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Jürgen Kayser

Publications and source records attributed to Jürgen Kayser.

9 recordsLinked to original sources
PubMed2006

ERP/CSD indices of impaired verbal working memory subprocesses in schizophrenia.

To disentangle subprocesses of verbal working memory deficits in schizophrenia, long EEG epochs (>10 s) were recorded from 13 patients and 17 healthy adults during a visual word serial position test. ERP generator patterns were summarized by temporal PCA from reference-free current source density (CSD) waveforms to sharpen 31-channel topographies. Patients showed poorer performance and reduced left inferior parietotemporal P3 source. Build-up of mid-frontal negative slow wave (SW) in controls during item encoding, integration, and active maintenance was absent in patients, whereas a sustained mid-frontal SW sink during the retention interval was comparable across groups. Mid-frontal SW sinks (encoding and retention periods) and posterior SW sinks and sources (encoding only) were related to performance in controls only. Data suggest disturbed processes in a frontal-parietotemporal network in schizophrenia, affecting encoding and early item storage.

Adolescent↗
PubMed2005

Principal components analysis of Laplacian waveforms as a generic method for identifying ERP generator patterns: II. Adequacy of low-density estimates.

OBJECTIVE: To evaluate the comparability of high- and low-density surface Laplacian estimates for determining ERP generator patterns of group data derived from a typical ERP sample size and paradigm. METHODS: High-density ERP data (129 sites) recorded from 17 adults during tonal and phonetic oddball tasks were converted to a 10-20-system EEG montage (31 sites) using spherical spline interpolations. Current source density (CSD) waveforms were computed from the high- and low-density, but otherwise identical, ERPs, and correlated at corresponding locations. CSD data were submitted to separate covariance-based, unrestricted temporal PCAs (Varimax of covariance loadings) to identify and effectively summarize temporally and spatially overlapping CSD components. Solutions were compared by correlating factor loadings and scores, and by plotting ANOVA F statistics derived from corresponding high- and low-resolution factor scores using representative sites. RESULTS: High- and low-density CSD waveforms, PCA solutions, and F statistics were remarkably similar, yielding correlations of .9 < or = r < or = .999 between waveforms, loadings, and scores for almost all comparisons at low-density locations except for low-signal CSD waveforms at occipital sites. Each of the first 10 high-density factors corresponded precisely to one factor of the first 10 low-density factors, with each 10-factor set accounting for the meaningful CSD variance (> 91.6%). CONCLUSIONS: Low-density surface Laplacian estimates were shown to be accurate approximations of high-density CSDs at these locations, which adequately and quite sufficiently summarized group data. Moreover, reasonable approximations of many high-density scalp locations were obtained for group data from interpolations of low-density data. If group findings are the primary objective, as typical for cognitive ERP research, low-resolution CSD topographies may be as efficient, given the effective spatial smoothing when averaging across subjects and/or conditions. SIGNIFICANCE: Conservative recommendations for restricting surface Laplacians to high-density recordings may not be appropriate for all ERP research applications, and should be re-evaluated considering objective, costs and benefits.

Acoustic Stimulation↗
PubMed2005

Principal components analysis of Laplacian waveforms as a generic method for identifying ERP generator patterns: I. Evaluation with auditory oddball tasks.

OBJECTIVE: To evaluate the effectiveness and comparability of PCA-based simplifications of ERP waveforms versus their reference-free Laplacian transformations for separating task- and response-related ERP generator patterns during auditory oddball tasks. METHODS: Nose-referenced ERPs (31 sites total) were recorded from 66 right-handed adults during oddball tasks using syllables or tones. Response mode (left press, right press, silent count) and task was varied within subjects. Spherical spline current source density (CSD) waveforms were computed to sharpen ERP scalp topographies and eliminate volume-conducted contributions. ERP and CSD data were submitted to separate covariance-based, unrestricted temporal PCAs (Varimax) to disentangle temporally and spatially overlapping ERP and CSD components. RESULTS: Corresponding ERP and CSD factors were unambiguously related to known ERP components. For example, the dipolar organization of a central N1 was evident from factorized anterior sinks and posterior sources encompassing the Sylvian fissure. Factors associated with N2 were characterized by asymmetric frontolateral (tonal: frontotemporal R > L) and parietotemporal (phonetic: parietotemporal L > R) sinks for targets. A single ERP factor summarized parietal P3 activity, along with an anterior negativity. In contrast, two CSD factors peaking at 360 and 560 ms distinguished a parietal P3 source with an anterior sink from a centroparietal P3 source with a sharply localized Fz sink. A smaller parietal but larger left temporal P3 source was found for silent count compared to button press. Left or right press produced opposite, region-specific asymmetries originating from central sites, modulating the N2/P3 complex. CONCLUSIONS: CSD transformation is shown to be a valuable preprocessing step for PCA of ERP data, providing a unique, physiologically meaningful solution to the ubiquitous reference problem. By reducing ERP redundancy and producing sharper, simpler topographies, and without losing or distorting any effects of interest, the CSD-PCA solution replicated and extended previous task- and response-related findings. SIGNIFICANCE: Eliminating ambiguities of the recording reference, the combined CSD-PCA approach systematically bridges between montage-dependent scalp potentials and distinct, anatomically-relevant current generators, and shows promise as a comprehensive, generic strategy for ERP analysis.

Acoustic Stimulation↗
PubMed2005

Reference-free quantification of EEG spectra: combining current source density (CSD) and frequency principal components analysis (fPCA).

OBJECTIVE: Definition of appropriate frequency bands and choice of recording reference limit the interpretability of quantitative EEG, which may be further compromised by distorted topographies or inverted hemispheric asymmetries when employing conventional (non-linear) power spectra. In contrast, fPCA factors conform to the spectral structure of empirical data, and a surface Laplacian (2-dimensional CSD) simplifies topographies by minimizing volume-conducted activity. Conciseness and interpretability of EEG and CSD fPCA solutions were compared for three common scaling methods. METHODS: Resting EEG and CSD (30 channels, nose reference, eyes open/closed) from 51 healthy and 93 clinically-depressed adults were simplified as power, log power, and amplitude spectra, and summarized using unrestricted, Varimax-rotated, covariance-based fPCA. RESULTS: Multiple alpha factors were separable from artifact and reproducible across subgroups. Power spectra produced numerous, sharply-defined factors emphasizing low frequencies. Log power spectra produced fewer, broader factors emphasizing high frequencies. Solutions for amplitude spectra showed optimal intermediate tuning, particularly when derived from CSD rather than EEG spectra. These solutions were topographically distinct, detecting multiple posterior alpha generators but excluding the dorsal surface of the frontal lobes. Instead a low alpha/theta factor showed a secondary topography along the frontal midline. CONCLUSIONS: CSD amplitude spectrum fPCA solutions provide simpler, reference-independent measures that more directly reflect neuronal activity. SIGNIFICANCE: A new quantitative EEG approach affording spectral components is developed that closely parallels the concept of an ERP component in the temporal domain.

Adolescent↗
PubMed2003

Event-related brain potentials during auditory and visual word recognition memory tasks.

Event-related brain potentials (ERPs) recorded during presentation of a series of words or pictures show enhanced positivity between 300 and 800 ms after presentation of repeated items. However, little attention has been directed to the characterization of this ERP recognition memory effect using auditory stimuli. The present study directly compared the ERP 'old/new effect' for words presented in the visual and auditory modalities. Nose-referenced ERPs were recorded from 30 electrode sites while participants (N=16) were engaged in visual and auditory continuous word recognition memory tasks. Spatially and temporally overlapping ERP components were identified and measured by covariance-based principal components analysis. The expected old/new effect was observed in both modalities, with a comparable time course peaking at 560 ms, but having a more anterior scalp topography for visual items. This suggests a common cognitive process (i.e. successful retrieval of information from memory) associated with separable neural generators in each modality. Despite this temporal synchronization, the old/new effect overlapped ERP components having distinct scalp topographies (N2) or peak latencies (P3) for each modality. The positive-going old/new effect was preceded by an earlier negativity peaking at 370 ms that was greater across modalities for old than new words, likely reflecting semantic processing aspects of word recognition memory. A late (beyond 900 ms), broadly-distributed negativity was also greater for old than new words, prolonged for auditory items, and may represent activity of a post-retrieval process.

Acoustic Stimulation↗
PubMed2003

Optimizing PCA methodology for ERP component identification and measurement: theoretical rationale and empirical evaluation.

OBJECTIVE: To determine how specific methodological choices affect "data-driven" simplifications of event-related potentials (ERPs) using principal components analysis (PCA). The usefulness of the extracted component measures can be evaluated by knowledge about the variance distribution of ERPs, which are characterized by the removal of baseline activity. The variance should be small before and at stimulus onset (across and within cases), but large near the end of the recording epoch and at ERP component peaks. These characteristics are preserved with a covariance matrix, but lost with a correlation matrix, which assigns equal weights to each sample point, yielding the possibility that small but systematic variations may form a factor. METHODS: Varimax-rotated PCAs were performed on simulated and real ERPs, systematically varying extraction criteria (number of factors) and method (correlation/covariance matrix, using unstandardized/standardized loadings before rotation). RESULTS: Conservative extraction criteria changed the morphology of some components considerably, which had severe implications for inferential statistics. Solutions converged and stabilized with more liberal criteria. Interpretability (more distinctive component waveforms with narrow and unambiguous loading peaks) and statistical conclusions (greater effect stability across extraction criteria) were best for unstandardized covariance-based solutions. In contrast, all standardized covariance- and correlation-based solutions included "high-variance" factors during the baseline, confirming findings for simulated data. CONCLUSIONS: Unrestricted, unstandardized covariance-based PCA solutions optimize ERP component identification and measurement.

Adult↗
PubMed2002

Cognitive ERPs in depressive and anxiety disorders during tonal and phonetic oddball tasks.

This report compares event-related brain potentials (ERPs) of patients having a depressive disorder alone (n = 58), an anxiety disorder alone (n = 22), comorbidity of these disorders (n = 18), and healthy controls (n = 49). ERPs were recorded from 30 electrode sites during auditory oddball tasks using consonant-vowel syllables (phonetic) or complex tones (tonal). Overlapping ERP components were identified and measured using covariance-based principal components analysis. An early P3 subcomponent (P315) was larger in patients having an anxiety disorder alone when compared to depressed patients with or without an anxiety disorder and healthy controls, whereas a late P3 subcomponent (P400) was larger in patients having comorbidity of anxiety and depressive disorders than in the other groups. Also, the N2-P3 complex showed task-dependent hemispheric asymmetries, including larger N2-P3 amplitude over left than right temporoparietal sites during the phonetic oddball task. This hemispheric asymmetry was greatest in patients having a depressive disorder alone and smallest in patients having an anxiety disorder alone. The opposite nature of the alterations of hemispheric asymmetry and early P3 amplitude in depressive and anxiety disorders underscores the importance of taking comorbidity with anxiety into account in studies of cognitive ERPs in depressive disorders.

Adult↗