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Biomedical subjects

B Pidoux

Publications and source records attributed to B Pidoux.

At least 37 records · Page 2Linked to original sources
PubMed1997

Pallidal stimulation for Parkinson's disease. Two targets?

There has been renewed interest in functional surgery as treatment for Parkinson's disease (PD). Although pallidotomy and chronic pallidal stimulation are highly effective in suppressing levodopa-induced dyskinesia (LID), both methods also seem to be effective in reducing parkinsonian disability. However, the simultaneous improvement of LID and motor signs is hard to explain with the classic model of basal ganglia circuitry. Taking advantage of the fact that deep brain stimulation is reversible and that implanted electrodes contain four discrete stimulation sites, we investigated the effect of stimulation on different sites of the globus pallidus (GP) in five PD patients. Stimulation in the dorsal GP (upper contact) significantly improved gait, akinesia, and rigidity and could induce dyskinesia when patients were in the "off" state. In contrast, stimulation in the posteroventral GP (lower contact) significantly worsened gait and akinesia, although the reduction in rigidity remained. For patients in the "on" state, stimulation in the posteroventral GP dramatically reduced LID but, as in the "off" state, worsened gait and akinesia, thus canceling out the antiparkinsonian effect of levodopa. Our results indicate that stimulation had a striking different effect on parkinsonism and dyskinesia when applied at two different loci of the GP and that stimulation applied in the posteroventral GP produced opposite effects on rigidity and on akinesia. We conclude that parkinsonian signs and LID are a reflection of at least two different anatomofunctional systems within the GP and that this functional organization of the GP needs to be considered when determining the optimal target for surgical treatment of PD.

Adult↗
PubMed1996

A clinical and neurophysiological study of a patient with an extensive transection of the spinal cord sparing only a part of one anterolateral quadrant.

In 1976, Noordenbos and Wall studied sensory functions in a woman with a surgically verified T3 spinal cord transection which spared only a part of the left anterolateral quadrant, We re-investigated this unique case 18 years after the lesion and included a comparable sensory examination, MRI of the spinal cord, somatosensory evoked potentials, PET-activation study during hand and foot vibration and analysis of flexion reflex modulation during the Jendrassik manoeuvre. Our results show that the residual anterolateral quadrant contains ascending pathways carrying a wide range of sensory information as well as descending pathways modulating flexion reflex activity at the spinal level. Moreover, the changes in sensory functions and the unique pattern of cortical activation suggest a functional reorganization of the connectivity between the periphery and the cerebral cortex. Changes of facilitation and/or of inhibition at different levels of the somatosensory system may account for these longterm plastic changes.

Evoked Potentials, Somatosensory↗
PubMed1995

Flumazenil therapy for hepatic encephalopathy in cirrhotic patients: a double-blind pragmatic randomized, placebo study.

OBJECTIVE: To evaluate the effects of flumazenil on hepatic encephalopathy in patients with cirrhosis. DESIGN: Double-blind randomized study. SETTING: Liver intensive care unit over a 2-year period. PATIENTS: Fourteen patients with cirrhosis (median age 54 years, range 41-73 years), comprising 10 men and four women enrolled during 18 episodes of hepatic encephalopathy. METHODS: Placebo or flumazenil (1 mg at 0.1 mg/min infusion rate) was infused in coded vials. The patients' hepatic encephalopathy was graded clinically and by electroencephalography (EEG). RESULTS: In eight episodes of hepatic encephalopathy the placebo was infused first and no improvement occurred (0%). During 12 episodes of hepatic encephalopathy, flumazenil was administered and the EEG recording improved within 7 min (range 4-47 min; 12 out of 18 cases; 66 versus 0% for flumazenil versus placebo, respectively; P < 0.01); a modest clinical improvement in hepatic encephalopathy was observed within 83 min (range 30-340 min). The amount of flumazenil infused averaged 0.7 mg (range 0.4-1 mg). CONCLUSIONS: The infusion of 0.4-1 mg flumazenil results in a modest but rapid improvement in the EEG grading of hepatic encephalopathy and to a moderate but delayed improvement in the clinical grade of hepatic encephalopathy.

Adult↗
PubMed1990

[Tridimensional cartography of potential recorded on the human scalp: II. Calculation of current density by derivation of tridimensional interpolation function].

Scalp charge density or current density distributions may be computed from the electrical potential recorded from neighbouring electrodes. It can also be derived from an interpolating function in order to draw maps on which current sources can be seen more easily than on potential maps. We describe the computation of current density by derivation of a tri-dimensional interpolation function.

Action Potentials↗
PubMed1990

[Tridimensional cartography of potentials recorded on the human scalp: I. Interpolation with tridimensional functions].

Human cerebral electrophysiological studies make an increasing use of mapping to represent potentials recorded on the scalp. In order to draw potential maps a projection on a plane of the recording electrodes is required. An interpolation of the values of points between electrodes must then be performed. We have compared three interpolation methods (surface splines, spherical splines and tridimensional interpolation functions). The last two methods are interesting because, avoiding one projection, they do not create map distortions. Statistical evaluation of the three methods, using a dipolar model, shows the overall superiority of the tridimensional interpolation.

Brain Mapping↗
PubMed1989

[Electroencephalographic study of the effect of a benzodiazepine antagonist in hepatic encephalopathy].

Observing animal models of fulminant hepatic failure lead to the hypothesis of a GABAergic origin of the comatose state in hepatic encephalopathy (HE). The hypothesis of hyperstimulation of gamma-aminobutyric acid-benzodiazepine (GABA-BZ) receptors in HE has been tested with a BZ antagonist (flumazenil, Anexate) on 7 patients suffering from severe HE. The standard EEG has been recorded 30 min before and after slow IV perfusion of 1 mg flumazenil. Although we did not observe a complete EEG normalization, a significant improvement of EEG was observed after only a few minutes in 6 out of the 7 cases studied. Modification of the reactivity parallels clinical improvement of encephalopathy. These effects persist mostly 4 h after perfusion. The results are consistent with the hypothesis of hyperstimulation of GABA-BZ receptors in HE. The positive effect of flumazenil on vigilance level should encourage its use in chronic hepatic encephalopathy.

Adult↗
PubMed1987

[Long latency auditory evoked potentials: value of multichannel analysis and of high-resolution graphic mapping].

Auditory Evoked Potentials maps (AEP) were computed from 32 simultaneously recorded channels over both hemispheres using a linear interpolation algorithm. Reference electrode was extracephalic. Stimulus was a 781 Hz tone (intensity 70 dB HL, duration 256 msec). Average AEP were from 128 responses to randomly delivered stimuli. Direct current and frequencies over 50 Hz were removed by means of a digital filter (FFT). Results from 15 subjects showed before 120 msec a symmetrical response of AEP at vertex with left ear, right ear or binaural stimulation. Between 120 and 170 msec, maps of evoked responses were asymmetrical showing greater potentials over temporal areas contralateral to the stimulated ear.

Cerebral Cortex↗
PubMed1986

[Effects of Ginkgo biloba extract on functional brain activity.. An assessment of clinical and experimental studies].

Electroencephalography is the only convenient method for functional exploration of the brain. The recent introduction of signal analysis techniques has given it a quantitative dimension and has resulted in pharmacological studies of electoencephalograms. In four studies of this kind the effects of Ginkgo biloba extract were investigated on three pathological animal models, in young healthy volunteers and in elderly people with dementia disorders. In man, the EEG tracings could be analyzed in relation to different psychometric tests. The results obtained confirm those of clinical trials, and notably the activity of Ginkgo biloba extract on alertness.

Adolescent↗
PubMed1984

Computerized topo-EEG spectral maps: difficulties and perspectives.

An electric potential measurement tells us only about the difference between two electrode locations. When prior experiments or present measurements prove that an electrode's location is inactive (especially in 'mono-polar' or scalp-to-reference technique), then EEG records and EEG maps can be interpreted regionally near each electrode location. Topographical mapping requires spatial interpolation which is one factor involved in spatial resolution. The interpolation algorithm has been studied by changing the power exponent n of the interelectrode distance d. When n is close to zero, interpolated values are all equal to the average of the four electric potential measurement Vs bounding the quadrilateral in which the interpolated points of the EEG map are located. When n is very high (n = 20 or higher), the values are essentially equal to the V which is at the minimum distance d. For n = 1, the map seems unlikely to represent the true scalp field. The choice between n = 2 and n = 3 is difficult, but n = 3 EEG mapping looks better (more plausible) and is our regular choice. The choice of recording/reporting method has also been studied. If the quantitative EEG map is linearly calculated from observations, the interpretation of record activity resulting from charge separation near the non-reference electrode attached to a particular channel is only possible when inactivity can be assured. This is completely different when the quantity mapped is not linearly calculated from observations (like power values or rms amplitudes in microvolts).(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Mapping↗
PubMed1983

[Computerized quantitative topo-electroencephalography].

A method is described which has been developed to topographically display the values of spectral EEG analysis from 11 electrodes on each hemisphere and 5 electrodes on the midline. The EEG from 16 channels at a time is multiplexed and sampled at 3.2 kHz. From power spectra averaged every 10 sec for 5 min a few spectral parameters are computed among which are the spectral intensities within the delta, theta, alpha and beta bands. The whole values are then displayed on maps representing lateral views of cerebral hemispheres by means of spectral iso-intensity surfaces with extrapolation of the intermediate points. Different spectral intensities are coded by means of different gray levels. These maps clearly illustrate the topographical distribution of EEG rhythms and their peculiarities related to the side of the head recorded.

Alpha Rhythm↗
PubMed1983

[Topographic aspects of drug-induced fast rhythms in quantitative topo-electroencephalography].

The topographical aspects of fast rhythms induced by different psychotropic drugs have been studied in patients by means of a previously described method. This method is based on the spectral analysis of 28 EEG channels over both cerebral hemispheres. The spectral parameters, computed over 2 min 40 sec, are put into a data base. The clinician can then decide which of these parameters will be extracted from the data base and then displayed by means of maps on a graphic terminal. Those maps are useful for immediate comparison not only of the fast rhythms' characteristic values but also of those from other spectral bands. As quantitative EEG analysis is more and more frequently used in psychotropic drug studies, a good knowledge of the topography of the rhythms induced by these drugs will help in the selection of the most useful derivations.

Adult↗
PubMed1982

[Multivariate correspondence analysis of a visually screened EEG. Application to a study of psychotropic drugs compared with placebos (author's transl)].

Eighty-seven EEG recordings were obtained from 9 healthy volunteers, medical students who were part of a controlled, double-blind, randomized study. After a first control recording, they received orally, at 1 week interval, either 3 placebos or 3 compounds: yohimbine chlorhydrate (4 mg), propranolol (40 mg), a psychotropic compound in experimentation. The polygraphic recordings were obtained 2 or 6 h after placebos or active compounds. Four EEG channels were recorded simultaneously (T4-C4, T3-C3, P4-O2, P3-O1). The EEGs were sampled at 200 Hz, for 120 successive epochs, free of artifacts. The recordings of 5 min were then submitted to spectral analysis followed by data reduction providing characteristic spectral parameters. A descriptive questionnaire of EEG made of 100 items was filled out by two electroencephalographists for each of 87 recordings. The items, with dichotomic choices, described 4 EEG frequency bands: delta, theta, alpha, and fast frequencies (beta). For each frequency band the following was evaluated: frequency, amplitude, asymmetry, morphology, relative abundance, irregularity, lability of frequency, diffusion, dominant localization, EMG activity and superposition of rhythms. The number of periods of drowsiness in 5 min and fluctuations of rhythms were also ascertained in the same way. The items were coded on punch cards and submitted to a first analysis of correspondences. The 3 factorial planes were plotted with the projections of each item together with the centers of gravity of placebos and treatments. The first factor can be interpreted as a bipolar axis 'mental activation-diffused vigilance', the first pole being characterized by a 'beta cluster' and the second by alpha and theta superimposed clusters. The second factor can be also considered as a bipolar axis 'drowsiness -quiet wakefulness', the first pole being characterized by a 'theta cluster' and a larger 'delta cluster' containing a smaller 'alpha cluster' of labile alpha rhythm intermingled with slower rhythms. In respect to the barycentric centers of gravity, yohimbine and propranolol are opposed to the placebo center along the factor-two axis. This may be considered as an 'anti-sedation effect'. However, along the first factor axis, the propranolol center can be associated with a greater diffusion of vigilance than the yohimbine center.

Adult↗
PubMed1979

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↗
PubMed1979

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↗
PubMed1979

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↗