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PubMed1998

Computer-based electroencephalography: technical basics, basis for new applications, and potential pitfalls.

EEG has been recorded on paper-based analog systems for over 50 years. In the past 5 years, computer-based digital systems have become more widely used. Digital systems eliminate some artifacts that plagued analog recordings but introduce subtle new problems including aliasing and dynamic range. Digital systems allow reformatting of the same EEG segment using different gain, filter and montage settings. The digital signal allows for measurement and computations on the EEG, leading to applications such as power spectrum, topographic mapping, and spike or seizure detection.

Electroencephalography↗
PubMed1998

The future of electroencephalography in assessing neurocognitive functioning.

High temporal resolution is necessary to resolve the rapidly changing patterns of brain activity underlying mental function. Additionally, simple, non-intrusive equipment is needed to routinely measure such functions in doctors' offices, at home and work and in other naturalistic contexts as people perform normal everyday activities. When compared with all other modalities for measuring higher brain functions, EEG is unique in that it has both these attributes. Two factors are limiting the further development and application of EEG for measuring cognitive functioning: a technical one that is easy to overcome and a sociological one that is more problematic. The technical limitation is that traditional EEG technology and practice provides insufficient spatial detail to identify relationships between brain electrical events and structures and functions visualized by magnetic resonance imaging (MRI) or other modalities. Recent advances overcome this problem by recording EEGs from more electrodes, by registering EEG data with anatomical information from each subject's MRI, by correcting the distortion caused by volume conduction of EEG signals through the skull and scalp, and by computing hypotheses about the sources of signals recorded at the scalp. The sociological limitation is that clinical EEGs are mostly performed by neurologists with no particular special interest in cognitive brain function, while cognitive research using EEG is largely done by psychology professors and their graduate students with no clinical ambitions. The diminishing clinical role of traditional EEGs in localizing lesions in the brain, and the obvious and insistent medical need for inexpensive and accessible tests of cognitive brain functioning may serve to soon dissipate this sociological obstruction. This will lead to a golden age of EEG in which Hans Berger's vision of the EEG as a window on the mind will be realized. Rather than slowly fading into obsolescence, EEG will retain its role as the primary means of measuring higher brain function when the purpose is not 3D localization per se, and will serve as an invaluable complement to functional MRI in those instances when both high temporal and high spatial resolution are required.

Cognition↗
PubMed1998

Quantitative electro-oculography and electroencephalography as indices of alertness.

Even though both electro-oculography (EOG) and EEG have been widely used for assessing alertness, the relationship between these two measures has not yet been clarified at various alertness levels. We estimated the frequencies of eye movements faster than 15 degrees/s (NoEM15) and EEG power at every 0.5 Hz step frequency point, quantitatively as well as continuously from alert to very light sleep (Stage 1) in 14 healthy adults. We devised a new EOG derivation for a computerized analysis, because conventional EOG recordings suffer from EEG contamination and have been analyzed manually. EOG electrodes were attached to the left orbitale in this study. The eye movements were detected as peaks in differentiated EOG signals. Significant correlations were found between NoEM15 and EEG powers at several frequency points, mainly in the alpha and beta bands. Though fluctuating EEG components in close correspondence to the frequency of the eye movements varied depending on the individual, EEG power at the peak frequency of the awake state was most closely associated with the eye movements. A broad band power that centers at the peak frequency may be a better measure for alertness assessment than powers in fixed bands.

Adolescent↗
PubMed1998

Quantitative electroencephalography in amyotrophic lateral sclerosis.

OBJECTIVES: The authors evaluated quantitative EEG (QEEG) in patients with amyotrophic lateral sclerosis (ALS), in order to see if the confined cortical degeneration found in anatomical and functional examinations of central (rolandic) regions could give rise to abnormalities of cortical electrical activity. MATERIAL AND METHODS: Eighteen patients with ALS were compared with 14 control subjects comparable for age and sex. The QEEG analysis was blind to the clinical data. Frequency analysis of 30 EEG epochs, each of 2.6 s duration, was performed. RESULTS: QEEG in ALS patients showed a significant well-localized decrease of alpha activity only in the central regions, while theta and delta relative power did not show any difference from controls. CONCLUSION: We suggest that QEEG is able to show evidence of subtle EEG changes probably due to loss of cells in the somatomotor cortex selectively affecting the generator sites.

Adult↗
PubMed2001

Changes in striatal electroencephalography and neurochemistry induced by kainic acid seizures are modified by dopamine receptor antagonists.

We investigated the involvement of striatal dopamine release in electrographic and motor seizure activity evoked by kainic acid in the guinea pig. The involvement of the dopamine receptor subtypes was studied by systemic administration of the dopamine D(1) receptor antagonist, R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390; 0.5 mg kg(-1)), or the dopamine D(2) antagonist, (5-aminosulphonyl)-N-[(1-ethyl-2-pyrrolidinyl)-methyl]-2-methoxybenzamide (sulpiride, 30 mg kg(-1)). Microdialysis and high performance liquid chromatography were used to monitor changes in extracellular levels of striatal dopamine and its metabolites, glutamate, aspartate and gamma-amino-butyric acid (GABA). These data were correlated with changes in the striatal and cortical electroencephalographs and clinical signs. We found that, although neither dopamine receptor antagonist inhibited behavioural seizure activity, blockade of the dopamine D(1)-like receptor with SCH 23390 significantly reduced both the 'power' of the electrical seizure activity and the associated change in extracellular striatal concentration of glutamate, whilst increasing the extracellular striatal concentration of GABA. In contrast, blockade of the dopamine D(2)-like receptor with sulpiride significantly increased the extracellular, striatal content of glutamate and the dopamine metabolites. These results confirm previous evidence in other models of chemically-evoked seizures that antagonism of the dopamine D(1) receptor tends to reduce motor and electrographic seizure activity as well as excitatory amino-acid transmitter activity, while antagonism of the dopamine D(2) receptor has relatively less apparent effect.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1988

The first seizure in adult life. Value of clinical features, electroencephalography, and computerised tomographic scanning in prediction of seizure recurrence.

408 adults (age 16 and over) were followed up after their initial seizure. The actuarial risk of recurrence was highest in the early weeks. For those seen within the first week, the risk of recurrence was 52% by the end of 3 years. In univariate analysis, the only clinical variable that was associated with recurrence was the time of day at which the initial seizure occurred. There was a tendency, that did not reach statistical significance, for younger age (less than 50 years) and a family history of seizures of any type, including febrile convulsions, to be associated with recurrence. Such risk factors appear to be additive, so that the risk of recurrence at 1 year for a subject with all three factors is about three times that of a subject with none of them. Sex, type of seizure, and features of the electroencephalogram were not of predictive value. Computerised tomographic scanning revealed tumours in 3% of subjects, and these individuals were particularly likely to have recurrent seizures.

Adolescent↗
PubMed2000

Novel method of monitoring electroencephalography at the site of microdialysis during chemically evoked seizures in a freely moving animal.

This paper covers the design, development and operation of a novel piece of equipment, based around the CMA/12 guide probe (Carnegie Medicin, Sweden), which offers a low cost alternative for monitoring EEG at the site of microdialysis in a freely moving animal. This equipment is entirely based on commercially available parts, and thus can be easily replicated. Moreover, it is less intrusive than earlier models, offering advantages for experiments in which behavioural testing or chronic monitoring is required. We illustrate its use in a study of changes in electrical seizure activity, in both cortex and basal nuclei, evoked by the administration of the chemoconvulsant soman. The inference from the many experimental paradigms looking at the mechanisms of chemoconvulsants is that paroxysmal discharges are a better correlate of seizure activity than behavioural signs. The correlation of the EEG with extracellular neurotransmitter data, over a period of hours post-injection of chemoconvulsant, allows the determination of whether extracellular neurotransmitter changes are a cause or consequence of the evoked electrical activity.

Animals↗