Person: BAŞAR, EROL
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BAŞAR
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EROL
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Publication Open Access Multiple gamma oscillations in the brain: A new strategy to differentiate functional correlates and P300 dynamics(Elsevıer Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlandi, 2015-03) Tülay, Elif; Güntekin, Bahar; BAŞAR, EROL; 142226; 204666Brain oscillations in the gamma frequency band, - i.e. oscillations greater than 25 Hz - have attracted increasing attention over the last few decades in the research of sensory-cognitive processes. In the neuroscience research literature, a great number of reports aim to describe the functional correlates of oscillatory responses in the gamma frequency window. However, analysis using a broadband frequency window often leads to divergent functional interpretations and controversies. In order to provide a more exact approach, we have used a strategy by defining multiple frequency and multiple time windows according to the combined analysis of conventional power spectral windows, frequency adaptive multiple filters, and inter-trial coherence. The analysis in frequency windows of 25-30 Hz, 30-35 Hz, and 4048 Hz enables the investigator to provide a distinction of cognitive and/or sensory responses. Moreover, according to topological differentiation and the consideration of neuroanatomic pathways, more reliable interpretations of gamma responses are reached. (C) 2015 The Authors. Published by Elsevier B.V.Publication Open Access Increased long distance event-related gamma band connectivity in Alzheimer's disease(Elsevier Sci Ltd, The Boulevard, Langford Lane, Kidlington, Oxford Ox5 1Gb, Oxon, England, 2017) Femir, Banu; Emek Savaş, Derya Durusu; Güntekin, Bahar; Yener, Görsev G.; BAŞAR, EROL; 142226; 227002; 204666; 143760Background: Brain oscillatory responses can be used for non-invasive analyses of cortico-cortical connectivity, local neuronal synchronization, and coherence of oscillations in many neuropsychiatric conditions including Alzheimer's disease (AD). In the present paper, we examine sensory-evoked and event-related gamma coherences elicited by visual stimuli in three sub-gamma bands in two sub-groups of patients with AD (i.e., acetylcholinesterase-inhibitor treated and untreated) and healthy controls. Methods: We studied a total of 39 patients with probable mild AD (according to NINCDS-ADRDA criteria) who had been sub-divided into untreated (n = 21) and treated (n = 18) (patients either on cholinergic monotherapy or combined therapy with memantine) AD groups, and 21 age-, gender-, and education-matched healthy elderly controls. A simple flash visual paradigm was applied for the acquisition of sensory-evoked coherences. Event-related coherences were elicited using a classical visual oddball paradigm. Both sensory-evoked and event-related gamma coherences were calculated for long-distance intrahemispheric pairs for three frequency ranges: 2530 Hz, 30-35 Hz, and 40-48 Hz in post-stimulus 0-800 ms duration. The long-distance intrahemispheric pairs from both sides were fronto-parietal, fronto-temporal, fronto-temporoparietal, fronto-occipital, centro-occipital and parieto-occipital. Results: The sensory-evoked or event-related gamma coherences revealed that both treated and untreated AD patients had significantly increased values compared to healthy controls in all three sub-gamma bands. Moreover, the treated AD patients demonstrated significantly higher fronto-parietal gamma coherences during both sensory stimulation and oddball paradigm and lower occipito-parietal coherences during oddball paradigm in comparison to untreated AD patients. Conclusion: The present study demonstrated that an increase of gamma coherences was present in response to both visual sensory and cognitive stimulation in AD patients in all gamma sub-bands. Therefore, gamma oscillatory activity seems to be fundamental in brain functions at both the sensory and cognitive levels. The increase of gamma coherence values was not due to cholinergic treatment to any significant extent, as both treated and untreated AD patients had increased gamma coherence values compared to healthy controls. The use of coherence values reflecting brain connectivity holds potential for neuroimaging of AD and understanding brain dynamics related to the effects of medication. (C) 2017 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Publication Metadata only Reduced Visual Event-Related Delta Oscillatory Responses in Amnestic Mild Cognitive Impairment(Ios Press, Nieuwe Hemweg 6B, 1013 Bg Amsterdam, Netherlands, 2013) Yener, Görsev; Kurt, Pınar; Emek Savaş, Derya Durusu; Güntekin, Bahar; BAŞAR, EROL; 143760; 24351; 227002; 204666; 142226Mild cognitive impairment (MCI) is considered as a prodromal stage for Alzheimer's disease (AD) in the majority of cases. Event-related oscillations might be used for detection of cognitive deficits. Our group's earlier results showed diminished delta visual and auditory target oscillatory responses in AD, and we investigated whether this prevails for MCI. Eighteen MCI subjects and 18 age-matched healthy elderly controls were investigated. The maximum peak-to-peak amplitudes of oscillatory responses for each subject's averaged oscillatory target responses in delta, theta, and alpha frequency bands upon application of visual oddball paradigm were measured. Repeated measures of ANOVA was used to analyze four locations (frontal, central, parietal, occipital), at three coronal (left, midline, right) sites. Independent t tests were applied for post-hoc analyses. The oddball target delta response (0.5-3.0 Hz) was 26-32% lower in MCI than healthy controls over fronto-central-parietal regions [F(1.34) = 4.562, p = 0.04]. Without a group effect, theta oscillatory responses (4-7 Hz) showed significant differences in coronal electrodes indicating highest values over mid-electrode sites, and a anteriorposterior x coronal effect, being maximum at mid-central. Alpha frequency band analyses indicated no statistical differences. Peak-to-peak amplitudes of visual target delta oscillatory responses were lower in fronto-central-parietal regions in MCI than in healthy controls. This supports our earlier findings in AD, showing hypoactive delta fronto-central-parietal regions during cognitive tasks. These results indicate that event-related oscillations may detect early changes of brain dynamics in MCI, and deserves to be investigated as a candidate biomarker in further studies using multimodal techniques.Publication Metadata only Selective Gamma Activation in Alzheimer, Bipolar Disease and Schizophrenia(Elsevier Science Inc, 360 Park Ave South, New York, Ny 10010-1710 Usa, 2011-05-01) Başar Eroğlu, Canan; Güntekin, Bahar; Özerdem, Ayşegül; Yener, Görsev; BAŞAR, EROL; 142226; 274866; 204666; 140995; 143760Publication Metadata only Disturbance In Long Distance Gamma Coherence In Bipolar Disorder(Pergamon-Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington, Oxford Ox5 1Gb, England, 2010-08-16) Özerdem, Ayşegül; Güntekin, Bahar; Saatçı, Ertuğrul; Tunca, Zeliha; BAŞAR, EROL; TR140995; TR204666; TR10488; TR142226The aim of this study was to investigate long distance event-related gamma (28-48 Hz) coherence in mania before and after valproate monotherapy. Gamma coherence in response to visual oddball paradigm in ten medication-free, manic patients was studied before and after six weeks of valproate monotherapy in comparison to ten controls. Inter-hemispheric F(3)-F(4), C(3)-C(4), T(3)-T(4), T(5)-T(6), P(3)-P(4), O(1)-O(2) and intra-hemispheric F(3)-P(3), F(4)-P(4), F(3)-T(5), F(4)-T(6), F(3)-O(1), F(4)-O(2), C(3)-O(1), C(2)-O(4) electrode pairs were included in the analysis. Repeated measures ANOVA revealed a significant difference between groups with regard to pre-treatment coherence values (p: 0.018). The coherence to the target stimuli at the right fronto-temporal location was significantly reduced by 35.41% in the patients compared to controls (p: 0.003). Patients showed significantly lower pretreatment coherence values in response to non-target stimuli compared to controls at the right frontotemporal (28.51%, p: 0.004), right fronto-occipital (23.71%, p: 0.024), and right centro-occipital (25.69%, p: 0.029) locations. After six weeks of valproate monotherapy, manic symptoms improved significantly. Post-treatment change in target and non-target coherence values was statistically non-significant. EEG coherence is a measure of functional connectivity in the brain. Event-related gamma oscillations are essential for brain electrical activity. The results show that acute mania presents right sided long distance connectivity disturbance, thus pointing to the potential importance of measuring oscillatory responses in the search for consistent neurobiological markers in such a complicated condition as bipolar disorder. (C) 2010 Elsevier Inc. All rights reserved.Publication Open Access Cognitive Impairment in Parkinson's Disease Is Reflected with Gradual Decrease of EEG Delta Responses during Auditory Discrimination(Frontiers Media Sa, Avenue Du Tribunal Federal 34, Lausanne, Ch-1015, Switzerland, 2018-02-21) Güntekin, Bahar; Hanoğlu, Lütfü; Güner, Dilan; Helvacı Yılmaz, Nesrin; Çadırcı, Fadime; Mantar, Nagihan; Aktürk, Tuba; Emek Savaş, Derya Durusu; Özer, Fahriye Feriha; Yener, Görsev G.; BAŞAR, EROL; 204666; 171122; 194489; 259227; 259226; 275116; 227002; 38782; 143760; 142226Parkinson's disease (PD) is a neurodegenerative disease that is characterized by loss of dopaminergic neurons in the substantia nigra. Mild Cognitive impairment (MCI) and dementia may come along with the disease. New indicators are necessary for detecting patients that are likely to develop dementia. Electroencephalogram (EEG) Delta responses are one of the essential electrophysiological indicators that could show the cognitive decline. Many research in literature showed an increase of delta responses with the increased cognitive load. Furthermore, delta responses were decreased in MCI and Alzheimer disease in comparison to healthy controls during cognitive paradigms. There was no previous study that analyzed the delta responses in PD patients with cognitive deficits. The present study aims to fulfill this important gap. 32 patients with Parkinson's disease (12 of them were without any cognitive deficits, 10 of them were PD with MCI, and 10 of them were PD with dementia) and 16 healthy subjects were included in the study. Auditory simple stimuli and Auditory Oddball Paradigms were applied. The maximum amplitudes of each subject's delta response (0.5-3.5 Hz) in 0-600 ms were measured for each electrode and for each stimulation. There was a significant stimulation x group effect [F(df = 6; 88 = 3,21; p < 0.015; eta(2)(p) = 0.180], which showed that the difference between groups was specific to the stimulation. Patients with Parkinson's disease (including PD without cognitive deficit, PD with MCI, and PD with dementia) had reduced delta responses than healthy controls upon presentation of target stimulation (p < 0.05, for all comparisons). On the other hand, this was not the case for non-target and simple auditory stimulation. Furthermore, delta responses gradually decrease according to the cognitive impairment in patients with PD. Conclusion: The results of the present study showed that cognitive decline in PD could be represented with decreased event related delta responses during cognitive stimulations. Furthermore, the present study once more strengthens the hypothesis that decrease of delta oscillatory responses could be the candidate of a general electrophysiological indicator for cognitive impairment.Publication Metadata only Brain oscillations are highly influenced by gender differences(ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS, 2007-09) Güntekin, Bahar; BAŞAR, EROL; TR204666; TR142226There are few studies describing gender differences in event related oscillations (EROS). In the present report we demonstrate that gender differences are apparent in EROS even during simple visual stimulation, possibly activating very basic sensory networks. The data of 32 (16 males) healthy subjects were recorded from thirteen different scalp locations (F-3, F-4, C-z, C-3, C-4, T-3, T-4, T-5, T-6, P-3, P-4, O-1, O-2). Analysis was performed in the delta (0.5-3.5 Hz), theta (5-8.5 Hz), alpha (9-13 Hz), beta (15-24 Hz), and gamma (28-48 Hz) frequency ranges. The results showed that the maximum peak-to-peak delta response amplitudes for women were significantly higher than for men over occipital, parietal, central and temporal electrode locations. There were also differentiations in the beta and gamma oscillatory responses. These gender differences were most pronounced over the electrode Site O-2, that is, over primary visual areas. It is suggested that this study might serve as a standard to investigate gender differences in electrophysiology. (c) 2007 Elsevier B.V All rights reserved.Publication Metadata only Facial Affect Manifested By Multiple Oscillations(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2009-01) Güntekin, Bahar; BAŞAR, EROL; TR204666; TR142226The present study describes electrophysiological differentiation of "Facial Expressions" by using the method of event-related oscillations (EROS). These measures were used to assess electrical manifestations of emotional expressions of 20 healthy subjects exposed to neutral, angry, and happy" faces. The present study extended previous analysis to frequency windows of delta (0.5-3.5 Hz) and theta (5-8.5 Hz) oscillations. No significant differences among responses to various face expression stimuli were observed, however, topological differences in response to all facial expressions were found. Delta oscillatory responses in the parietal-temporal-occipital locations were larger than the frontal and central locations, whereas theta oscillatory responses in the right temporal-occipital electrodes were larger than the right central electrodes. Assessment of topologically distributed multiple oscillations opens a new avenue for understanding of the electrophysiology of recognition of "faces" and "facial expressions". (c) 2008 Elsevier B.V. All rights reserved.Publication Metadata only Reduced long distance gamma (28-48 Hz) coherence in euthymic patients with bipolar disorder(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2011-08) Özerdem, Ayşegül; Güntekin, Bahar; Atagün, İlhan; Turp, Bilge; BAŞAR, EROL; TR142226; TR25145; TR204666; TR140995Background: EEG coherence represents the brain's functional connectivity. Synchronous neural gamma oscillations are critical for cortico-cortical communication and large-scale integration of distributed sets of neurons. We investigated long distance gamma (28-48 Hz) coherence in bipolar disorder. Methods: Sensory evoked coherence (EC) and event related coherence (ERC) values for the gamma frequency band during simple light stimulation and visual odd-ball paradigm was assessed in 20 drug-free euthymic bipolar patients in comparison to healthy controls. Groups were compared for the coherence values of the left (F(3)-T(3), F(3)-TP(2), F(3)-P(3), F(3)-O(1)) and right (F(4)-T(4), F(4)-TP(8), F(4)-P(4), F(4)-O(2)) intra-hemispheric electrode pairs by means of a repeated measure analysis of variance (ANOVA) and t-tests. Results: Patients showed significantly lower gamma coherence values in response to target stimuli than the healthy controls between left and right fronto-temporal, as well as between frontal and temporo-parietal electrode pairs. Coherence values for the non-target stimuli were significantly lower in the patients than the healthy controls between frontal and temporo-parietal regions on both right and left sides. EP coherence values did not differ significantly between the groups. Limitations: A relatively small sample size is the major limitation of the study. Conclusions: Bipolar patients present disturbance in functional long-range connectivity between the frontal and temporal as well as temporo-parietal brain structures during a cognitive paradigm requiring attention and immediate recall. The location of the connectivity disturbance corresponds to the underlying neurobiology of executive function, memory and attention impairments in bipolar disorder and raises the question of whether gamma coherence reduction may be a candidate biomarker for bipolar disorder. (C) 2011 Elsevier B.V. All rights reserved.Publication Metadata only Emotional Face Expressions are Differentiated With Brain Oscillations(ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS, 2007-04) Güntekin, Bahar; BAŞAR, EROL; TR204666; TR142226The differentiation of "facial expressions" is a process of higher mental activity, which has considerable applications in "psychology of moods and emotions". We applied the approach of event-related oscillations (EROs) to investigate the modulation of electrical manifestations related to emotional expression in EEG recordings of 20 healthy subjects. EROs of "neutral, angry and happy" faces in 13 electrical recordings sites (F-3, F-4, C-z, C-3, C-4, T-3, T-4, T-5, T-6, P-3, P-4, O-1, O-2) were analyzed. Following the recording session, the subjects were asked to express the degree of their emotional involvement (valence and arousal) using the Self-Assessment Manikin ratings. Amplitude frequency characteristics (AFCs) were used to determine the frequencies of interest and the ranges for digital pass-band filtering applied accordingly. Consecutively, peak to peak amplitude measures of oscillatory responses were computed for the selected frequency bands and for the differentiation of the different stimuli. A differentiation between angry and happy facial expressions was observed especially in the alpha (9-13 Hz) and beta (15-24 Hz) frequencies, however, only when selecting stimuli with high mood involvement. Therefore, these frequency bands are the main focus of this report. The amplitudes of the alpha responses upon angry face stimulation were significantly higher than upon presentation of the happy faces at posterior locations. At F3, C, and C3, beta responses upon angry face stimulation were significantly higher in amplitude compared with the happy face stimulation. It is discussed that the frontal theta response is highly increased in comparison to all theta responses also encountered in studies of face recognition: During observation of facial expression, the occipital theta is much higher. We conclude and emphasize that the analysis of brain oscillatory responses distributed over the scalp in combination with subjective ratings of emotional impact of stimuli provide a good basis for analysing the influence of emotional information processing in the brain. In congruence with others, the results support the phylogenetical viewpoint suggesting that angry face stimulations are faster and more ample in responding. Furthermore, frontal, temporal, parietal and occipital lobes seem to be involved in processing of facial expressions, as reflected in an ensemble of different frequency brain oscillatory responses distributed over the scalp. (c) 2006 Published by Elsevier B.V.