Biomedical subjects

M Thevenet

Publications and source records attributed to M Thevenet.

16 recordsLinked to original sources

PubMed1994

Two auditory components in the 130-230 ms range disclosed by their stimulus frequency dependence.

The auditory P2 wave has been studied by means of scalp potential and scalp current density (SCD) mapping. Two components were described. One, peaking around 150 ms, probably reflects a major activity in both supra temporal planes as revealed by SCD maps (P150). The other is a bilateral temporo-parietal component peaking around 220 ms (P220). These two components were functionally disclosed by their stimulus frequency dependence. The P150 potential and SCD amplitudes significantly decrease with increasing frequencies. Whereas this could be interpreted as a modulation of the neural activity, it may also be related to a tonotopical organization of the underlying generators distinct from that previously found for the N100. No frequency effect was found on P220.

Adult↗

PubMed1994

An electrophysiological study of the mental rotation of polygons.

Reaction times and event-related potentials (ERPs) were recorded during a task requiring subjects to decide whether two sequentially presented polygons had the same shape regardless of differences in orientation. Reaction times increased approximately linearly with angular departure from upright orientation, which suggests that mental rotation was involved in the comparison process. The ERPs showed, between 665 and 1055 ms, a late posterior negativity also increasing with angular disparity from upright, which we assumed to reflect mental rotation. Two other activities were exhibited, from 265 to 665 ms, which may be related either to an evaluation of the stimulus or a predetermination of its orientation, and from 1055 to 1600 ms attributed to the decision process.

Adult↗

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↗

PubMed1979

[Acébutolol: conditions of its interference in the estimation of urinary 17-oxosteroids. Method of estimation by Zimmerman's reaction (author's transl)].

Acebutolol at therapeutic dosage may considerably disturb the determination of urinary 17-oxosteroids by Zimmerman's reaction. This interference, very variable according to the various technics which may be used, depends mainly on the pH of the urine at the time of extraction. In very acid medium (pH less than 1,5) no acebutolol metabolite passes into the solvents of low polarity; in very alkaline medium, (pH greater than 13) the passage la quantitative. The estimation of 17-oxostéroids in the presence of acebutolol, is possible provided the extraction is carried out in sufficiently acid medium, such as that used for hydrolysis in presence of hydrochloric acid. This is moreover the procedure used for classical methods were no interference is observed. The selective estimation of acebutolol and of its metabolites may be carried out simply by Zimmerman's reaction, after extraction at pH 13 of non-hydrolysed urine, thanks to the absence of conjugated derivatives.

17-Ketosteroids↗

PubMed1970