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Biomedical subjects

J Pernier

Publications and source records attributed to J Pernier.

At least 19 recordsLinked to original sources
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↗
PubMed1992

The combined monitoring of brain stem auditory evoked potentials and intracranial pressure in coma. A study of 57 patients.

Continuous monitoring of brainstem auditory evoked potentials (BAEPs) was carried out in 57 comatose patients for periods ranging from 5 hours to 13 days. In 53 cases intracranial pressure (ICP) was also simultaneously monitored. The study of relative changes of evoked potentials over time proved more relevant to prognosis than the mere consideration of "statistical normality" of waveforms; thus progressive degradation of the BAEPs was associated with a bad outcome even if the responses remained within normal limits. Contrary to previous reports, a normal BAEP obtained during the second week of coma did not necessarily indicate a good vital outcome; it could, however, do so in cases with a low probability of secondary insults. The simultaneous study of BAEPs and ICP showed that apparently significant (greater than 40 mm Hg) acute rises in ICP were not always followed by BAEP changes. The stability of BAEP's despite "significant" ICP rises was associated in our patients with a high probability of survival, while prolongation of central latency of BAEPs in response to ICP modifications was almost invariably followed by brain death. Continuous monitoring of brainstem responses provided a useful physiological counterpart to physical parameters such as ICP. Serial recording of cortical EPs should be added to BAEP monitoring to permit the early detection of rostrocaudal deterioration.

Adolescent↗
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↗
PubMed1988

Transient drug-induced abolition of BAEPs in coma.

Combined infusion of high doses of lidocaine and thiopental in a comatose patient induced major latency and amplitude BAEP changes, which progressed to complete BAEP abolition. Responses returned to normal after drugs were discontinued. EEGs during the episodes showed long-lasting periods of activity suppression, but were never isoelectric. BAEPs are resistant to hypothermia and barbiturates, but must be interpreted cautiously in patients treated with a combination of anesthetic drugs that includes lidocaine.

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↗
PubMed1987

Brain-stem monitoring. I. A system for high-rate sequential BAEP recording and feature extraction.

A computerized system is proposed for the continuous automatic monitoring of BAEPs in the intensive care unit or in the operating room. A new adaptive optimal digital filtering technique has been developed to allow BAEP recording with 200-400 stimulations, i.e., within 10-20 sec only, every 2 min. This method permits a selective cancellation of the major artifacts as soon as they occur: electrical interference and myogenic activities which are commonly encountered in such environments. An algorithm for automatic peak detection (waves I-V) has been implemented, and the whole system has been evaluated in terms of reduction of the intra-individual variability of latencies and amplitudes. Some clinical examples of comatose patient monitoring are briefly presented to illustrate the performance and the reliability of the system.

Brain Stem↗
PubMed1987

Brain-stem monitoring. II. Preterminal BAEP changes observed until brain death in deeply comatose patients.

Preterminal BAEP changes were studied until brain death in 8 head-injured patients out of a series of 38 comas monitored by means of a system allowing high-rate sequential recording. Two different modalities of BAEP degradation were disclosed: (1) simultaneous latency increase of all components associated with a decrease of cerebral perfusion pressure (CPP), consistent with ongoing ischaemia of the posterior fossa; (2) deterioration of brain-stem components (waves III-V) with preserved or even enhanced wave I. The latter pattern was not consistently associated with any haemodynamic change and might be related to mechanical factors causing rostro-caudal deterioration of brain-stem function. The time course of BAEP degradation ranged from a few minutes to more than 10 h. In the case of slow preterminal evolution definitely pathological trends were identified even when individual BAEPs were still within normal limits. Such trends would have remained unnoticed in single BAEP records. Hypothermia and anaesthetic drugs were found to induce falsely alarming BAEP changes very similar to those seen during preterminal evolution. Our results suggest that continuous brain-stem monitoring could be helpful for management of comatose head-injured patients.

Blood Pressure↗