[Perceptual conflict and response competition: event-related potentials of the stroop effect]. / Algisal Celiski ve Tepki Rekabeti: Stroop Etkisine Iliskin Olay-Iliskili Potansiyeller.

OBJECTIVE: The aim of the present study was to analyze electrophysiological activity associated with the Stroop effect. METHOD: The sample included 50 healthy volunteer adults (23 female and 27 male) from the university population. Stimulation, recording and analyses were carried under NeuroScan 4.2 hardware-software system. The effect of the experimental variables (stimulus congruency, response accuracy and electrode location) on event-related potentials (ERPs) was studied using 2x2x3 analysis of variance for repeated measures. RESULTS: The Stroop effect was demonstrated as prolonged reaction time to incongruent stimuli and increased total number of missed stimuli. Principal components analysis (PCA) showed that Stroop performance was related such factors as selective attention, interference, and resistance to interference. The electrophysiological Stroop effect was demonstrated as increased amplitude of P3 and N4 peaks for incongruent stimuli, and of N2, P3, N3, and N4 peaks for incorrect responses. CONCLUSION: Increased amplitude of P3 and N4 peaks associated with stimulus-related activation has been suggested to reflect conflict detection process. The variations in amplitudes for incorrect responses were complicated. While the amplitude of the N2 and P3 components increased only for incongruent stimuli, those of the N3 and N4 components increased for both congruent and incongruent stimuli. It was concluded that these earlier and later activations were associated with response competition and error detection processes, respectively. In this respect, these findings support both the perceptual conflict and the response competition hypotheses of Stroop interference.

Oscillatory responses representing differential auditory processing in sleep.

The goal of the study was to investigate the contribution of the delta and theta responses to the peaks on the event-related potential waveform and specifically to find the possible cognitive correlates of these oscillatory responses in rapid eye movements (REM) sleep and Stage 2 (spindle sleep), Stage 3 (light sleep) and Stage 4 (deep sleep; slow wave sleep) of non-REM sleep. Data on overnight sleep was acquired from 12 healthy, young adult, volunteer males; those on awake stage were obtained from 19 matched males. Brain activity was obtained 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 in sleep, active and passive oddball (OB-a, OB-p, respectively) paradigms in wakefulness. The effect of the experimental variables (stimulus type, sleep stage) was studied using 2 x 4 analysis of variance for repeated measures and stepwise multiple regression analysis. Overall, three types of configurations were obtained for the oscillatory responses which varied according to sleep stage and stimulus type: Large amplitude, differentiated delta and distinct theta response of long duration; distinct theta response with short duration; distinct delta response. As in wakefulness, the morphology of the time-domain peaks was found to be due to the superposition of the delta and theta responses. The configuration in REM resembled the responses to the OB-p paradigm and that NREM stages resembled the responses to the OB-a paradigm in wakefulness. Auditory information processing selectively varied according to sleep stages and took longer in sleep. Comparable peaks were obtained at longer latencies and later components appeared that did not exist under wakefulness. With respect to the long-duration theta activity, and greater differentiation between the deviant- and standard-elicited stimuli, Stage 2 appeared to represent the more effortful cognitive processing.

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.

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.

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, Karakas 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.

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.