Basar-Eroglu, Canan
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Basar-Eroglu, Canan
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Basar-Eroglu, Canan
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Item-typ:Veröffentlichung, Oszillatorische Gehirnaktivität von Patienten mit schizophrenen Störungen und Gesunden bei multistabiler Wahrnehmung(2017-09-19); ; ; Objective: Patients with schizophrenia seem to be impaired in binding single visual stimuli-features into coherent objects. For this process, interaction of top-down and bottom-up processing has to be intact. Neural oscillations seem to be a fundamental mechanism for coordinated communication of neural circuits. They have been proposed to reflect the spatio-temporal integration of sensory and cognitive information for creating coherent perception. Method: An EEG examination of schizophrenia patients as well as healthy control subjects was performed during the processing of an apparent motion stimulus, a stroboscopic effect, which induces two possible endogenously generated perceptions. Furthermore, a modified control stimulus was presented with exogenous reversals of the stimulus. Event-related oscillations resp. event-related spectral perturbation (ERSP) of delta (0-4 Hz), theta (3-8 Hz), alpha (8-13 Hz), beta (14-28 Hz) and gamma oscillations (28-48 Hz) were analyzed. Results: The reaction time of patients in the control conditions is significantly slower. They show anslightly reduced delta power for both conditions, their theta-activity was significantly less increased than in the control group. Moreover, patients had a stronger decrease of alpha activity during the reversal activity over posterior electrodes. Both groups show this decrease in the beta frequency. In ambiguous perception, there are topographical differences between the groups. Patients show a shift from posterior to central regions in the gamma response. Conclusion: The results indicate a functional involvement of all five frequencies in multistable perception. Patients with schizophrenia seem to suffer from an impaired top-down influence of delta and theta in perceptual organisation of ambiguous patterns. With respect to the weaker performance in reaction time, it seems as if there is a reduced impact of top-down organisation, while generating the coherent percepts. Posterior alpha and beta desynchronizations are interpreted as reflecting bottom-up mechanisms which help to fulfill the endogenous reversals. It becomes obvious that patients depend more on the sensory input, which can be interpreted as a compensation of the inferior top-down control. The reduced gamma posterior synchronisation in the patient group while reversal processing is debated in literature in respect to inefficient binding to features. There are no obvious group differences for the gamma frequency in multistable processing. Significance: This is the first comparative study, that takes into account the event-related oscillations of all frequency bands during perceptual organization of the apparent motion. Therewith, dysfunctional integration processing in schizophrenia patients is investigated. Coherent perception of the environment originates from an intact interaction of sensory and cognitive processing. An understanding of altered oscillatory dynamics in schizophrenia may provide new insights in the pathomechanisms of the disorder.Dissertation437 734 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Brain maturation during adolescence and young adulthood - an EEG studyObjective: Adolescence is a period of major maturational changes in the brain. It is particularly the maturation of the frontal cortex and its interactions with other brain regions that dominates this late stage of development and has important implications for the cognitive abilities during the entire adult life. Methods: In this thesis, developmental changes in the delta (0 - 4 Hz), theta (4 - 7 Hz) and gamma (28 - 48 Hz) frequency bands were investigated in adolescents (13 - 15 years) and adults (20 - 27 years) during resting and cognitive states. Four tasks were conducted: the spontaneous EEG (eyes-open), the ambiguous task, the unambiguous task and the visual oddball task. During the ambiguous task, participants were exposed to the Stroboscopic Ambiguous Motion (SAM) paradigm. SAM is a multistable stimulus that, when viewed continuously, induces internally-generated changes in the perceived direction of motion. For the unambiguous task, a modified version of the SAM was used. In this case, the perceived direction of motion was controlled externally. In the visual oddball task, randomly interspersed targets had to be identified in a train of frequent non-targets. Single-trial amplitudes of delta, theta and gamma activity obtained during the spontaneous EEG were compared between the groups to assess general maturational changes in the developing brain. The task-related enhancement of the oscillatory activity was compared between the groups in order to assess developmental changes in task performance. Results: The previous findings of delta and theta amplitudes decreasing with age during the spontaneous EEG were replicated. Similarly to previous studies, our results also indicate that for spontaneous EEG gamma amplitudes do not profoundly differ between adolescents and adults. Moreover, the present study supports previous findings from adult research which have established a functional relationship between delta, theta and gamma activities and higher cognitive processes. It has further been found that the developmental changes correlated with task difficulty. Only for the - most challenging - ambiguous task the gamma oscillations were found to reflect a change in task-related cortical processing during adolescence, whereas no age-related differences of gamma responses were detected for less demanding tasks (the unambiguous and visual oddball tasks). The event-related theta responses were found to increase with age for the ambiguous and visual oddball tasks and did not depend on age for the unambiguous task. Furthermore, the event-related delta responses increased with age for all tasks. Conclusions: The main finding of this study is that functional networks of delta, theta and gamma activity undergo maturational changes during adolescence. The found differences in the task-related activations may indicate a protracted development of higher-order cognitive processes during adolescence. The developmental changes of task-related activations seem to vary with task difficulty and frequency band. Significance: Systematic studies on developmental changes of brain oscillations in cognitive tasks are still infrequent and specifically the time period of adolescence has been rarely investigated. The typical age of onset for mental disorders, such as schizophrenia, is the late stages or shortly after the onset of adolescence, rendering the outcome of brain maturation during this period of immense importance for life-long mental health. Thus, it is critical to extend our understanding of the mechanism behind the appearance of cognitive functions during adolescence.Dissertation357 138 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Ereigniskorrelierte Oszillationen nach Präsentation alkoholbezogener Hinweisreize in der visuellen Modalität bei alkoholabhängigen Patienten(2012-04-18); ; ; New models of alcohol dependence postulate an attentional bias for alcohol-related cues in abstinent alcoholics that is associated with the motivation to drink alcohol. An understanding of the underlying neurophysiological mechanisms is important for an effective treatment of alcohol dependence. Aim of this study was to analyze whether event-related delta, theta and alpha oscillations elicited by alcohol-related pictures reflect such an attentional bias in abstinent alcoholics. Furthermore the influence of subacute abstinence phenomenon and the effect of stimulus repetition were investigated. Nine controls and nine abstinent patients with alcohol dependence viewed alcohol-related and neutral pictures while EEG was recorded one week after start of detoxification as well as six weeks later. One week after detoxification, 60 alcohol-related pictures and 60 neutral pictures were presented pseudo-randomized (condition 1). Six weeks later, the EEG session consisted of three conditions: 60 new alcohol-related and neutral pictures (condition 2), 25 alcohol-related and 25 neutral pictures chosen from condition 2 (condition 3, habituation-session) which were presented four times, and 60 new alcohol-related and 60 neutral pictures (condition 4, transfer-session). Repeated measures ANOVAs revealed an enhanced alpha activity elicited by alcohol-related stimuli compared to those elicited by neutral pictures in the patients with alcohol dependence during condition 2 and 4 whereas there was no alpha band enhancement in condition 1 and 3. Patients also showed enhanced alpha activity in contrast to controls elicited by alcohol-related pictures in condition 2 and 4. No significant differences were found for delta and theta oscillations. Taken together the alpha enhancement in condition 2 and 4 could reflect an early attentional bias in alcoholics toward the alcohol-related stimuli. However, this alpha enhancement merely occurs after termination of detoxification. The repetition of the alcohol-related stimuli in session 3 apparently leads to a habituation effect in the patients whereas there is no transfer effect for new the alcohol-related pictures: in session 4 the alpha band enhancement elicited by the alcohol-related pictures points to the early attentional bias for the new alcohol-related pictures again.Dissertation362 569 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Multistabile Wahrnehmung bei Kindern: Eine EEG-Studie(2008-12-17); ; ; Multistable perception occurs when reversible patterns are presented in the absence of changes in the stimuli properties. The aim of the study was to examine age-related changes in brain activity associated with multistable perception. Fourteen 10-year old children observed an ambiguous pattern, known as the stroboscopic alternative motion (SAM) and were instructed to press a button following each reversal. The results showed the occurrence of a slow positive wave about 100 ms prior to the button-press. The amplitude of the component revealed a strong posterior topography. The positive wave induced by the SAM, did not differ from a slow wave elicited by a stimulus-driven control paradigm, whereas the adult brains strongly differentiate between internal and external generated perception. Moreover, the children seem to be incapable to produce a stable reversal related component over frontal areas, which reflect the yet insufficient integration of these areas into the entire brain work.Dissertation406 242 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Der Beitrag von Beta- und Gamma-Oszillationen zur Wahrnehmungsorganisation unter Berücksichtigung der Bottom-up - Top-down-Dichotomie : Studien zu multistabiler visueller Wahrnehmung und auditiver Daueraufmerksamkeit bei Gesunden und schizophren Erkrankten(2014-05-09); ; ; In the last decade many research reports have provided evidences, that high-frequency oscillatory (HFO) brain activity is inevitably involved in the organization of human perception. Especially the contribution of beta- and gamma-oscillations, has been discussed extensively. Thereto researchers often use the bottom-up and top-down-processing dichotomy to characterize electrophysiological activities. Hence this work investigates HFO electrophysiological correlates of multistable perception in an ambiguous visual motion pattern, the stroboscopic alternative motion, in healthy subjects. In a second study correlates of an auditory sustained attention paradigm were investigated in schizophrenics and healthy controls. The results bear several new aspects of the contribution of HFO, especially in the beta-activity range, to the investigated phenomena and underpin the need for new causal experimental approaches to confirm the functional role of these oscillations. The bottom-up top-down-dichotomy did not prove to be helpful as a nomenclature to characterize the underlying oscillatory processes.Dissertation412 156 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Using Multimodal MRI Techniques to Derive a Biomarker for Tracking the Pathological Changes Occurring at Different Stages of Cognitive Decline in Parkinson's Disease in a Cross-Sectional Study Design(2017-09-20); ; ; Cognitive impairment is common in Parkinson's disease (PD) and can range from mild cognitive impairment (PD-MCI) to dementia (PDD). The aim of this study was to derive a multi-modal MRI-based biomarker for the reliable discrimination of PD patients at different stages of cognitive decline and to identify pathologic patterns related with dementia risk. The resting-state functional MRI (rs-fMRI), diffusion tensor imaging (DTI), Arterial Spin Labeling and MR spectroscopic imaging data of 60 PD patients (PD-N, PD-MCI, PDD) were collected. The rs-fMRI data revealed a combination of resting-state networks with significant discriminative power based on the expression scores of the resting-state networks. In combination with the DTI data we obtained a successful model for the discrimination of PDD patients and were able to identify progressive pathological changes that can be used as biomarker for PDD and could be established as clinical diagnostic tool for PD patients with high dementia risk.Dissertation426 347 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Alters- und geschlechtsspezifische Unterschiede bei der Nutzung einer P300-basierten Brain Computer Interfaces: Eine Studie ereigniskorrelierter EEG-Oszillationen(2014-05-09); ; ; Brain-Computer-Interfaces (BCI) are currently a subject of high interest in the field of rehabilitation technology. BCI will allow patients without control of their muscles to access certain functions of a computer, eg a speller for communication. Especially the possibility to establish methods of communication for the paralyzed is a main focus of BCI research. Among others, one common approach for Brain-Computer-Interfacing is the P300-Speller. It applies a modified Oddball-Paradigm to evoke a P300-Komponente, which is subsequently detected by automated means. Detection of the P300-Wave is connected to the related character, which is then displayed on a computer screen. The P300-Speller is an established method in laboratory research; still it is not yet applied in a clinical setting. Most applications and tests, using the P300-Speller, still take place in young, healthy subjects. This study investigates differences in the P300-Speller usability between male and female users as well as between young and old users. Under certain conditions, i.e. difficult conditions, robust and reproducible differences are found. Aged men are worse in their ability to use the speller than young men and women of both age groups. In a visual Oddball-Paradigm, bad performance in the P300-Speller is reflected in event-related EEG oscillations. Especially in the frequency bands associated with attention, the group with the worst performance shows less pronounced signals than the other experimental groups. It is concluded, that older men s attention is less pronounced than that in the other groups, effecting EEG-Oscillations and performance in the P300-Speller. A visual Oddball-Paradigm may be suitable as a predictor for a persons ability to use the P300-Speller.Dissertation455 290