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P Bächer

Publications and source records attributed to P Bächer.

7 recordsLinked to original sources
PubMed1988

Development of the EEG of school-age children and adolescents. I. Analysis of band power.

Development in quantitative EEG parameters is studied for a sample of 158 normal children and adolescents aged 6-17 years. This is of interest both for increasing basic knowledge of human neurophysiology and for obtaining age standardized norms, useful in clinical research and applications. After selecting an appropriate epoch and correcting for EOG artifacts, the EEG at 8 derivations was submitted to spectral analysis in order to extract broad-band parameters in absolute and relative power. Change in EEG band power across age was quantified by polynomial regression analysis. This opened automatically the possibility to obtain age-standardized EEG norms. Development was for most EEG parameters non-linear, with more pronounced changes for absolute than for relative power. No sex differences and no pubertal spurt could be identified in contrast to most somatic quantities. A detailed statistical analysis revealed, however, that this might be due to using cross-sectional data. All bands except for alpha 2 decreased in absolute power, whereas the fast bands increased and the slow bands decreased in relative power. Strong evidence was found for a substituting process between theta activity and fast alpha activity.

Adolescent↗
PubMed1985

Test-retest reliability of spectral parameters of the EEG.

The topic of this paper is the intraindividual stability of the EEG at rest for repeated recordings with respect to two sets of spectral parameters. Variability arises due to changes in experimental conditions (such as vigilance) and also due to the inherent random elements of the EEG. The two sets of parameters considered are broad-band parameters and parameters characterizing rhythmic and 'diffuse' activity separately, derived from autoregressive fitting. In spite of some imprecision in the definition of the EEG at rest, satisfactory test-retest correlations were found. They proved to be quite homogeneous topographically, but not across frequency bands: delta power is less reliable and to some extent also beta activity, whereas the alpha bands perform well. The frequency of the alpha rhythm shows a good reliability and, given the difficulties involved with the concept, also the degree of synchronization. The power of rhythmic and of diffuse activity showed more modest retest correlations, probably to be attributed to methodological problems in determining these quantities. On the whole, the results confirm that the normal EEG can be treated as an intraindividually rather stable trait, that artifacts play a minor role in this respect and that 20 sec of activity are sufficient to reduce adequately the variability inherent in the EEG.

Adolescent↗
PubMed1984

EEG-responsiveness to eye opening and closing in mildly retarded children compared to a control group.

Changes in the ongoing EEG when repeatedly closing and opening the eyes are quantified and compared for a group of mildly retarded children and a matched control group. The most prominent changes occur for the alpha-rhythm at posterior derivations. Blocking of the alpha is faster than its restriction, but there is no group difference in this respect. Many of the amplitude changes are also quite similar for the two groups. The differences found are associated with a lowered arousal by the experimental group.

Adolescent↗
PubMed1983

Correlating EEG and IQ: a new look at an old problem using computerized EEG parameters.

Explorations of the relationship between EEG activity and scores of tests of intelligence have a long history. Results have been rather discrepant and several explanations can be offered for this. Almost all previous studies relied on parameters derived from a visual rather than a computerized analysis of the EEG. Here broad band spectral parameters were mainly used, and in addition the frequency of the dominant peak (at Pz, O1 and O2) between 6.5 and 14.0 Hz. All EEG parameters were standardized for age, as were tests of intelligence. Correlations of EEG with IQ were computed separately for a group of normal and a group of mildly retarded children. As postulated in advance, correlations were substantially higher for the retarded groups. Even more remarkable than the size of the correlations found was their pattern, associated with an interesting interpretation: the sign of the larger correlations was such that children developmentally more advanced in their EEG parameters had on the average higher IQ scores. Moreover, correlations were large for those frequency bands, and to a lesser degree for those derivations where we found a high developmental relevance in a previous investigation for the age range considered. Some disappointing or even discrepant results in earlier studies can be explained in the light of the results given here.

Brain↗
PubMed1983

The EEG of mildly retarded children: developmental, classificatory, and topographic aspects.

Our investigation was concerned with 25 children, 10-13 years old, with an IQ 50-70 ("mild mental retardation," following the ICD). Among these, 14 attended a school for the mentally retarded and 11 one for the learning disabled. A control group was recruited, matched in age, sex and social class. The unipolar 8-channel record of EEG at rest was subjected to blind clinical rating, and a computerized analysis (broad band spectral parameters delta, theta, alpha 1, alpha 2, beta 1, beta 2). A significantly higher frequency of paroxysms was found by the clinical rating. It also allowed the diagnosis of a maturational lag with respect to the items "maturity" and "prominence of alpha rhythm"). Spectral parameters differentiated the two matched groups particularly in bands and leads of developmental relevance (theta, delta, and fronto-central beta in absolute power and theta, delta occipitally and alpha 2, with the exception of frontal leads for relative power).: As is well known, the mentally retarded constitute a heterogeneous group: this could also be verified with respect to EEG activity for the segment of mild mental retardation. A multivariate classification by nonmetric multidimensional scaling yielded a subgroup of 10 children deviant with respect to its overall EEG activity and a group of 15 children within the normal range. This assignment did not overlap with the assignment to the two schools. By computing ratios of broad band power in antero-posterior and symmetric-interhemispheric leads a reduced topographic differentiation was found for the experimental group in their antero-posterior distribution.

Adolescent↗
PubMed1982

Transformations towards the normal distribution of broad band spectral parameters of the EEG.

In this report transformations are evaluated for obtaining normally distributed broad band spectral parameters (both for absolute and relative power) in a sample of healthy individuals. This problem leads automatically to the question of defining a normative sample, both in terms of sampling and recording conditions; as to the latter, the electro-oculogram proved to be crucial. For relative power the transformation log(x/(1-x)) was excellent in all regards, whereas the best transformation for absolute power--log(x)--was not fully satisfactory for all bands.

Adolescent↗