Biomedical subjects

P Etévenon

Publications and source records attributed to P Etévenon.

9 recordsLinked to original sources

PubMed2001

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.

Adult↗

PubMed1999

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.

Acoustic Stimulation↗

PubMed1998

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.

Arousal↗

PubMed1996

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.

Data Interpretation, Statistical↗

PubMed1993

[Quadri-dimensional analysis of the electroencephalography. First application to an episode of paradoxical sleep in man].

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)

Adult↗

PubMed1990

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)

Adult↗

PubMed1987

[Value of quantitative EEG and EEG mapping in medicine].

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.

Brain Diseases↗

PubMed1985

[EEG mapping during a visuo-spatial task. Averaged maps and group statistics].

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.

Adult↗

PubMedDate not supplied

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)

Brain Mapping↗