Oguz Tan - Academia.edu (original) (raw)

Papers by Oguz Tan

Obsessive-compulsive disorder (OCD) is a common mental illness and a ubiquitous cause of disabili... more Obsessive-compulsive disorder (OCD) is a common mental illness and a ubiquitous cause of disability. Approximately half of patients with OCD only partially respond or do not respond at all to current ways of treatment. Even patients who respond to treatment usually need high doses of medication and/or intense psychotherapy for a long time. It is obvious that therapeutic approaches to OCD need to be improved. In this article, we review the role of pharmacogenetics in the treatment of OCD.

Objectives: It was aimed to review the literature about the use of repetitive transcranial magnet... more Objectives: It was aimed to review the literature about the use of repetitive transcranial magnetic stimulation (rTMS) therapy in psychiatric disorders. Methods: A medline research was done concerning rTMS use in mood disorders, anxiety disorders, psychotic disorders and substance use disorders. Results: Application of rTMS in depressive patients usually lead to significant clinical improvement. Findings about the use of rTMS in manic episodes, anxiety disorders psychotic disorders and substance use disorders are limited. Conclusion: rTMS is probably a useful therapeutic approach in depressive disorders. Further research is needed to clarify the role of rTMS in psychiatric disorders other than depression.

In the present study, multichannel EEG complexity has newly been examined for identification of o... more In the present study, multichannel EEG complexity has newly been examined for identification of obsessive-compulsive disorder (OCD). Since, EEG series is non stationary signal in nature, resting state eyes closed 19-channel EEG measurements of 3 min were segmented by using a specified window of 2 sec before applying the complexity and coherence metrics. In tests, the well known statistical entropy computation methods so named Approximate Entropy, Sample Entropy and Permutation Entropy (PermEn) were used to obtain the quantitative EEG complexity values. And, Mutual Information (MI) in addition to Coherence Function were used to measure the hemispheric dependency of each symmetrically placed electrode couples. Individual entropy values of 19-channels and both MI and CF values of 8 electrode couples were classified by using Support Vector Machine Classifiers. The results show that PE provides the good discrimination with accuracy of 97%, however, MI can provide the clearly error free E...

Purpose: To compare effects of bright light therapy (BLT) alone or combined with the selective se... more Purpose: To compare effects of bright light therapy (BLT) alone or combined with the selective serotonin reuptake inhibitor (SSRI) fluoxetine, on severity of depression, circadian rhythms, mood disturbance, and sleep quality, in patients with non-seasonal depression. Patients and methods: Drug-free patients who were administered 10,000 lux of BLT for 30 minutes for 7 days comprised the BLT group (n = 7), while patients who started fluoxetine as an add-on treatment day comprised the SSRI + BLT group (n = 8). The primary outcomes were severity of depression, measured using the Hamilton Depression Rating Scale (HAM-D) and the Beck Depression Inventory (BDI); chronotype, measured using the Morningness Eveningness Questionnaire (MEQ); mood disturbance, measured using the Profile of Mood States (POMS) survey; and sleep quality, measured using the Pittsburgh Sleep Quality Index (PSQI), before and after treatment in both groups. Results: All patients completed the study, and none reported o...

Despite the significance of major depressive disorder, objective procedures for selecting optimal... more Despite the significance of major depressive disorder, objective procedures for selecting optimal treatments are lacking, there is a need for reliable and objective measures capable of differentiating between those who may or may not respond to specific treatments. Studies using neuroimaging, neurocognitive, and electrophysiologic measures have found that pre-treatment differences among depressed patients are related to subsequent clinical response to antidepressant drugs. Besides some clinical features and biological markers, the modern methods of brain imaging and quantitative electroencephalogram might be useful in prediction of treatment response. INTRODUCTION In industrialized countries, mental illnesses may account for about 16% of total health care costs and 30% of disability claims [1]. A tool capable of differentiating between those who may or may not respond to specific treatments is needed. Such a measure should be reliable, objective, and readily available.

International Journal of Neural Systems, 2015

In the present study, both single channel electroencephalography (EEG) complexity and two channel... more In the present study, both single channel electroencephalography (EEG) complexity and two channel interhemispheric dependency measurements have newly been examined for classification of patients with obsessive-compulsive disorder (OCD) and controls by using support vector machine classifiers. Three embedding entropy measurements (approximate entropy, sample entropy, permutation entropy (Per-mEn)) are used to estimate single channel EEG complexity for 19-channel eyes closed cortical measurements. Mean coherence and mutual information are examined to measure the level of interhemispheric dependency in frequency and statistical domain, respectively for eight distinct electrode pairs placed on the scalp with respect to the international 10-20 electrode placement system. All methods are applied to short EEG segments of 2 s. The classification performance is measured 20 times with different 2-fold cross-validation data for both single channel complexity features (19 features) and interhemispheric dependency features (eight features). The highest classification accuracy of 85 ±5.2% is provided by PermEn at prefrontal regions of the brain. Even if the classification success do not provided by other methods as high as PermEn, the clear differences between patients and controls at prefrontal regions can also be obtained by using other methods except coherence. In conclusion, OCD, defined as illness of orbitofronto-striatal structures [Beucke et al., JAMA Psychiatry 70 (2013) 619-629; Cavedini et al., Psychiatry Res. 78 (1998) 21-28; Menzies et al., Neurosci. Biobehav. Rev. 32(3) (2008) 525-549], is caused by functional abnormalities in the pre-frontal regions. Particularly, patients are characterized by lower EEG complexity at both pre-frontal regions and right fronto-temporal locations. Our results are compatible with imaging studies that define OCD as a sub group of anxiety disorders exhibited a decreased complexity (such as anorexia nervosa [Toth et al., Int. J. Psychophysiol. 51(3) (2004) 253-260] and panic disorder [Bob et al., Physiol. Res. 55 (2006) S113-S119]).

Neurocomputing, 2015

Cite this article as: Turker Tekin Erguzel, Serhat Ozekes, Gokben Hizli Sayar, Oguz Tan, Nevzat T... more Cite this article as: Turker Tekin Erguzel, Serhat Ozekes, Gokben Hizli Sayar, Oguz Tan, Nevzat Tarhan, A Hybrid artificial intelligence method to classify trichotillomania and obsessive compulsive disorder, Neurocomputing, http://dx. Abstract: Classification of psychiatric disorders is becoming one of major focus of research using artificial intelligence approach. The combination of feature selection and classification methods generates satisfactory outcomes using biological biomarkers. The use of quantitative electroencephalography (EEG) cordance has enhanced the clinical utility of the EEG in psychiatric and neurological subjects. Trichotillomania (TTM), a kind of body focused repetitive behavior, is defined as a disorder characterized by repetitive hair pulling that results in noticeable hair loss. Phenomenological observations underline similarities between hair-pulling behaviors and compulsions seen in obsessivecompulsive disorder (OCD). Despite the recognized similarities between OCD and TTM, there is evidence of important differences between these two disorders. In order to dichotomize the subjects of each disorder, artificial intelligence approach was employed using quantitative EEG (QEEG) cordance values with 19 electrodes from 10 brain regions (prefrontal, frontocentral, central, left temporal, right temporal, left parietal, occipital, midline, left frontal and right frontal) in 4 frequency bands (delta, theta, alpha and beta). Machine learning methods, artificial neural networks (ANN), support vector machine (SVM), k-nearest neighbor (k-NN) and Naïve Bayes (NB), were used in order to classify 39 TTM and 40 OCD patients. SVM, with its relatively better performance, was then combined with an improved ant colony optimization (IACO) approach in order to select more informative features with less iterations.

2014 18th National Biomedical Engineering Meeting, 2014

Obsesif Kompulsif Bozukluk (OKB) hastalığı nöropsikiyatrik bir beyin hastalığıdır ve bu hastalığı... more Obsesif Kompulsif Bozukluk (OKB) hastalığı nöropsikiyatrik bir beyin hastalığıdır ve bu hastalığın teşhis, tedavi sürecinde EEG analizi kullanılmaktadır. Yapılan çalışmalar bu hastalığın beynin frontal lobunda bulunan işlev bozuklukları nedeniyle oluştuğunu göstermektedir. EEG senkronizasyonunda yeni bir ölçüt olarak geliştirilen Global Alan Senkronizasyonu (GAS) yöntemi beyindeki nöral osilasyonlar arasındaki faz farklılıklarını hesaplayan bir yöntemdir. Alzheimer ve şizofreni gibi psikiyatrik hastalıklarda GAS değerlerinin düştüğünü gösterir çalışmalar yayınlanmıştır. Bu çalışmada ise OKB hastalığının beynin nöral osilasyonları arasındaki faz farkını nasıl etkilediği araştırılmıştır. Bu amaçla 19-kanal EEG sinyaline uygulanan GAS yönteminin sonuçları; OKB hastalığının beynin frontal bölgesinde, Delta ve Beta 3 frekans bantlarında nöral senkronizasyonun azaldığını göstermiştir.

... Springer-Verlag Berlin Heidelberg 2010 155 Combining Transcranial Magnetic Stimulation with (... more ... Springer-Verlag Berlin Heidelberg 2010 155 Combining Transcranial Magnetic Stimulation with (f)MRI Gesa Hartwigsen, Tanja Kassuba, and Hartwig Roman Siebner 16 16.1 Introduction Transcranial magnetic stimulation (TMS) is ...

Journal of affective disorders, Jan 12, 2014

Understanding the biological underpinnings of unipolar (UD) and bipolar depression (BD) is vital ... more Understanding the biological underpinnings of unipolar (UD) and bipolar depression (BD) is vital for avoiding inappropriate treatment through the misdiagnosis of bipolar patients in their first depressive episode. One plausible way to distinguish between UD and BD is to compare EEG brain dynamics to identify potential neurophysiological biomarkers. Here we aimed to test group differences in EEG power, cordance and coherence values between UD and BD. Twenty-five bipolar and 56 unipolar depression patients were recruited. Sociodemographic and clinical variables were collected in addition to resting state EEG. Data was analyzed with multivariate and repeated analyses of variance where parametric assumptions were met. Accordingly, we did not find any differences in the EEG absolute power and frontal asymmetry indexes between UD and BD. Regarding cordance, significant group differences were observed in the right theta cordance values (p=0.031). Regarding coherence, BD patients (as compar...

Primary care companion to the Journal of clinical psychiatry, 2008

Neuropsychiatric Disease and Treatment, 2013

The aim of the study reported here was to examine the safety and effectiveness of high-frequency ... more The aim of the study reported here was to examine the safety and effectiveness of high-frequency repetitive transcranial magnetic stimulation (rTMS) in elderly patients with depression. Patients and methods: Sixty-five depressed elderly patients received rTMS over their left prefrontal cortex for 6 days per week, from Monday to Saturday, for 3 weeks. The rTMS intensity was set at 100% of the motor threshold and 25 Hz stimulation with a duration of 2 seconds and was delivered 20 times at 30-second intervals. A full course comprised an average of 1000 magnetic pulses. Depression was rated using the Hamilton Depression Rating Scale (HAMD) before and after treatment. Response was defined as a 50% reduction in HAMD score. Patients with HAMD scores , 8 were considered to be in remission.

Clinical EEG and Neuroscience, 2014

Feature selection is an important step in many pattern recognition systems aiming to overcome the... more Feature selection is an important step in many pattern recognition systems aiming to overcome the so-called curse of dimensionality. In this study, an optimized classification method was tested in 147 patients with major depressive disorder (MDD) treated with repetitive transcranial magnetic stimulation (rTMS). The performance of the combination of a genetic algorithm (GA) and a back-propagation (BP) neural network (BPNN) was evaluated using 6-channel pre-rTMS electroencephalographic (EEG) patterns of theta and delta frequency bands. The GA was first used to eliminate the redundant and less discriminant features to maximize classification performance. The BPNN was then applied to test the performance of the feature subset. Finally, classification performance using the subset was evaluated using 6-fold cross-validation. Although the slow bands of the frontal electrodes are widely used to collect EEG data for patients with MDD and provide quite satisfactory classification results, the outcomes of the proposed approach indicate noticeably increased overall accuracy of 89.12% and an area under the receiver operating characteristic (ROC) curve (AUC) of 0.904 using the reduced feature set.

Clinical EEG and Neuroscience, 2012

We examined the efficacy of high-frequency repetitive transcranial magnetic stimulation (rTMS) in... more We examined the efficacy of high-frequency repetitive transcranial magnetic stimulation (rTMS) in 419 patients with treatmentresistant depression. The patients received daily sessions of rTMS over the left prefrontal cortex as an adjuvant to pharmacotherapy. The rTMS intensity was set at 100% of the motor threshold and 25 Hz stimulation, with train duration of 2 seconds delivered at 30-second intervals. A full course comprised 1000 magnetic pulses. Depression was rated using the Hamilton Depression Rating Scale (HAMD) before and after treatment. Response was defined as a 50% reduction in the HAMD score. Patients with HAMD scores of less than 8 were considered to be in remission. The mean HAMD score for the study group decreased from 22.59 + 5.92 to 10.50 + 5.83 (P < .001). After the treatment period, 268 (64%) out of 419 patients demonstrated significant mood improvements, as indexed by a reduction of more than 50% on the HAMD score. In addition, 140 patients (33.4%) attained remission (HAMD score <8); and 11 patients achieved a partial response. Treatment was generally well tolerated, and no serious adverse effects were reported. In conclusion, high-frequency (25 Hz) rTMS was well tolerated and found to be statistically and clinically effective in patients with treatment-resistant depression. This study contributed to the existing evidence of the antidepressant effect of rTMS in the treatment of depression.

Anatolian Journal of Psychiatry, 2013

Transkraniyal manyetik uyarım (TMU) tekniği, gerek serebral korteks işlevlerinin lokalizasyonunu ... more Transkraniyal manyetik uyarım (TMU) tekniği, gerek serebral korteks işlevlerinin lokalizasyonunu belirlemeyi amaçlayan nörofizyolojik araştırmalarda, gerekse sinir sistemi hastalıklarının tedavisini hedefleyen klinik çalışmalarda kullanılır. TMU beyin dokusunun uyarımını sağlayan, invazif olmayan bir tekniktir. Sinir sisteminin belli bir bölgesine ayarlanabilir bir şiddette ve frekansta, bir defa veya çok sayıda manyetik atım verilmesinden oluşur. TMU'nun klinik uygulamaya girdiği 1985 yılından bu yana en fazla çalışma depresyon hastaları üzerine yapılmıştır. Klinik çalışmaların çoğu, TMU'nun depresyon tedavisinde etkili olduğunu göstermektedir. TMU farmakolojik tedavilere yanıt vermeyen dirençli depresyonda da uygulanmış ve yalancı (sham) TMU'ya üstün bulunmuştur. Beynin her iki hemisferinin çeşitli bölgeleri farklı parametreler kullanılarak uyarılmıştır, ama araştırmalara katılan depresyon hastalarının %90'ına sol dorsolateral prefrontal kortekse yüksek frekanslı ve tekrarlayan uyarımlar verilmiştir. Yüksek frekanslı ve tekrarlayan TMU'nun en ciddi yan etkisinin, oldukça nadir görülmekle birlikte nöbet olduğu bildirilmektedir. Bu yazıda tekrarlayan TMU (tTMU) uygulaması sırasında jeneralize tonik-klonik nöbet geçiren bir olgu sunulmakta ve TMU ile indüklenen nöbet üzerine literatür gözden geçirilmektedir. (Anadolu Psikiyatri Derg 2013;14:287-9) Anahtar kelimeler: transkraniyal manyetik uyarım tedavisi, depresyon, nöbet

The Primary Care Companion to The Journal of Clinical Psychiatry, 2008

Conference Presentations by Oguz Tan

Nöropsikiyatrik bir hastalk olan Obsesif Kompulsif Bozukluğun (OKB), patofizyolojik araştrmalar... more Nöropsikiyatrik bir hastalk olan Obsesif Kompulsif Bozukluğun (OKB), patofizyolojik araştrmalarnda EEG analizi kullanlmaktadr. Önceki yllarda gerçekleştirilen EEG tabanl OKB araştrmalarnda beyin korteksinde anormal fonksiyonlar gözlenmiştir. Kaynak lokalizasyonu amacyla kullanlan ve konvansiyonel Hzl Fourier Dönüşümü (HFD) Yöntemine göre daha iyi sonuçlar verdiği bilinen HFD Dipol Yaklaşm (HFDDY) Yöntemi, EEG senkronizasyon seviyelerinin ölçülmesi amacyla kullanlabilmektedir. Bu çalşmada; HFDDY yöntemi kullanlarak beyin korteksinde gerçekleşen nöral osilasyonlar arasndaki faz farklar hesaplanmştr. Uluslar-aras 10-20 elektrot sistemine göre ölçülen 19 kanal EEG sinyalinin analizi sonucunda OKB hastalarnda Theta frekans bandnn faz senkronizasyonunda azalma tespit edilmiştir. Anahtar Kelimelerobsesif kompulsif bozukluklar (OKB); EEG; hzl fourier dönüşümü dipol yaklaşm yöntemi (HFDDYY) Abstract EEG analysis has been used in pathophysiological research of Obsessive Compulsive Disorder (OCD) that is one of the neuropsychiatric disease. EEG abnormalities was observed in brain cortex of patients with OCD. Fast Fourier Transform (FFT) Dipol Approximation Method (FFTDA), used for source localization and superior to conventional FFT method, has also been used for measurement of the level of EEG synchronization. In this research, phase differences between cortical neural oscillations was computed by using FFTDA. Then, analysis of 19 channel EEG series, collected with international 10-20 electrode placement system, shows the loss of Theta band phase synchronization in patients with OCD.. -