An ERD mapping study of the neurocognitive processes involved in the perceptual and semantic analysis of environmental sounds and words.

The aim of this paper was to investigate and compare the EEG mechanisms underlying the perceptual and semantic processes involved in environmental and language sounds perception by manipulating the degree of identification of sounds and using the ERD (event-related desynchronization) method in healthy subjects. Four types of stimuli were analyzed: meaningful environmental sounds, meaningless sounds, words and non-words. We report many similarities in the ERDs and ERSs (event-related synchronizations) patterns among all stimuli, with: (i) similar time-course of ERDs and ERSs between meaningful environmental sounds and words, and between meaningless sounds and non-words; (ii) similar topography of the maximal ERDs for meaningful environmental sounds, words and non-words; and (iii) same right posterior ERSs for all four stimuli. However, differences were also observed: (i) in time-course, with earlier ERSs for meaningless than meaningful stimuli, whether environmental or verbal; and (ii) in topography, with ERDs predominating in left and right hemisphere channels for meaningful and meaningless environmental sounds, respectively; (iii) ERSs predominating in the left temporal channel for non-words and in the left posterior and right frontal channels for meaningless sounds. The results of this study suggest that meaningful stimuli involve greater and longer-lasting semantic processes than meaningless stimuli, while the occurrence of ERSs for the latter points to the possible involvement of an inhibitory processing of semantic representations. Finally, the findings concerning the comparison between verbal and non verbal stimuli suggest the involvement of left-lateralized phonological and semantic processes for the former, and more distributed neurocognitive processes in both hemispheres for the latter although with predominant left laterality for their semantic processing.

High temporal resolution dynamic mapping of instantaneous EEG amplitude modulation after tone-burst auditory stimulation.

A new method of instantaneous EEG analysis based on amplitude modulation (AM-EEG) was applied to analyze the AM-EEG changes in the alpha frequency band (8.20-12.89 Hz) for successive 5 ms epochs. Repeated auditory tone-burst stimuli (of 220 ms duration) were presented at fixed 2.56 second intervals to 12 attending right-handed young female volunteers, who were EEG-recorded over 19 EEG channels at 200 Hz sampling frequency. The time-course of functional activation was characterized in terms of percent decrease in instantaneous amplitude modulation, as compared to baseline, in analogy with the classical event-related desynchronization paradigm. A dynamic sequence of the successive 122 AM-EEG maps obtained for the 610 ms from beginning of tone-burst was stored and later animated on PC microcomputer. Topological changes among successive maps were extracted into 40 specific AM-EEG maps. Early left temporal and centro-temporal activation was observed, followed first by strong bilateral frontal, and then by left temporal activation. These changes induced by a warning tone-burst are discussed in terms of functional neurophysiology. The present method therefore allows an improved time-resolution for functional brain activation paradigms.

Effect of environmental sound familiarity on dynamic neural activation/inhibition patterns: an ERD mapping study.

The aim of this study was to analyze the timing and topography of brain activity in relation to the cognitive processing of different types of auditory information. We specifically investigated the effects of familiarity on environmental sound identification, an issue which has been little studied with respect to cognitive processes, neural substrates, and time course of brain activity. To address this issue, we implemented and applied an electroencephalographic mapping method named event-related desynchronization, which allows one to assess the dynamics of neuronal activity with high temporal resolution (here, 125 ms); we used 19 recording electrodes with standard positioning. We designed an activation paradigm in which healthy subjects were asked to discriminate binaurally heard sounds belonging to one of two distinct categories, "familiar" (i.e., natural environmental sounds) or "unfamiliar" (i.e., altered environmental sounds). The sounds were selected according to strict preexperimental tests so that the former should engage greater semantic, and the latter greater structural, analysis, which we predicted to preferentially implicate left posterior and right brain regions, respectively. During the stimulations, significant desynchronizations (thought to reflect neuronal activations) were recorded over left hemisphere regions for familiar sounds and right temporofrontal regions for unfamiliar sounds, but with only few significant differences between the two sound categories and a common bilateral activation in the frontal regions. However, strongly significant differences between familiar and unfamiliar sounds occurred near the end of and following the stimulations, due to synchronizations (though to reflect deactivations) which appeared over the left posterior regions, as well as the vertex and bilateral frontal cortex, only after unfamiliar sounds. These unexpected synchronizations after the unfamiliar stimuli may reflect an awareness of the unfamiliarity of such sounds, which may have induced an inhibition of semantic and episodic representations because the latter could not be associated with meaningless sounds.

A new method for quantifying EEG event-related desynchronization:amplitude envelope analysis.

Amplitude modulation (AM) analysis defines precisely the EEG signal envelope changes at sampling frequency. Here we demonstrate mathematically that event-related desynchronization (ERD) corresponds to the integration of AM-EEG. We applied this new approach to a group of 12 healthy human volunteers hearing repeated auditory stimuli and statistically compared the results from ERD to those from AM-EEG. The results indicate that AM-EEG characterized more precisely a specific evoked EEG cortical activation event and may be a powerful method for studying the time-course of functional dynamic brain EEG mapping with improved time resolution.

Topographic EEG activations during timbre and pitch discrimination tasks using musical sounds.

Successive auditory stimulation sequences were presented binaurally to 18 young normal volunteers. Five conditions were investigated: two reference tasks, assumed to involve passive listening to couples of musical sounds, and three discrimination tasks, one dealing with pitch, and two with timbre (either with or without the attack). A symmetrical montage of 16 EEG channels was recorded for each subject across the different conditions. Two quantitative parameters of EEG activity were compared among the different sequences within five distinct frequency bands. As compared to a rest (no stimulation) condition, both passive listening conditions led to changes in primary auditory cortex areas. Both discrimination tasks for pitch and timbre led to right hemisphere EEG changes, organized in two poles: an anterior one and a posterior one. After discussing the electrophysiological aspects of this work, these results are interpreted in terms of a network including the right temporal neocortex and the right frontal lobe to maintain the acoustical information in an auditory working memory necessary to carry out the discrimination task.

[Quadri-dimensional analysis of the electroencephalography. First application to an episode of paradoxical sleep in man]. / Analyse quadri-dimensionnelle de l'électroencéphalogramme. Première application à un épisode de sommeil paradoxal chez l'Homme.

A first example of quadri-dimensional EEG analysis is presented which is characteristic of a series of ten analyses episodes of paradoxical sleep recorded in polygraphy during 5 nights' sleep in three human volunteers. A first EEG recording of wakefulness, eyes open, with visual fixation of a central point, was followed by a polygraphic night of sleep recording after habituation. The first subject was recorded during three nights; two other subjects during one night only after habituation. An EEG montage of 16 channels was quantified by spectral analysis and parametrization, after artefact rejection, for the reference sequence of wakefulness and further episodes of paradoxical sleep. After temporal and spatial interpolation algorithms, for each sequence, a series of root-mean-square successive EEG maps were computed and displayed, between 0.5 to 30 Hz. Low amplitude values of locally activated areas were chosen during the wakefulness EEG sequence and provided filtering thresholds for isolating activated areas during paradoxical sleep. The first 30 maps of each episode were piled up one on top of the other, along a vertical time axis, then dynamically visualised in colors and 3D. The "trajectories of activated areas" were then displayed in a quadri-dimensional functional space (x-y: spatial map of the scalp; t: time; color or black and white: filtered or unfiltered rms EEG amplitudes). The EEG trajectories of awakened areas, appeared through time like unique "fibres" or double fibres after bifurcation. The unique fibres were located over left temporo-central activated areas and a double fibre appeared after bifurcation over the right parietal area.(ABSTRACT TRUNCATED AT 250 WORDS)

EEG cartography before and after visual stimulation: a group study with descriptive non-parametric analysis of EEG data.

Ten right-handed students were submitted to a protocol of cognitive visual stimulations based on six successive sequences: EC1, EO, B1, B2, B3, EC2. Following a first "eyes closed" (EC1) multiple EEG recording (16 EEG leads, plus polygraphy), and an "eyes-open" recording (EO) with central visual fixation, 60 computer-controlled slides were presented successively for each of three successive recordings (B1, B2, B3) before the last "eyes-closed" recording (EC2). In B1, the subjects were asked to look at the meaningful black and white drawings presented without comment. In B2, a second set of similar pictures was presented, with the advice to try to remember later on the visually projected slides. In B3, a memory recognition task was introduced with 20 slides coming from the B1 set, 20 from the B2 set, completed by 20 new slides. Each slide was presented for 10.24s. followed by a beep audio-signal indicating that the subjects should press electronic mouse knobs alternatively in B1, B2, and for indicating their answers in B3. After artifact rejection, EEG spectral analysis was followed by parametrization and group studies applying Fisher non-parametric paired exact probability tests. Nine comparisons were computed: EC1-EC2, EC1-EO, EC2-EO, EO-B1, EO-B2, EO-B3, B1-B2, B1-B3, B2-B3. A statistical strategy of descriptive inter-individual non-parametric. Fisher tests was undertaken, together with computation and mapping of averaged spectral parameter differences (mean amplitudes and frequencies, mean amplitudes %, resonance coefficients) for raw EEG, delta, theta, alpha, alpha 1, alpha 2, beta 1 and beta 2 frequency bands and probability maps.(ABSTRACT TRUNCATED AT 250 WORDS)

Inter- and intra-individual probability maps in EEG cartography by use of nonparametric Fisher tests.

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 2.3 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.(ABSTRACT TRUNCATED AT 250 WORDS)

[Caffeine and EEG mapping: effects of visuo-spatial task in healthy volunteers]. / Caféine et cartographie EEG: effets d'une tache visuospatiale chez des volontaires sains. Stratégie d'analyse des données électropharmacologiques.

A group of 10 subjects, normal volunteers (6 men, 4 women), mean age 27.2 years, right-handers, has been selected for a double-blind study of caffeine effects (400 mg per os) versus placebo. One week delay separated the two EEG sessions quantified by spectral analysis. During each session (16 EEG channels, common reference), each subject was recorded four times: 2.5 min, in eyes-closed condition, under diffuse attention, followed by 2.5 min, during a visuo-spatial task ("eyes open" condition: presentation of a picture). These two EEG recordings were obtained before the oral administration and repeated 1 hr after the administration of caffeine or placebo. Individual and group results presented globally: 1) an increase in mean frequencies of alpha activity in "eyes closed" condition, and of delta activity in "eyes open" condition; 2) a decrease of alpha activity amplitudes (both RMS and % values) in both conditions; 3) a decrease of total RMS amplitudes in "eyes closed" condition; 4) an increase of relative % amplitudes for beta 2% fast activity in the "eyes open condition". These results characterize the psycho-stimulant effects of caffeine, especially over the left temporal area which was confirming an initial statistical hypothesis of specific cerebral local activation. The non-parametric permutation tests of Fisher, were not always reaching statistical significance for the same EEG channel quantified by one of the 17 analyzed spectral parameters, except on the left temporal area. During the visuo-spatial task, the decrease in alpha amplitudes (RMS and %) was also statistically significant, but over larger areas: over left and right temporal, central and parietal regions. In both conditions, eyes closed and eyes open, the alpha RMS amplitude was also decreased over the right anterior frontal area.

[Value of quantitative EEG and EEG mapping in medicine]. / Intérêt de l'EEG quantitatif et de la cartographie EEG en médecine.

Quantitative EEG consists in digitising the EEG from one or several leads and then mathematically processing the signal usually by Fourier spectral analysis. A reduction of the digital information gives characteristic parameters (frequency, amplitude or power, asymmetry, etc.), which can themselves be averaged and submitted to different statistical analysis. Quantitative EEG is particularly suitable for clinical electropharmacology for the assessment of the profiles of psychotropic drugs, for pharmacokinetic correlations of dose-effect relationships and studies of drug bioavailability. The signals obtained from schizophrenic and depressed patients have well defined quantitative EEG characteristics: dissymmetry of the amplitude and hypovariability of the EEG signals. EEg mapping is performed by computer processing of 16 simultaneous EEG lead recordings. This new form of medical imaging is fast, relatively economical and non-invasive, and it is used in psychophysiology to study cognitive tasks and the states of vigilance and sleep. It is also used to study the EEG topography of cerebrovascular accidents, brain tumours, cranial trauma, cerebral degeneration and dementia, and the EEGs of psychiatric patients on psychotropic drugs. EEG mapping represents not only a static and statistical approach by drawing the averaged maps of groups of patients but also a dynamic approach by the recording of sequential individual maps presented as an animated film. The results of this method can be correlated with other medical imaging techniques used to investigate the central nervous system.

EEG cartography of a night of sleep and dreams. A longitudinal study with provoked awakenings.

A night of sleep has been recorded under the conditions of a sleep laboratory. The subject was a woman of 55 years, well-trained in dream recall. The subject was awakened three times at the end of sleep cycles. EEG was monitored for 7 h with a 16-channel polygraph (REEGA 16, Alvar) connected to two systems of EEG cartography: minicomputers (HP Fourier Analyser 5451 C and HP 1000) and a microinformatic system (Cartovar, Alvar). A second 8-channel polygraph (Mini-huit, Alvar) was used in parallel for polygraphy (EOG, EMG, respiration, actogram, EKG). Based on immediate visual inspection of EEG and polygraphic tracings, 500 EEG recordings of selected epochs (of 6, 30 or 60 s length) have been quantified, submitted on-line to spectral analysis (on Cartovar) and stored on floppy disks for further printing of EEG maps. The 16 EEG channels were placed over the scalp according to the 10/20 system and following Giannitrapani's placement. We have chosen a common average electrode. For each of the 500 EEG epochs, four EEG maps were edited (raw EEG between 0 and 30 Hz, 0 and 7 Hz, 8 and 12 Hz, 13 and 30 Hz). Each of these 2,000 maps has been checked visually in comparison with the polygraphic recordings for visual rejection of artifacts or transitory states. The remaining EEG epochs and EEG maps, scored by 2 independent trained sleep scorers, were classified into stages I, II, III-IV, and REM, apart from control runs of active wakefulness with eyes open (EO) and quiet wakefulness with eyes closed (EC), which were undertaken on mini- and microsystems of EEG analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

[EEG mapping during a visuo-spatial task. Averaged maps and group statistics]. / Cartographie EEG au cours d'une tache visuo-spatiale. Cartes moyennes et statistiques de groupes.

Twenty young volunteers (10 men, 10 women), righthanded, students, have been recorded in EEG cartography in different situations. We have compared the quantified EEGs when the subjects were resting, eyes closed and later, eyes opened, looking at a cartoon. The EEGs were quantified by spectral Fourier analysis and submitted to data reduction. Ten spectral parameters were computed, yielding 51 variables allowing computations and drawings of 90 EEG maps. Mean parameters, mean variables, averaged EEG maps have been computed for the entire group, between sub-groups, between hemispheres. Non-parametric permutation Fisher tests have been applied for statistical comparisons and statistical validations of the EEG maps computed between subjects. The activation of EEG tracings produced by the opening of the eyes were caracterized topographically by: mean alpha frequencies increased over temporal and rolandic areas; mean alpha amplitudes in microV divided by a factor 3 for occipital areas but unchanged in topography; mean relative amplitudes divided by a factor 2 but with a topography being more parietal than occipital for the alpha rhythm; a resonance coefficient greater over the left parietal than the right (alpha more regular), whereas it was greater over the right occipital than the left during the resting condition. Statistically for the whole group, the left hemisphere, recorded after the right, is more 'activated' in the eyes closed situation. During visual attention, the left hemisphere is less activated than the right.

Electroencephalographic cartography. II. By means of statistical group studies-activation by visual attention.

10 male volunteers, right-handers, mean age 30.4 years, were recorded in four successive sequences: under 'eyes closed' conditions, right and then left hemisphere, followed by an 'eyes open' situation with visual attention fixed on a cartoon, right and then left hemisphere recordings. Each EEG recording was made simultaneously over 16 EEG channels for each hemisphere, according to a protocol previously described as well as Fourier analysis and EEG mapping on a minicomputer (HP 5451 C, HP 1000). Each EEG recording was stored on a cartography data base, and 90 maps could be drawn from 10 spectral parameters applied to the raw EEG and 5 frequency bands. Permutation paired Fisher tests were applied to three main EEG parameters: mean centroid frequencies, RMS amplitudes in microvolts and relative (%) amplitudes. Activation of EEG in the 'eyes open' situation during visual fixation was found compared to the 'eyes closed' situation: decreasing dominant EEG frequency and low delta and theta mean frequencies, no change in a mean alpha frequency; increasing fast mean beta frequencies, together with a major decrease in theta, alpha, beta 1 amplitudes, and a concomitant increase in raw EEG, delta and beta 2 amplitudes. Finally, the percent alpha amplitude was decreased when other percent amplitudes were increased in delta, theta, beta 1 and beta 2 frequency bands. A symmetry between hemispheres was observed in the 'eyes closed' situation. Averaged EEG maps between subjects illustrate these findings, especially relative (%) alpha amplitude maps and also maps of coefficients of resonance of the alpha rhythm.

Electroencephalographic Cartography. I. By means of mini- or microcomputers. Reliability and interest of this electrical non-invasive brain imagery.

We have recorded control subjects, neurological and psychiatric patients (n = 217 sequences recorded over both hemispheres). Minicomputers (HP Fourier analyzer, HP 1000) for spectral analysis provided 10 spectral parameters over 5 spectral frequency bands (delta, theta, alpha, beta 1, beta 2, raw EEG). For each recorded sequence, 90 EEG maps could be computed over both hemispheres. Topo-EEGs were stored in an EEG image data bank. An EEG mapping microcomputer system linked with a digital polygraph (Alvar Electronic, REEGA 2000) has been used simultaneously. White noises have been fed into both computers for testing spatial resolution. Ten topo-EEGs have been recorded in control subjects and patients. The microcomputer system has provided very reliable topographical results when compared to similar maps generated by the minicomputer. A common average reference has been used. First clinical applications have been studied (brain strokes, brain tumors). The method appears very reliable in comparison with CT scans.

Intra and inter-hemispheric changes in alpha intensities in EEGs of schizophrenic patients versus matched controls.

62 EEGs of 5 min recordings, over C4-P4, P4-02, C3-P3, P3-01, have been recorded from 31 schizophrenic patients and 31 controls, matched for age (27 years) and sex (males). Patients were clinically classified into 3 sub-groups: paranoid-type P(7), residual type R(10) and others O(14). Controls were statistically classified into 2 sub-groups as high alpha subjects HA(15) or low alpha subjects LA(16). Following computer Fourier statistical analysis, evolutive power spectra, averaged power spectra and spectral variances were obtained for each EEG recording. Date reduction provided for each EEG: Mean frequencies, mean amplitudes in microvolts and percentage asymmetries, resonance, spectral parameters; theta/alpha, with their variabilities. Power spectra were averaged between patients or between subjects for each sub-group. The alpha peak and the mean RMS amplitude was higher over P3-01 than over P4-02 for the residual-type of schizophrenic patients, when compared to his matched control sub-group of high-alpha subjects which presented almost symmetrical occipital alpha peaks and RMS amplitudes. However, the most important changes appear to be intra-hemispheric. The alpha peaks and RMS amplitudes were almost equal between C3-P3 and P3-O1 for the paranoid type of schizophrenic patients in contrast to other sub-groups and especially both control sub-groups. This seems to imply left hemispheric changes in terms of EEG spectral alpha intensities, when tracings of schizophrenics were compared with recordings of volunteers.

Computerized topo-EEG spectral maps: difficulties and perspectives.

An electric potential measurement tells us only about the difference between two electrode locations. When prior experiments or present measurements prove that an electrode's location is inactive (especially in 'mono-polar' or scalp-to-reference technique), then EEG records and EEG maps can be interpreted regionally near each electrode location. Topographical mapping requires spatial interpolation which is one factor involved in spatial resolution. The interpolation algorithm has been studied by changing the power exponent n of the interelectrode distance d. When n is close to zero, interpolated values are all equal to the average of the four electric potential measurement Vs bounding the quadrilateral in which the interpolated points of the EEG map are located. When n is very high (n = 20 or higher), the values are essentially equal to the V which is at the minimum distance d. For n = 1, the map seems unlikely to represent the true scalp field. The choice between n = 2 and n = 3 is difficult, but n = 3 EEG mapping looks better (more plausible) and is our regular choice. The choice of recording/reporting method has also been studied. If the quantitative EEG map is linearly calculated from observations, the interpretation of record activity resulting from charge separation near the non-reference electrode attached to a particular channel is only possible when inactivity can be assured. This is completely different when the quantity mapped is not linearly calculated from observations (like power values or rms amplitudes in microvolts).(ABSTRACT TRUNCATED AT 250 WORDS)

[Topographic aspects of drug-induced fast rhythms in quantitative topo-electroencephalography]. / Aspects topographiques des rythmes rapides médicamenteux en topo-électroencéphalographie quantitative.

The topographical aspects of fast rhythms induced by different psychotropic drugs have been studied in patients by means of a previously described method. This method is based on the spectral analysis of 28 EEG channels over both cerebral hemispheres. The spectral parameters, computed over 2 min 40 sec, are put into a data base. The clinician can then decide which of these parameters will be extracted from the data base and then displayed by means of maps on a graphic terminal. Those maps are useful for immediate comparison not only of the fast rhythms' characteristic values but also of those from other spectral bands. As quantitative EEG analysis is more and more frequently used in psychotropic drug studies, a good knowledge of the topography of the rhythms induced by these drugs will help in the selection of the most useful derivations.

[Computerized quantitative topo-electroencephalography]. / Topo-électroencéphalographie quantitative par ordinateur.

A method is described which has been developed to topographically display the values of spectral EEG analysis from 11 electrodes on each hemisphere and 5 electrodes on the midline. The EEG from 16 channels at a time is multiplexed and sampled at 3.2 kHz. From power spectra averaged every 10 sec for 5 min a few spectral parameters are computed among which are the spectral intensities within the delta, theta, alpha and beta bands. The whole values are then displayed on maps representing lateral views of cerebral hemispheres by means of spectral iso-intensity surfaces with extrapolation of the intermediate points. Different spectral intensities are coded by means of different gray levels. These maps clearly illustrate the topographical distribution of EEG rhythms and their peculiarities related to the side of the head recorded.

[Value of quantitative electroencephalography in psychiatry]. / Intérêt de l'électroencéphalographie quantitative en psychiatrie.

Computerized quantitative EEG processes the signal in four sequential steps: 1) EEG sampling with rejection of artefacts; 2) Fourier analysis (power spectrum according to frequency); 3) data reduction with computation of spectral parameters in five-minute recordings on at least four EEG channels (mean frequencies, mean amplitudes in microvolts and %, with standard deviations for delta, theta, alpha and beta frequency bands); 4) data base and multivariate statistical analyses. Five main results are obtained by computerized quantitative EEG analysis in psychiatry and clinical pharmacology: 1) longitudinal studies of patients before and after treatment; 2) transversal studies of homogeneous EEG groups (discrimination between tracings of residual-type or paranoid-type schizophrenic patients) comparatively with control groups (high and low alpha subjects); 3) study of psychotropic drugs: profiles, prediction of action, dose-effect curves, pharmacokinetic studies, biodisponibility, correlations with plasmatic levels and behavioural or clinical psychiatric rating scales; 4) typologic classification and discrimination by multivariate analysis, studies of functional activities: functional interhemispheric lateralisation of amplitudes and its variations during the course of psychotic processes; 5) new techniques: computerized topo-electroencephalography (CT-EEG, BEAM technique) based on 16 EEG recordings, comparison with other imaging techniques.