A Review of Childhood Developmental Changes in Attention as Indexed in the Electrical Activity of the Brain

This review aims to present age-related changes in the neuroelectric responses of typically developing children (TDC) who are presumed to meet developmental stages appropriately. The review is based on findings from the frequently used neuropsychological tasks of active attention, where attention is deliberately focused versus passive attention where attention is drawn to a stimulus, facilitatory attention, which enhances the processing of a stimulus versus inhibitory attention, which suppresses the processing of a stimulus. The review discusses the early and late stages of attentional selectivity that correspond to early and late information processing. Age-related changes in early attentional selectivity were quantitatively represented in latencies of the event-related potential (ERP) components. Age-related changes in late attentional selectivity are also qualitatively represented by structural and functional reorganization of attentional processing and the brain areas involved. The purely bottom-up or top-down processing is challenged with age-related findings on difficult tasks that ensure a high cognitive load. TDC findings on brain oscillatory activity are enriched by findings from attention deficit hyperactivity disorder (ADHD). The transition from the low to fast oscillations in TDC and ADHD confirmed the maturational lag hypothesis. The deviant topographical localization of the oscillations confirmed the maturational deviance model. The gamma-based match and utilization model integrates all levels of attentional processing. According to these findings and theoretical formulations, brain oscillations can potentially display the human brain's wholistic-integrative functions.

Differentiation of memory processing stages and effect of demographic variables with alternative scoring approaches to the Rey auditory verbal learning test

BACKGROUND

The Rey Auditory Verbal Learning Test (RAVLT) is the third most popular verbal memory test and the tenth most frequently used neuropsychological test. The original scoring system of RAVLT does not differentiate stages of memory processing, but a recently developed composite scoring system has this potential. The objectives were to compare the two systems in terms of their capacity to differentiate the stages of memory processing and to study the effect of demographic variables on the learning trials (T) of the Turkish form of RAVLT (T-RAVLT).

METHOD

The sample consisted of 600 Caucasian Turkic adults, who were categorized into three levels of age, three levels of education, and two levels of gender. Individual administration of T-RAVLT was performed using the standard procedures of RAVLT.

RESULTS

The components in the exploratory factor analysis (EFA) and latent variables in the confirmatory factor analysis (CFA) of the original scores were consistent with sequentially ordered T-RAVLT stages. Demographic variables (age, education, and gender) affected performances in all of the learning trials. The composite scores revealed retrieval and retention as separate components, but these scores could not be predicted from the relevant T-RAVLT scores.

CONCLUSIONS

Findings recommend a combined utilization of the two scoring systems: The original system to provide scores on the performance at each stage of T-RAVLT and the combined system to provide separate scores on learning, retention, and retrieval, the three stages of memory processing. A selective effect of demographic variables on T1 was not observed, indicating a need for cross-cultural studies that are meticulously controlled for age and education.

Spontaneous age-related changes of attention in unmedicated boys with attention deficit hyperactivity disorder

OBJECTIVE

Neuropsychological, neuroanatomical, and electrophysiological studies have reported a steady increase in the different attention types until the age of 10 years. Moreover, differences between healthy control (HC) boys and those with attention deficit hyperactivity disorder (ADHD) become nonsignificant in late childhood. This cross-sectional study aimed to perform a comparative analysis of attentional processing in boys with ADHD and HC in the 6:00-10:11 years age range. Methods: Age-related changes in attentional processing were compared between Caucasian Turkic boys (72-131 months of age) with ADHD (n = 144) and HC (n = 112). Selective, focused, and inhibitory attention were measured using the Stroop Test (5 scores); sustained attention was measured using the Cancellation Test (3 scores); and attention span was measured using the Visual Aural Digit Span Test-Revised (6 scores). Results: At the age of 6 years, the ADHD group had a significantly lower performance for all attention types. By the age of 10 years, there were no significant between-group differences. However, the component structure of the neuropsychological test scores in the ADHD group differed from that in the HC group and previous studies. Conclusions: Attentional processing in boys with ADHD changes within the age-range of 6:00-10:00 years where it finally becomes similar to that in HC boys. This delayed maturation is consistent with the maturational lag model of ADHD. However, there was a between-group difference in the component structure of attentional processing, which is consistent with the maturational deviance model of ADHD.

Using Neuropsychometric Measurements in the Differential Diagnosis of Specific Learning Disability

INTRODUCTION

The aim of this study was to develop a neuropsychometric battery for the differential diagnosis of specific learning disability (SLD), with specific respect to attention deficit hyperactivity disorder (ADHD), and to help resolve the conflicting results in the literature by an integrative utilization of scores on both the Bannatyne categories and neuropsychological tests.

METHODS

The sample included 168 primary school boys who were assigned to SLD (n=21), ADHD (n=45), SLD and ADHD (n=57), and control groups (n=45). The exclusion criteria were a neurological or psychiatric comorbidity other than ADHD, a level of anxiety and/or depression above the cutoff score, medication affecting cognitive processes, visual and/or auditory disorders, and an intelligence level outside the IQ range of 85-129. Psychometric scores were obtained from the SLD Battery and Wechsler Intelligence Scale for Children-Revised in the form of Bannatyne category scores. Neuropsychological scores were from the Visual-Aural Digit Span Test-Form B, Serial Digit Learning Test, Judgment of Line Orientation, and Mangina Test. The battery was called the Integrative Battery of SLD.

RESULTS

The correctness of estimation for classifying cases into the diagnostic dyads (SLD/ADHD, SLD/SLD+ADHD, and SLD+ADHD/ADHD) by an integrative utilization of both the Bannatyne category scores (n=4) and scores from the four neuropsychological tests (n=10) was 92.4%, 81.4%, and 71.8%, respectively. These proportions were generally higher than those obtained using the Bannatyne category scores alone (86.4%, 75.5%, and 73.1%, respectively). The same trend was seen in the classification of children into diagnostic and control groups. However, the proportion of the correctness of estimation was higher than that obtained for the diagnostic dyads.

CONCLUSION

When conducted using appropriately chosen research designs and statistical techniques and if confounding variables are sufficiently controlled, a neuropsychometric battery that includes capacities that relate to intelligence (Bannatyne categories) and those that relate to neurocognitive processes (neuropsychological tests) can be useful in the differential diagnosis of SLD.

Surgical Treatment of Portal Vein Thrombosis With the Use of Cadaveric Venous Patch After Donor Hepatectomy: A Case Report

Live donors should be the priority of transplant professionals to prevent surgery-related morbidity and mortality during living-donor liver transplantation. Portal vein thrombosis after donor hepatectomy is an important complication which can be prevented by careful preoperative as well as perioperative evaluation. If portal vein thrombus occurs after donor hepatectomy, anticoagulation and surgical thrombectomy and even portal vein reconstruction should be kept in mind. Cadaveric venous patches can be used for the reconstruction of narrowed and angulated portal veins. Here we report the surgical treatment of a donor with a cadaveric venous patch who developed portal vein thrombosis after donor hepatectomy.

Functional MRI compliance in children with attention deficit hyperactivity disorder

PURPOSE

We aimed to test the effect of prescan training and orientation in functional magnetic resonance imaging (fMRI) in children with attention deficit hyperactivity disorder (ADHD) and to investigate whether fMRI compliance was modified by state anxiety.

METHODS

Subjects included 77 males aged 6-12 years; there were 53 patients in the ADHD group and 24 participants in the healthy control group. Exclusion criteria included neurological and/or psychiatric comorbidities (other than ADHD), the use of psychoactive drugs, and an intelligence quotient outside the normal range. Children were individually subjected to prescan orientation and training. Data were acquired using a 1.5 Tesla scanner and an 8-channel head coil. Functional scans were performed using a standard neurocognitive task.

RESULTS

The neurocognitive task led to reliable fMRI maps. Compliance was not significantly different between ADHD and control groups based on success, failure, and repetition rates of fMRI. Compliance of ADHD patients with extreme levels of anxiety was also not significantly different.

CONCLUSION

The fMRI compliance of ADHD children is typically lower than that of healthy children. However, compliance can be increased to the level of age-matched healthy control children by addressing concerns about the technical and procedural aspects of fMRI, providing orientation programs, and performing on-task training. In patients thus trained, compliance does not change with the level of state anxiety suggesting that the anxiety hypothesis of fMRI compliance is not supported.

Is laparoscopic surgery safe in patients with an elevated shock index due to ruptured ectopic pregnancy?

PURPOSE

To evaluate the effectiveness of laparoscopic surgery in patients with elevated shock index (SI), which is a unique determinant of acute hemorrhage.

MATERIALS AND METHODS

A retrospective chart review of all patients treated for ectopic pregnancy (EP) in the present gynaecology department between January 2007 and March 2011 was performed. For each measurement of heart rate (HR) and systolic blood pressure (SBP), a SI was calculated by dividing HR by SBP (normal, 0.5 - 0.7).

RESULTS

One hundred sixty patients were selected as SI above 0.7. There were 111 (69.4%) patients in the laparotomy group and 49 (30.6%) patients in the laparoscopy group. The postoperative hemoglobin (Hb) level was 8.46 +/- 1.56 (g/dl) in the laparotomy group and 9.37 +/- 1.52 (g/dl) in the laparoscopy group, with lower postoperative levels in the laparotomy group. The mean duration of postoperative hospital stay was 2.37 +/- 0.74 days in the laparotomy group and 2 +/- 0.84 days in the laparoscopy group.

CONCLUSION

The availability of suitable operative equipment, nursing teams, and advanced laparoscopic skills, all justify operative laparoscopy for the surgical treatment of EP in women with elevated SI.

Recording event-related activity under hostile magnetic resonance environment: Is multimodal EEG/ERP-MRI recording possible?

Event-related potentials (ERPs) have high temporal resolution, but insufficient spatial resolution; the converse is true for the functional imaging techniques. The purpose of the study was to test the utility of a multimodal EEG/ERP-MRI technique which combines electroencephalography (EEG) and magnetic resonance imaging (MRI) for a simultaneously high temporal and spatial resolution. The sample consisted of 32 healthy young adults of both sexes. Auditory stimuli were delivered according to the active and passive oddball paradigms in the MRI environment (MRI-e) and in the standard conditions of the electrophysiology laboratory environment (Lab-e). Tasks were presented in a fixed order. Participants were exposed to the recording environments in a counterbalanced order. EEG data were preprocessed for MRI-related artifacts. Source localization was made using a current density reconstruction technique. The ERP waveforms for the MRI-e were morphologically similar to those for the Lab-e. The effect of the recording environment, experimental paradigm and electrode location were analyzed using a 2x2x3 analysis of variance for repeated measures. The ERP components in the two environments showed parametric variations and characteristic topographical distributions. The calculated sources were in line with the related literature. The findings indicated effortful cognitive processing in MRI-e. The study provided preliminary data on the feasibility of the multimodal EEG/ERP-MRI technique. It also indicated lines of research that are to be pursued for a decisive testing of this technique and its implementation to clinical practice.

[Perceptual conflict and response competition: event-related potentials of the stroop effect]

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.

[Change with age of information processing meta-operations in children]

OBJECTIVE

The aim of this study was to examine meta-systems of cognition and their development,and the pattern of relationships between types of information processing, executive functions, mental ability, and level of cognitive development in children.

METHOD

The sample consisted of 80 healthy children (39 female and 41 male). Meta-cognition was measured with the Word List and Evaluation of the Degree of Correctness of Knowledge, Feeling of Knowing, and Criterion Test. Executive functions were assessed using the Wisconsin Card Sorting Test (WCST) and the TBAG form of the Stroop Test. Mental ability was assessed using Raven's Standard Progressive Matrices (RSPM). Level of cognitive development was assessed using the Logical Reasoning Test (LRT).

RESULTS

MANOVA and correlation analyses showed that meta-memory, executive functions, mental ability, and level of cognitive development increased up to the age of 11 years. There were low correlations between executive function and meta-memory test scores, and LRT. There was a low correlation between meta-cognition score and LRT score. There was a low to medium correlation between meta-cognition score and RSPM score. Principal component analysis showed that by 11 years of age, cognitive patterns in the children began to resemble those of adults.

CONCLUSION

The study showed that the cognitive structure of the children was different from that of adults, as executive functions and meta-cognitive processes in children were similar, but not identical. These processes did not entirely match the Piagetian stages of cognitive development. The results of this study are discussed within the context of the related literature.

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.

Multicomponent attention deficits in attention deficit hyperactivity disorder

The aim of this study was to examine the specific aspects of attention, such as selective attention, sustained attention, and short-term memory in children with attention deficit hyperactivity disorder, combined subtype (ADHD-C). A total of 40 children with a diagnosis of ADHD from the 4th edition of the Diagnostic and Statistical Manual, aged 6-11 years old were compared with 40 controls matched for age and gender on a battery of tests. Short-term memory span and attention was measured by Visual Aural Digit Span Test-Revised. Stroop test and the Turkish version of Cancellation Test were used to assess selective and sustained attention, respectively. In order to check for factor structure in two groups on the test scores, principal component analysis was conducted for both groups separately. Relative to the comparison children, children with ADHD showed significant deficits on tests that are related to different aspects of attention. The results are consistent with the theories explaining the biological basis of ADHD by scattered attention networks in the brain, which have reciprocal dynamic interactions. Further comparative studies are needed to elucidate whether the cognitive processes that are known to be assessed by these tests are specific to ADHD.

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.

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.

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.

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.

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.

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.

Analysis of the time-varying energy of brain responses to an oddball paradigm using short-term smoothed Wigner–Ville distribution

Cognitive brain responses to external stimuli, as measured by event related potentials (ERPs), have been analyzed from a variety of perspectives to investigate brain dynamics. Here, the brain responses of healthy subjects to auditory oddball paradigms, standard and deviant stimuli, recorded on an Fz electrode site were studied using a short-term version of the smoothed Wigner-Ville distribution (STSW) method. A smoothing kernel was designed to preserve the auto energy of the signal with maximum time and frequency resolutions. Analysis was conducted mainly on the time-frequency distributions (TFDs) of sweeps recorded during successive trials including the TFD of averaged single sweeps as the evoked time-frequency (ETF) brain response and the average of TFDs of single sweeps as the time-frequency (TF) brain response. Also the power entropy and the phase angles of the signal at frequency f and time t locked to the stimulus onset were studied across single trials as the TF power-locked and the TF phase-locked brain responses, respectively. TFDs represented in this way demonstrated the ERP spectro-temporal characteristics from multiple perspectives. The time-varying energy of the individual components manifested interesting TF structures in the form of amplitude modulated (AM) and frequency modulated (FM) energy bursts. The TF power-locked and phase-locked brain responses provoked ERP energies in a manner modulated by cognitive functions, an observation requiring further investigation. These results may lead to a better understanding of integrative brain dynamics.

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.

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.

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.

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.

Gamma, alpha, delta, and theta oscillations govern cognitive processes

The increased interest in gamma oscillations, now widely regarded as functionally relevant signals of the brain, underlines the importance of the concept of event-related oscillations for bridging the gap between single neurons and neural assemblies. Taking this concept further, we review experiments showing that oscillatory phenomena such as alpha, theta, and delta responses to events are, just as the gamma band, strongly interwoven with sensory and cognitive functions. This review argues that selectively distributed delta, theta, alpha and gamma oscillatory systems act as resonant communication networks through large populations of neurons. Thus, oscillatory processes might play a major role in functional communication in the brain in relation to memory and integrative functions.

Gamma response of the brain: a multifunctional oscillation that represents bottom-up with top-down processing

This paper deals with the functional correlates of the gamma response of the brain. A critical review of the literature findings reveals the existence of two types of gamma responses: an early gamma that fulfills sensory functions and a late gamma that fulfills perceptual-cognitive functions. However, even the early gamma shows individual differences. Such a finding points to the existence of top-down influences on sensory processes and to a parallel-processing model for brain function.

A new strategy involving multiple cognitive paradigms demonstrates that ERP components are determined by the superposition of oscillatory responses

OBJECTIVES

The goal of the present paper was to study the contribution of the delta and theta responses to two components of the event-related potential (ERP) waveform, the N200 and P300, which were recorded from 3 topographical sites of the brain.

METHODS

This contribution was studied using a set of systematically varying experimental paradigms. Such a strategy enabled the demonstration of the variations in the event-related potentials and the event-related oscillations as task conditions and respective cognitive operations systematically changed. The study employed easy oddball, hard oddball, mismatch negativity and single stimulus paradigms and it was conducted on 42 healthy adults (age range 19-30 years, 26 females, 16 males) from the university student population. Data were analyzed with electrophysiological (selective averaging, amplitude frequency characteristics, digital filtering) and statistical methods (analysis of variance, multivariate step-down regression).

RESULTS

The data showed that the morphology of the ERP components for different experimental paradigms represented a specific pattern of superposition of the delta and theta oscillatory responses.

CONCLUSIONS

The cognitive correlates of the oscillatory responses were discussed and the results were evaluated on the basis of the superposition principle and the theory of oscillatory neural assemblies.

The genesis of human event-related responses explained through the theory of oscillatory neural assemblies

The goal of the study is to investigate the contribution of delta and theta responses to N200 and P300 ERP components that are recorded from two topographical sites (Fz and Pz) under two experimental paradigms (mismatch negativity and oddball) that trigger different cognitive processes for the respective task performances. The present study was conducted on 42 normal young adults. The results showed that it is the 'interplay' between the theta and the delta oscillations that produces the morphology and the amplitude not only of the P300 but also the N200 component. The functional and physiological meaning of the delta and theta responses are discussed within the framework of the theory of oscillatory neural assemblies and the principle of superposition.

Brain oscillations in perception and memory

Gamma oscillations, now widely regarded as functionally relevant signals of the brain, illustrate that the concept of event-related oscillations bridges the gap between single neurons and neural assemblies. Taking this concept further, we review experiments showing that oscillatory phenomena such as alpha, theta, or delta responses to events are strongly interwoven with sensory and cognitive functions. This review argues that selectively distributed delta, theta, alpha, and gamma oscillatory systems act as resonant communication networks through large populations of neurons. Thus, oscillatory processes might play a major role in relation with memory and integrative functions. A new 'neurons-brain' doctrine is also proposed to extend the neuron doctrine of Sherrington.

Are cognitive processes manifested in event-related gamma, alpha, theta and delta oscillations in the EEG?

Gamma oscillations, now widely regarded as functionally relevant signals of the brain, illustrate that the concept of event-related oscillations bridges the gap between single neurons and neural assemblies. Taking this concept further, we review experiments concerning oscillatory responses to events (in the alpha, theta and delta ranges) as possible correlates of sensory and cognitive functions. It is argued that selectively distributed delta, theta, alpha and gamma oscillatory systems act as resonant communication networks through large populations of neurons, with functional relations to memory and integrative functions.

Early gamma response is sensory in origin: a conclusion based on cross-comparison of results from multiple experimental paradigms

The study investigates the functional correlates of the early, time-locked gamma response. The study utilized a unique experimental strategy which involved the utilization of a series of experimental paradigms to which all subjects (n = 20) were exposed to in the same recording session. These paradigms induced an increasingly complex configuration of processes for their respective task performance and also required different levels of attention allocation. In their order of administration, the paradigms were single stimulus (SS), mismatch negativity (MMN), evoked potential (EP), easy oddball (OB-EZ) and hard oddball (OB-HD). Auditory stimuli were used in the study (10 ms r/f time, 50 ms duration, 65 dB SPL) with the standards as 1000 Hz or 1900 Hz and deviants as 2000 Hz. The early gamma showed a frontocentral topography. The difference between Fz and Pz recording sites were statistically significant. A comparative analysis of the gamma responses showed that the gamma that was obtained at the early time-window of 0-150 ms as a time-locked activity occurred irrespective of experimental paradigm; the early gamma did not vary with the degree of task complexity or with attentional allocation. It was concluded from these findings that the early gamma is basically a sensory phenomenon. Various studies have previously shown that under perceptual/cognitive tasks, gamma response is obtained as a non-phase-locked activity in the late time-windows. These studies concluded that the gamma response is basically perceptual/cognitive in function. However, in these studies the early sensory gamma was also present in the data. Collectively taken, these findings may lead to the conclusion that the gamma response is a multifunctional phenomenon, with the early portion representing sensory and the late portion perceptual/cognitive processing.

Alpha oscillations in brain functioning: an integrative theory

The old concept stating that EEG alpha (10-Hz) activity reflects passive or idling states of the brain is giving way to modern views of 10-Hz oscillations in relation to diverse brain functions comprising sensory, motor, and memory processes: (1) Spontaneous alpha activity is not pure noise as shown by methods of chaos analysis. (2) Evoked alpha oscillations patterns (precisely time-locked to a stimulus; duration approx. 200-300 ms) depend on the modality of stimulation and the recording site. (3) Induced alpha oscillations are initiated by, but not closely time-locked to a stimulus. (4) 10-Hz oscillations are recorded in nervous systems of different complexities, from the human brain to isolated ganglia of invertebrates. The neural origins of 10-Hz oscillations are demonstrated by recordings at the cellular level. (5) Rather than trying to locate a unique alpha generator, it is preferable to assume that a 'diffuse and distributed alpha system' exists. A particular support for this hypothesis is given by stimulus-dependent hippocampal alpha responses in the cat brain. (6) The major physiological meaning of 10-Hz oscillations may be comparable to the putative universal role of gamma responses in brain signaling.

High-frequency components of human visual evoked potentials

This study was aimed to further our investigations on the high frequency components of human visual evoked potentials (VEP). By using stimulations in the form of optic step functions, we measured (Cz-ear lobe) VEPs with 512 real data points in a total recording time of 20.48 msec in normal adults (N = 12). The peaks in the transient evoked potentials occurred with approximate latencies of 0.5, 1.0, 1.5, 2.5 and 5.0 msec. Transforming the individual time responses to the frequency domain by the Fourier Transform, maxima were obtained in 200, 400, 700, 1200 and 2200 Hz positions in the amplitude frequency characteristics. The findings were compared with those of a similar study on the auditory system. It is stated that the response activities of 200 Hz and 2200 Hz are unique to the visual system.