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Previous studies have revealed significant differences in performance on nonlanguage dependent cognitive tests across international settings among younger individuals, with less pronounced differences evident among older individuals (54 years of age). The present study examined a broad range of cognitive performance as well as electrophysiological indices of brain function in a multisite and international context. A total of 200 individuals in the United States, 233 individuals in Europe, and 829 individuals in Australia were administered a standardized computerized neuropsychological battery, and complementary electroencephalogram (EEG) recordings were completed. Results revealed no significant differences in cognitive function or electrophysiology across the three continents. Similarly, although there was a main effect for age, the interaction between age and continent was not significant in any of the omnibus analyses. These findings indicate a high degree of similarity in neurocognitive and electrophysiological function among individuals residing in developed Western cultures, consistent with a traitlike status and the high heritability of the EEG.

The quantified analysis of the electroencephalogram (qEEG) has enabled the extraction of additional psychophysiological information from the raw EEG, but in turn has introduced a number of distortions. This study compared Dynamic Spectral Analysis (DSA), a novel and mathematically stringent technique for the evaluation of qEEG activity with conventional power spectral analysis in subjects with both first episode and chronic schizophrenia and matched controls. Advantages of the technique in the automated processing of data, rejection of artefact, avoidance of artefact introduced by the mathematical trans-formation of the data and the identification of irregular low frequency artefactual activity "pi" are discussed in detail. Using this method, the study has confirmed past observations of increased slow wave activity in schizophrenia, and identified a decrease in peak frequency in the alpha band in the subjects with chronic schizophrenia. The two clinical groups differed in mean peak frequency in the delta band with the first episode schizophrenia subjects having a raised mean peak frequency and the subjects with chronic schizophrenia having a lowered mean peak frequency. The results suggest continued change in the EEG with illness chronicity in schizophrenia. These changes were most evident in the frequency domain emphasizing the importance of routine measurement of mean band frequencies in qEEG studies.

Psychophysiological theories characterize Attention Deficit Hyperactivity Disorder (ADHD) in terms of cortical hypoarousal and a lack of inhibition of irrelevant sensory input, drawing on evidence of abnormal electroencephalographic (EEG) delta-theta activity. To investigate the mechanisms underlying this disorder a biophysical model of the cortex was used to fit and replicate the EEGs from 54 ADHD adolescents and their control subjects. The EEG abnormalities in ADHD were accounted for by the model's neurophysiological parameters as follows: (i) dendritic response times were increased, (ii) intrathalamic activity involving the thalamic reticular nucleus (TRN) was increased, consistent with enhanced delta-theta activity, and (iii) intracortical activity was increased, consistent with slow wave (

Electroencephalography (EEG) and Event Related Potentials (ERPs) studies in ADHD have generally been studied separately. This study examined these measures simultaneously in 54 adolescent unmedicated ADHD males and age and gender matched normal controls during an auditory oddball paradigm. Compared with controls, ADHD patients showed increased pre-stimulus EEG Theta activity and post-stimulus reduced N200 amplitude, increased P200 amplitude and delayed N200 and P300 latencies evoked to target stimuli. Moreover, Theta activity was negatively correlated with N200 amplitude and positively correlated with P200, N200 and P300 latency in ADHD. There were no correlations in the control group. Pre-stimulus preparatory state increases in Theta activity in ADHD may underlie some of the reported disturbances in information processing reflected in ADHD.

Specialised network disturbances such as abnormalities in processing faces, may be associated with functional disturbances of interpersonal communication in schizophrenia. This study focused on the temporal dimension, investigating facial processing deficits in patients with schizophrenia (and non-patient controls) in a passive event-related potential (ERP) paradigm. ERPs invoked to an angry and neutral face stimulus were recorded in 27 patients with schizophrenia and 27 age and sex matched normal controls. Patients with schizophrenia showed a significant generalised delay, and diminished P200 amplitude (primarily frontal) for both stimuli-with more widespread regions of disturbance associated with the angry face. Normal controls, on the other hand, showed relatively reduced posterior P200 amplitude for angry compared to neutral faces, and a lateralised pattern of engagement in response to both stimuli. These findings indicate suboptimal processing of neutral faces in patients with schizophrenia, further exacerbated for affect laden angry faces.

In this study, we measured traditional late components of the Event Related Potential (ERP: N 100, P 200, N 200 and P 300) in a conventional auditory oddball paradigm, but additionally and simultaneously assessed electrodermal "orienting reflexes (ORs)" in 40 patients with schizophrenia and 40 age and gender matched normal controls. The single epoch ERPs that did and did not evoke an OR, were sub-averaged separately. The control subjects (but not the patient group), revealed delayed P 300 latency in the ERP sub-averages without ORs (ERP-OR), compared with ERP sub-averages with ORs (ERP+OR). Between-group analysis showed reduced N 100, N 200 and P 300 amplitudes (as well as delayed P 300 latency) in the ERP+OR sub-average in patients with schizophrenia. In the ERP-OR sub-average, the patient group also had smaller N 100, N 200 and P 300 amplitudes, but larger P 200 amplitude (compared with normal controls). This study shows the potential to tease out physiologically based OR sub-processes, by simultaneous acquisition and analysis of ERPs and autonomic electrodermal activity. Such ERP sub-averages (based on autonomic responses) highlight that multiple processes overlap across the trial, and their delineation may elucidate more specific patterns of disturbance in schizophrenia, than traditional averaged measures.

Previous studies have revealed various abnormalities in late-component ERP amplitude and latency in schizophrenia, considered as a diagnostic category. The aim of this study was to investigate the within-sample associations between late-component ERPs and three primary syndromes of schizophrenia Reality Distortion, Psychomotor Poverty and Disorganisation. Subjects included 40 schizophrenics and 40 age and sex matched nonpsychiatric controls. Auditory ERPs (N100, N200, P200, P300) were elicited using an auditory oddball paradigm. Between-group analyses of target data showed reduced N100, N200 and P300 amplitude, increased P200 amplitude and delayed N200 latency in schizophrenics compared to controls. For non-target data, schizophrenics showed similarly reduced N100 amplitude and delayed N200 latency. Within-group analyses of target data showed that the three syndromes (determined by principal component analysis of PANSS ratings) were differentiated by ERP latency, but not amplitude (Disorganisation delayed left hemisphere P200 and P300 latency; Reality Distortion earlier global, midline and left hemisphere N200 latency; Psychomotor Poverty delayed posterior N100 latency). Notably, only Disorganisation showed a divergent pattern of associations with non-target ERP data: reduced P200 amplitude and delayed N100 latency.

A number of studies have examined the average late component Event Related Potential (ERP) and Reaction Time (RT) in response to multiple target stimuli (across-trial averages). This study demonstrates within-trial differences in ERP brain function associated with relatively fast and slow RTs in 50 normal subjects. A conventional auditory oddball paradigm (with a 1 ISI) was employed. Increased ERP N100 and N200 amplitude (and decreased P200 amplitude), as well as earlier P200, N200 and P300 latency were found in the fast compared with the slow ERP subaverages. These results show the potential to elucidate temporal and spatial dynamics of brain function associated with changes in performance, in conventional "cognitive" paradigms applicable to both health and disease states.

Alterations in mean frequency and power in the alpha band of the electroencephalogram (EEG) is thought to reflect fundamental attentional and cognitive factors. This study investigated changes in the mean alpha frequency of the quantified EEG in 21 subjects with schizophrenia, compared to an equal number of age and sex matched controls. Four standard electrophysiological paradigms (eyes closed, eyes open, habituation and oddball) were used to manipulate the level of cognitive demand required of each subject. Significant differences were found both between normal and schizophrenic groups in mean alpha frequency as well as within groups between different paradigms. Whilst a consistent linear relationship between site and paradigm was observed in controls subjects (slower frontally and slower with cognitive load), this was not observed in subjects with schizophrenia. The subjects with schizophrenia showed a loss of this linear relationship and increased mean alpha frequency frontally with cognitive load.