Search results for "Cognition"
showing 10 items of 7054 documents
Surrogate data analysis of sleep electroencephalograms reveals evidence for nonlinearity
1996
We tested the hypothesis of whether sleep electroencephalographic (EEG) signals of different time windows (164 s, 82 s, 41 s and 20.5 s) are in accordance with linear stochastic models. For this purpose we analyzed the all-night sleep electroencephalogram of a healthy subject and corresponding Gaussian-rescaled phase randomized surrogates with a battery of five non-linear measures. The following nonlinear measures were implemented: largest Lyapunov exponent L1, correlation dimension D2, and the Green-Savit measures delta 2, delta 4 and delta 6. The hypothesis of linear stochastic data was rejected with high statistical significance. L1 and D2 yielded the most pronounced effects, while the G…
The dimensionality of human's electroencephalogram during sleep.
1991
In order to perform an analysis of nonlinear EEG-dynamics we investigated the EEG of ten male probands during sleep. According to Rechtschaffen and Kales (1968) we scored the sleep-EEG and applied an algorithm, proposed by Grassberger and Proccaccia (1983) to compute the correlation dimension of different sleep stages. The correlation dimension characterizes the dynamics of the EEG signal and estimates the degrees of freedom of the signal under study. We could demonstrate, that the EEG of slow wave sleep stages depicts a dimensionality, which is two units smaller than that of light or REM sleep.
Nonlinear analysis of continuous ECG during sleep I. Reconstruction.
2000
In recent years evidence has accumulated that ECG signals are of a nonlinear nature. It has been recognized that strictly periodic cardiac rhythms are not accompanied by healthy conditions but, on the contrary, by pathological states. Therefore, the application of methods from nonlinear system theory for the analysis of ECG signals has gained increasing interest. Crucial for the application of nonlinear methods is the reconstruction (embedding) of the time series in a phase space with appropriate dimension. In this study continuous ECG signals of 12 healthy subjects recorded during different sleep stages were analysed. Proper embedding dimension was determined by application of two techniqu…
A Nonlinear Approach to Brain Function: Deterministic Chaos and Sleep EEG
1992
In order to perform a nonlinear dimensional analysis of the sleep electroencephalogram (EEG), we applied an algorithm proposed by Grassberger and Procaccia to calculate the correlation dimension D2 of different sleep stages under Lorazepam medication versus placebo. This correlation dimension characterizes the dynamics of the sleep EEG and it estimates the degrees of freedom of the signal under study. We demonstrate that slow-wave sleep depicts a much smaller dimensionality than light or rapid eye movement (REM) sleep, and that Lorazepam does not alter the EEG's dimensionality except in stage II and REM.
Alterations of Continuous MEG Measures during Mental Activities
2000
In a pilot study, we investigated the topography of 11 continuous MEG measures for the eyes-opened and eyes-closed condition together with three simple mental tasks (mental arithmetic, visual imagery, word generation). One-minute recordings for each condition from 16 right-handed subjects were analyzed. The electrophysiological measures consisted of 6 spectral band measures together with spectral edge frequency and spectral entropy, plus the time-domain-based entropy of amplitudes (ENA) and the nonlinear measures correlation dimension D2 and Lyapunov exponent L1. In summary, our results indicate a pronounced task-dependent difference between the anterior and the posterior region, but no lat…
Emotion regulation strategies moderate the relationship of fatigue with depersonalization and derealization symptoms.
2017
Abstract Background The aim of the present study was to investigate the relationships of common emotion regulation strategies (suppression and reappraisal) to self-reported fatigue and depersonalization/derealization symptoms. Specifically, we tested the moderating effect of suppression and reappraisal on the link of fatigue with depersonalization and derealization symptoms. Opposite effects were expected for both emotion regulation strategies assuming that cognitive reappraisal has an adaptive buffering effect, while suppression intensifies the association of fatigue and depersonalization/derealization experiences. Methods In a representative study (N = 2524) we assessed emotion regulation…
Taking both sides: do unilateral anterior temporal lobe lesions disrupt semantic memory?
2010
The most selective disorder of central conceptual knowledge arises in semantic dementia, a degenerative condition associated with bilateral atrophy of the inferior and polar regions of the temporal lobes. Likewise, semantic impairment in both herpes simplex virus encephalitis and Alzheimer's disease is typically associated with bilateral, anterior temporal pathology. These findings suggest that conceptual representations are supported via an interconnected, bilateral, anterior temporal network and that it may take damage to both sides to produce an unequivocal deficit of central semantic memory. We tested and supported this hypothesis by investigating a case series of 20 patients with unila…
Is the go/no-go lexical decision task an alternative to the yes/no lexical decision task?
2002
In the go/no-go lexical decision task (LDT), participants are instructed to respond as quickly as they can when a word is presented and not to respond if a nonword is presented. By minimizing part of the response selection process in the experimental task, the impact of response decision time on the obtained lexical decision time is probably reduced relative to the standard yes/no LDT (Gordon, 1983). Experiments 1 and 2 show that the go/no-go LDT is sensitive to the effects of word frequency and associative priming--the magnitude of these effects is similar with the two tasks. More important, the go/no-go LDT has a number of advantages with respect to the "standard" yes/no LDT: It offers fa…
Approximal plaque and gingival sulcus bleeding in routine dental care patients: relations to life stress, somatization and depression.
2005
Objectives: Previous research on relations between life stress and periodontal conditions was often based on indicators of periodontal destruction history and stimulus-specific measures of life stress. The present study was undertaken to compare patients showing different degrees of gingival sulcus bleeding with patients without signs of bleeding, using an instrument measuring cognitive impacts of events and assessing reported symptoms of depression and somatization. Additionally the patient groups were compared with regard to dental status and dental visiting behaviour. Analog comparisons were conducted in patients with different degrees of approximal plaque. Materials and Methods: 140 rou…
Explicit and implicit memory biases in depression and panic disorder.
2000
The purpose of the present study was to investigate the presence of a bias for emotional information (panic-related, depression-related, positive and neutral) in explicit memory and implicit memory (by means of free recall and word-stem completion tasks, respectively) among depressed (N=20) and panic (N=20) patients. Three different encoding conditions (graphemic, semantic and self-reference) were used. The results of this study failed to show the existence of a mood-congruent memory bias for both implicit and explicit memory in these emotional disorders. According to the correlational analyses performed, differences among categories of emotional words meant less than the difference among v…