTIVE: It was our primary objective to provide evidence supporting the existence of neural detectors for postural instability that could trigger the compensatory adjustments to avoid falls. METHODS: Twelve young healthy subjects performed self-initiated oscillatory and discrete postural movements in the anterior-posterior (AP) directions with maximal range of motion predominantly at ankle joint. Movements were recorded by the system and included force plate and EMG, and EEG measures from 25 electrode sites. The center of pressure dynamics and stability index were calculated, and EEG potentials both in voltage and frequency domains were extracted by averaging and Morlet wavelet techniques, respectively. RESULTS: The initiation of self-paced postural movement was preceded by slow negative DC shift, similar to movement-related cortical potentials (MRCP) accompanying voluntary limb movement. A burst of gamma activity preceded the initiation of compensatory backward postural movement when balance was in danger. This was evident for both oscillatory and discrete AP postural movements. The spatial distribution of EEG patterns in postural actions approximated that previously observed during the postural perceptual tasks. CONCLUSIONS: The results suggest an important role of the higher cortical structures in regulation of posture equilibrium in dynamic stances. Postural reactions to prevent falls may be triggered by central command mechanisms identified by a burst of EEG gamma activity. SIGNIFICANCE: The results from this study contribute to our understanding of neurophysiological mechanisms underlying the cortical control of human upright posture in normal subjects.     

Subcortical functioning in obsessive-compulsive disorder: an exploratory EEG coherence study.

BACKGROUND: Given the paucity of quantitative EEG studies using coherence measures to understand the electrophysiological functional integrity of sub-cortical structures in obsessive-compulsive disorder, the current study was carried out. METHODS: We obtained EEG coherence values for 20 adult OCD patients (10 males; 10 females) and 19 appropriately matched healthy controls across delta (0.5-3.5 Hz), theta (4-7.5 Hz), alpha (8-12 Hz), beta1 (12.5-20 Hz) and beta2 (20.5-30 Hz) bands. As coherence between distant brain regions reflects physiological activities at sub-cortical neural networks, we chose EEG channels at four distant brain regions - anterior interhemispheric, posterior interhemispheric, fronto-temporal and fronto-occipital. RESULTS: In comparison to controls we found significant increase of theta band EEG coherence in the fronto-occipital region in OCD patients (P = 0.045) which did not correlate significantly with either medication status or disease severity. CONCLUSION: This EEG coherence study that suggests hyperactivity at subcortical circuitry in OCD patients is in agreement with existing neuro-imaging findings. Furthermore, this finding provides external validity for sub-cortical dysfunction hypothesis of OCD.     

Psychomotor EEG variant of Gibbs: an association with underlying structural pathology.

OBJECTIVE: To describe the association between a unilateral mid-temporal rhythmic theta discharge ("psychomotor variant of Gibbs") with neuroimaging-demonstrated underlying mass lesion. METHODS: Standard routine awake and scalp electroencephalography, continuous video-EEG monitoring and magnetic resonance brain imaging were employed in the diagnostic work-up of a 9-year-old boy with a severe behavioural disturbance and episodic outbursts of aggression. RESULTS: EEG showed a unilateral mid-temporal rhythmic discharge which was continuous in drowsiness and which remained confined to the right hemisphere. MRI showed a lesion in the temporal horn of the right lateral ventricle displacing superiorly the white matter stem of the right temporal lobe. CONCLUSION: A rhythmic mid-temporal theta discharge, commonly regarded as a benign EEG variant, may, in some patients, reflect underlying structural pathology. Neuroimaging should be considered particularly when this EEG pattern remains confined to one hemisphere.     

Theta bursts: an EEG pattern in normal subjects practising the transcendental meditation technique.

In a survey of the EEG characteristics of persons practising the Transcendental Meditation technique, 21 of 78 people demonstrated intermittent prominent bursts of frontally dominant theta activity. On the average across subjects, the theta bursts occurred about every 2 min, had an average duration of 1.8 sec, and an average maximal amplitude of 135 muV. Typically, the bursts were preceded and followed by alpha rhythm. Subject reports elicited during theta bursts indicated pleasant states with intact situational orientation and no subjective experiences related to sleep. Fifty-four non-meditating controls showed no theta bursts during relaxation and sleep onset. It is hypothesized that theta burst may be the manifestation of a state adjustment mechanism which comes into play during prolonged low-arousal states, and which may be related to EEG patterns of relaxation in certain behavioural conditions.     

Nonlinear dynamical analysis of EEG and MEG: review of an emerging field.

Many complex and interesting phenomena in nature are due to nonlinear phenomena. The theory of nonlinear dynamical systems, also called 'chaos theory', has now progressed to a stage, where it becomes possible to study self-organization and pattern formation in the complex neuronal networks of the brain. One approach to nonlinear time series analysis consists of reconstructing, from time series of EEG or MEG, an attractor of the underlying dynamical system, and characterizing it in terms of its dimension (an estimate of the degrees of freedom of the system), or its Lyapunov exponents and entropy (reflecting unpredictability of the dynamics due to the sensitive dependence on initial conditions). More recently developed nonlinear measures characterize other features of local brain dynamics (forecasting, time asymmetry, determinism) or the nonlinear synchronization between recordings from different brain regions. Nonlinear time series has been applied to EEG and MEG of healthy subjects during no-task resting states, perceptual processing, performance of cognitive tasks and different sleep stages. Many pathologic states have been examined as well, ranging from toxic states, seizures, and psychiatric disorders to Alzheimer's, Parkinson's and Cre1utzfeldt-Jakob's disease. Interpretation of these results in terms of 'functional sources' and 'functional networks' allows the identification of three basic patterns of brain dynamics: (i) normal, ongoing dynamics during a no-task, resting state in healthy subjects; this state is characterized by a high dimensional complexity and a relatively low and fluctuating level of synchronization of the neuronal networks; (ii) hypersynchronous, highly nonlinear dynamics of epileptic seizures; (iii) dynamics of degenerative encephalopathies with an abnormally low level of between area synchronization. Only intermediate levels of rapidly fluctuating synchronization, possibly due to critical dynamics near a phase transition, are associated with normal information processing, whereas both hyper-as well as hyposynchronous states result in impaired information processing and disturbed consciousness.     

EEG in the elderly: seizures vs. syncope.

The EEGs of elderly patients with a definite seizure disorder (161 patients; 302 EEGs) were compared to patients with "syncope" (122 patients; 133 EEGs), especially to determine if the latter patients were sufficiently similar to the seizure patients that the syncope could be viewed as a seizure phenomenon. The two groups were similar only by the predominance of females in both groups (61-62%) and otherwise were very different. The seizure group had a higher incidence of (1) etiology (83 vs. 39%), (2) epileptiform discharges (93 vs. 49%), with a different location, more often parasagittal, and different number often with active or very active foci, (3) frontal slow waves, (4) more severe slow wave abnormalities, (5) slower background frequencies, that were less well organized and developed and (6) abnormal records. The conclusion is that the syncope patients as a group are usually not simply seizure patients. Regardless of etiology, the patients with "syncope" (33% with cerebrovascular and 21% cardiac etiologies) showed nearly a 50% incidence of epileptiform discharges, demonstrating a complex interrelationship between cardiac and cerebral mechanisms, which are discussed. The conclusion is that epileptiform activity in elderly patients with syncope is likely to be mildly epileptogenic, and may require additional cardiovascular mechanisms to generate an attack of unconsciousness.     

Video EEG telemetry using an ambulatory EEG cassette recorder

A system of video/EEG monitoring is described which is complementary to out-patient ambulatory EEG recording and prolonged hospital admission for intensive assessment. An ambulatory EEG cassette recorder is incorporated in the system which increases the usefulness of this equipment. In addition all the recorded EEG may be rapidly reviewed. This system has proved valuable in the management of selected patients seen in a special clinic for epilepsy.     

Otto lowenstein, pioneer pupillographer.

Otto Lowenstein, a pioneer in the study of pupil function, began his professional life as an academic neuropsychiatrist at the University of Bonn with an interest in experimental psychology. From his teacher Alexander Westphal, he developed a fascination with the pupil. He invented ingenious recording devices and took motion pictures of the pupils, graphing their movements. Forced to flee Nazi persecution in 1933, he took temporary refuge in Switzerland and eventually sacrificed a flourishing career in Europe to escape to New York. During the next 25 years, he collaborated with Irene Loewenfeld on experiments and publications related to the clinical use of pupillary signs and introduced pupillography to American neuro-ophthalmology.     

EEG operant conditioning in a monkey model: II. EEG spectral analysis.

EEG power spectral analysis was studied from 14 (alumina-gel) chronically epileptic, undrugged monkeys during an EEG operant conditioning experiment. The composite profile of the average epileptic monkey shows the majority of power to be below 10 Hz. Because of the large variance in the data, no significant changes in the EEG power spectra could be detected as a function of conditioning. The possible reasons for this large variance are discussed. Hypothesis from previous human "biofeedback" studies would allow the prediction that those frequencies corresponding to the mu and sensory-motor-rhythm should negatively covary with seizure frequency. Data from this study did not support such assertions. The method of using spectral analysis for quantifying changes in the EEG which covary with operant conditioning is evaluated.