Showing papers in "Brain Topography in 1989"
TL;DR: Estimation of a signal's correlation dimension is applied to the characterization of human electroencephalographic signals and event-related brain potentials and suggests that this procedure can provide a partial characterization of changes in cerebral electrical activity associated with changes in cognitive behavior that complements classical analytic procedures.
Abstract: In addition to providing important theoretical insights into chaotic deterministic systems, dynamical systems theory has provided techniques for analyzing experimental data. These methods have been applied to a variety of physical and chemical systems. More recently, biological applications have become important. In this paper, we report applications of one of these techniques, estimation of a signal's correlation dimension, to the characterization of human electroencephalographic (EEG) signals and event-related brain potentials (ERPs). These calculations demonstrate that the magnitude of the technical difficulties encountered when attempting to estimate dimensions from noisy biological signals are substantial. However, these results also suggest that this procedure can provide a partial characterization of changes in cerebral electrical activity associated with changes in cognitive behavior that complements classical analytic procedures.
235 citations
TL;DR: It is demonstrated that from phase shifts the authors may estimate transmission delays between at least certain classes of EEG signals, and can asses, unambiguously, how the transmission of information between different brain sites develops.
Abstract: To investigate the degree of interdependence of EEG signals, we have to use signal analysis methods. Three of these are described and their performance is compared: the cross-correlation (coherence and phase), the average amount of mutual information (AAMI) or the normalized AAMI, also called transmission coefficient T, and the correlation ratio h2 that is a general measure of nonlinear fit between any two signals. The three methods were applied to simulated and real signals in order to put in evidence how nonlinear relationships may affect differently these three measures of association. The nature of the interdependence between EEG signals is not characterized only by the degree of association, but also by the corresponding phase relationship. A basic question is whether such a phase shift can be interpreted as a transmission delay. However, a fundamental problem is that a phase shift may be difficult to interpret in terms of a biophysical model. A procedure is described in order to solve this problem. This involves computing the phase spectrum between the pair of signals, estimating the gain of the corresponding linear transfer function and the associated minimum phase. By subtracting the minimum phase from the phase spectrum, a corrected phase function can be obtained. From the slope of this phase function, a transmission delay can be estimated. This procedure is illustrated by applications to simulated and real EEG signals. It is demonstrated that from phase shifts we may estimate transmission delays between at least certain classes of EEG signals. In this way we can asses, unambiguously, how the transmission of information between different brain sites develops.
199 citations
TL;DR: A mechanism by which removal of diffuse input from the reticular formation may cause an abrupt drop in EEG frequency (as in the transition from the awake to sleeping state) is postulated.
Abstract: A theory of neocortical interactions is developed involving both local delays (PSP rise and decay times) and global delays due to finite velocity of action potentials in corticocortical fibers. The theory is based on plausible assumptions regarding input/output relations in neocortical columns and realistic neural parameters. The simultaneous existence of short wavelength waves propagating away from multiple epicenters and long wavelength standing waves due to global boundary conditions is predicted. Both phenomena appear to have dominant oscillation frequencies in the general range of observed EEG phenomena in humans. A mechanism by which removal of diffuse input from the reticular formation may cause an abrupt drop in EEG frequency (as in the transition from the awake to sleeping state) is postulated.
161 citations
TL;DR: Improved neuroelectric recording and analysis tools are yielding increasingly specific information about the spatial and temporal features of neurocognitive processes.
Abstract: Improved neuroelectric recording and analysis tools are yielding increasingly specific information about the spatial and temporal features of neurocognitive processes. Such tools include recordings with up to 125 channels, digital signal processing techniques, and correlation of neuroelectric measures with anatomical information from magnetic resonance images. These tools, and their application to the study of cognitive functions, are presented in this paper.
103 citations
TL;DR: Methods of data analysis of multichannel recordings where components of evoked brain activity are identified quantitatively are illustrated, and the results of spatial PCA relate to experimental conditions in a meaningful way.
Abstract: Electroencephalographic data recorded for topographical analysis constitute multidimensional observations, and the present paper illustrates methods of data analysis of multichannel recordings where components of evoked brain activity are identified quantitatively. The computation of potential field strength (Global Field Power, GFP) is used for component latency determination. Multivariate statistical methods like Principal Component Analysis (PCA) may be applied to the topographical distribution of potential values. The analysis of statistically defined components of visually elicited brain activity is illustrated with data sets stemming from different experiments. With spatial PCA the dimensionality of multichannel data is reduced to only three components that account for more than 90% of the variance. The results of spatial PCA relate to experimental conditions in a meaningful way, and this method may also be used for time segmentation of topographic potential maps series.
88 citations
TL;DR: By means of autoregressive processes EEG signals with given power and coherence properties were simulated and different recording situations using the same data set were reconstructed and the essential result is that computation and mapping of coherences yield the most reliable results when reference recording is used.
Abstract: Four techniques are applied to record EEG signals: bipolar recording, referential recording, common average reference recording and source derivation For the interpretation of EEG parameter maps knowledge of the properties of the applied recording technique is essential Bipolar recordings are not discussed in this paper The application of reference and common average reference recording has the disadvantage of an unknown reference potential This disadvantage is much larger with the use of source derivation because every electrode signal has its particular reference signal This must be taken into consideration when coherence estimations are made With actual EEG records the influence of the reference cannot be determined unambiguously However, simulation studies enable some essential conclusions In this paper by means of autoregressive processes EEG signals with given power and coherence properties were simulated and different recording situations using the same data set were reconstructed The essential result is that computation and mapping of coherences yield the most reliable results when reference recording is used However, measures to ensure a low reference signal must be taken
78 citations
TL;DR: A number of computer simulations using a three-concentric spheres model of the head are used to illustrate relationships between distributed neocortical sources at the macrocolumn scale and resulting scalp potentials.
Abstract: Relationships between neural current sources recorded at different spatial and temporal scales are considered. A number of computer simulations using a three-concentric spheres model of the head are used to illustrate relationships between distributed neocortical sources at the macrocolumn scale and resulting scalp potentials. Computer simulations also illustrate the advantages of calculating surface Laplacians which are more sensitive than potentials to local sources. Surface Laplacians of interictal, epileptic spikes and auditory evoked potentials (including P300) are presented as examples of this sensitivity.
71 citations
TL;DR: Late auditory potentials from lateral and medial regions in the frontal, temporal and parietal lobes of patients with temporal lobe epilepsy implanted with horizontal depth electrodes lend further support to the multiple generator hypothesis of late potentials and suggest that some of the cerebral sources of theLate potentials are stimulus dependent while others are not.
Abstract: We recorded late auditory potentials from lateral and medial regions in the frontal, temporal and parietal lobes of patients with temporal lobe epilepsy implanted with horizontal depth electrodes. Tone sequences were presented in three tasks: 1) auditory target detection in a tone sequence, 2) target detection with interspersed novel stimuli, and 3) detection of stimulus omissions. At frontal sites, potentials to targets showed a triphasic response with peak latencies around 200, 270 and 350 ms. At temporal sites, potentials consisted of a generally positive 285 ms peak which was sometimes accompanied by a negative peak at 200 ms or at 400 ms. At parietal sites, potentials were generally triphasic with latencies of about 230, 300, and 370 ms. At most sites, potentials evoked by novel stimuli had shorter latencies than those evoked by targets. The frontal and parietal potentials were either absent or strongly attenuated during stimulus omissions. The results lend further support to the multiple generator hypothesis of late potentials and suggest that some of the cerebral sources of the late potentials are stimulus dependent while others are not.
59 citations
TL;DR: Mapping techniques with a 5-sensor system have revealed preferential suppression of alpha activity within certain regions of the occipital lobe to tasks involving mental comparisons of abstract figures, providing evidence that the machinery of visual cortex is involved in mental imagery.
Abstract: Rapid progress in neuromagnetic technology has been achieved during the past two years with the introduction of a method for accurately indicating magnetic sensor locations with respect to a head-based coordinate system and the advent of refrigerator-cooled sensors and larger arrays of sensors. These make possible the real-time monitoring of evoked activity at several widely separated locations over the scalp, thus revealing sequential activity in, e.g., sensory-motor tasks. Arrays of magnetic sensors also provide sufficient information to locate the sources of spontaneous activity, such as alpha rhythm. The locations of discrete generators (alphons) of individual alpha spindles is now possible with an array of 14 sensors. Mapping techniques with a 5-sensor system have revealed preferential suppression of alpha activity within certain regions of the occipital lobe to tasks involving mental comparisons of abstract figures. These studies provide evidence that the machinery of visual cortex is involved in mental imagery.
58 citations
TL;DR: The described method opens a way to compute intracerebral source localizations of ongoing EEG activity by constructing a sine-cosine diagram of the Fourier-transformed data, which is the least error compromise landscape of all possible landscapes during the paradigmatic cycle of the given FFT frequency.
Abstract: The described method opens a way to compute intracerebral source localizations of ongoing EEG activity. A sine-cosine diagram of the Fourier-transformed data is constructed for each frequency point, forming a "FFT constellation" of entries. Into the FFT constellation of each diagram, a straight line is fitted which produces the least squared deviation sum between the original entry positions and their orthogonal projections onto that line. The map landscape described by the voltages between the projected positions ("FFT approximation") is the least error compromise landscape of all possible landscapes during the paradigmatic cycle of the given FFT frequency. The map thus constructed can be used in the usual dipole source localization procedures. There is one for each FFT frequency point. The squared forward solution of the fitted dipole source and the squared FFT approximation map are "power maps" which are very similar to the original power map. For an average-reference power map with two peaks, the source tends to lie between the peaks; a power map with one peak might show closely neighboring maximal and minimal potential values in the FFT approximation, indicative of a tangential source close to the surface.
55 citations
TL;DR: EEG data from 30 channels were recorded during movement and reading tasks and analyzed in the three frequency bands 6– 8 Hz, 8–10 Hz and 10–12 Hz, showing that the ERD pattern varies with the frequency component analyzed.
Abstract: EEG data from 30 channels were recorded during movement and reading tasks and analyzed in the three frequency bands 6– 8 Hz, 8–10 Hz and 10–12 Hz. For each frequency band, the ERD (event-related desynchronization) was quantified and displayed in the form of time courses and maps. The results show that the ERD pattern varies with the frequency component analyzed. In general, upper alpha components (10–12 Hz) demonstrate a short-lasting, task-specific and localized ERD; the ERD of lower alpha components is long-lasting (> 1 sec) and widespread. The ERD can be interpreted as a sign of cortical activation, whereby desynchronization of upper alpha components may reflect more task-specific processes, and desynchronization of middle and lower alpha components may be related to the level of expectancy and attention.
TL;DR: The hypothesis that the topographic behaviour of a spike focus is closely associated with its clinical characteristics is supported, as the variation of spike topography in 20 children with rolandic epilepsy of childhood by the dipole localization method was investigated.
Abstract: The interictal spike discharges present in rolandic epilepsy has a dominant horizontal dipolar topography, centered near the rolandic area. In order to examine the generator configuration of this focus, we investigated the variation of spike topography in 20 children with rolandic epilepsy of childhood by the dipole localization method (DLM). A quantitative measure ("stability index" or SI) of the degree of source fluctuation was devised, based on the consistency of the source parameters (location, direction and magnitude) over contiguous time points. A high SI was associated with overlapping source locations and parallel directions over many time points, while a low SI was seen with poor and variable solutions. At the peak and trough of the spike, the corresponding sources were found to have different locations. If the patients were separated into those with and without neurological findings, the mean times at which stable sources existed were significantly different: 35 and 150 ms respectively after the spike apex. Further, the group without abnormal neurological findings tended to have higher values of SI. These results suggest that such stability analysis allows measurement of the spatial and temporal extents of source estimates. These results further support the hypothesis that the topographic behaviour of a spike focus is closely associated with its clinical characteristics.
TL;DR: The plagiocephaly index, an index that reflects an underlying anatomic asymmetry of the brain, was assessed in schizophrenic patients and its values were correlated with the lateral distribution of quantitatively evaluated EEG, suggesting it may be important to determine cranial and brain parenchymal asymmetries where brain laterality is pertinent to studies of EEG.
Abstract: The plagiocephaly index, an index that reflects an underlying anatomic asymmetry of the brain, was assessed in ten schizophrenic patients and its values were correlated with the lateral distribution of quantitatively evaluated EEG. The correlations between the index and alpha power at F7 were significant, positive for frontal asymmetry (frontal bulging) and negative for occipital flattening. We then studied ten normal subjects in an attempt to illuminate the contribution of several cephalic and cranial variables to the imbalance of alpha-afterdischarges (AD) of VEP recorded at O1-O2. The asymmetry index of AD was computed and correlated with asymmetries of CT-derived measures of occipital bone thickness, occipital lobe width, mastoid area, and sulcal asymmetry (the asymmetry of intraparietal sulcus location from the longitudinal fissure). With the exception of the sulcal variable all measures significantly covaried with alpha AD. These findings caution that it may be important to determine cranial and brain parenchymal asymmetries where brain laterality is pertinent to studies of EEG.
TL;DR: Singular value decomposition is a robust numerical method for decomposing a matrix of multichannel EEG or EP data into a sharply reduced set of features with corresponding waveform, amplitude, and spatial vectors.
Abstract: Singular value decomposition is a robust numerical method for decomposing a matrix of multichannel EEG or EP data into a sharply reduced set of features with corresponding waveform, amplitude, and spatial vectors. In 19 normal subjects aged 19 to 40 years, the three largest features computed by the SVD algorithm accounted for 93–98 percent of the total variance of the averaged flash-evoked potential. There was good separation of major brain areas as well as clustering of related electrode sites. Orthogonal rotation of the three spatial vectors is essential to see clustering of brain areas across subjects. Three-dimensional display showed the regular presence of orthonormal occipital, frontopolar, and vertex spatial vectors. Since the spatial feature vectors cluster tightly and yet are orthonormal, statistical comparison of patients with normal control groups will be facilitated.
TL;DR: Topographic EEG based on the power spectral data were correlated with cortical CBF and CMRO2 which were provided by positron emission tomography in patients with cerebral infarction, and z-score maps were considered to be useful tool in topographical extraction of the features of the EEG power data.
Abstract: Topographic EEG based on the power spectral data were correlated with cortical CBF and CMRO2 which were provided by positron emission tomography (PET) in patients with cerebral infarction. Delta and theta activities correlated negatively with CBF and CMRO2 whereas alpha activity correlated positively. For delta activity, both absolute (AP) and relative power (RP) showed significant correlation with CBF and CMRO2. For alpha activity, RP showed closer correlation with CBF and CMRO2 than did AP. The z-scores for these power data also showed significant correlation with the PET data although the degree of correlations did not improved even with the z-score. Topographic EEG images including AP, RP and their z-score maps well corresponded with the PET images: z-score maps were considered to be useful tool in topographical extraction of the features of the EEG power data.
TL;DR: The novelty of the stimulation paradigm and of the off-line data analysis, as well as the capability of the neuromagnetic technique to localize and follow in time the generators responsible for the SSA are used to characterize SSA and to study the underlying spontaneous activity.
Abstract: We present an overview of the investigations on Synchronized Spontaneous Activity (SSA) in the somatosensory and visual modality. The novelty of the stimulation paradigm and of the off-line data analysis, as well as the capability of the neuromagnetic technique to localize and follow in time the generators responsible for the SSA are used to characterize SSA and to study the underlying spontaneous activity. Synchronization of alpha and mu rhythms have been recognized and studied. The possibilities opened by the technique are discussed.
TL;DR: It appears that computerized techniques may hold promise as an adjunct to standard EEG evaluation of patients with mild cognitive change in whom diagnosis of dementia or depression is in doubt, according to the present study.
Abstract: In elderly patients presenting to an ambulatory practice with complaints of cognitive disturbance, early dementia must be differentiated from depression. The present paper describes the application of standard electroencephalography and evoked potential testing (EEG/EP) and computerized electroencephalography with evoked potential mapping (CEEG/EPM) in the analysis of 64 elderly patients complaining of cognitive disturbance. Although previous reports have claimed a sensitivity level of up to 80% for EEG in demented patients, it appears that a lower sensitivity (37% for EEG alone and 61% for EEG/EP) may be expected at the time of early presentation according to the present study. No EEG/EP abnormalities were detected in patients with depression. In demented patients, CEEG/EPM was abnormal in 85% (46 of 54) of cases compared to 10% (1 of 10) of cases with depression. Specific information was obtained from EEG/EP studies that helped differentiate the various causes of dementia in three cases. In CEEG/EPM studies, a pattern of relative suppression of alpha activity or suppressed auditory P300 amplitude in the posterior parietal regions was observed in 11 or 23 (48%) patients with Alzheimer's disease and 2 of 31 (6%) patients with other forms of dementia. None of the depressed patients demonstrated such changes. Based on the present study, it appears that computerized techniques may hold promise as an adjunct to standard EEG evaluation of patients with mild cognitive change in whom diagnosis of dementia or depression is in doubt. Although standard EEG rarely demonstrates characteristic changes that may help differentiate causes of dementia, CEEG/EPM appears to demonstrate, on occasion, abnormalities in the posterior temporal and parietal regions in patients with a diagnosis of probable Alzheimer's disease and rarely in other forms of dementia or depression.
TL;DR: Both questionable and legitimate uses of mapping in psychiatry and possible future applications of this technique are considered and multidisciplinary approaches to the study of the brain are discussed.
Abstract: 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.
TL;DR: Correlations between PO values and asymmetries of occipital and parietal width, mastoid area, basal angle, cephalic, and plagiocephaly indices were established in simple correlation and stepwise multiple regression analysis.
Abstract: The parieto-occipital (PO) index of the VEP alpha-afterdischarge (AD) was assessed bilaterally in normal subjects in three successive sessions separated by one-three weeks with two within-session retests. Correlations between PO values and asymmetries of occipital and parietal width, mastoid area, basal angle, cephalic, and plagiocephaly indices were established in simple correlation and stepwise multiple regression analysis. Occipital width, notably in the right hemisphere correlated reliably with the PO index in relaxed wakefulness and the vigilance task. The population having normal and reversed occipital brain width is predicted to have different parieto-occipital AD distribution. Some errors of lateral EEG measurements introduced by slant cranial deformity are discussed in order to call attention to the fact that anatomy-related lateral EEG changes may masquerade as cognition-related asymmetries.
TL;DR: It is suggested that waves earlier than P3 (N1, P2 and N2) are all correlated with global measures of cognitive functions, however, they are differentially correlated with specific measures of Cognitive functions.
Abstract: Thirty subjects (normal controls, patients with putative subcortical dementia and non-demented patient controls) were studied using advanced neurophysiological (16 scalp-electrode positions, computer-assisted brain electrical activity mapping, auditory oddball paradigm) and neuropsychological techniques. Our study suggests that waves earlier than P3 (N1, P2 and N2) are all correlated with global measures of cognitive functions. They are, however, differentially correlated with specific measures of cognitive functions, N1 and P2 with mental speed and N2 with short-term memory. The abnormalities of these waves (earlier than P3) may be an electrophysiologic marker of dementia in patients with putative subcortical states.
TL;DR: Three methods for analyzing the spatial organization of visual evoked potentials were compared and all three techniques revealed "paradoxical" lateralization of P100.
Abstract: Three methods for analyzing the spatial organization of visual evoked potentials were compared. Pattern reversal visual evoked potentials were obtained from a single subject under three viewing conditions: stimulation of the left, right, and both visual fields. The scalp distribution of the VEP to 1 deg checks was displayed using three recording and analysis techniques: a conventional horizontal occipital array of electrodes, topographic mapping, and 3-dimensional evoked potentials. All three techniques revealed "paradoxical" lateralization of P100. The relative merits of each technique are discussed.
TL;DR: This new ordinal method can be applied to different types of multiple EEG recordings protocols, for intra-individual statistical comparisons before validating a group study.
Abstract: The three types of non-parametric permutation Fisher tests have been applied to inter-individual group studies and further to intra-individual multiple EEG recording sequences, providing computations of EEG probability maps testing two ordinal hypotheses Two examples of previous group studies with "EEG local cerebral activation" are given: mental computation in a group of 20 controls and caffeine effects versus placebo in a group of 10 controls For the intra-individual study, two successive recordings of 23 min eyes closed (EC1 and EC2), obtained at 50 min intervals, were compared by paired exact permutation Fisher tests (over 15 or 42 synchronous EEG sequences) These tests were applied to descriptive spectral parameters: RMS and % amplitudes, mean frequencies, resonance coefficient, for raw unfiltered EEG and delta, theta, alpha, alpha 1, alpha 2, beta 1, beta 2 frequency bands Two hypotheses were tested for each of the computed 31 parameters, providing two probability maps indicating if the parameter was greater or lower in the first EEG recording or in the second The second EEG sequence, EC2, was "EEG activated" compared to the first sequence EC1 if the following were present: decreased amplitudes mainly in raw EEG, low activity and alpha bands; increased frequencies mainly, in raw EEG, delta and beta 1 fast activities; increased fast activity percentages; decreased coefficient of resonance The effect of choice of reference was also evaluated: probability maps for a frontal reference were different than other probability maps obtained after computation of average reference or source derivation This new ordinal method can be applied to different types of multiple EEG recordings protocols, for intra-individual statistical comparisons before validating a group study
TL;DR: The magnetic field maps generated by six dipoles in the temporal region of a plastic skull filled with conducting gel were studied and the localizing capability of MEG improved from an average distance of 2.9cm to 0.9 cm when volume current effects were considered.
Abstract: We studied the magnetic field maps generated by six dipoles in the temporal region of a plastic skull filled with conducting gel. The data were processed with two mathematical models. One, using Biot-Savart's law, considered only the magnetic field generated by a localized current dipole, and the other considered a dipole in a sphere and included volume current effects. The contribution of volume current effects to the MEG maps was significant. The localizing capability of MEG improved from an average distance of 2.9 cm to 0.9 cm when volume current effects were considered.
TL;DR: The observed age independence of the R values in the normal population, their ease of computation and possible physiological interpretability, suggest that R values could be used as confirmatory diagnostic measures.
Abstract: Children with cortical visual impairment (CVI) usually have a typical clinical presentation. However, in some cases, it may be useful to have confirmatory evidence based on objective electrophysiologicinformation. To achieve this, we examined some mathematically derived parameters constructed from 20 channel visual evoked potential (VEP). A group of 30 children diagnosed with CVI by clinical and CT findings was compared to a normal control group of 52 children. Each recorded VEP was mathematically transformed using Hjorth's source derivation, to reduce reference contamination and enhance local features. The area under the response curve, computed for each channel within a fixed time window, was used as a measure of the response activity at that channel. These areas were then used to construct several parameters ("R values") describing ratios of activities between different recording electrode areas. Some of these ratios provided good separation between patient and control groups, especially for children older than 5 years of age; in particular CVI patients were found to have a low occipital-to-parietal activity ratio. This finding, together with the observed age independence of the R values in the normal population, their ease of computation and possible physiological interpretability, suggest that R values could be used as confirmatory diagnostic measures.
TL;DR: Equivalent dipole sources estimated from the spatial distribution of the scalp potentials were found to be consistent with regions of high HMPAO uptake as imaged by Single Photon Emission Computed Tomography (SPECT).
Abstract: This study examined the effect of modality of stimulation on two measures of cerebral function: (a) the scalp distribution of sensory evoked potentials and (b) the cerebral distribution of radiolabelled HMPAO. Steady-state stimulation in the auditory, somatosensory or visual modality was presented to six subjects. Scalp potentials were measured from a distribution of electrodes, and the radiopharmaceutical was injected through an indwelling intravenous catheter midway through the stimulation/ recording session. Equivalent dipole sources estimated from the spatial distribution of the scalp potentials were found to be consistent with regions of high HMPAO uptake as imaged by Single Photon Emission Computed Tomography (SPECT).
TL;DR: How the method for assigning locations to uncorrelated EEG basic waveforms named eigenfunctions can be further developed by normalizing the EEG samples to unity global field power before computation of covariance enhances local persistence as a feature for revealing low-amplitude activity of possible diagnostic significance, even in the presence of more dominant activity.
Abstract: As a supplement to the article "An Eigenfunction Approach to the Inverse Problem of EEG" by Hjorth and Rodin in Brain Topography, 1988, 1 (2): 79–86, this paper discusses in greater detail the interrelations between the concepts of EEG sample vector, eigenvalue and eigenvector. It also describes how the method for assigning locations to uncorrelated EEG basic waveforms named eigenfunctions can be further developed by normalizing the EEG samples to unity global field power before computation of covariance. This enhances local persistence as a feature for revealing low-amplitude activity of possible diagnostic significance, even in the presence of more dominant activity.
TL;DR: The application of mathematical programming techniques to the "inverse" problem of three-dimensional localization of brain activity from scalp potentials, yields encouraging results on simulated data and points new directions for research.
Abstract: Although there has been progress in EEG and evoked potential analysis, the identification of underlying neural activity has eluded researchers despite its importance. This paper introduces the application of mathematical programming techniques to the "inverse" problem of three-dimensional localization of brain activity from scalp potentials. Preliminary computer experience with these optimization methods reported herein, yields encouraging results on simulated data and points new directions for research.
TL;DR: The instantaneous amplitude of different EEG patterns found in a 36 week newborn baby were mapped by isopotential display, using 3 different references, and it was found that in certain cases, the nose reference recalculated average and source derivations give the same results.
Abstract: The instantaneous amplitude of different EEG patterns found in a 36 week newborn baby were mapped by isopotential display, using 3 different references. We found that in certain cases, the nose reference recalculated average and source derivations give the same results. If the different EEG activities on the skull have too an high amplitude, and are not in phase opposition, the average reference differs from the zero potential of the common reference. In this case, the nose may be a better reference. However, it is possible that under other conditions high amplitude activity contaminates the nose, rendering the other references as better choices. From these preliminary results, we recommend the simultaneous display of maps obtained with the different references, and the comparison of the maps with the tracings for topographic studies in babies. It is absolutely necessary to record at least two polygraphic derivations to be able to recognize the sleep stages in which the analyses were performed. The eyes movement lead lets us to see if the EEG activity contaminates the face with multiple displays. It is then possible to decide which reference system is most appropriate.
TL;DR: The idea for a high level technical workshop that would bring together leading experts in the field of topographic EEG analysis came from an informal meeting of Richard Harner, Dietrich Lehmann and Peter Wong in 1987 as mentioned in this paper.
Abstract: The idea for a high level technical workshop that would bring together leading experts in the field of topographic EEG analysis came from an informal meeting of Richard Harner, Dietrich Lehmann and Peter Wong in 1987. The possibility of holding the workshop in the superb conference and hotel facilities of St. Vincent was suggested and converted into reality by Silvana Riggio in 1988. Subsequently a basic course in topographic EEG analysis, originally conceived by Frank Duffy, Roy John and Richard Harner, was organized to precede and introduce the workshop.