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Biomedical subjects

M F Levesque

Publications and source records attributed to M F Levesque.

26 records · Page 2Linked to original sources
PubMed1990

Focal functional anatomy of dorsolateral frontocentral seizures.

We compared 6 patients with dorsolateral frontocentral seizures to 7 patients with temporal lobe seizures. We determined general seizure location by structural lesions in 7 patients, bilateral depth electrodes in 4, and EEG and semiology in 2. We then mapped seizure cortex and essential cortex using chronic ECoG arrays. Two ECoG patterns were similar in frontal and temporal seizures. Focal patterns were near lesions and resections. Regional patterns were distant from lesions but not associated with worse surgical outcome. "Dipolar" seizure patterns occurred in one-half of frontal patients with maps like somatosensory evoked responses, consistent with focal seizure anatomy and involvement of sensorimotor cortex. Dipole location estimates were near centers of seizure cortex determined by lesions, semiology, and outcome. Six temporal patients had focal excisions that gave significant seizure reduction in all. All frontocentral patients had focal excisions that significantly reduced seizures except in 1 patient with progressive disease. We conclude that dorsolateral frontocentral seizures have focal functional anatomy that can be predicted by ictal ECoG.

Adult↗
PubMed1990

Presurgical evaluation for partial epilepsy: relative contributions of chronic depth-electrode recordings versus FDG-PET and scalp-sphenoidal ictal EEG.

One hundred fifty-three patients with medically refractory partial epilepsy underwent chronic stereotactic depth-electrode EEG (SEEG) evaluations after being studied by positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) and scalp-sphenoidal EEG telemetry. We carried out retrospective standardized reviews of local cerebral metabolism and scalp-sphenoidal ictal onsets to determine when SEEG recordings revealed additional useful information. FDG-PET localization was misleading in only 3 patients with temporal lobe SEEG ictal onsets for whom extratemporal or contralateral hypometabolism could be attributed to obvious nonepileptic structural defects. Two patients with predominantly temporal hypometabolism may have had frontal epileptogenic regions, but ultimate localization remains uncertain. Scalp-sphenoidal ictal onsets were misleading in 5 patients. For 37 patients with congruent focal scalp-sphenoidal ictal onsets and temporal hypometabolic zones, SEEG recordings never demonstrated extratemporal or contralateral epileptogenic regions; however, 3 of these patients had nondiagnostic SEEG evaluations. The results of subsequent subdural grid recordings indicated that at least 1 of these patients may have been denied beneficial surgery as a result of an equivocal SEEG evaluation. Weighing risks and benefits, it is concluded that anterior temporal lobectomy is justified without chronic intracranial recording when specific criteria for focal scalp-sphenoidal ictal EEG onsets are met, localized hypometabolism predominantly involves the same temporal lobe, and no other conflicting information has been obtained from additional tests of focal functional deficit, structural imaging, or seizure semiology.

Adolescent↗
PubMed1988

The magnetic and electric fields agree with intracranial localizations of somatosensory cortex.

We measured the magnetoencephalogram (MEG), electroencephalogram (EEG), and electrocorticogram (ECoG) after stimulation of contralateral median nerve in four patients with partial epilepsy evaluated for surgery. Quantitative localization estimates from equivalent source modeling were compared with locations of central fissure in hand sensorimotor area determined by cortical stimulations, intraoperative photographs, and examination after excision in frontal lobe. We also measured MEG and EEG in nine control subjects. MEG and EEG localizations were within 2.5 cm of the estimated location of central fissure in all 13 subjects. In the three patients who had complete mapping of all three fields, the average distance of localizations from central fissure was approximately 4 mm in both MEG and EEG, 3 mm in ECoG, and 3 mm in combined MEG and EEG. MEG was simpler than EEG, which was simpler than ECoG. MEG resolved ambiguities in both EEG and ECoG. The combination of the three fields added information about the spatiotemporal activity of somatosensory cortex. Localization of central fissure was essential to surgical treatment.

Brain Mapping↗
PubMedDate not supplied

Human hand and lip sensorimotor cortex as studied on electrocorticography.

We investigated functional topography of human hand and lip sensorimotor cortex using somatosensory evoked potentials (SEPs) from chronically indwelling subdural grid electrodes (ECoG) in 3 epilepsy patients during stimulation of median nerve, ulnar nerve, and lower lip. We used dipole modeling to determine the cortical location of each peripheral sensory field. The cortical locations were in the postcentral gyrus and showed a clear somatotopic organization from medial superior to lateral inferior in the order: ulnar nerve, median nerve, and lip. The source localizations agreed with the results of cortical stimulations and anatomical features on intraoperative photographs. The cortical regions of median and ulnar nerve each could be modeled by sequential tangential and radial dipoles. The cortical region of lip was different and could be explained mostly by tangential dipoles. These findings suggest a difference in the cortical organization of human lip and hand sensory cortex and are consistent with a larger representation of lip in the posterior bank of central fissure in area 3b than on the gyral surface in area 1, similar to findings in macaque. Further studies in a larger population of patients with ECoG or normal subjects with scalp-EEG and MEG are warranted to test this hypothesis.

Brain Mapping↗
PubMedDate not supplied

Somatotopy of human hand somatosensory cortex as studied in scalp EEG.

We recorded somatosensory evoked potentials (SEPs) in scalp EEGs during stimulation of the median nerve, the ulnar nerve and the individual digits in 3 normal subjects and in 1 epilepsy patient. In this patient we also measured SEPs from chronically indwelling subdural grid electrodes during electrocorticography (ECoG). We applied dipole modelling technique to study the 3-dimensional intracerebral locations and time activities of the neuronal sources underlying stimulation of different peripheral receptive fields. The sources underlying median nerve SEPs were located an average of 10.8 mm lateral inferior to those underlying ulnar nerve SEPs. Digit SEP sources showed a somatotopic arrangement from lateral inferior to medial superior in the order thumb, index finger, middle finger, ring finger and little finger, with some overlap or reversal for adjacent digits. The average distance between thumb and little finger was 12.5 mm. Thumb, index finger and middle finger were clustered around median nerve cortical representation, whereas ring finger and little finger were arranged around ulnar nerve cortex. In the epilepsy patient, the source localizations obtained in scalp EEGs showed good agreement with those on ECoGs. We conclude that SEPs recorded in scalp EEGs can be used to study functional topography of human somatosensory cortex non-invasively.

Adult↗
PubMedDate not supplied

Interictal cerebral metabolism in partial epilepsies of neocortical origin.

We performed interictal [18F]fluorodeoxyglucose positron emission tomography (FDG PET) in 24 patients with partial epilepsy of neocortical origin. Two-thirds of patients had regions of hypometabolism. The zone of intracranially recorded electrographic ictal onset was always located in a region of hypometabolism, in those with hypometabolism. Hypometabolic regions in partial epilepsies of neocortical origin were usually associated with structural imaging abnormalities. Regional hypometabolism occasionally occurred without localizing ictal scalp EEG and cerebral magnetic resonance imaging findings, however. FDG PET may be useful in directing placement of intracranial electrodes for presurgical evaluation of refractory neocortical seizures.

Adolescent↗
PubMedDate not supplied

Temperature changes in nickel-chromium intracranial depth electrodes during MR scanning.

The authors sought to determine whether there are any heating effects of 1.5-T MR scanning upon nickel-chromium electrodes and to confirm the safety of scanning these electrodes after intracranial surgical implantation in epilepsy patients. Since there was no significant temperature increase of the electrodes tested in their experiments, the authors conclude that nickel-chromium electrodes implanted in the brain are thermally safe for MR scanning.

Brain↗