Browsing by Author "Schmiedt-Fehr, Christina"

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Citation - WoS: 2
Citation - Scopus: 2
Aging Attenuated Theta Response During Multistable Perception
(Wiley, 2023) Küçük, Kurtulus Mert; Mathes, Birgit; Schmiedt-Fehr, Christina; Başar Eroğlu, Canan
Multistable stimuli are physically unchanging, but elicit spontaneous perceptual reversals between multiple internally generated perceptual alternatives. Perceptual reversal rates seem to decrease in older adults; however, there is no literature on the electrophysiological correlates of this performance decrease. Here, we aimed to identify age-related changes in theta activity that relate to decreased reversal rates of older adults. Electroencephalography (EEG) of young (n = 15) and older adults (n = 15) was recorded during presentation of stroboscopic alternative motion (SAM) and a control stimulus. Time-frequency amplitudes were extracted in 4-8 Hz via Morlet wavelet convolution. Older adults had lower SAM reversals as well as decreased accuracy, increased reaction time (RT) and increased RT variability in the control task. In older adults, reversal-related frontal theta response was diminished, yet parietal theta was intact. In the parietal area, the relationship between theta response and reversal rates was robust, but in the frontal area, was dependent on age-related variance. Result indicated that, in older adults, top-down facilitation of perceptual reversals was impaired. This appears to result in a predominantly bottom-up resolution of perceptual multistability. Age-related degradation of sensory areas in this bottom-up-driven resolution process might have slowed reversals. This study presents the first electrophysiological correlates of age-related impairment in multistable perceptual integration.
Citation - WoS: 18
Citation - Scopus: 18
Altered Gamma and Theta Oscillations During Multistable Perception in Schizophrenia
(Elsevier, 2020) Rurup, Linda; Mathes, Birgit; Schmiedt-Fehr, Christina; Wienke, Annika Susann; Ozerdem, Aysegul; Brand, Andreas; Başar Eroğlu, Canan
Objective: Coherent object perception in patients with schizophrenia is known to be impaired. Oscillatory brain dynamics constitute a fundamental mechanism for the coordinated communication of neural circuits. Such dynamics have been proposed to reflect impaired spatio-temporal integration of sensory and cognitive processes during object perception in schizophrenia. Method: EEG recordings of patients with schizophrenia (n = 23) and control participants (n = 23) were examined. Presented were either an ambiguous (multistable) stimulus, endogenously inducing switching between two perceptual alternatives, or a slightly modified unambiguous control stimulus, during which perceptual reversals were triggered by a minor change in the stimulus configuration. Event-related amplitude modulation induced by perceptual reversals was analyzed for theta (3-8 Hz) and gamma band oscillations (28-48 Hz). Results: Patients displayed increased reaction times and more errors when indicating unambiguous reversals. The patients ' amplitude enhancement of theta oscillations was diminished in both task conditions. During the control task were gamma amplitudes larger in patients than in healthy participants. Conclusion: The results indicate that impairments in generating coherent percepts are reflected in alterations of multiple frequency bands and time windows. Changes in gamma band oscillations may reflect the patients' impairments in perceptuo-cognitive integration processes. Diminished theta amplitude modulation in patients further emphasize diminished top-down cognitive control during perceptual reversals. Significance: This study provides insight into how theta and gamma oscillations underlie changes in object perception, and thereby possibly the generation of core symptoms, in schizophrenia. This paper is dedicated to Prof. Dr. Erol Basar, a pioneer in research on oscillatory braindynamics. He was tireless in his effort to understand brain functions and integratedphilosophy, physics, biology and psychology in his research. His vision on how informationis coded in brain networks inspired many researchers in the last 40 years. With him, we not only lose an exceptional researcher, but also a supportive academic teacher and mentor with a persistent, prolific enthusiasm for international and collaborative projects.
Event Related Theta Oscillations During Sustained Attention
(Elsevier, 2021) Uelgen, Zehra; Kuecuek, Mert; Schmiedt-Fehr, Christina; Başar Eroğlu, Canan
[Abstract Not Available]
Citation - WoS: 11
Novelty N2-P3a Complex and Theta Oscillations Reflect Improving Neural Coordination Within Frontal Brain Networks During Adolescence
(Frontiers Media Sa, 2018) Wienke, Annika Susann; Başar Eroğlu, Canan; Schmiedt-Fehr, Christina; Mathes, Birgit
Adolescents are easily distracted by novel items than adults. Maturation of the frontal cortex and its integration into widely distributed brain networks may result in diminishing distractibility with the transition into young adulthood. The aim of this study was to investigate maturational changes of brain activity during novelty processing. We hypothesized that during adolescence, timing and task-relevant modulation of frontal cortex network activity elicited by novelty processing improves, concurrently with increasing cognitive control abilities. A visual novelty oddball task was utilized in combination with EEG measurements to investigate brain maturation between 8-28 years of age (n = 84). Developmental changes of the frontal N2-P3a complex and concurrent theta oscillations (4-7 Hz) elicited by rare and unexpected novel stimuli were analyzed using regression models. N2 amplitude decreased, P3a amplitude increased, and latency of both components decreased with age. Pre-stimulus amplitude of theta oscillations decreased, while inter-trial consistency, task-related amplitude modulation and inter-site connectivity of frontal theta oscillations increased with age. Targets, intertwined in a stimulus train with regular non-targets and novels, were detected faster with increasing age. These results indicate that neural processing of novel stimuli became faster and the neural activation pattern more precise in timing and amplitude modulation. Better inter-site connectivity further implicates that frontal brain maturation leads to global neural reorganization and better integration of frontal brain activity within widely distributed brain networks. Faster target detection indicated that these maturational changes in neural activation during novelty processing may result in diminished distractibility and increased cognitive control to pursue the task.