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Biomedical subjects

F Perrin

Publications and source records attributed to F Perrin.

At least 19 recordsLinked to original sources
PubMed2000

Functional dissociation of the early and late portions of human K-complexes.

We analyzed K-complexes (KCs) evoked during sleep stage II by the subject's own name and by other names. KCs were composed either of four consecutive waves (full KCs, N2-P3-N3-P4) or of the two first components only (N2-P3). The amplitude of the late phase of KCs (N3-P4) was identical to all stimuli; conversely, own names enhanced selectively the N2-P3 waves, whether they were or not part of a full KC. Two independent phenomena appear to coexist during a full KC, one being connected to the physical characteristics of the stimulus (N3-P4) and the other to its intrinsic significance. This latter may appear either within a full KC or in isolation, and in this case it is reminiscent of the N200-P300 complex observed in wakefulness.

Acoustic Stimulation↗
PubMed1999

A differential brain response to the subject's own name persists during sleep.

METHODS: Auditory evoked potentials (AEPs) to the subject's own name and to seven other first names were recorded in ten normal adults during wakefulness, in both passive listening and active detection conditions, and during sleep stage II (SII) and paradoxical sleep (PS). All stimuli were disyllabic, equiprobable and presented in random order. RESULTS: During wakefulness, a parietal positive 'P3' component, peaking at about 500 ms, probably equivalent to the endogenous P300 wave, was enhanced in response to the subject's own name, even in the passive condition. During SII, K-complexes (KCs) were evoked by all first names and were formed by two biphasic consecutive waveforms. While the amplitude of the late complex (N3/P4) was identical for both types of stimuli, the early portion of the KC (N2/P3), and notably the positive wave 'SII-P3' at about 600 ms, was selectively enhanced after the subject's own name. This supports the hypothesis that at least two distinct neuronal systems are activated in parallel in response to auditory stimuli during SII, one reflecting the detection of stimulus' salience and the other the processing of its intrinsic relevance. During PS, the AEP morphology was comparable to that observed in wakefulness. Notably, a posterior 'PS-P3' wave appeared exclusively in response to own names at about 550 ms, and was considered as an equivalent of the waking P300. CONCLUSIONS: These results suggest that the sleeping brain, during SII and PS, elicits a differential cognitive response to the presentation of the subject's own name, comparable to that occurring during wakefulness, and therefore that the sleeping brain is able to detect and categorize some particular aspects of stimulus significance.

Acoustic Stimulation↗
PubMed1995

Tonotopic organization of the human auditory cortex: N100 topography and multiple dipole model analysis.

The tonotopic organization of the human auditory cortex has been investigated by means of scalp potential mapping and dipole modelling of the evoked response occurring around 100 msec after the stimulus onset. The major characteristics of the topographical changes observed with increasing stimulus frequency were statistically demonstrated. Using a 3-concentric sphere head model, the scalp potential distributions can be explained in first approximation by two equivalent current dipoles, located in the supratemporal plane and mimicking the activity of both auditory cortices. To take into account the temporal aspects of the brain activities, 3 time-varying dipole strategies were tested. Frequency dependence of the dipole orientation has been evidenced in both hemispheres with the 3 models, whereas no significant change in dipole position was found. The tilt in dipole orientation could be related to the folding geometry of Heschl's gyrus, which varies with depth. In agreement with previous MEG findings, this brings new evidence for a tonotopic organization of the auditory cortical area involved in the N100 wave generation. Moreover, distinct frequency dependences of the equivalent current dipoles were observed in the early and the late parts of the N100. This study demonstrates that simple dipolar models, applied on electrical data, make it possible to reveal functionally distinct cortical areas.

Adult↗
PubMed1994

Dissociation of temporal and frontal components in the human auditory N1 wave: a scalp current density and dipole model analysis.

This study reports a combined scalp current density (SCD) and dipole model analysis of the N1 wave of the auditory event-related potentials evoked by 1 kHz tone bursts delivered every second. The SCD distributions revealed: (i) a sink and a source of current reversing in polarity at the inferotemporal level of each hemiscalp, compatible with neural generators in and around the supratemporal plane of the auditory cortex, as previously reported; and (ii) bilateral current sinks over frontal areas. Consistently, dynamic dipole model analysis showed that generators in and outside the auditory cortex are necessary to account for the observed current fields between 65 and 140 msec post stimulus. The frontal currents could originate from the motor cortex, the supplementary motor area and/or the cingulate gyrus. The dissociation of an exogenous, obligatory frontal component from the sensory-specific response in the auditory N1 suggests that parallel processes served by distinct neural systems are activated during acoustic stimulation. Implications for recent models of auditory processing are discussed.

Adult↗
PubMed1994

A survey of medical undergraduate community-based teaching: taking undergraduate teaching into the community.

This article summarizes the findings of a survey investigating the extent to which medical schools in the United Kingdom have developed community-based undergraduate teaching: the types of courses being run and their content; whether they are being evaluated; and how the students are assessed. Courses have been categorized under four main headings: (1) based in general practice, for teaching about general practice as a clinical specialty or using practice patients for teaching general medicine and basic clinical skills; (2) community-oriented, led by GP or community tutors; (3) specialist teaching led by hospital consultants; and (4) agency-based teaching. Twenty-eight schools responded to a written request for information and details of 83 courses were received.

Community Medicine↗
PubMed1994

The personal tutor system: an evaluation.

The stressful nature of medical student training is being increasingly recognized. This study describes a questionnaire survey of the long running personal tutor system (intended to help with social as well as educational needs of clinical students), at a London medical school. Just over one half of students and one third of tutors were highly satisfied with the system. Satisfaction in students was linked with regularity, but not frequency, of meetings, being 'chased' by tutors, and engaging in social as well as educational activities. A small but worrying percentage of students reported that they would not be able to share personal or academic difficulties with tutors, highlighting the need for other avenues of support/counselling to be made available to students.

Attitude of Health Personnel↗
PubMed1992

Computer-assisted placement of electrodes on the human head.

A system has been studied with 3 purposes: digitization of the head and mathematical representation of the scalp surface, assistance for electrode placement, and digitization of the exact 3-D position of each electrode after placement. The system has been validated in several ways, mainly by comparing the electrode locations obtained using the classical manual procedure based on the international 10-20 system of electrode placement, and through the assisted procedure based on the described system. The main result is improved reproducibility of the assisted procedure which is 3 times better than in the manual procedure.

Brain Mapping↗
PubMed1991

The finite element method for a realistic head model of electrical brain activities: preliminary results.

In order to model the brain's electrical activity realistically, the finite element method has been used to compute the potential distribution due to a current dipole. This approach has the advantage over the boundary element method of being able to consider anisotropies of the different conducting sub-volumes. The forward solution has been evaluated in the particular case of a three-layer concentric sphere isotropic head model of the head where an analytical formula is known. The errors on the dipole position and orientation have been estimated in the inverse problem procedure.

Brain↗
PubMed1990

Precautions in topographic mapping and in evoked potential map reading.

First, we consider the main points that must be addressed when constructing topographic maps: types of projection, methods of interpolation, number and locations of recording electrodes, and color scales. Data integrity and precautions in map interpretation are then examined for the case of evoked potential data.

Brain↗
PubMed1990

Brain generators implicated in the processing of auditory stimulus deviance: a topographic event-related potential study.

The neurophysiological mechanisms underlying mismatch negativity (MMN) can be inferred from an examination of some of the brain generators involved in the process of this event-related potential (ERP) component. ERPs were recorded in two studies in which the subjects were involved in a selective dichotic listening task. Subjects were required to silently count rare stimuli deviating in pitch from a sequence of standard stimuli in one ear, while ignoring all the stimuli (standards and deviants) delivered randomly to the other ear. The results showed that, in all cases, the negative wave elicited by the deviant stimuli showed the highest amplitudes over the right hemiscalp irrespective of the ear of stimulation or the direction of attention. Scalp radial current density analysis showed that this asymmetric potential distribution could be attributed to the sum of activities of two sets of neural generators: one temporal, located in the vicinity of the primary auditory cortex, predominantly activated in the hemisphere contralateral to the ear of stimulation, and the other frontal, involving mainly the right hemisphere. The results are discussed in light of Näätänen's model: we suggest the dissociation of two functional processes on the basis of activity of distinct brain areas: a sensory memory mechanism related to the temporal generators, and an automatic attention-switching process related to the frontal generators.

Adult↗
PubMed1989

Spherical splines for scalp potential and current density mapping.

Description of mapping methods using spherical splines, both to interpolate scalp potentials (SPs), and to approximate scalp current densities (SCDs). Compared to a previously published method using thin plate splines, the advantages are a very simple derivation of the SCD approximation, faster computing times, and greater accuracy in areas with few electrodes.

Computer Simulation↗
PubMed1988

Several attention-related wave forms in auditory areas: a topographic study.

The purpose of this study was to progress in the understanding of the electrogenesis of attention-related wave forms in order to highlight some of the underlying attentional processes. ERPs were recorded from 16 electrodes, from 12 subjects who attended selectively to either high or low pitch tones delivered at a constant inter-stimulus interval of 800 msec to either right or left ear, while ignoring a concurrent sequence of tones of the other pitch delivered to the other ear. The attention-related wave forms were obtained by subtracting ERPs to unattended tones from ERPs to the same tones when they were attended. These wave forms were topographically displayed by both potential maps and scalp current density maps and compared with the corresponding maps of the N1 component of the ERPs, to determine the similarity of their generators. It has been shown that the attention effect is expressed by at least two components in specific auditory areas, one of small amplitude, occurring during the ascending slope of the N1 component, sensitive to the pitch of the attended stimulus, and possibly originating in the supratemporal plane of the auditory cortex; another of large amplitude, peaking symmetrically over both hemispheres and having a different topography from that of the N1 component. As described by other authors, a third, later, component appears over frontal areas, but probably originates from deeper sources of the brain. Models of selective attention processes, particularly the 'attentional trace' concept, are discussed in the light of these results.

Adult↗
PubMed1988

Scalp current density fields: concept and properties.

The physical meaning of scalp current density (SCD) is presented and its properties are described using simulations of brain generators by dipolar models inside an inhomogeneous sphere. Its properties are compared with those of potentials and magnetic fields.

Brain Mapping↗
PubMed1987

Comparison of high-frequency jet ventilation to conventional ventilation in adults with respiratory distress syndrome.

Sixteen patients with acute respiratory failure (ARF) were studied. In group I (12 patients, 15 explorations) patients were treated with continuous positive pressure ventilation (CPPV) during conventional ventilation (CV), pulmonary lesions (PL) were severe (Qsp/Qt = 0.24 +/- 0.16 with PEEP = 14 +/- 7 cm H2O) and high-frequency jet ventilation (HFJV) was performed without spontaneous ventilation (SV). In group II (5 patients, 12 explorations) patients were treated with intermittent mandatory ventilation (IMV) during CV, PL were moderate (Qsp/Qt = 0.13 +/- 0.05 with PEEP = 8 +/- 3 cm H2O) and HFJV was performed with SV. In both groups, frequency was 120 c/mn and I:E ratio = 1:2. The cannula size, the driving pressure and the PEEP (water column) were progressively adapted to obtain the same blood gases as those observed during CV, FIO2 being the same. Results on HFJV were compared to CV. In both groups there were no differences between PaCO2, PaO2, FIO2, Qsp/Qt during CV and HFJV. In group I peak airway pressure (PAWP), mean artery pressure (MAP), heart rate (HR), transmural mean pulmonary and wedge pressure (MPAPtm, PWPtm) were not different. Mean airway pressure (MAWP), PEEP and pleural pressure (PP) were higher, cardiac index (CI) was lower. In group II, PP, CI, MAP, HR, MPAPtm, MPWPtm were not different. PAWP was lower, MAWP and PEEP were higher. We conclude that during HFJV it is possible to obtain the same blood gas as during CV, but HFJV without CV may not be indicated in patients with severe PL, because circulatory impairment is higher.

Adult↗
PubMed1987

Mapping of scalp potentials by surface spline interpolation.

Evoked potentials and EEGs record punctate electrical activity at electrode sites. To represent the overall potential distribution on the entire scalp it is necessary to interpolate between these sampled values. Surface splines are mathematical tools for interpolating functions of two variables. In comparison to the classical methods of interpolation, based on linear combination of the potentials of the 4 nearest electrodes, spline methods are smoother, give more precisely located extrema and converge faster toward the 'true' potential surface when the number of recording electrodes is increased. These advantages are at the expense of lengthier computation time.

Brain Mapping↗