QEEG norms for the first year of life.

BACKGROUND: QEEG allows a more objective evaluation of cerebral electrical activity as well as the production of topographical maps for easier comprehension. Here we have developed qEEG norms for the first year of life using methods previously published for other age ranges, including for example, regression for Gausssianity before Z transformation. These norms constitute a non-invasive and low cost tool for the functional evaluation of the infant's brain. RESULTS: Developmental equations were obtained from 101 healthy infants recording at spontaneous quiet sleep stage II. Polynomial regression equations, with age as independent variable, were calculated for full Broad Band Spectral Parameters (BBSP) using the Least Squares technique. Interpolated maps of the BBSP values or their Z transformation were constructed for linked-ear reference, average reference and Laplacian montages. All montages produced similar tendency curves and Z maps of absolute and relative power, and mean frequency at all frequency bands. The norms obtained were validated against an independent group of 50 healthy infants and some pathological cases. 91-98% of cases were well classified as normal across all measures and montages. To exemplify, two pathological cases are presented of which their qEEG maps show resemblance to CT and MRI. CONCLUSIONS: These qEEG norms are highly useful as an aid to visual interpretation and for the study of pathology further evolution as well as for assessment of infants showing brain risk factors. To our knowledge this is the first normative qEEG study for the initial year of life with such large sample and validation-group.

Follow-up study of learning-disabled children treated with neurofeedback or placebo.

This report is a 2-year follow-up to a previous study describing positive behavioral changes and a spurt of EEG maturation with theta/alpha neurofeedback (NFB) training in a group of Learning Disabled (LD) children. In a control paired group, treated with placebo, behavioral changes were not observed and the smaller maturational EEG changes observed were easily explained by increased age. Two years later, the EEG maturational lag in Control Group children increased, reaching abnormally high theta Relative Power values; the absence of positive behavioral changes continued and the neurological diagnosis remained LD. In contrast, after 2 years EEG maturation did continue in children who belonged to the Experimental Group with previous neurofeedback training; this was accompanied by positive behavioral changes, which were reflected in remission of LD symptoms.

Schizencephaly with occlusion or absence of middle cerebral artery.

In a study of 160 infants with prenatal and/or perinatal risk factors for brain damage, we observed three cases of schizencephaly. All cases were unilateral, and the clefts had open lips. In two cases, magnetic resonance angiography showed occlusion or absence of the middle cerebral artery (MCA) on the affected side. Two of the patients, including one with absent flow in the MCA of the affected side, had ipsilateral cerebellar atrophy.

EEG and behavioral changes following neurofeedback treatment in learning disabled children.

Neurofeedback (NFB) is an operant conditioning procedure, by which the subject learns to control his/her EEG activity. On one hand, Learning Disabled (LD) children have higher values of theta EEG absolute and relative power than normal children, and on the other hand, it has been shown that minimum alpha absolute power is necessary for adequate performance. Ten LD children were selected with higher than normal ratios of theta to alpha absolute power (theta/alpha). The Test Of Variables of Attention (TOVA) was applied. Children were divided into two groups in order to maintain similar IQ values, TOVA values, socioeconomical status, and gender for each group. In the experimental group, NFB was applied in the region with highest ratio, triggering a sound each time the ratio fell below a threshold value. Noncontingent reinforcement was given to the other group. Twenty half-hour sessions were applied, at a rate of 2 per week. At the end of the 20 sessions, TOVA, WISC and EEG were obtained. There was significant improvement in WISC performance in the experimental group that was not observed in the control group. EEG absolute power decreased in delta, theta, alpha and beta bands in the experimental group. Control children only showed a decrease in relative power in the delta band. All changes observed in the experimental group and not observed in the control group indicate better cognitive performance and the presence of greater EEG maturation in the experimental group, which suggests that changes were due not only to development but also to NFB treatment.

An accurate and efficient bayesian method for automatic segmentation of brain MRI.

Automatic three-dimensional (3-D) segmentation of the brain from magnetic resonance (MR) scans is a challenging problem that has received an enormous amount of attention lately. Of the techniques reported in the literature, very few are fully automatic. In this paper, we present an efficient and accurate, fully automatic 3-D segmentation procedure for brain MR scans. It has several salient features; namely, the following. 1) Instead of a single multiplicative bias field that affects all tissue intensities, separate parametric smooth models are used for the intensity of each class. 2) A brain atlas is used in conjunction with a robust registration procedure to find a nonrigid transformation that maps the standard brain to the specimen to be segmented. This transformation is then used to: segment the brain from nonbrain tissue; compute prior probabilities for each class at each voxel location and find an appropriate automatic initialization. 3) Finally, a novel algorithm is presented which is a variant of the expectation-maximization procedure, that incorporates a fast and accurate way to find optimal segmentations, given the intensity models along with the spatial coherence assumption. Experimental results with both synthetic and real data are included, as well as comparisons of the performance of our algorithm with that of other published methods.

Cerebral blood flow and sources of abnormal EEG activity (VARETA) in neurocysticercosis.

OBJECTIVES: To compare two different functional procedures in the assessment of brain ischemia in patients with neurocysticercosis (NCC): (1) electroencephalography (EEG) evaluated by brain maps and EEG current sources in the frequency domain using variable resolution electromagnetic tomography and (2) blood flow analyzed by computerized tomography assessed with stable Xe (Xe-CT). METHODS: Eleven patients with NCC at different evolution stages were studied. CT and Xe-CT scans, as well as quantitative electroencephalography with source calculation in the frequency domain, were obtained. All patients showed cysts and in 6 of them there were also vascular complications: two of them presented calcifications of the middle cerebral artery, two other subjects showed calcifications of the vessels in the circle of Willis and the remaining two had brain infarctions. RESULTS: In the cyst areas important hypoperfused zones were observed, as intense as those observed in infarcted areas. Damage to the blood-brain barrier was originated by parasites in colloidal phase (final cysticerci stage) producing large areas of edema and hypoperfusion. Abnormal delta EEG activity was observed in very large lesions, probably generated by partial cortical deafferentation; and abnormal theta activity was mainly related to the presence of edema. CONCLUSIONS: Sources of abnormal EEG activity were very similar in topography to the hypoperfused areas.

EEG changes during word and figure categorization.

OBJECTIVE: To analyze whether the EEG changes observed during figure and word categorization are compatible with either the dual, the common amodal, or the alternative model (modality-specific codes for words and pictures, where meaning is represented for both in a higher-order amodal system) for semantic knowledge. METHODS: EEG was recorded during word and figure categorization of animals or non-animals in a group of 28 children 8-10 years old. Computation of EEG sources in the frequency domain using variable resolution electrical tomography (VARETA) and their statistical evaluation by statistical parametric mapping were carried out. RESULTS: At all frequencies, there were significant changes between EEG segments prior to the presentation of the stimuli and EEG segments recorded after the stimuli. Post-segments showed more power from 1.56 to 7.02 Hz, and less power than pre-segments from 8 to 12.48 Hz. EEG changes were only observed in the word task at: 3.9 (left occipital), 4.68, 5.46, and 6.24 Hz (temporo-occipital regions). These changes may be associated with visual encoding of words. Frequencies 7.8 and 17.94 Hz increased in prefrontal, anterior cingulate, and anterior temporal regions only during figure categorization. The prefrontal region may be related to object working memory. Thus, these frequencies might be related to figure codification. No significant differences between tasks were observed at 3.12 and 7.02 Hz in very wide brain areas (all lobes except occipital), suggesting that the amodal semantic system storage could be the model compatible with figure and word categorization. CONCLUSIONS: Thus, our results support the modified amodal semantic hypothesis, which advocates that the meanings of both kinds of stimuli are represented in a conceptual memory that receives input from the logogen and iconogen systems.

Delayed P300 during Sternberg and color discrimination tasks in poor readers.

The P300 ERP component was studied in poor and normal readers, using Sternberg and color discrimination (Spaceships) tasks. During the first one, subjects must decide if a probe item belongs or not to a set of digits previously presented. In the second one, the participants must shoot violet spaceships with one key and other than violet spaceships with another key. There were no significant differences between groups with respect to reaction times, but a larger proportion of errors was observed in poor readers. Longer P300 latencies were recorded for poor readers than controls in both tasks. P300 amplitudes showed topographical differences between the two groups: Poor readers' P300 is larger frontally during the Sternberg task, but smaller at posterior sites during the Spaceships task. These results suggest that poor readers may have deficiencies during the early processing stage, such as visual stimulus evaluation. Poor readers also appear to have deficits for classifying and memorizing visual stimuli.

Sources of abnormal EEG activity in brain infarctions.

EEGs from 16 patients with stroke in three different stages of evolution were recorded. EEG sources were calculated every 0.39 Hz by frequency domain VARETA. The main source was within the delta band in 2 out of 4 chronic patients, and in 67% of the patients in the acute or subacute stages when edema (cytotoxic or vasogenic) was present. Moreover, all patients showed abnormal activity in the theta band. Sources of abnormal activity in cortical or corticosubcortical infarcts were located in the cortex, surrounding the lesion. At the site of the infarct, a decrease of EEG power was observed. Sources of abnormal theta power coincided with edema and/or ischemic penumbra.

Specific EEG frequencies at specific brain areas and performance.

In this study it was shown that in adults, the frequency characteristics of EEG preceding stimuli that were followed by incorrect responses were different from the characteristics of EEG preceding stimuli that were followed by correct responses. In the recording during three different tasks that explore different neuronal networks, higher values of current preceding incorrect performance in those areas directly related to the task were found in frequencies within the delta (1.56 and 3.12 Hz) and beta bands (13.26, 14.04, 14.82, 15.6, 17.16 and 17.94 Hz), suggesting that these frequencies signal inhibition. Frequencies within the alpha band (9.36 and 12.48 Hz) showed greater energy preceding correct responses in task-specific areas, supporting previous results observed in children.

Calcification of intracranial vessels in neurocysticercosis.

We report calcification of intracranial vessels in neurocysticercosis. Calcification was observed in the middle cerebral arteries in two patients, and the circle of Willis in two others. The patients with middle cerebral artery calcification underwent CT with inhaled stable xenon and an area of mild hypoperfusion was observed in the ipsilateral cerebral hemisphere.

Auditory event-related potentials in poor readers.

Although poor readers (PR) are considered the major group among reading-disabled children, there are not event-related potentials (ERP) studies reported of PR on the subject. In this study, attentional and memory processes were studied in an auditory oddball task in PR and normal controls. ERP to auditory stimuli were recorded in 19 leads of the 10/20 system, using linked earlobes as references, in 20 normal children (10 female) and 20 PR (10 female) of the same age (10-12 years old). Two pure tones (1000 and 3000 Hz) were used in an oddball paradigm. No significant differences were observed in the amplitudes and latencies of N100 between the groups. However, N200 to frequent stimuli and P200 to both frequent and infrequent stimuli were of higher amplitude in poor readers than in normal children. There were no differences between groups in the latency and amplitude of P300. The results suggest that PR use more attentional resources in the components occurring before P300 to both frequent and infrequent stimuli than the normal children, and this finding is particularly marked for PR girls.

Primary task demands modulate P3a amplitude.

Auditory event-related brain potentials (ERPs) were recorded from 10 subjects in two different conditions: (1) subjects were required to reorder five visually presented letters in order to form a word and provide a verbal response (task condition); (2) subjects were presented with a control stimulus with the same physical characteristics as the experimental stimulus, but containing just one type of letter (i.e., AAAAA). Subjects had to verbally respond to such stimuli by saying "A" (control condition). Tones of 1000 Hz (standard) and 1050 Hz (deviant) were also presented to the subjects in a 85%-15% probability paradigm 2 s before, during and 8 s after the presentation of the visual stimuli. Recordings were obtained from Fpz, Fz, Cz and Pz vs. linked ears. Auditory ERPs to the auditory stimuli after the presentation of the visual letter string and during the performance of the task were averaged for the standard and deviant tones in both conditions. Only correct responses were considered for the averages. The N100 was affected by stimulus type (standard vs. deviant) but not by condition (task vs. control); however, larger P3a waves were observed during the control than during the task condition. No significant differences between conditions were observed in the mismatch negativity (MMN) latency range. These results suggest that primary task demands modulate involuntary attention processing.

Brain infarcts due to scorpion stings in children: MRI.

We report two children with severe neurological complications after having been stung by a scorpion. Clinical and MRI findings suggested brain infarcts. The lesions seen were in pons in one child and the right hemisphere in the other. The latter also showed possible hyperemia in the infarcted area. No vascular occlusions were observed and we therefore think the brain infarcts were a consequence of the scorpion sting. The cause of the infarct may be hypotension, shock or depressed left ventricular function, all of which are frequent in severe poisoning by scorpion sting.

N400 and lexical decisions: automatic or controlled processing?

OBJECTIVE: To investigate whether the N400 effect is sensitive to automatic or controlled processes. METHODS: Two experiments were performed. In one experiment, directly related word pairs were used. In the other experiment, mediated-related word pairs were used. In order to reduce controlled processes, each experiment consisted of 3 tasks: Low- and high-proportion of related pairs, and single presentation lexical decision task. RESULTS: In the first experiment, the amount of priming was equivalent for the 3 tasks. The N400 effect appeared in the high and low proportion of directly related words, but not in the single presentation task. In the second experiment, behavioral priming was also found in the 3 tasks. However, the N400 effect was observed only in the task with low proportion of related pairs. CONCLUSION: These results suggest that the N400 effect may be related to controlled processes.

Sources of abnormal EEG activity in the presence of brain lesions.

In routine clinical EEG, a common origin is assumed for delta and theta rhythms produced by brain lesions. In previous papers, we have provided some experimental support, based on High Resolution qEEG and dipole fitting in the frequency domain, for the hypothesis that delta and theta spectral power have independent origins related to lesion and edema respectively. This paper describes the results obtained with Frequency Domain VARETA (FD-VARETA) in a group of 13 patients with cortical space-occupying lesions, in order to: 1) Test the accuracy of FD-VARETA for the localization of brain lesions, and 2) To provide further support for the independent origin of delta and theta components. FD VARETA is a distributed inverse solution, constrained by the Montreal Neurological Institute probabilistic atlas that estimates the spectra of EEG sources. In all patients, logarithmic transformed source spectra were compared with age-matched normative values, defining the Z source spectrum. Maximum Z values were found in 10 patients within the delta band (1.56 to 3.12 Hz); the spatial extent of these sources in the atlas corresponded with the location of the tumors in the CT. In 2 patients with small metastases and large volumes of edema and in a patient showing only edema, maximum Z values were found between 4.29 and 5.12 Hz. The spatial extent of the sources at these frequencies was within the volume of the edema in the CT. These results provided strong support to the hypothesis that both delta and theta abnormal EEG activities are the counterparts of two different pathophysiological processes.

Do specific EEG frequencies indicate different processes during mental calculation?

EEG recordings during mental calculation and a control task (with presentation of stimuli with similar physical characteristics to the arithmetic symbols) were obtained in 10 subjects. Narrow band analyses of the EEG and distributed sources for each EEG frequency were calculated using variable resolution electromagnetic tomography. Significant differences between the sources for arithmetic and control tasks were observed at 3.9 Hz within Broca's and left parietotemporal cortices, suggesting that this frequency may be related with the production of internal speech, storage and rehearsal of verbal working memory. Differences at 5.46 Hz within the right dorsolateral prefrontal cortex were considered to be associated to sustained attention. The decrease at 12.46 Hz within the left parietal cortex was interpreted as a sign of retrieval of arithmetic facts from long term memory.

Relationship of specific EEG frequencies at specific brain areas with performance.

This study shows that incorrect responses are preceded by different EEG characteristics than correct responses, and that these differences appear in specific brain regions that participate in each particular task. EEGs were recorded in children during three different tasks: color discrimination (CDT), verbal working memory (VWM), and word categorization task (WCT). EEG segments previous to the presentation of the stimulus were analysed. Incorrect responses were preceded by lower EEG power values at 7.8 Hz in posterior temporal and right parietal leads in CDT, 8.59 and 9.36 Hz in frontal areas in VWM, and 10.72 Hz in the left hemisphere in WCT. In the former task > 1.56 Hz power in frontal areas prior to an incorrect response was also observed.

Evolution of cerebral edema and its relationship with power in the theta band.

In previous papers we have proposed that in patients with space-occupying lesions, delta power was related with the volume of the lesion and theta power with the volume of the edema. In this report we analyze the evolution of 10 patients with space-occupying lesions in whom we measured the volume of the lesion and of the edema before and after treatment that produced changes in these volumes. EEGs were recorded in the leads of the 10-20 system referenced to linked earlobes. Delta and theta powers were calculated for voltage and current source densities (CSD) and compared with age-norms to compute conventional Z-maps. These maps provide probability statements about the deviation of observed values from the norm. Rank correlations between the change in the volume of the lesion before and after treatment and the change in Z-values before and after treatment were significant only in the delta band. However, rank correlations between the change in the volume of the edema and the change in EEG Z-values were only significant in the theta band. These correlations were higher for CSD than for voltage estimates. We also observed that the site of the lesion and of the edema was better represented by CSD maps than by voltage maps. These results are also in agreement with our previous reports, in which we observed more precise localization of brain lesions by CSD than by voltage estimates.

Comparison of Z and multivariate statistical brain electromagnetic maps for the localization of brain lesions.

Conventional Z maps provide probability statements about the deviation of observed values from the norm. Galán et al. (1994) introduced Simultaneous Significance Probability Scales to detect abnormalities over the whole map, making use of the information provided by the topographic structure of dependencies. They also described multivariate brain electromagnetic (MBE) maps for compact presentation of complex spatio-temporal information. In this paper, using the distance-based localization receiver operating characteristic curves (DL-ROC curves), we compare the localization provided by computed tomography with that provided by Z and MBE maps in 61 patients with brain lesions. Maps were calculated for absolute power and relative power in delta, theta, alpha and beta bands for voltage and current source densities (CSD). In each patient, all maps were compared and the map with the highest value of the area of the DL-ROC curve was considered to be the "best map." Z maps of CSD were the "best maps" in 24 patients. In the voltage montage, we observed that multivariate maps add some information not contained in the Z maps. However, for CSD, Z maps were more accurate than multivariate maps. A very consistent finding was the observation that lesions were better detected by maps analyzing the delta band, while edema was better represented by maps in the theta range.