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A comparative study of auditory and visual event related coherences
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2012-09) Tülay, Elif; Turp Gölbaşı, Bilge; Güntekin, Bahar; BAŞAR, EROL; 142226; 204666
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A review of alpha activity in integrative brain function: Fundamental physiology, Sensory coding, cognition and pathology
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2012-10) BAŞAR, EROL; TR142226
Aim of the review: Questions related to the genesis and functional correlates of the brain's alpha oscillations around 10 Hz (Alpha) are one of the fundamental research areas in neuroscience. In recent decades, analysis of this activity has been not only the focus of interest for description of sensory-cognitive processes, but has also led to trials for establishing new hypotheses. The present review and the companion review aim to constitute an ensemble of "reasonings and suggestions" to understand alpha oscillations based on a wide range of accumulated findings rather than a trial to launch a new "alpha theory". Surveyed descriptions related to physiology and brain function: The review starts with descriptions of earlier extracellular recordings, field potentials and also considers earlier alpha hypotheses. Analytical descriptions of evoked and event-related responses, event-related desynchronization, the relationship between spontaneous activity and evoked potentials, aging brain, pathology and alpha response in cognitive impairment are in the content of this review. In essence, the gamut of the survey includes a multiplicity of evidence on functional correlates in sensory processing, cognition, memory and vegetative system, including the spinal cord and heart. (C) 2012 Elsevier B.V. All rights reserved.
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A Review of Gamma Oscillations in Healthy Subjects and in Cognitive Impairment
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2013-11) BAŞAR, EROL; 142226
This review describes a wide range of functional correlates of gamma oscillations in whole-brain work, in neuroethology, sensory-cognitive dynamics, emotion, and cognitive impairment. This survey opens a new window towards understanding the brain's gamma activity. Gamma responses are selectively distributed in the whole brain, and do not reflect only a unique, specific function of the nervous system. Sensory responses from cortex, thalamus, hippocampus, and reticular formations in animal and human brains, and also cognitive responses, were described by several authors. According to reviewed results, it becomes obvious that cognitive disorders, and medication which influence the transmitter release change entirely the understanding of the big picture in cognitive processes. Gamma activity is evoked or induced by different sensory stimuli or cognitive tasks. Thus, it is argued that gamma-band synchronization is an elementary and fundamental process in whole-brain operation. In conclusion, reasoning and suggestions for understanding gamma activity are highlighted. (C) 2013 Elsevier B.V. All rights reserved.
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A short review of alpha activity In cognitive processes and in cognitive impairment
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2012-10) Güntekin, Bahar; BAŞAR, EROL; TR142226; TR204666
Aim of the report: In the companion report (Basar, this volume), the physiological fundaments of alpha activity in integrative brain function are described. The present report is a review of the significant role of alpha activity in memory and cognitive processes in healthy subjects, and in cognitive impairment. The role of neurotransmitters is also described, briefly, in this context. Towards an understanding of brain alpha: Despite numerous experimental studies, it is indicated that the presented results are only appropriate to establish an ensemble of reasonings and suggestions for analyzing "alphas" in the whole brain. In turn, in the near future, these reasonings and suggestions may serve (or are indispensable to serve) as fundaments of more general and tenable hypotheses on the genesis and function of "alphas". (C) 2012 Elsevier B.V. All rights
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Brain oscillatory dynamics in Alzheimer's disease and mild cognitive impairment
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2012-09) Yener, Görsev; Kurt, Pınar; Güntekin, Bahar; BAŞAR, EROL; 143760; 24351; 204666; 142226
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Brain's oscillatory responses in perception of emotional pictures
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2014-11) Güntekin, Bahar; Tülay, Elif; Turp Gölbaşı, Bilge; BAŞAR, EROL; 204666; 142226
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Changes in brain oscillations and connectivity deficit in bipolar disorder
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2012-09) Güntekin, Bahar; Atagün, Murat İlhan; Özerdem, Ayşegül; BAŞAR, EROL; 204666; 25145; 140995; 142226
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Darwin's Evolution Theory, Brain Oscillations, And Complex Brain Function In A New "Cartesian View"
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2009-01) Güntekin, Bahar; BAŞAR, EROL; TR142226; TR204666
Comparatively analyses of electrophysiological correlates across species during evolution, alpha activity during brain maturation, and alpha activity in complex cognitive processes are presented to illustrate a new multidimensional "Cartesian System" brain function. The main features are: (1)The growth of the alpha activity during evolution, increase of alpha during cognitive processes, and decrease of the alpha entropy during evolution provide an indicator for evolution of brain cognitive performance. (2) Human children younger than 3 years are unable to produce higher cognitive processes and do not show alpha activity till the age of 3 years. The mature brain can perform higher cognitive processes and demonstrates regular alpha activity. (3) Alpha activity also is significantly associated with highly complex cognitive processes, such as the recognition of facial expressions. The neural activity reflected by these brain oscillations can be considered as constituent "building blocks" for a great number of functions. An overarching statement on the alpha function is presented by extended analyzes with multiple dimensions that constitute a "Cartesian Hyperspace" as the basis for oscillatory function. Theoretical implications are considered. (c) 2008 Elsevier B.V. All rights reserved.
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Event related desynchronization: Precaution is needed to be used as an indicator of cognitive processes
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2014-11) Turp Gölbaşı, Bilge; BAŞAR, EROL; 142226
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Event-related oscillatory gamma responses appear late in Alzheimer disease
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2014-11) Emek Savaş, Derya Durusu; Güntekin, Bahar; Yener, Görsev; BAŞAR, EROL; 142226; 227002; 204666; 143760
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Evoked And Event Related Coherence Of Alzheimer Patients Manifest Differentiation Of Sensory-Cognitive Networks
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2010-10-21) Güntekin, Bahar; Tülay, Elif; Yener, Görsev G.; BAŞAR, EROL; TR143760; TR142226; TR204666; TR142311
In previous studies on Alzheimer's patients it was shown that, in frontal and parietal locations, delta and theta responses of AD patients were greatly reduced. The present study analyzed coherence functions in these highly affected frontal and parietal areas. Visual sensory and event related coherences of patients with Alzheimer type dementia (AD) were analyzed comparatively. A total of 38 mild, probable AD subjects (19 untreated, 19 treated with cholinesterase inhibitors) were compared with a group of 19 healthy controls. The sensory evoked coherence and event related target coherences were analyzed for delta (1-3.5 Hz), theta (4-7 Hz), alpha (8-13 Hz), beta (15-30 Hz) and gamma (28-48 Hz) frequency ranges for long-range 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) electrode pairs. The healthy control group showed significantly higher values of event related coherence in "delta", "theta" and "alpha" bands in comparison to the de nova and medicated AD groups (p<0.01 for the delta, theta and alpha) upon application of a target stimuli. In contrast, almost no changes in event related coherences were observed in beta and gamma frequency bands. Furthermore, no differences were recorded between healthy and AD groups upon application of simple light stimuli. Besides this, coherence values upon application of target stimuli were higher than sensory evoked coherence in all groups and in all frequency bands (p<0.01). The cognitive networks of AD patients were highly impaired in comparison to networks activated by sensory stimulation, thus showing separate activation of sensory and cognitive networks. (C) 2010 Elsevier B.V. All rights reserved.
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Facial Affect Manifested By Multiple Oscillations
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2009-01) Güntekin, Bahar; BAŞAR, EROL; TR204666; TR142226
The 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.
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Is research on brain oscillations in a new "Take Off-State" in integrative brain function?
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2012-09) BAŞAR, EROL; TR142226
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Prolongation Of Alpha Oscillations İn Auditory Oddball Paradigm
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2009-03) Öniz, Adile; BAŞAR, EROL; TR59951; TR142226
Although an important component of the P300 target response is the "prolonged alpha response". no relevant analysis is found in the literature. The present study emphasizes the relevance of prolongation of alpha responses in auditory oddball paradigm. Two types of stimuli were applied to twenty subjects. As standard stimuli 80 dB-1500 Hz tones and the target stimuli 80 dB-1600 Hz tones were used. The prolongations of alpha responses were measured in 13 recording sites in the frequency range of 8-13 Hz. At the Cz recording site, the time period for reaching one third (duration of prolongation) of its peak-to-peak amplitude (1/3 latency) of alpha response to target was 446 ms. The prolongation of nontarget stimuli was 277 ms. Thus, the alpha response to target was significantly more prolonged than the alpha response to nontarget stimuli. Similarly, at C3, the alpha response to target stimuli was prolonged to 373 ms. The alpha response to nontarget stimuli was prolonged to 284 ms. The target alpha response was more prolonged in comparison to the non-target alpha results. The alpha response to target stimuli (431 ms) was also more prolonged in comparison with the alpha response upon non-target stimuli (266 ms) at the C4 recording site. The results indicate that the alpha responses are prolonged under a certain level of cognitive load and working memory. Alpha prolongation is a significant component of P300 responses. It can be Suggested that the cognitive load dependency of alpha responses upon the targets could be related to working memory. (C) 2008 Elsevier B.V. All rights reserved.
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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; TR140995
Background: 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.
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The visual cognitive network, but not the visual sensory network, is affected in amnestic mild cognitive impairment: A study of brain oscillatory responses
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2014-10-17) Yener, Görsev; Emek Savaş, Derya Durusu; Güntekin, Bahar; BAŞAR, EROL; 143760; 227002; 204666; 142226
Mild Cognitive Impairment (MCI) is considered in many as prodromal stage of Alzheimer's disease (AD). Event-related oscillations (ERO) reflect cognitive responses of brain whereas sensory-evoked oscillations (SE) inform about sensory responses. For this study, we compared visual SEO and ERO responses in MCI to explore brain dynamics (Background). Forty-three patients with MCI (mean age=74.0 year) and 41 age- and education-matched healthy-elderly controls (HC) (mean age=71.1 year) participated in the study. The maximum peak-to-peak amplitudes for each subject's averaged delta response (0.5-3.0 Hz) were measured from two conditions (simple visual stimulation and classical visual oddball paradigm target stimulation) (Method). Overall, amplitudes of target ERO responses were higher than SEO amplitudes. The preferential location for maximum amplitude values was frontal lobe for ERO and occipital lobe for SEO. The ANOVA for delta responses showed significant results for the group Xparadigm. Post-hoc tests indicated that (1) the difference between groups were significant for target delta responses, but not for SEO, (2) ERO elicited higher responses for HC than MCI patients, and (3) females had higher target ERO than males and this difference was pronounced in the control group (Results). Overall, cognitive responses display almost double the amplitudes of sensory responses over frontal regions. The topography of oscillatory responses differs depending on stimuli: visualsensory responses are highest over occipitals and -cognitive responses over frontal regions. A group effect is observed in MCI indicating that visual sensory and cognitive circuits behave differently indicating preserved visual sensory responses, but decreased cognitive responses (Conclusion). (C) 2014 Elsevier B.V. All rights reserved.
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The visual oddball target delta oscillatory responses are decreased in amnestic mild cognitive impairment
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2012-09) Yener, Görsev; Kurt, Pınar; Emek Savaş, Derya Durusu; Güntekin, Bahar; BAŞAR, EROL; 143760; 24351; 227002; 204666; 142226
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Treatment-induced manic switch in the course of unipolar depression can predict bipolarity: Cluster analysis based evidence
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2011-11) Dumlu, Kemal; Orhon, Zahide; Özerdem, Ayşegül; Tural, Ümit; Ulaş, Halis; Tunca, Zeliha; 140995; 155394; 143327
Background: Antidepressants are known to induce manic switch in patients with depression. Treatment-induced mania is not considered as bipolar disorder in DSM IV. The aim of this study was to assess whether clinical characteristics of patients with unipolar depression with a history of treatment-induced mania were similar to those of patients with bipolar disorder. Method: The study included 217 consecutive patients with DSM-IV mood disorders, diagnosed as: bipolar disorder type I (BP-I, n = 58) or type II (BP-II, n = 18) whose first episodes were depression, recurrent (unipolar) major depressive disorder with a history of antidepressant treatment-induced mania (switchers = stir); n = 61) and without such an event (rUD; n = 80). First, the groups were compared with regard to clinical features and course specifiers using variance and chi-square analysis. Variables that differed significantly between the four groups were included in two-step cluster analysis to explore naturally occurring subgroups in all diagnoses. Subsequently, the relationship between the naturally occurring clusters and pre-defined DSM-IV diagnoses were investigated. Results: Two-step cluster analysis revealed two different naturally occurring groups. Higher severity of depressive episodes, with higher rate of melancholic features, higher number of hospitalization and suicide attempts were represented in one cluster where switchers (77%), bipolar I (94.8%) and II (83.3%) patients clustered together. Conclusion: The findings of this study confirm that treatment-induced mania is a clinical phenomenon that belongs within-the bipolar spectrum rather than a coincidental treatment complication, and that it should be placed under "bipolar disorders" in future classification systems. Limitations: The study includes the limitations of any naturalistic retrospective study. (C) 2011 Elsevier B.V. All rights reserved.

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