Search PubMed⌕ Search

Biomedical subjects

R Verleger

Publications and source records attributed to R Verleger.

18 recordsLinked to original sources
PubMed1992

Late cognitive event-related potentials in adult Down's syndrome.

Event-related electroencephalogram (EEG) potentials (ERPs) using two different tasks were measured in 14 adults with Down's syndrome (DS; mean age 32 years) without clinically detectable cognitive decline. Two groups, young healthy (YH) and old healthy (OH) adults, served as controls. In the oddball task, DS had prolonged N1 and earlier P2 latencies than the control groups. P3 latency was delayed in comparison to YH. In the PushWait task, P3 latency was later in DS than in YH and OH. In both tasks, DS showed a marked amplitude shift towards positivity overlapping the N1-P2 complex and seemingly also P3: The P3 amplitude evoked by target tones and by "Push" was shifted towards anterior sites resulting in a Cz maximum. Changes of the N1 latency and amplitude in DS may be related to enhanced arousal during stimulus processing, indicating a possible defect of central inhibitory mechanisms. The study suggests that differentiated ERP procedures provide information on adult DS cognition exceeding those given by mere P3 latency measurements. Such procedures may be useful in the evaluation of the cognitive decline due to precocious aging or Alzheimer-type dementia in DS.

Adult↗
PubMed1991

The instruction to refrain from blinking affects auditory P3 and N1 amplitudes.

Often subjects have been instructed to refrain from blinking lest their evoked EEG potentials should be distorted. We studied whether these very instructions have any impact on P3 amplitude. Two tones were presented in random order, and subjects had to count the high-pitched tones. Half the subjects were instructed not to blink, whereas this instruction was omitted for the other subjects. Target tones evoked larger P3s than non-targets in the latter group but not in the former, in particular not in those subjects that actually blinked rarely. The groups also differed in their N1 amplitudes. These findings might be relevant to P3 studies working with patients and controls: the harder some frequently blinking subjects try to refrain from blinking, the smaller might become their P3 amplitudes. Omitting the instruction and using off-line blink subtraction procedures seems a viable alternative. This study was actually motivated by discrepant findings on the effects of the preceding tone sequence on P3. These discrepancies could be largely resolved by the instructional variable, in conjunction with different tone intensities. It is suggested that subjects who are discouraged from blinking try to protect themselves against the arousing effects of stimuli.

Adult↗
PubMed1991

On the reasons for the delay of P3 latency in healthy elderly subjects.

The P3 component reaches its peak later in elderly subjects than in young subjects. The aim of this study was to repeat this finding in the usual auditory oddball task and to look for reasons for the delay by analysing other components and by applying another task, the visual Push/Wait task. It was found in the oddball that the age delay was present for mismatch negativity already but further increased until P3's peak. In the Push/Wait task, the size of the age delay was independent of another delay caused by reduced visual intensity of the stimuli. Further, the age delay had its onset after the occipital P140 component whereas the intensity delay was present before this component. Within the elderly, P3 latencies correlated between the auditory and the visual tasks, and the common factor extracted from both latencies correlated with a test of short-term memory span. It is concluded that the age delay of P3 is not due to a delay of perceptual encoding but perhaps due to delayed memory processes in the elderly. As usual, P3 amplitudes were larger and more parietally focussed in the young than in the elderly. Possible differences in motivation might account for this finding.

Acoustic Stimulation↗
PubMed1991

The waltzing oddball.

We investigated whether task relevance and probability interact to influence P3 amplitude. High and low tones were presented in random order with equal probability. In the control condition (standard oddball), every high tone had to be counted. In the waltz condition, high tones had to be counted only if they were preceded by two other high tones. It was predicted that the P3s evoked by targets in the waltz condition would be larger than the P3s evoked by the same sequence of targets in the oddball condition. That is, the frequency of occurrence of the targets should have an effect on P3, in addition to effects of the frequency of stimulus occurrence and stimulus task relevance (target/nontarget). This prediction was upheld. However, the largest P3s were evoked by nontargets following two high tones in the waltz condition. These P3s had a more anterior topographic maximum than usual. We contend that these anterior P3s reflect the interruption of an ongoing task and cannot be easily fit into the framework of the two concepts of task relevance and probability.

Adult↗
PubMed1991

[Presenile dementia in xeroderma pigmentosum].

Neurological manifestations of xeroderma pigmentosum, a rare autosomal recessive neurocutaneous syndrome, are variable. The association with progressive mental retardation, usually with onset in childhood, is well known. We present a case of x.p. with progressive presenile dementia. This combination has, to our knowledge, not yet been reported in the literature. Although no hints on another aetiology have been found, the coincidental combination of x.p. with M. Alzheimer has to be taken into consideration. CT scan and MRI showed a marked cerebral atrophy.

Atrophy↗
PubMed1990

P3-evoking wrong notes: unexpected, awaited, or arousing?

The effect of melodic deviance on P3 was investigated. In one condition, the opening phrases of well-known melodies were presented. Melodies ended in the midst of the phrases, either properly or with a deviant tone, as in the study of Besson and Macar (1987). In the other condition, ending phrases of melodies were presented, with the final tone either having its proper pitch or a deviant one. It was predicted that not only deviant tones of openings would evoke P3s, as in Besson and Macar's study, but also both deviant and normal tones of endings because all these tones unambiguously marked the end of the present epoch. Contrary to prediction, late positive components were evoked by deviant tones only. However, it was in the endings condition only that these components displayed a parietal maximum, as P3s do. It is concluded that two factors were necessary for evoking P3s in this paradigm, one factor that was associated with deviance, the other associated with endings. It is argued that the first factor is arousal, the second factor is subjects' expectation of the closing stimulus.

Adult↗
PubMed1990

Slow potentials in a melody recognition task.

In a previous study, slow negative shifts were found in the EEG of subjects listening to well-known melodies. The two experiments reported here were designed to investigate the variables to which these slow potentials are related. In the first experiment, two opposite hypotheses were tested: The slow shifts might express subjects' acquaintance with the melodies or, on the contrary, the effort invested to identify them. To this end, some of the melodies were presented in the rhythms of other melodies to make recognition more difficult. Further, melodies rated as very well-known and as very unknown were analysed separately. However, the slow shifts were not affected by these experimental variations. Therefore in the second experiment, on the one hand the purely physical parameters intensity and duration were varied, but this variation had no impact on the slow shifts either. On the other hand, recognition was made more difficult by monotonously repeating the pitch of the 4th tone for the rest of some melodies. The slow negative shifts were enhanced with these monotonous melodies. This enhancement supports the "effort" hypothesis. Accordingly, the ofter shifts obtained in both experiments might likewise reflect effort. But since the task was not demanding, it is suggested that these constant shifts reflect the effort invested for coping with the entire underarousing situation rather than with the task. Frequently, slow eye movements occurred in the same time range as the slow potentials, resulting in EOG potentials spreading to the EEG recording sites. Yet results did not change substantially when the EEG recordings were corrected for the influence of EOG potentials.

Adult↗
PubMed1989

[Comments on the analysis of the P300 components using brain mapping].

Recently, Maurer and colleagues reported that the peak amplitude of the P300 was distributed in specific topographical patterns for demented, hebephrenic, and paranoid patients. This evidence is critically discussed. For the hebephrenic and paranoid patients, it is doubtful whether their topographic patterns differed from normal subjects, while for the demented patients the impact of EOG artifacts is not clear. Some recommendations are given how to deal with artifacts before mapping the P300.

Brain Mapping↗
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↗
PubMed1988

Development of the EEG of school-age children and adolescents. II. Topography.

Topographic aspects of EEG development of normal children and adolescents from 6 to 17 years are investigated with respect to various spectral parameters. The topographic distribution of spectral band power does not change between hemispheres across age. Changes take place, however, in the antero-posterior dimension. For the bands theta, alpha 1 and alpha 2 (and less so for delta) maturation starts at posterior derivations and ends at anterior derivations. For the band beta 2 (and to some extent also for beta 1), development progresses from Cz to Pz and further to occipital, lateral, central and frontal derivations. Principal component analysis (PCA) leads to a more parsimonious and better interpretable description of broad-band power and of its topographic distribution. Broad-band coherences increase with age, though to a modest degree. The different magnitudes of coherence between different regions can be largely accounted for by the interelectrode distances. Coherences, too, can be described in a more parsimonious and better interpretable way via PCA. The 3 components extracted reflect firstly the overall level of coherence, secondly the coherences of the occipital regions with all other regions and thirdly antero-posterior versus left-right coherences.

Adolescent↗
PubMed1988

The true P3 is hard to see: some comments on Kok's (1986) paper on degraded stimuli.

Kok (1986) investigated why P3 amplitudes are reduced when stimuli are degraded. He proposed that a positive moment-related component might overlap P3 after intact stimuli and a negative one after degraded stimuli ("MRP overlap" hypothesis). Discussing his findings, it is suggested that MRP overlap can only account for the result if another overlap hypothesis ("nogo overlap") is added. But even this combined hypothesis cannot explain reducing effects of degradation found in other paradigms. While other overlap hypotheses have been proposed in the literature, the most parsimonious hypothesis is to assume that P3 itself gets smaller after degraded stimuli.

Arousal↗
PubMed1987

EEG coherence at rest and during a visual task in two groups of children.

EEG coherence was studied in a group of n = 31 normal children (NG) and in a group of n = 25 mildly mentally retarded children (EG), 10-13 years old. This was done for a recording at rest, eyes closed, and one during which a visual matching task was presented. Coherence showed little structure across frequency, apart from a slow decline towards higher frequencies. For the EEG at rest, coherence was higher for the EG and a slight increase with age was found. The visual task changed the coherence pattern in a complex way, and differently for the two groups. Coherence decreased in the fronto-central region (about the same in both groups) and increased in occipito-parietal central combinations (more so for the NG). The delta band showed predominantly an increase for the NG.

Adolescent↗
PubMed1987

Sequential effects on P3 in a counting task: a partial replication.

High and low tones were presented in random order, and the high tones had to be counted. It was intended to replicate the sequential effects on P3 reported by Squires et al. (1976, 1977) and to test by means of an ANOVA approach how each one of the preceding four tones contributes to these sequential effects. However, results deviated from those studies: (1) P3s were generally somewhat larger with target tones than with nontargets; (2) Squires et al.'s (1976, 1977) sequential effects were replicated for nontargets, but were more or less reversed for targets. The preceding sequence was found also to exert influence on prestimulus baselines, N1, and EOG. It is suggested that target effects constitute the rule rather than the exception and that sequential effects on P3 may be altered by subtle differences of subjects' sets, similarly to sequential effects on choice reaction times.

Adolescent↗
PubMed1986

Principal component analysis of event-related potentials: a note on misallocation of variance.

Wood and McCarthy (1984) found a 'misallocation of variance' when applying PCA, including Varimax rotation, to simulated data. Here it is demonstrated that this effect can be produced by Varimax rotation, without PCA as an intervening step. PCA does not distort or lose information when extracting components, since it is shown that the prototypes may be perfectly reconstructed from the unrotated solution. However, it is stressed that infinitely many sets of prototypes may render the same final solution, a fact which cannot be overcome by any method. The role of the rotation step within this framework is discussed.

Electroencephalography↗
PubMed1985

Short term changes of event related potentials during concept learning.

In a concept learning task, the time course of P3 amplitudes following the stimuli to be categorized was investigated. That time course did not coincide with the learning curve: it was not until the 4th to 6th trial after learning that P3 amplitudes grew larger. Some implications of this effect are discussed.

Adolescent↗
PubMed1978

Effects of certainty, modality shift and guess outcome on evoked potentials and reaction times in chronic schizophrenics.

Evoked potentials and reaction times were obtained from chronic schizophrenics and normal controls to light and sound stimuli presented in random order. In the 'certain' condition subjects were told what the next stimulus would be, in the 'uncertain' condition they were asked to guess. Amplitudes were usually larger for normals than for schizophrenics, for 'uncertain' than for 'certain' conditions, and in cross- than in ipsimodal stimulus-sequences. The effect of certainty was stronger in normals across 4 leads; so was the effect of modality shift at vertex. While these findings replicate earlier results from acute schizophrenics, no condition X group interactions could be found in the reaction time measures. Two additional results were interpreted as showing basically different attitudes with respect to the predictability of events: (1) there was a slow positivity between the verbal information and the following stimuli which was largest for schizophrenics in the conditions of certainty; (2) while normals showed long-term habituation only in N1- but not in P3-amplitudes, the reverse was true for schizophrenics.

Acoustic Stimulation↗
PubMedDate not supplied

Event-related EEG potentials in mild dementia of the Alzheimer type.

Most studies on event-related EEG potentials in dementia have focussed on the P3 component and used auditory stimuli only. In the present study, N2b was analysed in the usual auditory oddball task in addition to P3, and a visual task was employed ("Push"/"Wait"), with recordings including an occipital scalp site. Seven Alzheimer-type patients, with their mean IQ still in the normal range, were compared to age-matched normal controls. In the oddball task, P3 did not differ between groups but the patients' N2b was delayed. The main difference in the Push/Wait task was in an occipital P270, which component was distinctly larger in the patients. It is suggested that both differences reflect the disintegration of patients' cognition: stimuli are perceived in a normal way but then a gap arises due to uncertainty what to do with the perceived event.

Acoustic Stimulation↗