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.

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.

Rare events and the CNV--the oddball CNV.

Event-related brain potentials (ERPs), such as Nd and P300, change as a function of the proportion of time if a rare, significant, stimulus occurs. This 'oddball' paradigm has had a significant influence on the interpretation of ERPs in terms of the psychological and information-processing functions they reflect. Interpretations of transient components have differed considerably from that of the sustained potential known as the Contingent negative Variation (CNV), the latter appearing to reflect proactive rather than reactive brain processes. However, experiments in monkeys indicated that the CNV was also sensitive to the oddball effect. The purpose of this experiment was to replicate that finding in humans. The CNVs and P300s of five male and five female college students were studied under three conditions involving different proportions of two types of warning stimuli in a cued reaction time task (paired tone and light). The proportions of one of the warning stimuli, with respect to the total number of trials, were 0.10, 0.30 and 0.50. P300s were larger when elicited by rare warning tones only in the 0.10 condition with maximum P300 amplitude at the parietal site. CNVs at frontal and central areas were larger when the warning cue was the rare event, but there was no effect at the parietal site. These findings may require a rethinking of specific information processing interpretations of other endogenous ERPs, although the results also indicate that the 'oddball' effect on the P300 and CNV was distinctive in terms of scalp distributions and sensitivity to the manipulation.

[The anticipatory potential (contingent negative variation) as an indicator of neuronal information processing in relation to changes in slow potentials in the EEG]. / Die Erwartungswelle (CNV) als Indikator neuronaler Informationsverarbeitung in Abhängigkeit von spontanen Gleichspannungsänderungen im EEG.

The aim of this study was to investigate the interaction between spontaneous Slow Potential Shifts (SPSs) and the probability effect on CNV amplitudes. Fifteen right-handed volunteers participated in this experiment. The presentation of the stimuli was triggered by spontaneous SPSs (duration: 2 seconds, mean-amplitude: 10 microV) in the EEG signal at Cz. Thus, two different S1s (S1a: 1500 Hz, S1b: 2000 Hz) were presented in a random order with a fixed probability of occurrence of 0.8 for S1a and 0.2 for S1b. Each S1 was followed by a light stimulus (S2) with a constant ISI of 4 seconds. According to the cue, the subjects had to push the left (S1a) or the right (S1b) response button as fast as possible with their right index finger. The order of the 4 experimental conditions (stimulus presentation triggered by negative or positive shifts and recording of negative or positive shifts without any stimuli) in which each subject participated was balanced across subjects. Several significant effects could be found by means of a two-way ANOVA for repeated measures (condition x recording site): Negative shifts were accompanied by smaller CNVs as well as PINVs (resolution deficits) at all recording sites; the probability effect was found to be significant in the positive shift condition at F3, F4, and Cz, but not in the negative shift condition except at Cz for the E-wave. CNVs triggered by negative shifts only showed a significant correlation (-.55) with reaction time. These results together favor a two-component model suggesting that SPSs, spontaneous and evoked, are largely generated by glia depolarization, which is evoked by but outlasts neuronal activity.

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.