Correction of EOG Artifacts in Event-Related Potentials of the EEG: Aspects of Reliability and Validity

Correction of EOG artifacts using a regression approach is evaluated in terms of reliability and validity. Transmission rates are estimated for eight EEG channels in 67 subjects. The trimmed group means of these rates are shown to provide reliable measures. Eye artifact correction based on these group means is superior to the conventional rejection in terms of reducing correlation between EOG and EEG.     

Selective attention is impaired in amyotrophic lateral sclerosis--a study of event-related EEG potentials

In humans, selective attention is assumed to be under control of the frontal lobe. A significant proportion of patients with amyotrophic lateral sclerosis (ALS) shows impairments in various tasks touching frontal lobe function. We, therefore, undertook a study of event-related EEG potentials (ERPs) in eight non-demented ALS patients in order to investigate a possible deficit of auditory selective attention: tones were presented in random sequence to the left or right ear, one of which was to be attended. The negative shift of the ERPs evoked by attended tones in relation to unattended tones ('processing negativity': PN) was smaller in ALS patients than in age-matched healthy control persons. This was true for Fz and Cz and for both a slow and a fast presentation rate of the tones. In the patients, reduced PN amplitude correlated with functional motor impairment. The utility of ERP testing to assess impaired frontal lobe function is shown for the first time in ALS patients. The results of our study fit to recent positron emission tomography (PET) and fMRI data.     

Spatial S-R compatibility with centrally presented stimuli. An event-related asymmetry study on dimensional overlap

Lateral presentation of relevant information facilitates manual responses if the side of relevant information corresponds to the side of the response. Recently, temporally overlapping EEG asymmetries over the central motor cortex and posterior sites were reported as a possible correlate of the sensory-motor integration of spatial information. The present study investigated whether sensory-motor integration of spatial information can occur with symbolic spatial information the same way as with laterally presented stimuli. The task required participants to respond to arrows (target stimuli), which were "flanked" (from above and below) by neutral stimuli or by other arrows (compatible or not). In Experiment 1, this task was compared to the same task with letters as stimuli and to an incompatible task where participants had to respond "against" the arrow direction. The effect of the flankers on response times was largest if subjects had to respond to the arrows in the common way. This was also the only task of Experiment 1 for which marked EEG asymmetries related to the direction of the flankers were observed. In Experiment 2, the onsets of target stimulus and flankers differed in time. Event-related lateralizations of the EEG over sensory and primary motor areas--as a lateralized readiness potential--were always, apparently automatically, evoked by flanking arrows, indicating automatic response activation evoked by symbolic spatial information. In accordance to recent theories of temporally decaying response activation, manual responses were affected only if the target was either shortly preceded by or appeared simultaneously with the flankers. The temporal overlap of EEG asymmetries related to direction encoding, automatic response activation, and to response preparation indicated that a widespread cortical network is activated by a salient directional information that enables subjects to respond quickly if the directional code of the stimulus overlaps with the directional code of the response.     

An evaluation of methods for single-trial estimation of P3 latency

This study investigated the validity of procedures for estimating the P3 complex in single trials. In “pseudo‐real” simulations of the N1‐P2 complex of the occipital visual‐evoked potential, Möcks, Köhler, Gasser, and Pham (1988) had reported that their maximum‐likelihood method (Pham, Möcks, Köhler, & Gasser, 1987) performed better than Woody's (1967) method. Using pseudo‐real simulations of auditory oddball data, we wanted to know whether this finding also held true for the P3 complex. The performance of three methods was studied: peak picking, Woody's method, and Pham et al.'s method (as well as an extension of this latter method). Performance of all methods critically depended on the signal‐to‐noise ratio. There was some advantage for the more sophisticated methods, particularly when signal‐to‐noise ratios were realistic. “Good” trials may be selected by all methods, to improve the signal‐to‐noise ratio, but this selection entails the risk of bias. Further research should investigate whether these conclusions also hold true when the P3 complex consists of more than one component.     

New evidence for the theory of the stork

Data from Berlin (Germany) show a significant correlation between the increase in the stork population around the city and the increase in deliveries outside city hospitals (out-of-hospital deliveries). However, there is no correlation between deliveries in hospital buildings (clinical deliveries) and the stork population. The decline in the number of pairs of storks in the German state of Lower Saxony between 1970 and 1985 correlated with the decrease of deliveries in that area. The nearly constant number of deliveries from 1985 to 1995 was associated with an unchanged stork population (no statistical significance). However, the relevance of the stork for the birth rate in that part of Germany remains unclear, because the number of out-of-hospital deliveries in this area is not well documented. A lack of statistical information on out-of-hospital deliveries in general is a severe handicap for further proof for the Theory of the Stork.     

Indoor survey of moulds and prevalence of mould atopy in Israel

BACKGROUND: Moulds are ubiquitous indoor as well as outdoor allergens and therefore potential candidates for indoor environmental control measures. However, very few studies have been performed to examine the significance of indoor moulds in allergic diseases and the effectiveness of measures to reduce the quantity of indoor moulds has not been established. OBJECTIVE: To determine the significance and the contribution of moulds to allergic manifestations. METHODS: Prevalence of allergic rhinitis and asthma in 395 members of a rural community were examined by questionnaire and examination of medical files. The atopic status in general and allergy to moulds was determined by skin-prick tests (SPTs) to a panel of aeroallergens including Aspergillus, Penicillium, Alternaria and Cladosporium. A study of indoor mould levels was performed by placing SDA plates in 59 houses. The type of fungi and the number of colonies from each species were recorded. RESULTS: Forty-two subjects, comprising 10.9% of the study group had positive SPT to moulds, 61.9% of those were classified as symptomatic. When taking into account individuals with a borderline positive SPT to moulds, an additional 23 had positive results. Of the 65 mould-positive subjects, 48% were symptomatic and of the 13 who were allergic to moulds alone, only two had allergic symptoms. Viable moulds were recovered from all 59 houses examined. The most common isolated genus was Aspergillus, followed by Penicillium, Alternaria and Cladosporium. Aspergillus was also the most abundant mould in houses. There was no significant correlation between the abundance of moulds, positive SPT to that mould and symptomatology. CONCLUSIONS: Viable moulds are common in houses in temperate climates. Allergy to moulds itself has a low predictive value to development of allergic symptoms, but allergy to moulds in otherwise atopic subjects increases the risk of symptomatic allergic disease.     

Control of hand movements after striatocapsular stroke: high-resolution temporal analysis of the function of ipsilateral activation.

OBJECTIVE: Hemiparesis due to infarction of the middle cerebral artery has become an increasingly important focus of research on cortical plasticity. Positron emission tomography and functional magnetic resonance imaging studies in such patients found involvement of the hemisphere ipsilateral to the affected hand related to movements of this hand. To understand the function of this ipsilateral activation, the present study investigated movement-related electroencephalogram (EEG) potentials in patients and healthy control subjects to measure timing of ipsi- and contralateral activation relative to movement onset. METHODS: Thirteen patients were investigated in their chronic stage. Their pyramidal tracts were affected by infarctions of the middle cerebral artery at striatocapsular level. EEG potentials were recorded from 26 scalp electrodes while patients were pressing a key with their right or left index finger within a warned choice-response task. RESULTS: Beginning 200 ms before responses of the affected hand, there was normal contralateral preponderance of EEG negativity. Briefly after response onset, however, the other unaffected hemisphere, ipsilateral to the responding hand, became additionally active. This pattern did not occur with responses made by the unaffected hand nor in healthy participants. CONCLUSIONS: The timing of the onset of ipsilateral activity precludes its role in response initiation. Rather, this activity may indicate reflex-like activation of the unaffected motor system to compensate for possible failure of the affected hand.     

Changes in connectivity profiles as a mechanism for strategic control over interfering subliminal information

Human behavior can be influenced by information that is not consciously perceived. Recent behavioral and electrophysiological evidence suggests, however, that the processing of subliminal stimuli is not completely beyond an observer's conscious control. The present study aimed to characterize the cortical network that implements strategic control over interfering subliminal information at multiple stages. Fourteen participants underwent functional magnetic resonance imaging (fMRI) scanning while performing a metacontrast masking paradigm. We systematically varied the amount of conflicting versus non-conflicting trials across experimental blocks, and behavioral performance demonstrated strategic effects whenever a high proportion of subliminal prime stimuli induced response competition. A psychophysiological interaction analysis revealed the pre-supplementary motor area (pre-SMA) to exhibit context-dependent covariation with activation in the lateral occipital complex (LOC) and the putamen. The pre-SMA thereby appears to fulfill a superordinate function in the control of processing subliminal information by simultaneously modulating perceptual analysis and motor selection.