Jean-Michel Guérit | UCLouvain (University of Louvain) (original) (raw)
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Papers by Jean-Michel Guérit
Electroencephalography and clinical neurophysiology, 1997
This study examines how the recording of the lumbar and subcortical components of the posterior t... more This study examines how the recording of the lumbar and subcortical components of the posterior tibial nerve (PTN) SEPs may usefully replace that of cortical components in situations in which these components cannot be reliably obtained (infants, high concentrations of halogenated gasses). Lumbar, brain-stem, and cortical PTN SEPs were intraoperatively monitored in 7 patients undergoing repair of aortic coarctation under variable isoflurane concentration (up to 1.2%). Four patients were less than 1 year old. Two distinct activities were evidenced at the lumbar level in all of the patients: the dorsal root component (DRC) and the dorsal horn negativity (DHN). The equivalent of the adult P30 (lemniscal positivity; LP) was also present in all of the patients, whatever their age or the concentration of isoflurane. By contrast, the parietal activities were absent intraoperatively in the youngest patients. Spinal-cord ischemia consecutive to aortic cross-clamping gave rise to early DHN ch...
The Journal of Urology
To determine normal reference latencies pudendal cortical somatosensory evoked potentials were ev... more To determine normal reference latencies pudendal cortical somatosensory evoked potentials were evaluated in 20 healthy volunteers. The dorsal nerve of the penis or clitoris was stimulated electrically and the cortical response was recorded from the CZ-2 point (2 cm. behind the central vertex). Reproducible responses were obtained and reference values were established.
Electroencephalography and clinical neurophysiology. Supplement
Electroencephalography and clinical neurophysiology
Somatosensory evoked potentials (SEPs) to unilateral or bilateral posterior tibial nerve (PTN) st... more Somatosensory evoked potentials (SEPs) to unilateral or bilateral posterior tibial nerve (PTN) stimulation and to stimulation of the dorsal nerve (DN) of the penis/clitoris were recorded on 32 channels in 10 volunteers. SEPs to unilateral PTN stimulation consisted of the classic 'W' complex P38-N45-P56-N75 maximal on the ipsilateral central and parietal leads, and two negative waves, N33 and N37, maximal on the contralateral post- and prerolandic areas, respectively. A lemniscal P30 was also recorded. Bilateral PTN stimulation caused, by algebraic summation, the disappearance of both N33 and N37; the W complex was symmetrical and the amplitude of P30 increased. The SEPs to DN stimulation were also symmetrical, and N33 and N37 were absent. These features can be explained by the bilateral character of DN stimulation. They also differed from bilateral PTN SEPs in 3 respects; the absence of P30, the small amplitude and the weaker gradients of field distribution of the 'W'...
Electroencephalography and Clinical Neurophysiology, 1996
Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section, 1997
This paper presents the results of intraoperative median nerve SEP monitoring in 205 successive p... more This paper presents the results of intraoperative median nerve SEP monitoring in 205 successive patients undergoing isolated carotid endarterectomy (CE) (N = 172) or CE followed by coronary bypass (CBP) and/or vascular replacement (VR) (N = 33). The left and right median nerves were alternately stimulated and recordings performed on 4 channels: cervical, ipsi-and contralateral parietal, and frontal. SEPs were qualitatively rated in terms of mild, moderate, or severe ipsilateral, contralateral, or bilateral abnormalities. The SEP abnormalities were subdivided into 5 categories as a function of their relationships with intraoperative events: no alterations (67.3%), early or late SEP alterations after carotid cross-clamping (15.6%), SEP alterations after a drop in blood pressure (occurring outside of or within the cross-clamping period) (15.1%), SEP alterations of a most likely embolic origin (2.4%), SEP changes after head positioning (1%), and SEP changes after a modification of the anesthetic regimen (1.5%). Only moderate to severe SEP alterations occurring soon after carotid crossclamping justified shunt installation in 16% of the cases. SEP alterations after a drop in blood pressure were reversed merely by restoring blood pressure. The neurological outcome was uneventful in 94.2% of cases. Of the 12 patients who developed neurological sequellae, only one case presented transient sequellae after isolated CE without SEP changes while most cases either had undergone combined CE and CBP and/or VR (6 cases) or had presented SEP alterations of embolic origin (3 cases). We conclude that our system of qualitative rating of SEPs proved very sensitive to intraoperative hemodynamic disturbances or macroembolisms.
Electroencephalography and clinical neurophysiology, 1998
Neuroscience Letters, 2000
Damage to the primary visual cortex (V1) destroys the major source of anatomical input to extrast... more Damage to the primary visual cortex (V1) destroys the major source of anatomical input to extrastriate cortical areas (V2, V3, V4 and V5) and produces cortical blindness ± an absence of any sensation of light and colour ± in the visual ®eld contralateral to the side of the lesion. Neuroimaging studies, nevertheless, have recently demonstrated dorsal and ventral extrastriate activation for stationary stimuli presented to the blind visual ®eld in the absence of V1 activity in human subjects. To clarify the moment in time that visual information reaches extrastriate areas, by means of eventrelated potentials (ERPs) we tracked the temporal course of responses to complex visual stimuli (faces) presented in the blind ®eld of a hemianopic patient. Stimulation of the normal visual ®eld elicited a positive occipital de¯ection (P1) at 140 ms. A P1 response was also observed with stimulation of the blind ®eld, although slightly delayed (20 ms) and reduced. Its topography and timing demonstrate that early neural activity for stationary stimuli takes place within extrastriate regions despite V1 denervation. q
Neurophysiologie Clinique/Clinical Neurophysiology, 2005
To set up a reliable automated method of allowing to identify the ES1 and ES2 periods of exteroce... more To set up a reliable automated method of allowing to identify the ES1 and ES2 periods of exteroceptive suppression of the temporal muscle (EST), thereby reducing their intra- and inter-individual variability. Analyses were performed in 79 healthy subjects with strict inclusion and exclusion criteria. Each individual underwent two separate examinations 1 week apart. Activity of the left and right temporal muscles was recorded in response to unilateral stimulation of the left and right labial commissures. Wave forms were successively rectified, averaged, and filtered; the intersections of the resulting curve with values corresponding to 50%, 60%, 70%, 75%, and 80% of the control period (20 ms preanalysis time) were automatically determined. All subjects reached a 80% level of attenuation for ES2. The values of ES2 durations were normally distributed. The mean ES1 and ES2 durations didn't vary between the two recording session, and there was a good individual reproducibility from one session to the other. Though relatively high, the inter-individual variability was slightly lower in the second than in the first session. Computed analysis of EST may contribute to decrease inter- and intra-individual test variability. Letting patient habituate through a first recording session could increase test sensitivity, too. The obtained values for ES2 duration are normally distributed and well-reproducible at both the population and individual level. We suggest taking into account both ES2 duration and level of attenuation.
Neurophysiologie Clinique/Clinical Neurophysiology, 1999
Comparison between grand-average and individual analyses: an event-related potentials study.Purpo... more Comparison between grand-average and individual analyses: an event-related potentials study.Purpose —Event-related potentials (ERPs) studies in human subjects have shown inter-individual response variations, probably linked to anatomical and functional brain disparities. The present study was conducted to compare the results obtained by a standard grand-average method and a single subject analysis of VEPs to faces.Material and method —Fifty-eight channel ERPs (analysis time: 1,024 ms) were recorded in 13 normal volunteers during gender or familiarity judgements on unknown and known faces, as well as on a control task using meaningless patterns. Data were then submitted to individual and group averages.Results and conclusion —Three activities were identified by both procedures: a P1/N1 complex, a vertex positive potential (P2 or VPP) associated with a temporal negativity, and a N2 negativity. These peaks displayed a marked inter-individual topographical variability. Regarding the outcome of statistical analyses, a certain number of differences were found: on P1, in which individual analyses revealed a strong effect of experimental conditions, while the grand-average method did not; on VPP, in which grand-average analyses suggested an interaction between experimental conditions, face familiarity and cerebral lateralization, while individual analyses did not; and on N2, in which grand-average data showed a clear lateralization effect, while individual analyses did not. A P3 component (Pz, 250 ms) was also defined in grand-average data, but could not be clearly described in individual data. Statistical analyses on this P3 component were thus only performed on group data and revealed a right lateralization and an interaction between face familiarity and experimental conditions. These findings confirmed the existence of a marked topographical variability of ERPs to face and, therefore, question the validity of grand-average studies. Moreover, these results suggest a better efficiency of individual analyses for studying short and middle-latency peaks, while grand-averages appear to be better suited for studying late components.
Acta Neurochirurgica, 2005
Objective. To evaluate our microsurgical results in dealing with vestibular schwannomas (VS) grea... more Objective. To evaluate our microsurgical results in dealing with vestibular schwannomas (VS) greater than or equal to 30 mm when preservation of cranial nerve function was considered more important than total tumour removal.
Acta urologica Belgica
Electrophysiological techniques have significantly improved in the last decade. The authors prese... more Electrophysiological techniques have significantly improved in the last decade. The authors present a short list of the available current techniques.
Electroencephalography and clinical neurophysiology, 1997
This study examines how the recording of the lumbar and subcortical components of the posterior t... more This study examines how the recording of the lumbar and subcortical components of the posterior tibial nerve (PTN) SEPs may usefully replace that of cortical components in situations in which these components cannot be reliably obtained (infants, high concentrations of halogenated gasses). Lumbar, brain-stem, and cortical PTN SEPs were intraoperatively monitored in 7 patients undergoing repair of aortic coarctation under variable isoflurane concentration (up to 1.2%). Four patients were less than 1 year old. Two distinct activities were evidenced at the lumbar level in all of the patients: the dorsal root component (DRC) and the dorsal horn negativity (DHN). The equivalent of the adult P30 (lemniscal positivity; LP) was also present in all of the patients, whatever their age or the concentration of isoflurane. By contrast, the parietal activities were absent intraoperatively in the youngest patients. Spinal-cord ischemia consecutive to aortic cross-clamping gave rise to early DHN ch...
The Journal of Urology
To determine normal reference latencies pudendal cortical somatosensory evoked potentials were ev... more To determine normal reference latencies pudendal cortical somatosensory evoked potentials were evaluated in 20 healthy volunteers. The dorsal nerve of the penis or clitoris was stimulated electrically and the cortical response was recorded from the CZ-2 point (2 cm. behind the central vertex). Reproducible responses were obtained and reference values were established.
Electroencephalography and clinical neurophysiology. Supplement
Electroencephalography and clinical neurophysiology
Somatosensory evoked potentials (SEPs) to unilateral or bilateral posterior tibial nerve (PTN) st... more Somatosensory evoked potentials (SEPs) to unilateral or bilateral posterior tibial nerve (PTN) stimulation and to stimulation of the dorsal nerve (DN) of the penis/clitoris were recorded on 32 channels in 10 volunteers. SEPs to unilateral PTN stimulation consisted of the classic 'W' complex P38-N45-P56-N75 maximal on the ipsilateral central and parietal leads, and two negative waves, N33 and N37, maximal on the contralateral post- and prerolandic areas, respectively. A lemniscal P30 was also recorded. Bilateral PTN stimulation caused, by algebraic summation, the disappearance of both N33 and N37; the W complex was symmetrical and the amplitude of P30 increased. The SEPs to DN stimulation were also symmetrical, and N33 and N37 were absent. These features can be explained by the bilateral character of DN stimulation. They also differed from bilateral PTN SEPs in 3 respects; the absence of P30, the small amplitude and the weaker gradients of field distribution of the 'W'...
Electroencephalography and Clinical Neurophysiology, 1996
Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section, 1997
This paper presents the results of intraoperative median nerve SEP monitoring in 205 successive p... more This paper presents the results of intraoperative median nerve SEP monitoring in 205 successive patients undergoing isolated carotid endarterectomy (CE) (N = 172) or CE followed by coronary bypass (CBP) and/or vascular replacement (VR) (N = 33). The left and right median nerves were alternately stimulated and recordings performed on 4 channels: cervical, ipsi-and contralateral parietal, and frontal. SEPs were qualitatively rated in terms of mild, moderate, or severe ipsilateral, contralateral, or bilateral abnormalities. The SEP abnormalities were subdivided into 5 categories as a function of their relationships with intraoperative events: no alterations (67.3%), early or late SEP alterations after carotid cross-clamping (15.6%), SEP alterations after a drop in blood pressure (occurring outside of or within the cross-clamping period) (15.1%), SEP alterations of a most likely embolic origin (2.4%), SEP changes after head positioning (1%), and SEP changes after a modification of the anesthetic regimen (1.5%). Only moderate to severe SEP alterations occurring soon after carotid crossclamping justified shunt installation in 16% of the cases. SEP alterations after a drop in blood pressure were reversed merely by restoring blood pressure. The neurological outcome was uneventful in 94.2% of cases. Of the 12 patients who developed neurological sequellae, only one case presented transient sequellae after isolated CE without SEP changes while most cases either had undergone combined CE and CBP and/or VR (6 cases) or had presented SEP alterations of embolic origin (3 cases). We conclude that our system of qualitative rating of SEPs proved very sensitive to intraoperative hemodynamic disturbances or macroembolisms.
Electroencephalography and clinical neurophysiology, 1998
Neuroscience Letters, 2000
Damage to the primary visual cortex (V1) destroys the major source of anatomical input to extrast... more Damage to the primary visual cortex (V1) destroys the major source of anatomical input to extrastriate cortical areas (V2, V3, V4 and V5) and produces cortical blindness ± an absence of any sensation of light and colour ± in the visual ®eld contralateral to the side of the lesion. Neuroimaging studies, nevertheless, have recently demonstrated dorsal and ventral extrastriate activation for stationary stimuli presented to the blind visual ®eld in the absence of V1 activity in human subjects. To clarify the moment in time that visual information reaches extrastriate areas, by means of eventrelated potentials (ERPs) we tracked the temporal course of responses to complex visual stimuli (faces) presented in the blind ®eld of a hemianopic patient. Stimulation of the normal visual ®eld elicited a positive occipital de¯ection (P1) at 140 ms. A P1 response was also observed with stimulation of the blind ®eld, although slightly delayed (20 ms) and reduced. Its topography and timing demonstrate that early neural activity for stationary stimuli takes place within extrastriate regions despite V1 denervation. q
Neurophysiologie Clinique/Clinical Neurophysiology, 2005
To set up a reliable automated method of allowing to identify the ES1 and ES2 periods of exteroce... more To set up a reliable automated method of allowing to identify the ES1 and ES2 periods of exteroceptive suppression of the temporal muscle (EST), thereby reducing their intra- and inter-individual variability. Analyses were performed in 79 healthy subjects with strict inclusion and exclusion criteria. Each individual underwent two separate examinations 1 week apart. Activity of the left and right temporal muscles was recorded in response to unilateral stimulation of the left and right labial commissures. Wave forms were successively rectified, averaged, and filtered; the intersections of the resulting curve with values corresponding to 50%, 60%, 70%, 75%, and 80% of the control period (20 ms preanalysis time) were automatically determined. All subjects reached a 80% level of attenuation for ES2. The values of ES2 durations were normally distributed. The mean ES1 and ES2 durations didn't vary between the two recording session, and there was a good individual reproducibility from one session to the other. Though relatively high, the inter-individual variability was slightly lower in the second than in the first session. Computed analysis of EST may contribute to decrease inter- and intra-individual test variability. Letting patient habituate through a first recording session could increase test sensitivity, too. The obtained values for ES2 duration are normally distributed and well-reproducible at both the population and individual level. We suggest taking into account both ES2 duration and level of attenuation.
Neurophysiologie Clinique/Clinical Neurophysiology, 1999
Comparison between grand-average and individual analyses: an event-related potentials study.Purpo... more Comparison between grand-average and individual analyses: an event-related potentials study.Purpose —Event-related potentials (ERPs) studies in human subjects have shown inter-individual response variations, probably linked to anatomical and functional brain disparities. The present study was conducted to compare the results obtained by a standard grand-average method and a single subject analysis of VEPs to faces.Material and method —Fifty-eight channel ERPs (analysis time: 1,024 ms) were recorded in 13 normal volunteers during gender or familiarity judgements on unknown and known faces, as well as on a control task using meaningless patterns. Data were then submitted to individual and group averages.Results and conclusion —Three activities were identified by both procedures: a P1/N1 complex, a vertex positive potential (P2 or VPP) associated with a temporal negativity, and a N2 negativity. These peaks displayed a marked inter-individual topographical variability. Regarding the outcome of statistical analyses, a certain number of differences were found: on P1, in which individual analyses revealed a strong effect of experimental conditions, while the grand-average method did not; on VPP, in which grand-average analyses suggested an interaction between experimental conditions, face familiarity and cerebral lateralization, while individual analyses did not; and on N2, in which grand-average data showed a clear lateralization effect, while individual analyses did not. A P3 component (Pz, 250 ms) was also defined in grand-average data, but could not be clearly described in individual data. Statistical analyses on this P3 component were thus only performed on group data and revealed a right lateralization and an interaction between face familiarity and experimental conditions. These findings confirmed the existence of a marked topographical variability of ERPs to face and, therefore, question the validity of grand-average studies. Moreover, these results suggest a better efficiency of individual analyses for studying short and middle-latency peaks, while grand-averages appear to be better suited for studying late components.
Acta Neurochirurgica, 2005
Objective. To evaluate our microsurgical results in dealing with vestibular schwannomas (VS) grea... more Objective. To evaluate our microsurgical results in dealing with vestibular schwannomas (VS) greater than or equal to 30 mm when preservation of cranial nerve function was considered more important than total tumour removal.
Acta urologica Belgica
Electrophysiological techniques have significantly improved in the last decade. The authors prese... more Electrophysiological techniques have significantly improved in the last decade. The authors present a short list of the available current techniques.