Electrophysiological study of the topography of the vibrissae projections to the tactile thalamus and cerebral cortex in mutant mice with hair defects.
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Animals↗
Biomedical subjects
B Pidoux
Publications and source records attributed to B Pidoux.
Projections on the cortical somatic I barrel subfield from ipsilateral vibrissae in adult rodents.
In adult rats and mice, ipsilateral projections to SI posteromedial barrel subfield (PMBSF) are demonstrated for mystacial vibrissae (sinus hairs). Mechanical stimulation with angular deflections in the 2-5 degrees range, elicits potentials in limited areas of SI whose geometric centers coincide for two homologous (contra- and ipsilateral) vibrissae. The cortical domains for two adjacent vibrissae overlap one another slightly. Phase reversal of potentials and unit discharges are also present within the cortex. Ablation of the SI area contralateral to the SI area under study completely abolishes the ipsilaterally projected potentials. It is proposed that ipsilateral responses are mediated via the corpus callosum with an extra delay of 4-5 msec, thus giving each hemisphere the opportunity to compare vibrissal information originating from the two mystacial pads.
Animals↗
Projections of the common fur of the muzzle upon the cortical area for mystacial vibrissae in rats dewhiskered since birth.
In normal adult rats, the mystacial vibrissae and the common fur of the snout project at different loci on the SI cortex. The surface area of the normal fur projection is 0.8 mm2, whereas the vibrissa field amounts to 3-4 mm2. In rats dewhiskered since birth, the vibrissa area can still be identified through the projections from ipsilateral vibrissae (undamaged side). It is shown that in the absence of the vibrissae since birth, the vibrissa area, and this alone, is invaded by projections from the contralateral fur (damaged side).
Animals↗
Progresses of statistical spectral analysis in pharmaco-electroencephalography.
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Adult↗
Intra- and interhemispheric EEG differences quantified by spectral analysis. Comparative study of two groups of schizophrenics and a control group.
In this work we have studied comparatively the relationships between alpha intensity, alpha frequency, root-mean-square amplitude and their standard deviations, versus the location of the four recorded EEG channels: left and right rolando-parietal, left and right parieto-occipital. Twenty-four spectral parameters were computed for each 5-min EEG recording, in the eyes closed situation. The hebephrenic group (36 EEGs from six patients) presented higher values of alpha intensity and RMS amplitudes with low coefficient of variation when compared with the other groups. The left/right rolando-parietal amplitude ratio was 0.73 versus 1.52 for the parieto-occipital ratio. An amplitude hypovariability in the central regions, probably associated with hyperarousal, especially in the left hemisphere, can then be observed in hebephrenics, together with high alpha intensity on the left parieto-occipital area. The two groups of schizophrenics differ from the control group (27 EEGs from 12 subjects) in terms of spectral parameters, the hebephrenic group presenting a possible interhemispheric dysfunction.
Adult↗
[Alpha activity in a group of schizophrenics: spectral analysis and comparison with a control group (author's transl)].
Spectral analysis of tracings from four leads; C3-P3, P3-O1, C4-P4, and P4-O2, were used to compare the results of fiftyseven electroencephalograms from 10 schizophrenics, and 14 normal subjects used as controls. The results show that the mean frequencies of the alpha waves are identical in schizophrenics and controls. Patients with hebephrenia show the lowest variations in alpha wave frequency but with the highest voltage, whereas paranoid schizophrenics have tracings with the lowest amplitude and the greatest variation in frequency. There is also better left intrahemispheric correlation of relative alpha intensities in those patients with the lowest variation in right alpha intensity in relation to controls. The preliminary results suggest that there is a reduction in functional asymmetry of the hemispheres in the electroencephalograms from schizophrenics, when looking at the alpha activity.
Adult↗
[Statistical spectral study of alpha rhythms: modifications due to the tardive action of a hypnotic (author's transl)].
In a simple blind study to evaluate electroencephalographic criteria objectively, and to continue characterization of psychotropic compounds, 5 mg of nitrazepam, a hypnotic derivative, was given to seven subjects the night before the recording. We noted that in most subjects there was a reduction in the spectral intensity of the alpha rhythm, associated with a greater frequency instability, several hours after the absorption of nitrazepam. This corresponds to the tardive hypnotic action of the psychotrope, the importance of which is wellknown at the present time. In the same way as the increase in rapid rhythms, the slipping of 0.5 c/s of the dominant alpha frequency to the top could be characteristic of the action of nitrazepam.
Adult↗
[Fourier analysis, statistical analysis of amplitude and on-line quantification of the EEG].
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Electroencephalography↗
[Study of the functional structure of the EEG by means of the ambispectrum and ambicoherence (author's transl)].
An extension of spectral analysis by calculation of the ambispectrum and ambicoherence is defined, tested on pulsed and random signals, and then applied to the study of the functional structure of the electro-encephalogram. Preliminary results are similar to those obtained by the use of the biospectrum and bicoherence, and also allows comparison between frequency components of signals from different topographical origin.
Alpha Rhythm↗
Cortical organization of the postero-medial barrel-subfield in mice and its reorganization after destruction of vibrissal follicles after birth.
The postero-medial barrel-subfield (PMBSF) of the SI cortex of normal adult mice contains clusters of cells called "barrels". Each barrel histochemically shows increased activity of succinate, lactate, and glucose-6-phosphate dehydrogenase and also GABA-T activity. Some neuronal perikarya in the barrel walls show GABA-T activity. Mitochondrial alpha-GPDH and AChE show equal activities in the hollows and in the walls of the barrels. On this cortical vibrissa field, the contralateral and ipsilateral vibrissae project somatotopically in a way which coincides with the barrels. The mystacial vibrissae and the common fur of the muzzle project to different loci. The cortical surface area for the normal fur is 0.025 mm2, whereas the cortical vibrissal area is 1.0 mm2. In mice with lesioned whisker pads the succinate-dehydrogenase activity of the IVth layer in the vibrissal area becomes a continuous sheet similar to the adjacent IVth layer, the thickness of the cortex is relatively preserved, and the total enzyme activities, biochemically assayed, are unchanged. These features can be explained by a functional substitution. In mice with whisker pads lesioned since birth, the vibrissal area can still be identified by the projections from ipsilateral vibrissae (undamaged side). This vibrissal area, and this alone, is found to be invaded by projections from the contralateral common fur of the muzzle. Experimental data suggest that the compensatory process may result from an invasion of the vibrissal area by a new set of ascending fibers, and not merely from axonal sprouting either at the periphery or at the cortical level.
4-Aminobutyrate Transaminase↗
Chronic thalamic stimulation with three-dimensional MR stereotactic guidance.
PURPOSE: To report a method of electrode implantation in the ventralis intermedius nucleus of the thalamus for the treatment of tremor using a 3-D stereotactic MR imaging technique. METHODS: Five patients (three men and two women; mean age, 59 years) with medically refractory tremor had intrathalamic implantation of a stimulating electrode. Stereotactic MR imaging was performed on a 1.5-T unit equipped with an MR-compatible Leksell G stereotactic frame fixed to the patient's head. Calculation of the coordinates of the theoretical target was based on the coordinates of the anterior commissure, the posterior commissure, and the midline sagittal plane as determined via stereotactic MR imaging. During the surgical procedure, the best position for the stimulating electrode was determined by electrophysiological and clinical studies. Postoperative MR control studies were done in all cases to verify the position of the electrode. RESULTS: Stereotactic MR imaging allowed precise implantation of the stimulating electrode in all patients. Electrode stimulation produced a 90% reduction of the tremor in two patients, an 80% and 70% reduction in one patient each, and a persistent microthalamotomy-like effect in the fifth patient. Examination of the MR control studies showed that mean error in the positioning of the electrodes was 0.77 +/- 0.6 mm (mean +/- SD) in the x direction and 0.80 +/- 1.02 mm in the y direction. CONCLUSION: Although our series is relatively small, the precision achieved with stereotactic MR imaging proves that it can be used with confidence for precise functional neurosurgical procedures.
Brain Mapping↗