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Sirel Karakaş

Publications and source records attributed to Sirel Karakaş.

12 recordsLinked to original sources
PubMed2006

Early gamma response of sleep is sensory/perceptual in origin.

The goal of the study was to investigate the gamma response of the brain and its functional correlates in rapid eye movements (REM) sleep and the three stages of non-REM sleep. Data on overnight sleep were acquired from 16 healthy, young adult, volunteer males. Neuroelectric activity was recorded from seven recording sites (Fz, Cz, Pz, F3, F4, P3, P4) in response to auditory stimuli (2000 Hz deviant and 1000 Hz standard stimuli: 65 dB, 10 ms r/f time, 50 ms duration) under passive oddball paradigm. Data were analyzed with the Fourier transform and digital filtering and also the recently developed technique of time-frequency component analysis (TFCA). TFCA displayed the gamma response under all stages of sleep. Statistical analysis did not reveal a significant effect of stimulus type, recording site or sleep stage on the three parameters of TFCA, which included maximum value of the time-frequency representation of the extracted gamma component, maximum magnitude of the time-domain representation of the component and the energy of this component. The gamma period included N1 and the early theta response, both of which are related to sensory-perceptual processing in the literature. According to these findings, the gamma response is possibly related, as in wakefulness, to early stimulus processing that also includes sensory/perceptual operations.

Acoustic Stimulation↗
PubMed2006

Neuroscience is awaiting for a breakthrough: an essay bridging the concepts of Descartes, Einstein, Heisenberg, Hebb and Hayek with the explanatory formulations in this special issue.

The paper presents gedankenmodels which, based on the theories and models in the present special issue, describe the conditions for a breakthrough in brain sciences and neuroscience. The new model is based on contemporary findings which show that the brain and its cognitive processes show super-synchronization. Accordingly, understanding the brain/body-mind complex is possible only when these three are considered as a wholistic entity and not as discrete structures or functions. Such a breakthrough and the related perspectives to the brain/body-mind complex will involve a transition from the mechanistic Cartesian system to a nebulous Cartesian system, one that is basically characterized by parallel computing and is further parallel to quantum mechanics. This integrated outlook on the brain/body-mind, or dynamic functionality, will make the treatment of also the meta-cognitive processes and the greater part of the iceberg, the unconscious, possible. All this will be possible only through the adoption of a multidisciplinary approach that will bring together the knowledge and the technology of the four P's which consist of physics, physiology, psychology and philosophy. The genetic approach to the functional dynamics of the brain/body-mind, where the oscillatory responses were found to be laws of brain activity, is presented in this volume as one of the most recent perspectives of neuroscience.

Animals↗
PubMed2006

Models and theories of brain function in cognition within a framework of behavioral cognitive psychology.

The present article presents a nonexhaustive collection of contemporary models and theories on brain function and discusses these models and theories within a framework of explanatory formulations in behavioral cognitive psychology. Such a mission was accomplished by evaluating the cognitive implications in the explanatory formulations with respect to established laws/principles and models/theories of behavioral cognitive psychology. The article also points to problem areas of behavioral cognitive psychology for which the explanatory formulations have solutions to offer. The article shows that the cinematographic hypothesis, the new visual model, the synergetic model, and the theory of whole-brain-work emphasize various aspects of perception. The formulations on P300 theory emphasize attention and also working memory. The theory on cognits is a comprehensive account of memory. Characteristic to all of these explanatory formulations and also to that on the complexity and its evolution and that on neurocognitive networks is the emphasis on selective distribution, integration to the point of supersynergy, and dynamicity. Such a viewpoint was not only applied to the operations of the brain but also of cognition. With such a conceptualization, the explanatory formulations could account for cognitive processes other than the ones emphasized. A common aspect in a majority of the formulations is the utilization of the oscillatory activity as the valid activity of the brain. The article points out that a frontier in cognitive psychophysiology would be the study of the genetics of brain oscillations.

Brain↗
PubMed2006

Hormone replacement therapy and cognitive function in postmenopausal women.

OBJECTIVES: The study investigated the effect of hormone replacement therapy (HRT) on cognitive processes in healthy, naturally postmenopausal women. METHOD: Participants were 64 volunteer postmenopausal women (27 in HRT, 37 in non-HRT group). Groups were matched for age, level of education and postmenopausal period. Duration of HRT was more than 12 months. Cognitive processes were measured through 44 scores obtained from Wechsler Memory Scale-Revised, Line Orientation Test, Cancellation Test and Raven Standard Progressive Matrices. All of these tests had been studied with respect to their psychometric properties in the Turkish culture [for review, Karakaş S. BILNOT battery: research and development of neuropsychological tests. Ankara, Turkey: Dizayn Ofset; 2004]. RESULTS: Multivariate analysis of variance was performed where HRT and estradiol level were predictive (independent) variables and test scores were predicted (dependent) variables. The studied variables did not have a significant effect on a broad spectrum of neuropsychological scores that measured immediate and delayed visual and verbal memory, visuospatial perception and orientation, sustained attention/vigilance, visual search and scan, impulsivity and response speed, executive functions and general intelligence. Logistic regression analysis demonstrated a prediction rate of 86.89% of HRT status; the model was, however, based on four scores whose scientific relevance could not at this point be ascertained. CONCLUSION: The research design of the present observational study applied control techniques to demographic (age, level of education), menopausal (length of menopausal period, duration of HRT), and hormonal variables. The cognitive changes that some studies found concerning the effect of replacement therapy could not be found when the potentially confounding variables were thus controlled.

Cognition↗
PubMed2006

Learning of serial digits leads to frontal activation in functional MR imaging.

PURPOSE: Clinical studies have shown that performance on the serial digit learning test (SDLT) is dependent upon the mesial temporal lobes, which are responsible for learning and its consolidation. However, an effective SDLT performance is also dependent upon sequencing, temporal ordering, and the utilization of mnemonic strategies. All of these processes are among the functions of the frontal lobes; in spite of this, the relationship between SDLT performance and the frontal lobes has not been demonstrated with previously used mapping techniques. The aim of this study was to investigate the areas of the brain that are activated by SDLT performance. MATERIALS AND METHODS: Ten healthy, right handed volunteers (mean age, 20.1 years; SD: 3.3) who had 12 years of education were studied with a 1.0 T MR imaging scanner. BOLD (blood oxygen level dependent) contrast and a modified SDLT were used. Activated loci were automatically mapped using a proportional grid. RESULTS: In learning, the most consistent activation was observed in B-a-7 of the right (80%) and the left hemispheres (50%). In recall, the most consistent activation was observed in B-a-7 of the right hemisphere (60%). Activations were observed in 2.5+/-0.97 Talairach volumes in learning, whereas they encompassed 1.7+/-0.95 volumes in recall. The difference between both phases (learning and recall) regarding total activated volume was significant (p < 0.05). CONCLUSION: The prefrontal activation during SDLT performance was not related to learning or to recall, but to a function that is common to both of these cognitive processes. A candidate for this common factor may be the executive functions, which also include serial position processing and temporal ordering.

Adolescent↗
PubMed2005

Early time-locked gamma response and gender specificity.

The aim was to investigate whether gender is a causative factor in the gamma status according to which some individuals respond with time-locked, early gamma response, G+, while the others do not show this response, G-. The sample consisted of 42 volunteer participants (between 19 and 37 years of age with at least 9 years of education). There were 22 females and 20 males. Data were collected under the oddball paradigm. Auditory stimulation (10 ms r/f time, 50 ms duration, 65 dB SPL) consisted of target (2000 Hz; p = .20) stimuli that occurred randomly within a series of standard stimuli (1000 Hz; p = .80). Gamma responses were studied in the amplitude frequency characteristics, in the digitally filtered event-related potentials (f-ERPs) and in the distributions which were obtained using the recently developed time-frequency component analysis (TFCA) technique. Participants were classified into G+ and G- groups with a criterion of full agreement between the results of an automated gamma detection technique and expert opinion. The 2 x 2 x 2 ANOVA on f-ERPs and 2 x 2 x 2 multivariate ANOVA on TFCA distributions showed the main effect of gamma status and gender as significant, and the interaction between gamma status and gender as nonsignificant. Accordingly, individual difference in gamma status is a reliable phenomenon, but this does not depend on gender. There are conflicting findings in the literature concerning the effect of gender on ERP components (N100, P300). The present study showed that if the gamma status is not included in research designs, it may produce a confounding effect on ERP parameters.

Acoustic Stimulation↗
PubMed2005

Time-frequency component analyser and its application to brain oscillatory activity.

Currently, event-related potential (ERP) signals are analysed in the time domain (ERP technique) or in the frequency domain (Fourier analysis and variants). In techniques of time-domain and frequency-domain analysis (short-time Fourier transform, wavelet transform) assumptions concerning linearity, stationarity, and templates are made about the brain signals. In the time-frequency component analyser (TFCA), the assumption is that the signal has one or more components with non-overlapping supports in the time-frequency plane. In this study, the TFCA technique was applied to ERPs. TFCA determined and extracted the oscillatory components from the signal and, simultaneously, localized them in the time-frequency plane with high resolution and negligible cross-term contamination. The results obtained by means of TFCA were compared with those obtained by means of other commonly used techniques of ERP analysis, such as bilinear time-frequency distributions and wavelet analysis. It is suggested that TFCA may serve as an appropriate tool for capturing the localized ERP components in the time-frequency domain and for studying the intricate, frequency-based dynamics of the human brain.

Adolescent↗
PubMed2004

Neurocognitive functions after aortic arch repair with right brachial artery perfusion.

BACKGROUND: Satisfactory neurologic outcome following aortic arch repair through right brachial artery perfusion is well established. However, how neurocognitive functions are affected following selective cerebral perfusion, still needs to be elucidated. METHODS: In a period between April 2002 and March 2003, 22 patients (19 male, 3 female, with a mean age of 46.8 +/- 12; range: 26 to 70 years old), underwent aortic arch repair using right brachial artery low flow (8 to 10 mL x kg(-1) x min(-1)) selective antegrade cerebral perfusion under moderate hypothermia (26 degrees C). There were 6 Stanford type-A dissections and 16 ascending aortic aneurysms. All patients were evaluated preoperatively and postoperatively (at seventh day and second month) for neurocognitive functions. RESULTS: There was no operative mortality. The average cardiopulmonary bypass time was 115.0 +/- 24.2 minutes and the average antegrade cerebral perfusion time was 29.8 +/- 7.1 minutes (19 to 38 minutes). No major neurologic deficit was observed in the postoperative period. In terms of neurocognitive test results, between the preoperative and postoperative assessments for both hemispheric cognitive functions no deterioration was detected. CONCLUSIONS: The low-flow selective antegrade cerebral perfusion technique through the right brachial artery may safely be used for the great majority of patients undergoing aortic arch repair without causing deteriorations in neurocognitive functions.

Adult↗
PubMed2003

Early gamma response in human neuroelectric activity is correlated with neuropsychological test scores.

The goal of this study was to investigate whether early, time-locked 'sensory' gamma band response is correlated with a set of scores derived from neuropsychological tests. Neuroelectric responses were obtained under active auditory oddball paradigm. Of 67 reportedly healthy adults, 35 displayed time-locked early gamma, G (+), and 24 did not, G (-). Out of 52 neuropsychological test scores, G (+) and G (-) groups differed on the basis of Wisconsin Card Sorting Test, Wechsler Memory Scale-Revised and Serial Digit Learning Test scores. Results of logistic regression analysis was statistically reliable (overall success rate of prediction: 93.33%). The results showed that early gamma response can be classified on the basis of neuropsychological test performance and is thus associated with higher cognitive functions, supporting the view that brain integrates bottom-up with top-down processing.

Adult↗
PubMed2002

Discrimination of brain's neuroelectric responses by a decision-making function.

The aim of this work was to develop a mathematical decision-making procedure that might become a basis for real-time pattern recognition studies of the brain's neuroelectric responses. Data were collected from 77 volunteers under the auditory oddball paradigm with standard (1000 Hz) and deviant (2000 Hz) stimuli. The participants counted the deviants and reported them at the end of the experimental session. Event-related potentials (ERPs) were recorded and filtered with a bandpass between 0.16 and 70 Hz (3 dB down, 12 dB/octave) at Fz- and Pz-recording sites. The most significant potential values that discriminated the responses to the deviant stimuli group were at 136, 224, 328, 348, and 350 ms for Fz, and at 166, 220, and 350 ms for the Pz. The 328, 348, and 350 ms potential values define the curvature of the P300 peak; the 224 ms potential at Fz, and the 220 ms at Pz define that of the N2b peak. The differentiation between the deviant and standard group was checked through a discriminant function that allowed prediction of group membership; 98% of the ERP responses were correctly identified. The results showed that statistically derived time-points were congruent with the P300 and N2b ERP curvature.

Adult↗
PubMed2002

Digit span changes from puberty to old age under different levels of education.

The goal of this study is to demonstrate the age-related changes in multimodality digit span under a research design in which level of education is controlled. Volunteer participants (n = 1183) were distributed over levels of age (13-98 years) and education (5-8, 9-11, and 12+ years). Digit span was measured through 11 scores of the Visual Aural Digit Span Test-Revised on aural or visual stimulation and oral or written response execution, thus allowing for the measurement of intra- and intersensory integration. The increase in digit span scores reversed to a decrease with early adulthood. The slope of the regression line was small but significant. A 4 x 3 x 2 multivariate analysis of variance showed a significant effect of age and education on a combined score comprising the 11 digit span scores. Differences of age and education were predicted by the auditory and visual input scores. The article discusses the cognitive correlates and the age-related changes in digit span from the biological standpoint.

Acoustic Stimulation↗