Topographic maps of brain electrical activity--pitfalls and precautions

Multimodal quantitative neuroimaging databases and methods: the Cuban Human Brain Mapping Project

This article reviews the contributions of the Cuban Neuroscience Center to the evolution of the statistical parametric mapping (SPM) of quantitative Multimodal Neuroimages (qMN), from its inception to more recent work. Attention is limited to methods that compare individual qMN to normative databases (n/qMN). This evolution is described in three successive stages: (a) the development of one variant of normative topographical quantitative EEG (n/qEEG-top) which carries out statistical comparison of individual EEG spectral topographies with regard to a normative database--as part of the now popular SPM of brain descriptive parameters; (b) the development of n/qEEG tomography (n/qEEG-TOM), which employs brain electrical tomography (BET) to calculate voxelwise SPM maps of source spectral features with respect to a norm; (c) the development of a more general n/qMN by substituting EEG parameters with other neuroimaging descriptive parameters to obtain SPM maps. The study also describes the creation of Cuban normative databases, starting with the Cuban EEG database obtained in the early 90s, and more recently, the Cuban Human Brain Mapping Project (CHBMP). This project has created a 240 subject database of the normal Cuban population, obtained from a population-based random sample, comprising clinical, neuropsychological, EEG, MRI and SPECT data for the same subjects. Examples of clinical studies using qMN are given and, more importantly, receiver operator characteristics (ROC) analyses of the different developments document a sustained effort to assess the clinical usefulness of the techniques.

A Quantitative Electroencephalographic Correlate of Sustained Attention Processing

The objective of the present investigation was to develop a quantitative electroencephalographic measure (qEEG) that is sensitive and specific to changes in sustained human performance. A principal components analysis (PCA) was performed on the qEEG obtained from participants during a continuous performance test. Measures of sensitivity (proportion of correctly identified correct responses, or hits) and specificity (proportion of correctly identified incorrect responses, or misses) were calculated to assess the classification accuracy of each newly derived component. PCA solutions produced a right hemisphere component comprised of beta-wave activity measured from four unipolar sites (F8, C6a, C6, and T4) that appeared to be sensitive and specific to changes in human performance. Results provide evidence for the validity of a right hemisphere qEEG measure that is sensitive and specific to changes in sustained human performance. Consistent with the findings of previous research, the present findings implicate the right cerebral hemisphere in the sustained attention process.

Is there an effect of acupuncture on the resting EEG?

OBJECTIVE

To investigate if acupuncture has a measurable effect on the resting electron EEG.

SUBJECTS

14 healthy volunteers with no neurological condition took part in the study.

METHODS

Using a digital storage EEG recorder and quantitative frequency analysis techniques data were obtained before, during and after acupuncture stimulation. To minimize the effect of artefacts all data were collected with the subject alert, but with eyes closed. Manual stimulation of the LI 4 acupuncture site was undertaken for periods of 0.5, 1.0 and 2.0 min. Frequency analysis of the EEG data from each acupuncture event was compared to the baseline data to show any significant changes over the bandwidth 0.3 to 30 Hz. Only changes greater than 2 standard deviations were considered significant.

RESULTS

In 10 subjects the frequency spectra remained unchanged during acupuncture, but in three significant increases were recorded in the amplitude of very low frequencies between 0.5 and 2 Hz and in one subject there was an increase in the amplitude of the alpha band during acupuncture. All spectra returned to their baseline values immediately after acupuncture.

OUTCOME

The changes recorded in the delta band of individuals during acupuncture were large but highly variable. They arose at a frequency that is on the limit of the recording equipment and where recording and physiological artefacts are known to occur, although there was no evidence of artefactual contamination of the data. The one case in which there was an increase in the alpha band is attributed to suppression of the dominant rhythm initially brought about by anxiety concerning the procedure which subsequently disappeared during acupuncture as the subject relaxed.

CONCLUSION

It is clear that there are no changes brought about by acupuncture in the resting EEG in the frequency range 2-30 Hz and no evidence to attribute changes below 2Hz to a direct affect of acupuncture.

Growth spurts in brain maturation during middle childhood as indexed by EEG power spectra

Developmental changes in background EEG power spectra were examined in 5-12-year-old children. The results confirmed older and more recent studies that reported continuous maturation and more sudden growth spurts in power spectral amplitude. EEG power in the Delta and Theta frequency bands decreased gradually with age, while power in the Alpha and Beta bands changed very little. Changes in spectral power were relatively increased between 6 and 7 years and between 9, 10 and 11 years. Some methodological problems concerning the assessment of cross-sectional age changes in EEG power spectra were addressed. Peak frequency increased with age; between 5 and 12 years the peak in the power spectrum shifted from fast Theta via slow Alpha to fast Alpha. Transformation of absolute power into relative power produced a high degree of interdependency between the broad bands. This interdependency affected the change with age of relative Alpha. Absolute power Alpha only changed in the eldest children, but because of a substantial decrease in Delta and Theta with increasing age, the proportion of Alpha relative to the other three bands increased. Hence, relative Alpha provided a good indication of the general maturational trend.

Towards measurement of brain function in operational environments

In operational environments that demand sustained vigilance or that involve multiple tasks competing for limited attentional resources, continuous monitoring of the mental state of the operator could decrease the potential for serious errors and provide valuable information concerning the ergonomics of the tasks being performed. There is widespread discussion and appreciation of the basic feasibility of utilizing neurophysiological measurements to derive accurate, reliable, rapid and unobtrusive assessments of mental state. However, progress in transitioning this idea into practical applications has been impeded by the fact that at present no convenient, inexpensive and effective means exists to derive a meaningful index of brain activity outside of laboratory settings. In this paper, we review some recent advances in recording technology and signal processing methods that will help overcome this limitation. For example, rapid progress is being made in the engineering of recording systems that are small, rugged, portable and easy-to-use, and thus suitable for deployment in operational environments. Progress is also being made in the development of signal processing algorithms for detecting and correcting recording artifacts and for increasing the amount of useful information that can be derived from brain signals. Finally, results from basic research studies suggest that accurate and reliable inferences about the mental load and alertness of an individual can be derived from neurophysiological measures in a practical fashion. These research and engineering successes suggest that it is reasonable to expect that in the near term a basic enabling technology will be deployed that will permit routine measurement of brain function in operational environments.

Mapeamento Cerebral

O mapeamento cerebral é uma técnica digital que gera mapas topográficos coloridos da atividade eletrencefalográfica captada sobre o escalpo. O eletrencefalograma após passar por um microcomputador, que realiza a análise quantitativa em várias faixas de freqüência, pode ser visualizado em um monitor colorido (EEG digital). Posteriormente, as épocas do EEG digital são selecionadas para a realização dos mapas, impressão final e arquivo em disquetes. Este método tem demonstrado ser ON em várias doenças neurológicas e psiquiátricas e deve ser realizado sempre em conjunto com o EEG digital. Achamos que dentro de alguns anos os aparelhos de EEG digital/mapeamento cerebral substituam as máquinas que realizam o EEG convencional.

Personality and EEG beta in older adults with alcoholic relatives

Research indicates that biological relatives of alcoholics are more likely to develop alcoholism than individuals without alcoholic relatives. Most research on these groups had focused on individuals who were relatively young (i.e., under 30 years old). In the present study, we evaluated middle-aged and elderly nonalcoholic men and women who did and did not have alcoholic biological relatives to assess factors that might be involved in a later, rather than an earlier, onset of alcoholism. Psychological characteristics were assessed using the Tridimensional Personality Questionnaire. Biological characteristics were assessed using quantitative measures of the spontaneous electroencephalogram. The psychological measures did not distinguish the groups, but biological measures did. The results indicated that nonalcoholic individuals with alcoholic relatives showed elevated beta as compared with sex- and age-matched control subjects. Factors that might have mediated these findings are discussed, as are the implications of these outcomes.

A comparison of quantitative electroencephalography, computed tomography, and behavioral evaluations to localize impairment in patients with stroke and transient ischemic attacks

Brain computed tomography and a structured behavioral assessment provided a better correlation than did quantitative electroencephalography to the presence of mild stroke or transient ischemic attacks in 21 patients. When electroencephalography did not correlate well, it tended to localize too laterally or miss deep lesions. Computed tomography did not identify 2 lesions when done early after disease onset. No test was uniformly more sensitive or accurate than others. They may complement each other.

Guidelines for the recording and quantitative analysis of electroencephalographic activity in research contexts

Developments in technologic and analytical procedures applied to the study of brain electrical activity have intensified interest in this modality as a means of examining brain function. The impact of these new developments on traditional methods of acquiring and analyzing electroencephalographic activity requires evaluation. Ultimately, the integration of the old with the new must result in an accepted standardized methodology to be used in these investigations. In this paper, basic procedures and recent developments involved in the recording and analysis of brain electrical activity are discussed and recommendations are made, with emphasis on psychophysiological applications of these procedures.

Computerized pattern recognition of EEG artifact

Automated artifact classification of quantified EEG (QEEG) epochs from 9 males using linear discriminant analysis showed greater than 85% agreement with judges' opinions. These results were replicated (n = 600 epochs for each sample). Testing the entire sample (n = 5800) illustrated reliable eye artifact (94%) but reduced muscle artifact classification (70%) accuracy. Agreement was lowest in the case of more subtle forms of muscle artifact (i.e., low amplitude muscle), however, less than 4% of these were wrongly classified as non-artifact. Improved data collection techniques retaining high frequency energies are anticipated to improve muscle artifact recognition. Results indicate that low levels of artifact contamination would result when only those epochs classified as non-artifact were accepted for inclusion in further analysis.

Brain mapping: a contribution to linear interpolation

Topographic mapping of brain electrical activity has become a powerful tool in neurological diagnosis. Maps are obtained from a reduced number of actual measurements by means of mathematical interpolation. Most of these systems use linear combination of the values measured and, in spite of its importance, the choice of the exponent "n" in the weighting function is made ad hoc. In this paper we present a critical analysis of such method and propose an objective criterion for the estimation of that exponent. As well, we propose another criterion for determining the number of leads used in the interpolation of each point.

Spectral and topographic analysis of EEG in schizophrenic patients

The authors performed spectral analysis of electroencephalograms (EEG), recorded awake, with eyes closed, in 13 patients with schizophrenia and 9 age-matched individuals without psychiatric diagnosis. We tested several possible parameterizations of the data, and two data-reduction strategies; these yielded similar results. Comparison of the two groups revealed a relative increase in alpha frequency activity in the frontal regions in the patient group. The authors believe that this finding is consistent with data from neuropsychologic tests, metabolic imaging studies, and evoked potential studies that suggest impaired activation of frontal brain areas in patients with schizophrenia.

Topographic EEG mapping methods

After almost 40 years of research on EEG computer analysis, present clinical applications of this method remain limited. At the present time, EEG mapping is suited primarily for research. Despite the pitfalls of an uncritical application of EEG mapping, progress in clinical research made possible by EEG mapping techniques has been considerable. Some problems of data acquisition, display and statistical analysis are discussed in this paper. For headache research examination of the activated EEG, especially with photic stimulation, has greater diagnostic importance than mapping under resting conditions.

P300 topographic asymmetries are present in unmedicated schizophrenics

Our laboratory has repeatedly found a left < right auditory P300 temporal lobe topographic asymmetry in right-handed, medicated schizophrenics. To determine whether this asymmetry was attributable to the effects of antipsychotic medications, we collected auditory "odd-ball" P300 event-related potentials from 14 right-handed, unmedicated schizophrenics (withdrawn from medication for an average of 21 days) and 14 right-handed, normal controls. Analysis of normalized P300 amplitudes showed a statistically significant difference in the voltage distributions between groups (a group by temporal electrode site interaction) that was consistent with a left < right temporal voltage asymmetry in schizophrenics but not in the normal controls. We conclude that P300 topographic asymmetries are present in unmedicated schizophrenics. These data are compatible with the growing body of data suggesting left temporal lobe structural abnormalities in schizophrenia.

Artifact processing in topographic mapping of electroencephalographic activity in neuropsychopharmacology

Mapping of the electroencephalogram (EEG) has been found to be a valuable method in clinical neuropsychopharmacology. It is evident that careful treatment of artifacts is of utmost importance for EEG data processing, as artifacts that contaminate the EEG data can lead to spurious results. The artifact-processing method described in this article splits signal analysis into a preprocessing step, yielding individual electro-oculographic (EOG) regression factors for EOG minimization, and into a processing step, yielding target variables. The combination of avoiding, minimizing, and identifying artifacts, as well as visual checking of face validity, will help remove artifactual effects from the EEG.

Topographic quantitative EEG amplitude in recovered alcoholics

Topographic measures of electroencephalographic (EEG) amplitude were used to compare recovered alcoholics (n = 14) with sex- and age-matched control subjects. Delta, alpha, and beta activity did not distinguish the groups, but regional differences in theta distribution did. Recovered alcoholics showed more uniform distributions of theta amplitudes in bilateral anterior and posterior regions compared with controls. Because a minimum of 5 years had elapsed since the recovered alcoholic subjects fulfilled DSM-III-R criteria for alcohol abuse or dependence, it is unlikely these EEG theta differences reflect the effects of withdrawal.

Imaging of brain electrophysiologic activity: applications in psychiatry

Recent advances in computer technology make it relatively easy to generate color images representing the electrophysiologic activity of the brain. Because of the visual appeal of the images, and their similarity to computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) scans, there has been wide interest in these methods. Thorough understanding of these techniques is necessary to appreciate their strengths and limitations, and their proper application. This article explains the types of studies that are usually done, compares these methods with other imaging techniques, outlines their limitations, summarizes the literature on their use in psychiatry, and describes clinical situations in which these tests may be useful. This information will help the reader interpret clinical reports and research studies that employ these methods, evaluate representations made by commercial vendors of imaging systems, and understand the role these tests can play in his or her daily clinical practice.

Topographic mapping of somatosensory evoked potentials helps identify motor cortex more quickly in the operating room

Median nerve somatosensory evoked potentials were recorded from exposed cerebral cortex during craniotomies. This technique is valuable when knowledge of the motor cortex location can influence surgical decisions about resection limits or biopsy sites. Two different recording techniques were compared: strips of electrodes and arrays of electrodes. The arrays recorded electrical potentials suitable for topographic mapping. We found that motor cortex could be identified more quickly when using the topographic mapping of SEPs from arrays. We conclude that topographic mapping of SEP from sensorimotor regions during craniotomies works well in general and can be done more quickly than the traditional electrode strip technique.

Dynamic brain mapping methodology and application

Brain mapping has opened important perspectives for the neurophysiological evaluation of patients, for the discrimination of drug effects on the brain and for the study of the relationship between the brain and behavior. Our Dynamic Brain Mapping System is the result of many years of EEG quantification. It was designed as a software-oriented system to favor the largest clinical application and simultaneously stimulate new research objectives. Data collection and analysis procedures are critically important in brain mapping for a good understanding of the results. For clinical use, the maps should answer relevant EEG questions and be interpretable with the consolidated knowledge. Therefore, we have developed a new type of brain mapping technology which is called "Field blending interpolation" mapping offered together with the conventional technology with user-selectable interpolation algorithms. In addition to diagnosis, the use of computer-analyzed EEG and brain mapping can be instrumental in drug monitoring, drug selection and drug discriminations. Prospective studies are, however, required to validate the use of brain mapping in each of these new areas. Spatial analysis is the original goal of brain mapping. The development of a new data collection procedure and analysis will be instrumental in the determination of an adequate time and space resolution.

Topographic quantitative EEG in elderly subjects with major depression

Some previous quantitative EEG research indicates that depressed subjects show increased alpha and beta compared to controls. In this report, absolute and relative amplitude measures of topographic EEG were used to compare elderly subjects with major depression to sex and age matched control subjects. Elderly depressed subjects showed significantly higher absolute alpha amplitude than controls, but regional differences did not specifically distinguish them. Relative alpha amplitudes, and absolute and relative measures of beta, delta, and theta did not reliably distinguish depressed and control subjects. The results are discussed in the context of previous EEG research in depression and the elderly. Methodological features and the implications of these findings for state and trait dependent conceptualizations of depression are considered.

Preservation of P300 event-related potential topographic asymmetries in schizophrenia with use of either linked-ear or nose reference sites

Previous studies of the auditory P300 event-related potential (ERP) from our laboratory have reported a left- greater than right-sided attenuation in medicated chronic schizophrenics compared with normal controls. A possible confound in these studies has been the use of the linked-ear reference (LER), which has been criticized on the grounds that it might either induce or suppress topographic asymmetries. To test the effects of LER on P300 asymmetries in schizophrenia, we recorded ERPs with both LER and a nose reference (NR) in a group of 20 chronic medicated schizophrenics and in group of 20 age-matched normal controls. We here report: (1) confirmation of our previous P300 findings of left temporal scalp region deficit using both LER and NR with a 28-electrode montage; this feature was prominent in the wave form associated with the target stimulus, without the use of the wave form subtractions of our previous studies; (2) no statistically significant topographic differences between the LER and NR for either the schizophrenic or normal subjects; and (3) better performance of the LER in differentiating schizophrenics versus normal controls, due to lower wave form variability. We conclude that the LER is preferable for studies using subject groups and methodology similar to the present study.

Quantitative, waking EEG research on depression

Research published in the past decade that used quantitative indices to evaluate the waking EEG characteristics of depressed patients is reviewed. Methodological problems that make results of different research laboratories difficult to compare include diagnostic heterogeneity of depressed groups, lack of inclusion of control subjects, and differences in the EEG techniques. Despite interpretive problems that arise from such substantial variation, consistencies nevertheless emerge. Unmedicated, actively depressed patients appear to exhibit elevated EEG alpha and beta compared to control subjects. Delta and theta distinguished depressed patients from controls in some single studies, but variation in age, specific diagnostic depression categories, and EEG acquisition and analysis techniques rendered these results less definitive. Quantitative EEG differences that may distinguish depressed subject samples from those with other psychiatric disorders are considered. Factors that limit comparability of the findings are discussed in conjunction with strategies that deserve systematic study in future research.

Quantified neurophysiology with mapping: statistical inference, exploratory and confirmatory data analysis

Topographic mapping of brain electrical activity has become a commonly used method in the clinical as well as research laboratory. To enhance analytic power and accuracy, mapping applications often involve statistical paradigms for the detection of abnormality or difference. Because mapping studies involve many measurements and variables, the appearance of a large data dimensionality may be created. If abnormality is sought by statistical mapping procedures and if the many variables are uncorrelated, certain positive findings could be attributable to chance. To protect against this undesirable possibility we advocate the replication of initial findings on independent data sets. Statistical difference attributable to chance will not replicate, whereas real difference will reproduce. Clinical studies must, therefore, provide for repeat measurements and research studies must involve analysis of second populations. Furthermore, Principal Components Analysis can be employed to demonstrate that variables derived from mapping studies are highly intercorrelated and data dimensionality substantially less than the total number of variables initially created. This reduces the likelihood of capitalization on chance. The need to constrain alpha levels is not necessary when dimensionality is low and/or a second data set is available. When only one data set is available in research applications, techniques such as the Bonferroni correction, the "leave-one-out" method, and Descriptive Data Analysis (DDA) are available. These techniques are discussed, clinical and research examples are given, and differences between Exploratory (EDA) and Confirmatory Data Analysis (EDA) are reviewed.

Analysis of scalp voltage asymmetries using Hotelling's T2 methodology

Topographic mapping procedures are becoming increasingly popular, and scalp voltage asymmetries are a measure of specific interest. Standard statistical techniques in the field to detect voltage asymmetries, "significance probability mapping (SPM)" and repeated-measures analysis of variance (ANOVA) have statistical assumptions which are not in accord with electrophysiological data, and which therefore may lead to serious statistical errors. These limitations and a superior method using multivariate analysis are discussed. This paper provides a sample data set, for illustration of specific computational steps, and to provide an empirical example and reference for the theoretical discussion.

Topographic evoked potential mapping in obsessive-compulsive disorder: evidence of frontal lobe dysfunction

Several lines of evidence suggest that frontal lobe dysfunction may underlie obsessive-compulsive disorder (OCD). Eighteen patients with OCD were compared with 18 normals matched for age, gender, handedness, and education on a Go-NoGo task. Visual evoked potentials were measured during the task. Topographic evoked potential mapping revealed significantly smaller P300 magnitudes in orbital frontal areas in the OCD patients. Results are compared with those from studies using other methodologies, and etiological implications are discussed.

Topographical brain electrical activity mapping on an IBM-compatible personal computer

A new system for computing brain electrical activity maps on a standard IBM-compatible computer has been developed. The EEG is recorded using a CED1401 intelligent laboratory interface and stored in the computer; colour coded maps are generated using software developed in Turbo PASCAL and displayed on the EGA graphics screen. An acceptable computation time of 1.2 s for a 64 x 64 map displayed as a 128 x 128 pixel image has been achieved by incorporating assembly language routines and a maths coprocessor. The system may be readily upgraded as improved hardware becomes available and further software can be added. In addition to triggering auditory, visual and somatosensory stimulators, it provides the potential for the generation of complex stimuli for cognitive experiments by means of mass RAM and digital-to-analogue converters.

Topographic mapping of EEG and evoked potentials in psychiatry: delusions, illusions, and realities

This paper reviews the utility of topographic mapping of EEG and evoked potentials in psychiatry. Further, a wide variety of caveats related to this technique are reviewed including cerebral and extracerebral sources of artifact. Moreover, both questionable and legitimate uses of mapping in psychiatry are addressed and possible future applications of this technique are considered. Finally, multidisciplinary approaches to the study of the brain are discussed.

Facts and artifacts in brain electrical activity mapping

As computerized EEG (CEEG) analysis and display methods become increasingly powerful the user is lured toward increasingly abstract representations of data in which artifacts can easily go unrecognized. The presence of even small amounts of artifact can lead to distortion of CEEG results due to the sensitivity of the analysis methods employed. Several common artifacts are discussed, their distortion of CEEG data illustrated, and remedial measures suggested. Some of these artifacts (EOG, EMG, photomyoclonic, tremor, ECG, 60 Hz, volume conducted cortical activity) are familiar to traditional EEG (aliasing, extrapolation) are unique to CEEG and may be inadvertently introduced by workers not specifically trained in CEEG methods.