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from periorbital electrodes. Glasgow Coma Score (GCS) was assessed within 4 days of coma and 3 days of SP3 recording. Awaking was defined as Glasgow Outcome Score (GOS) >3 before death or dis- charge. Thirty percent (3/10) had a well-defined SP3. Sixty-seven per- cent (2/3) with a SP3 awoke. One patient with a SP3 had no AP3. In patients with a SP3, GCS ranged from 4 to 7; GOS from 1 to 5. Further study of the SP3 in coma prognosis is indicated.

Supported by NIH GCRC-43 and Marion Merrill Dow.

E127: Relationship between P3 event related potentials and neurop- sychological variables over time in HIV+ patients - J. Mes- senheimer, *R. Lyles, *F. Seillier-Moiseiwitsch, J. Wilkins, K. Robertson, J. Kalkowski, C. Hall (*Department of Neurology and Biostatistics, School of Medicine, University of North Carolina at Chapel Hill, NC 27599-7025)

Several authors have documented an increase in latency of the auditory event related potential (P3) in HIV+ patients. Because these changes have been found in non-demented, asymptomatic subjects, there is a question about the relationship of these evoked potential measures and cognitive function. We examined the relationship, at repeated six month intervals, between the component latencies of the auditory P3 event related potential and subsets of neuropsychological tests selected for sensitivity to the known effects of HIV on the central nervous system. Because, over time, event related potential latencies and the neuropsychological measures are not likely related (due to learning effects seen in the initial test periods for the neuropsychologi- cal measures). we used a method which compared segmental areas of plots rather than raw data for this analysis. We found statistically sig- nificant correlations between increasing P3 latencies and decreasing function on tests of memory and speed of processing. Across a total of six visits (3 years) there was a clear tendency for the slopes of these regressions to become increasingly negative over time, which is consis- tent with an increasing rate of progression with advancing time.

E128: Cortical potential differences in mild traumatic brain injury for the AEP P300 component - *Martin R. Ford, **Robert D. Sidman, *M.A. Khalil, and **Lan Ke (*Austin Neurological Institute, Austin, TX 78757; **Department of Mathematics, University of Southwestern Louisiana, Lafayette, LA 70504)

An objective scoring system has been developed to quantify the de- gree of AEP and VEP abnormality in patients suffering from mild traumatic brain injury (mTB1). In this study the AEP P300 responses for 20 patients with scores in the abnormal range were compared to the responses in 20 age and gender equivalent controls. Group averaged scalp and simulated cortical surface potential maps were computed using both aligned and unaligned P300 peak latencies. T-score com- parisons between groups were then calculated using both the aligned and unaligned latencies. The analysis of scalp recordings showed an apparent single, posterior generator site, although significant P300 attenuation was present at all anterior sites. However, the analysis of simulated cortical potential maps showed apparent anterior and poste- rior generator sites, with significant attenuation at the anterior one. The anterior attenuation appeared much more focal (midline) in comparison to the scalp recordings. These findings suggest that the actual site of injury is more focal. and may be deeper, perhaps at subcortical midline structures, and are consistent with prior reports of injury at the brain stem level, or in the brain stem-frontal cortical arousal and modulation system.

E129: PVER testing to rapid random stimulation: concurrent half field stimulation - M. John Rowe III (Department of Neurol- ogy, Texas Tech University Health Sciences Center, Lubbock, TX 79430)

When multiple stimuli are presented concurrently, each with its

own random timing protocol, independent transient EPs can be re- corded to each separate stimulus without evidence for significant inter- action (Rowe and Varilone, 1994). During stimulation, continuous EEG activity is recorded along with stimulus triggers, numbered individually for each stimulus. Off line, the continuous EEG is epoched at each trigger. The epochs are then averaged separately for each trigger num- ber. Left and right half field transient PVEPs can be recorded at average reversal rates of up to 20/set for each field (40/set overall stimulus rate). Higher stimulus rates lower response amplitudes. The most effi- cient rates (giving the highest signal/noise ratios) are 6-lO/sec for each field. Response topography for 8/set stimulation for each half field (16/set stimulation over all) is equivalent to that previously described for 2/set alternating stimulation. 8/set stimulation is more efficient than 2/set stimulation, allowing complete half field testing individually of both eyes in under 5 min of stimulation. Responses to specific in- terstimulus intervals can be recorded, allowing recovery function test- ing to each stimulus independently of the other.

E130: PVER testing to rapid random stimulation: concurrent stimulation with multiple check sizes - M. John Rowe III (Department of Neurology, Texas Tech University Health Sci- ences Center, Lubbock, TX 79430)

When multiple stimuli are presented concurrently, each with its own random timing protocol, independent transient EPs can be re- corded to each separate stimulus, without evidence for significant inter- action (Rowe and Varilone, 1994). During stimulation, continuous EEG activity is recorded along with stimulus triggers, numbered individually for each stimulus. Off line, the continuous EEG is epoched at each trigger. The epochs are then averaged separately for each trigger num- ber. Full field check patterns were drawn with 2 or 3 different check sizes intermixed. Individual check size reversal was produced using separate random timers for each check size. Transient EPs were ob- tained to pattern reversal at average rate of 4-IUsec for each check size. In adults, the relative amplitudes and latencies of responses to large and small checks correlated with visual acuity. Responses were obtained at the same level of attention or arousal, eliminating these variables found in sequential testing. Preliminary findings suggest that this protocol can be used as a screening test of vision in sedated, sleeping infants and toddlers. The field of stimulation can be enlarged by viewing through a large triangular mirror viewbox. This insures that the passively opened eye will be stimulated no matter what direction the pupil is pointed.

FlOl: Vagus nerve stimulation for intractable generalized epilepsy - *Douglas Labar, **Brent Tarver and *Richard Fraser (*Comprehensive Epilepsy Center, New York Hospital- Cornell, New York, New York and **Cyberonics, Webster, Texas)

We carried out vagus nerve stimulation (VNS) in 8 patients with medication-resistant symptomatic generalized epilepsy. Median age was 29 years (range 14-44 years). We compared postoperative seizure rates with a l-month preoperative baseline. Antiepileptic drugs were held constant for 4 months postoperatively, and then were tapered as tolerated. Sufficient postoperative follow-up now is available on the first 5 patients (median follow-up 7 months, range 3.5-9 months); data from the other 3 patients is pending. Median baseline seizure rate in these 5 patients was 62/month. VNS reduced all seizures by a median of 50% (range 33-86%). Reductions in specific seizure types were: tonic seizures, 100, 50 and 44%; absence, 75, 33 and 33%; complex partial, 100%; and tonic-clonic, 86% (2 patients had multiple seizure types). We successfully discontinued phenytoin in 1 patient; in 2 oth- ers, seizures recurred when we reduced phenytoin or phenobarbital. Our findings suggest VNS may be an effective adjunctive treatment for medication-resistant generalized epilepsy. Dr. Tarver receives support from, is a consultant to and as the speakers bureau of Cyberonics, Inc.