Previous research has indicated that the auditory ERPs of children are dominated by a frontal negative slow-wave. This paper outlines a preliminary attempt to separate event-related low-frequency activity from traditional ERP components as found in older subjects. An active auditory oddball task was completed by 30 normal children aged from 8 to 18 years, and ERPs to target and standard stimuli were derived. The original ERP files were digitally filtered to calculate separate ERPs containing only 0.01-2 Hz activity (termed the SW-ERP) or 2-12 Hz activity (termed the RESIDUAL ERP) for each subject. The SW-ERP was maximally correlated with the slow-wave factor from a principal components analysis of the original target and standard waveforms. The SW-ERPs to target stimuli contained an early negative component which showed an age-related decrease, and a late positive component which did not. The SW-ERP was found to be partly responsible for the differences in component amplitude and morphology between sites observed in the raw ERPs.
We compared effects of 0.3 Hz with 0.01 Hz settings of the high pass amplifier filter, and baseline-to-peak with peak-to-peak measurements of the P300 event-related potential. The key dependent variable of interest was intraindividual rate of accuracy in discrimination of oddball vs. frequent evoked P300 responses, in various paradigms. In Experiment 1 (a lab deception paradigm), we found that the combination of the 0.3 Hz filter setting and the peak-peak measurement of P300 correctly diagnosed oddball vs. frequent in 26 of 26 (100%) cases. This parameter combination outperformed all others. In a second, more field-like experiment (in that the participant knew that the experimenter was blind to ground truth), the peak-peak index again outperformed the base-peak index. It was also observed that the pre-stimulus EEG baseline variability exceeded that of the negative peak (NEG) following P300, i.e. the peak to which the peak-peak index refers P300 for computation. We also observed that the base-peak measurement of P300 is uncorrelated with NEG, and that NEG, seen only in 0.3 Hz channels, correlates highly (-0.67) with the duration of recovery of P300 to the pre-stimulus baseline EEG level as seen in the 0.01-Hz channel. However, in a final experiment using two simple visual and auditory oddball tasks, the base-peak measurement was as diagnostic as the peak-peak measurement.
Although the focus of attention on data degradation during simultaneous MRI/EEG recording has to date largely been upon EEG artefacts, the presence of the conducting wires and electrodes of the EEG recording system also causes some degradation of MRI data quality. This may result from magnetic susceptibility effects which lead to signal drop-out and image distortion, as well as the perturbation of the radiofrequency fields, which can cause local signal changes and a global reduction in the signal to noise ratio (SNR) of magnetic resonance images. Here, we quantify the effect of commercially available 32 and 64 electrode caps on the quality of MR images obtained in scanners operating at magnetic fields of 1.5, 3 and 7 T, via the use of MR-based, field-mapping techniques and analysis of the SNR in echo planar image time series. The electrodes are shown to be the dominant source of magnetic field inhomogeneity, although the localised nature of the field perturbation that they produce means that the effect on the signal intensity from the brain is not significant. In the particular EEG caps investigated here, RF inhomogeneity linked to the longer ECG and EOG leads causes some reduction in the signal intensity in images obtained at 3 and 7 T. Measurements of the standard deviation of white matter signal in EPI time series indicates that the introduction of the EEG cap produces a small reduction in the image signal to noise ratio, which increases with the number of electrodes used.
Electroencephalogram (EEG) data recorded simultaneously with functional magnetic resonance imaging (fMRI) suffer from severe artefacts. The ballistocardiogram (BCG) artefact in particular is as yet poorly understood and different BCG removal strategies have been proposed. In the present study, EEG data were recorded from four participants in three different MRI scanners with field strengths of 1.5, 3 and 7 T, with the aim of investigating the impact of the static magnetic field strength on the BCG artefact and independent component analysis (ICA). The results confirm that the amplitude of the BCG artefact is a function of the static magnetic field strength. Moreover, the spatial variability of the BCG artefact substantially increased at higher magnetic field strengths. A comparison of ICA before and after channel-wise BCG correction revealed that typical independent components could be more easily identified when ICA was applied after channel-wise BCG correction. Further analysis of EEG and electrocardiogram recordings points towards the contribution of at least two different processes to the origin of the BCG, which are blood movement or axial head rotation on the one hand and electrode movement at lateral sites of the head on the other. This is summarized in a preliminary BCG model that may help to explain recent inconsistencies regarding the usefulness of ICA for BCG removal. It may also guide the future development of more advanced BCG removal procedures.
Words correctly recognized as previously studied (i.e. old) elicit greater amounts of positive event-related brain potential (ERP) activity over posterior scalp between 400 and 800 ms than do previously unstudied (i.e. new) words. While investigators have reported that this old/new effect consists of more than one subcomponent, the spatio-temporal parameters of these possible subcomponents, as well as any other patterns of brain activity associated with recognition, remain incompletely specified. Thus, ERPs were recorded from 32 scalp sites while 13 subjects performed four repetitions of a study-test recognition paradigm. The subjects' task was to decide whether each word was old or new and press the appropriate button as quickly as possible. The timing and topography of the ERPs elicited by old and new words was assessed with topographic profile comparisons on the areas with a variety of temporal windows, and visualized with potential and CSD maps. The results revealed that seven patterns of ERP activity, dissociable on the basis of their topography, timing and response to experimental variables, were elicited between 300 and 2000 ms. Three of these appeared as subcomponents of the old/new effect (maximal over left medial frontal, left parietal-occipital and right central-frontal scalp), another was related to decision confidence and/or memory trace strength (maximal over left central scalp) and three others appeared to be related to more general aspects of recognition (maximal over the frontal poles, midline frontal scalp and right frontal scalp). Taken together, the seven distinct patterns of neural generator activity described here support the hypothesis that retrieval of information from episodic memory depends on a collection of different processes that occur in a temporally and spatially distributed neural circuit.
This paper presents an overview of a new method for the non-invasive measurement of brain function, the event-related optical signal (EROS). This technique is based on measures of the optical properties of cortical brain tissue, which change while the tissue is active. These changes are likely to be due to changes in light scattering, and are very rapid and localized, being related to phenomena occurring within or around the neuronal membrane. EROS, therefore yields images of cortical activity that combine spatial specificity (i.e. they can be related to patches of tissue less than a cubic centimeter in size) with temporal resolution (i.e. they depict the time course of the neural activity in the cortical areas under measurement). A limitation of this technique is its reduced penetration into the head (less than 3-5 cm). EROS appears to be a suitable technique for studying the time course of activity in selected cortical areas, and for providing a bridge between hemodynamic and electrophysiological imaging methods.
Prefrontal dysfunction has been associated with schizophrenia. Activation during Wisconsin card sorting test (WCST) is a common approach used in functional neuroimaging to address this failure. Equally, current knowledge states that oscillations are basic forms of cells-assembly communications during mental activity. Promising results were revealed in a previous study assessing healthy subjects, WCST and oscillations. However, those previous studies failed to meet the functional integration of the network during the WCST in schizophrenics, based on the induced oscillations and their distributed cortical sources. In this research, we utilized the brain electrical tomography (variable-resolution brain electromagnetic tomography) technique to accomplish this goal. Task specific delta, theta, alpha and beta-2 oscillations were induced and simultaneously synchronized over large extensions of cortex, encompassing prefrontal, temporal and posterior regions as in healthy subjects. Every frequency had a well-defined network involving a variable number of areas and sharing some of them. Oscillations at 11.5, 5.0 and 30 Hz seem to reflect an abnormal increase or decrease, being located at supplementary motor area (SMA), left occipitotemporal region (OT), and right frontotemporal subregions (RFT), respectively. Three cortical areas appeared to be critical, that may lead to difficulties either in coordinating/sequencing the input/output of the prefrontal networks-SMA, and retention of information in memory-RFT, both preceded or paralleled by a deficient visual information processing-OT.
There is mixed evidence for a relationship between impulsivity and executive functions. Although impulsivity is heterogeneous, previous research did not examine partial relationships controlling for shared variance across sub-traits to evaluate the specificity of these associations. Eighty-five undergraduates completed the Barratt Impulsiveness Scale-11 (BIS-11) and the AX-expectancy version of the Continuous Performance Task (AX-CPT). This task engenders a conflict between two response tendencies by manipulating the frequency of specific trial types. We conducted mixed model analyses to determine the unique variance in behavioral and electrophysiological indices of relevant cognitive functions accounted for by the facets of BIS-11. Motor Impulsiveness was associated with smaller P3 across sites and conditions suggesting a general cognitive limitation not specific to the condition requiring the most inhibition, and larger N2 in some conditions indicating heightened conflict detection. Non-Planning Impulsiveness was related to smaller N2 when inhibiting a primed response and with greater P3 in some contexts. Attentional Impulsiveness appeared to be associated with an inefficient conflict detection system indicated by relatively normal engagement in trials involving the non-potent response, but relatively over engagement in the prepotent condition. Our findings suggest that sub-traits of impulsivity are differentially related to executive processes.
Identification of markers of abnormal brain function in children at-risk of schizophrenia may inform early intervention and prevention programs. Individuals with schizophrenia are characterised by attenuation of MMN amplitude, which indexes automatic auditory sensory processing. The current aim was to examine whether children who may be at increased risk of schizophrenia due to their presenting multiple putative antecedents of schizophrenia (ASz) are similarly characterised by MMN amplitude reductions, relative to typically developing (TD) children. EEG was recorded from 22 ASz and 24 TD children aged 9 to 12years (matched on age, sex, and IQ) during a passive auditory oddball task (15% duration deviant). ASz children were those presenting: (1) speech and/or motor development lags/problems; (2) social, emotional, or behavioural problems in the clinical range; and (3) psychotic-like experiences. TD children presented no antecedents, and had no family history of a schizophrenia spectrum disorder. MMN amplitude, but not latency, was significantly greater at frontal sites in the ASz group than in the TD group. Although the MMN exhibited by the children at risk of schizophrenia was unlike that of their typically developing peers, it also differed from the reduced MMN amplitude observed in adults with schizophrenia. This may reflect developmental and disease effects in a pre-prodromal phase of psychosis onset. Longitudinal follow-up is necessary to establish the developmental trajectory of MMN in at-risk children.
There are two sorts of criteria of consciousness--objective and subjective ones. They are the ability for operating with the knowledge which could be addressed to other people in the abstract form and the feeling of 'ego' as a 'host' of these actions, respectively. These two signs of consciousness are provided with the mechanism based on the synthesis in the brain structures of different kinds of information: sensory information, the data extracted from the memory and the signals from the centers of emotions and motivation. As a result of this synthesis, the sense of 'ego' arises and the message designated for others is determined. A significant role in the informational synthesis is played by dynamic cortical structures--foci of interaction. In perception they are localized predominantly in the projectional cortex, in thinking and in the associative areas. Realization is closely connected with communication and appearance of the interaction foci in the verbal zones of the left hemisphere. Pavlov (1951), in his program lecture in Madrid early in the present century, said that he saw the final aim of his study in the revealing of the mechanism and the inner vital sense of human consciousness. It is important, that Pavlov placed the words 'mechanism' and 'vital sense' near each other, i.e., he considered that the sense of consciousness would be realized through revealing its mechanism. This insight attracts our attention now, when the problem on consciousness mechanism is in scientific plans and the search for the meaning of life by the end of the twentieth century, one full of dramatic events, acquires a special value.
The present study was based on data from a longitudinal research program which consisted of 12,032 children, born in the Stockholm area in 1953 of which there were 494 children born with low birth weight (LBW, 2500 g or less). For all children at age 16 it was apparent that adjustment and psychiatric disturbances as well as juvenile delinquency were not related to birth weight and gestational age. LBW girls born at term, had significantly lower school grades, at age 16, than NBW (normal birth weight) girls. NBW boys born pre-term had lower school grades than NBW boys born at term. It is suggested that childhood development is gender related; in girls the birth weight--and in boys the length of the pregnancy was related to school marks at age 16. For boys at 18 years of age at the military draft, it was shown that LBW boys had smaller body size and lower IQ-test scores as compared to NBW boys. Additionally the length of the pregnancy was related to some measures of body size but not to IQ-test scores.
The common assumption in EEG-neurofeedback is one of functional specificity of the trained spectral bands, though it has been posited that only a nonspecific generalised learning process may be engaged. Earlier we reported differential effects on attention in healthy participants measured with continuous performance tests and the P300, following training of the sensory-motor rhythm band (SMR, 12 - 15Hz) compared with the adjacent beta1 (15-18 hz) band. Here previously unreported results are presented with phenomenological data from an activation checklist in support of the putative calming effect of SMR neurofeedback. While within sessions both protocols induced tiredness, this was paralleled by an increase in calmness only following SMR training. The differential effect on mood was theoretically consistent and extends evidence of cognitive functional specificity with neurofeedback to affective processes.