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F Mauguiere

Publications and source records attributed to F Mauguiere.

At least 19 recordsLinked to original sources
PubMed1999

Evidence for an abnormal cortical sensory processing in dystonia: selective enhancement of lower limb P37-N50 somatosensory evoked potential.

We evaluated brain stem P30, contralateral frontal N37, and the vertex-ipsilateral central P37, N50 somatosensory evoked potentials (SEPs) obtained in response to stimulation of the tibial nerve in 10 patients with idiopathic dystonia. Results were compared with those obtained in 10 healthy subjects matched for age and sex. The amplitude of the brain stem P30 potential and of the contralateral frontal N37 response in dystonic patients was not significantly different from that recorded in normal subjects. The vertex- ipsilateral central P37-N50 complex, which is thought to originate in the pre-rolandic cortex, was significantly enhanced in patients compared with the control group. These results suggest the enhancement of the vertex-ipsilateral central P37-N50 complex might reflect an abnormal response to somatosensory inputs of a precentral cortex which is excessively activated because of a disorder of the basal ganglia. Such inefficient sensory processing in motor areas might contribute to motor impairment in dystonia.

Adult↗
PubMed1999

Timing and characteristics of perceptual attenuation by transcranial stimulation: a study using magnetic cortical stimulation and somatosensory-evoked potentials.

Transcranial cortical magnetic stimulation (CMS) is a noninvasive, non-noxious procedure to induce perceptual attenuation when applied concomitant to sensory stimuli. To investigate the perceptual timing of simple stimulus features in the somatosensory modality, we applied right hemisphere CMS at different intervals following a stimulus delivered to the left hand. Different intervals between peripheral stimuli and CMS were defined according to the components of the somatosensory-evoked potentials (SEP), previously obtained in response to the same stimulus. Perceptual attenuation was maximal when CMS coincided with the primary cortical response (parietal N20 potential); conversely, perception of stimulus intensity was not modified when CMS was concomitant with the N200 and P300 potentials. Using small CMS intensities, a "perceptual dip" was observed when CMS arrived in coincidence with the N120 potential, a SEP response thought to be originated in part in the second somatic area. Our results support the view that both N200 and P300 are post-perceptual responses. The results also suggest that the cortical processes active during the N20 and N120 potentials may be essential for the conscious perception of somatosensory stimuli delivered to the hand.

Adult↗
PubMed1998

Dipolar sources of the early scalp somatosensory evoked potentials to upper limb stimulation. Effect of increasing stimulus rates.

Brain electrical source analysis (BESA) of the scalp electroencephalographic activity is well adapted to distinguish neighbouring cerebral generators precisely. Therefore, we performed dipolar source modelling in scalp medium nerve somatosensory evoked potentials (SEPs) recorded at 1.5-Hz stimulation rate, where all the early components should be identifiable. We built a four-dipole model, which was issued from the grand average, and applied it also to recordings from single individuals. Our model included a dipole at the base of the skull and three other perirolandic dipoles. The first of the latter dipoles was tangentially oriented and was active at the same latencies as the N20/P20 potential and, with opposite polarity, the P24/N24 response. The second perirolandic dipole showed an initial peak of activity slightly earlier than that of the N20/P20 dipolar source and, later, it was active at the same latency as the central P22 potential. Lastly, the third perirolandic dipole explaining the fronto-central N30 potential scalp distribution was constantly more posterior than the first one. In order to evaluate the effect of an increasing repetition frequency on the activity of SEP dipolar sources, we applied the model built from 1.5-Hz SEPs to traces recorded at 3-Hz and 10-Hz repetition rates. We found that the 10-Hz stimulus frequency reduced selectively the later of the two activity phases of the first perirolandic dipole. The decrement in strength of this dipolar source can be explained if we assume that: (a) the later activity of the first perirolandic dipole can represent the inhibitory phase of a "primary response"; (b) two different clusters of cells generate the opposite activities of the tangential perirolandic dipole. An additional finding in our model was that two different perirolandic dipoles contribute to the centro-parietal N20 potential generation.

Adult↗
PubMed1997

Predictions of carbamazepine concentrations using a Bayesian program (PKS System, Abbott): a retrospective evaluation in an outpatient population.

This work evaluates the performance of a Bayesian program (PKS System, Abbott) for predicting carbamazepine concentrations in an outpatient population. The retrospective study involved 20 epileptic patients (12 adults and 8 children) receiving carbamazepine monotherapy orally. The program was used to predict measured serum levels after feedback of 0, 1 or 2 steady-state concentrations. A significant negative prediction bias was observed when no feedback concentration was used for estimation. However, the prediction bias (mean prediction error; m.e.) decreased as soon as one feedback concentration was used for estimation. Precision (mean absolute prediction error; m.a.e.) was significantly improved with one feedback concentration and was even better with two concentrations. Likewise, r.m.s.e. (root mean squared error; composite of bias and precision) regularly decreased when the number of feedback concentrations used was increased. Eleven percent of the estimates were unacceptable clinically (prediction error > 2 mg L-1) when 1 feedback concentration was used; less than 3% were unacceptable when two concentrations were used. Thus the performance of the Bayesian dosing program is acceptable when two feedback concentrations are known, and seems able to help the clinician adjust carbamazepine dosage in an outpatient population.

Administration, Oral↗
PubMed1995

Parameter and index images of benzodiazepine receptor concentration in the brain.

UNLABELLED: In vivo studies of ligand-receptor interactions with PET data are based on different approaches that provide either quantitative results (receptor density and affinity) or indices that are assumed to be correlated with the receptor concentration. The aims of this study are to obtain parametric images of benzodiazepine receptor concentration and of flumazenil affinity and to study the validity of two receptor concentration indexes. METHODS: A three-compartment ligand-receptor model, [11C]flumazenil, and experimental data obtained using a three-injection protocol in human volunteers were used to acquire parametric images. The delayed activity method and the apparent distribution volume (estimated using a two-compartment model) were also tested and their results compared with those of the multi-injection approach. RESULTS: Parametric images of receptor density, affinity and all kinetic parameters were obtained with acceptable variation coefficients. A correlation between receptor density and apparent affinity was found (r = 0.83; p < 0.0005). The correlation between receptor concentration and apparent distribution volume (estimated with three- and two-compartment models, respectively) was accessed using both a linear (the usual hypothesis) and a nonlinear correlation derived from the relationship between the receptor density and the affinity. CONCLUSION: In spite of the complexity of this protocol (three injections, a 2-hr experiment, blood sampling and a metabolite study), we showed that the multi-injection approach is suitable for parametric brain imaging. By using this approach as a reference, we deduced that the distribution volume and delayed activity images are valid methods in the usual range of the benzodiazepine receptor concentrations found in the human brain.

Brain↗
PubMed1990

[Cortical pain. Clinical, electrophysiologic and topographic study of 12 cases].

Vascular lesions of the cerebral cortex sparing the thalamus (MRI or CT with reconstructions) may be accompanied by burning or constrictive pain which suggests thalamic pain as it affects one half of the body and is associated with induced pain. Summation hyperpathia is rare; allodynia is more common and sometimes isolated (2 cases). Cortical pain may be paroxysmal, and in 3 of our patients it progressed like a jacksonian seizure. The territory of pain is also the site of global or spinothalamic hypoaesthesia (5 cases). Early SEPs are abolished or of low amplitude (8 cases). The lesion is located in area SI or extends to the thalamo-parietal radiations; in 11 out of 12 patients it was located in the minor hemisphere. Two physiopathological theories are discussed: hyperactivity of the intralaminar thalamus relieved from cortical inhibition, or denervation hyperactivity related to the cortical or subcortical lesion.

Adult↗
PubMed1989

Magnetic resonance imaging in refractory focal epilepsy with normal CT scans.

One hundred patients suffering from focal epilepsy with complex partial seizures refractory to medical treatment and showing no abnormality at CT were explored by MRI with an 0.5 Tesla magnet. MRI detected an abnormality in 25 patients with, in 17 of them, good correlation between MRI and clinical as well as electroencephalographic findings. Abnormal morphology and signal was found in 5 patients, with positive CT results on reexamination of previous CT images or on new CT scans in 4 of them. There was a diffuse temporal lobe high-intensity signal in 3 cases and a localized high-intensity signal in 9 cases (temporal lobe 4, occipital lobe 3, frontal lobe 1, fronto-parietal and parietal lobes 1). Thus, in 13% of the cases MRI demonstrated a lesion that had not been detected at CT, and the location of the lesion was concordant with clinical and electroencephalographic data.

Adolescent↗
PubMed1986

Listening with one or two hemispheres: verbal dichotic testing after intracarotid barbiturate injection.

A verbal dichotic test was given to 16 patients during right or left hemisphere narcosis induced by intracarotid barbiturate injection (Wada's procedure). During right hemisphere narcosis patients did not repeat left ear words. This demonstrates an intrahemispheric competition within the left hemisphere at the detriment of left ipsilateral ear words. After left dominant hemisphere narcosis, when aphasia had apparently disappeared, patients temporarily did not repeat right ear words. This suggests that, during this critical time period, two competitive processes took place. First the right hemisphere selected the left ear words by an intrahemispheric competition. Second it imposed them on the recovering left hemisphere at the detriment of right ear words, because of an interhemispheric competition.

Auditory Pathways↗
PubMed1986

Separate generators with distinct orientations for N20 and P22 somatosensory evoked potentials to finger stimulation?

Sequential spatial maps of scalp potentials, obtained with a 16-channel montage, were used in 12 healthy subjects in order to assess the temporal and spatial distribution of early cortical SEPs to single finger stimulation. It was found that when the contralateral parietal N20 negativity peaks there is a synchronous frontal P20 positivity, supporting the view of a tangentially orientated dipolar generator for this couple of scalp SEPs components. It was not possible to show a distribution of N20 peak on the scalp that would parallel the somatotopic finger representations in area S1; however, the orientation of the putative dipolar source of the N20/P20 complex was found to change according to the finger stimulated. A central P22 component was also constantly obtained without any synchronous negativity on the scalp surface corresponding to the electrode array; a clear somatotopic organisation was found for P22. These features favour the hypothesis that this latter component has a radially orientated generator situated in the prerolandic motor cortex, close to the scalp surface. Because of overlapping between the P20 and P22 components, the determination of P22 onset latency was hazardous in some cases, and spatial mapping was then essential to identify this component. The conclusion that the contralateral parietal N20 and central P22 could be generated by separate dipolar generators with distinct orientations is supported by recent data from combined electrical and magnetic field recording.

Adult↗
PubMed1985

[Peroperative monitoring of early auditory evoked potentials].

Brainstem auditory evoked potentials (BAEP) were monitored during 37 neurosurgical operations (acoustic neurinomas with preoperative useful hearing, microvascular decompression of cranial nerves for hemispasm or trigeminal neuralgia, cerebellopontine angle tumors other than acoustic neurinomas, brainstem tumors and posterior circulation surgery). Intraoperative BAEPs were unchanged in 13 patients. Transient BAEP alterations (delay of I-V interval, transient obliteration of BAEP for as long as 8 minutes and 20 minutes) were seen in 13 other patients; irreversible BAEP alterations (loss of evoked response in 6 patients, delay of I-V interval) were seen in 11 patients. BAEP stability or alterations have been correlated with the ongoing surgical maneuver, the neurological outcome and the postoperative auditory function. BAEPs were found to be good predictors of post-operative auditory function but poorer predictors of neurological outcome. Some alterations are strictly associated with surgical retraction or with eighth nerve manipulation either immediately after the surgical maneuver or several minutes later. No detectable cause of BAEP changes was found in a few cases. The value of this monitoring is discussed. It may also help elucidate the mechanisms of hearing loss in acoustic neurinoma surgery.

Auditory Pathways↗
PubMed1985

Anatomical evidence for medial pulvinar connections with the posterior cingulate cortex, the retrosplenial area, and the posterior parahippocampal gyrus in monkeys.

Reciprocal connections between the medial pulvinar and the limbic neocortex in monkeys were demonstrated by means of tritiated amino acid injections in the medial pulvinar and the cingulate cortex, and HRP injections in the medial pulvinar. It appears that the medial nucleus of the pulvinar sends projection fibres to the posterior cingulate gyrus (area 23), the retrosplenial area, and the posterior parahippocampal gyrus (areas TH and TF). The labeled terminals were concentrated in two bands, one in the deeper part of layer III and in layer IV, and the other in layer I. These projections were observed to be reciprocal, and the cortical afferent fibers to the medial pulvinar were found to originate from the deep layers of the cortex. The medial nucleus of the pulvinar was already known to be connected with the prefrontal cortex and with the inferior parietal lobule. Since this nucleus is now demonstrated to be connected with the posterior limbic neocortex, it is envisaged as being the thalamic counterpart of a cortical triad (prefrontal, parietal, and limbic) involved in modulating directed attention.

Animals↗
PubMed1985

Sequential colour mapping system of brain potentials.

We present a colour mapping system for the visualization of both the spatial scalp distribution and the temporal evolution of brain potentials. The system is applicable to recordings of auditory, visual and somatosensory potentials. It uses a Tektronix 4113 colour terminal connected to a Solar 16 (SEMS) mini-computer. The brain potentials are recorded on up to 16 scalp electrodes. The gain and the baseline are corrected separately on each channel. At each point of the scalp the potential is reconstructed by a linear interpolation of the measured potentials of the four nearest electrodes. Simultaneously n2 (1 less than n less than 8) colour maps can be presented on the screen. This allows the study of the temporal evolution of full scalp evoked potentials. The user chooses the two extreme latencies defining the time window to be explored and the latencies of the maps are regularly time-spaced within this window. In a typical case, in which four maps are desired, the latencies of the maps can be chosen independently. The 16-colour palette is predetermined but the user has three possibilities to establish the correspondence between the electrical potential and the colours. Examples are shown in the visual and somatosensory stimulation modalities. The advantages and limitations of such a representation are discussed.

Brain↗
PubMed1985

[Control of visual exploration: anatomic and physiologic data].

The idea that saccadic eye movements necessary for visual space exploration could be under the control of the frontal eye field was based mainly upon Ferrier's early experiments of electrical stimulation of the cortex. More recent anatomical as well physiological data have demonstrated in monkeys that the sensori-motor processing needed to locate visual targets and to program an accurate eye movement to them is achieved in the superior colliculus, the frontal prearcurate and the posterior parietal cortices. Cells in those three structures have been identified by microelectrode studies that modify their response to a visual target before any eye movement when a saccade directed to this stimulus is to occur. Motivation to move the eyes towards the stimulus is under the control of the limbic cortex of the cingulate gyrus. Lesions to any of these structures lead to a neglect phenomenon characterized by the paucity of spontaneous saccades towards the half of space opposite to the lesion. In primates and in man neglect is observed only after cortical or thalamic lesions but not, or very transiently, after collicular lesion. The prearcuate frontal, the cingulate, and the posterior parietal cortices are interconnected via direct cortico-cortical fibres and also by a cortico-thalamo-cortical circuit, the thalamic relay of which is the medial pulvinar. The medial pulvinar is known to receive polymodal sensory informations from the intermediate layers of the superior colliculus. Thus a complete network involving cortical, thalamic and subthalamic structures is responsible for a very secure and redundant control of gaze.

Afferent Pathways↗
PubMed1984

[Visual evoked potentials (VEP's) obtained by black and white or red and black checkerboard inversion. Results in healthy subjects and in multilocular sclerosis patients].

Visual evoked potentials (VEPs) were elicited in a control group and in 125 multiple sclerosis (MS) patients by reversal of TV black and white checkerboard patterns with two different check sizes and contrasts (44'/contrast 50%; 22'/contrast 20%), and also by a display of red light emitting diodes (LEDs) generating a 'true' pattern reversal. In control subjects LED pattern reversal produced responses of lower amplitude and of longer latency compared to responses to TV black and white checkerboards. The interindividual variability of P100 latency was lower with the LED display than with the low contrasted TV pattern. In 18 patients with definite or suspected MS, VEPs were normal with the two TV patterns when delayed or absent with the LED display. Thus LED pattern reversal was a more effective stimulus than black and white pattern reversal for the detection of demyelinating lesions of the optic nerves in MS. LED stimulation proved to be particularly useful in patients with progressive spastic paraparesis or with previous history of isolated optic neuritis.

Adult↗
PubMed1983

A crossed corticotectal projection from the lateral suprasylvian area in the cat.

Crossed cortical projections to the superior colliculus of the cat were demonstrated by unilateral superior colliculus injections of horseradish peroxidase (HRP) and by cortical injections of radioactive amino acids. This crossed corticotectal projection originates in the lateral bank of the middle suprasylvian sulcus and in both banks of the posterior suprasylvian sulcus. The site of termination of the contralateral corticotectal projection is restricted to the anterior margin of the superior colliculus (SC) while the ipsilateral projection spreads over the whole SC. The contralateral terminal areas are restricted to the superficial tectal layers. The projection fibers reach the contralateral superior colliculus by crossing the collicular commissure. The existence of such a connection may help to explain certain electrophysiological observations.

Animals↗