M. Leodolter

Technical requirements for high-quality scalp DC recordings

An easily applicable procedure for obtaining high-quality scalp DC recordings is described. A sophisticated amplifier technique, skin potential reduction and stabilisation of electrode potential make up this procedure.

Cortical activity of good and poor spatial test performers during spatial and verbal processing studied with Slow Potential Topography

Whether essential processing of spatial information is lateralized asymmetrically in the human cortex is still a matter of debate. In this study, items of an Item Response Theory calibrated test for spatial ability were used to ensure stimulus homogeneity and validity. Subjects were preselected as extreme groups of good and poor spatializers. Mapping of true DC-recorded slow potential shifts (SPSs) resulted in distinctly discriminable topographies with spatial and verbal-analytic material as well as with spatial performance groups within the spatial block. Left fronto-central negativity maxima in the verbal condition clearly contrasted with occipito-parietal peak activity in the spatial condition. Poor spatializers showed higher amplitudes as well as a tendency to asymmetric activity in right parietal (parieto-temporal) areas, whereas in good spatializers the activity was localized symmetrically in occipital and occipito-parietal regions. The findings emphasize the importance of the right posterior cortex for spatial processing (negativity maxima at occipital and right parietal sites) and suggest a task-specific lower cortical efficiency or, seen from a processing perspective, a higher Investment of Cortical Effort (ICE) on the part of poor spatializers.

Loss of control and negative emotions: a cortical slow potential topography study.

This study investigated cortical steady potential changes in 18 subjects while processing a series of solvable arithmetic items (induction of control) that became unsolvable (withdrawal of control). Two different phases of induction and withdrawal of control (early and late) were dealt with separately in the analyses. The DC EEG was recorded from 20 locations. In all experimental conditions the overall slow potential topographical pattern did not change. However, negative-going DC shifts at occipito-parietal and left posterior-frontal regions were observed during induction of control whereas a generalized positive-going DC shift developed during phases of withdrawal of control. This positive-going shift persisted for the duration of the item presentation, resulting in pronounced positive values at temporal sites. The authors assume that temporal lobe activity (inferior and/or ventral surface) correlated to emotional/motivational processes that was picked up via the linked mastoid reference locations contributed essentially to these observed phenomena.

Possible Glial Contribution in the Electrogenesis of SPs

Since the very beginning of electroencephalography DC potentials were known as parts of the compound brain electrical signal. The recording equipment used in those days (galvanometer and nonpolarisable electrodes) had no high pass filter components. Therefore, Caton (1875), Beck (1890) and Beck and Cybulski (1892) described the “steady potential level” and DC potentials accompanying stimuli of long duration. However, subsequent electroencephalography focused on the frequency range of about 2 to 30 Hz because of developments in electronics and the dramatic artefact reduction due to the use of high pass filters.