Magnetic evoked fields from the somatosensory cortex of juvenile swine after local kynurenic acid injection

Society Proceedings /Electroencephalography 13. Auditory magnetic fields in normal children. - M.L. Reite, R. Neumann, P.D. Teale, J.L. Sheeder and J. Wang (Neuromagnetism Laboratory, Dept. of Psychiatry, University of Colorado Health Sciences Center, Denver, CO) This study examines auditory magnetic evoked field (EF) component morphology in children aged 7-9 years. We have recorded 12 children to date, with data from both hemispheres in 4, using a 7-channel neuromagnetometer and averaging EFs to auditory tone pip stimuli. In the children with bilateral recordings, the magnetic equivalent of the adult P50 (MEG M50) appears to occur at latencies up to 90 msec, showing both age and hemispheric differences. An adult Ml00 component (magnetic analog of the Nl) is not obvious in this age range; a similar polarity component may be seen at latencies of about 200 msec, generally not well fit by a simple dipole. A later (275-350 msec latency) component is of higher amplitude, matching the adult M2 polarity. Our findings support the following: (1) auditory EF components in this age range children may occur with substantially longer latencies than in adults; (2) left and right hemispheres mature independently with respect to these components; (3) there may be sex/hemisphere interactions in component maturation; (4) component maturation may reflect other aspects of psychosocial maturation; (5) source geometry may be better modeled by a relatively large distributed source than by a simple dipole. Supported by a grant from the Developmental Psychobiology Research Group, Dept. of Psychiatry, UCHSC, and by USPHS Grants MH47476 and MH44212, and RSA MH46335. cortex of juve74. Magnetic evoked fields from the somatosensory nile swine after local kynurenic acid injection. - M.G. Lee, N. Papuashvili, C. Xu and Y.C. Okada (Magnetophysiology Lab., MEG Center (lOl), V.A. Medical Center, Albuquerque, NM, and Departments of Neurology and Physiology, University of New Mexico School of Medicine, Albuquerque, NM) Somatosensory magnetic evoked fields (SEFS) from the cortex of juvenile swine were measured in order to determine the role of neurotransmission for the generation of magnetic evoked fields. The animal was prepared with tracheal intubation and femoral vein catheterization under intramuscular ketamine/xylazine anesthesia. The anesthesia was maintained by intravenous ketamine/xylazine infusion during magnetic field recordings. Electrical stimulation was applied to the snout by bipolar electrode. Using @QUID magnetometer, SEFs were recorded on a plan l-3 mm above the somatosensory cortex contralateral to the site of stimulation. Ringer solution kynurenic acid (2.5 ~1, 6.5 mM) was injected into the active magnetic source estimated by the spatial pattern of the early component of SEFs measured over a 24 X 32 mm* field plane. Then the changes of SEFs were determined at 5, 10, 20, 30, 60, 120 min after the injection. The early component of SEFs was abolished immediately after kynurenic acid injection but the later components were less affected. The response in amplitude and spatial pattern recovered almost fully 20 min after the injection. The control Ringer solution injection did not alter the SEFs. 75. Presurgical localization of sensorimotor cortex by magnetoencephalography: intraoperative validation. - J.D. Lewine, N.G. Baldwin, J.A. Sanders, J. Anson, A. Halliday, J. Shih and W. Orrison, Jr. (Magnetic Source Imaging Facility (114M), New Mexico Regional Federal Medical Center, and University of New Mexico School of Medicine, Albuquerque, NM) Magnetoencephalography (MEG) was used to localize the sensorimotor area of 36 neurosurgical patients with fronto-parietal neoplasms/vascular malformations. Data were obtained in response to electrical stimulation of the median nerve, tactile stimulation of digits of the hand, and/or movement of the thumb. Dipole modeling was used to characterize the

and clinical Neurophysiology 95 (1995) 15P-41P

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primary cortical component of the evoked magnetic signal. MEG data were integrated with magnetic resonance data to create a series of images showing the spatial relationship between the lesion and sensorimotor cortex. In all cases there was agreement between preoperative MS1 identifications of primary motor and somatosensory gyri and intraoperative identifications achieved via corticographic monitoring of somatosensory evoked potentials and/or direct motor cortex stimulation. For 8 of the patients, the position of the corticography grid was determined stereotactically. Following a correction for source depth, MS1 and intraoperative localizations agreed to within 0.5 cm. It is noteworthy that for 6 of 8 patients that were thought, on the basis of their lesion’s position, to be inoperable (because of the lesion’s proximity to the presumed location of motor cortex), MS1 demonstrated sufficient displacement of the motor cortex so that surgical resection was possible without compromise of sensorimotor areas. A large array biomagnetometer gies, Inc.

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Technolo-

76. Interrater reliability on multiple sleep latency tests. - S. Benbadis, H. Warnes, M. Perry, D. Dinner and M. Piedmonte (Cleveland Clinic Foundation, Cleveland, OH)

The purpose of this study was to evaluate interrater reliability in the interpretation of the multiple sleep latency test (MSLT). We prospectively analyzed MSLTs performed on 21 patients with excessive daytime sleepiness. MSLTs were recorded on Grass model 78 polygraphs with EEG, electro-oculogram, and chin EMG. Each test was performed simultaneously at paper speeds of 10 and 30 mm/set, and was scored blindly by 3 readers using standard criteria. A nested covariance model was used to assess the interrater reliability and the intra-subject correlation for both sleep latency and presence of REM sleep. At the standard paper speed of 10 mm/set, the interrater reliability for sleep latency was 0.914, and for REM (present or absent) was 0.817. At a paper speed of 30 mm/set, the interrater reliability for sleep latency was 0.787, and for REM (present or absent) was 0.955. Finally, interrater reliability for sleep latency was somewhat higher at a paper speed of 10 versus 30 (0.914 vs. 0.787), but this was not statistically significant (P = 0.145). The interpretation of MSLTs shows high consistency between different readers. This interrater reliability is comparable between the 2 paper speeds tested, but somewhat higher at a paper speed of 10 mm/set.

77. Failure of tracheostomy treatment of the obstructive sleep apnea syndrome. - S.P. Duntley, J.W. Miller and M.L. Uhles (Department of Neurology, Washington University School of Medicine, St. Louis, MO)

Tracheostomy is often regarded as a definitive treatment for obstructive sleep apnea. We describe polysomnography on 3 patients showing persistent obstructive apnea despite tracheostomy. Patient no. 1 is a 52-year-old male with 33.4 obstructive hypopneas and apneas per hour of sleep. Technician observation and a review of the videotape recordings showed his chin to repetitively occlude the opening of his trdcheostomy. Patient no. 2 is a 74-year-old female who averaged 44 obstructive events per hour of sleep. Careful observation revealed the external opening of the tracheostomy to he unobstructed hut the tube was partially blocked by viscous secretions. Patient no. 3 is a 53-year-old male who averaged 50 obstructive hypopneas per hour of sleep. His tracheostomy opening was unobstructed with no visible blockage of the proximal lumen of the tube. Obstructive apneas and hypopneas can persist despite tracheostomy and may be caused by obstruction of the tracheostomy tube opening, blockage of the tube itself, or obstruction at the internal tip of the tube or the tracheal lumen. Patients with OSA treated with tracheostomy should