Seizure localization using ictal phase-locked high gamma: A retrospective surgical outcome study.

OBJECTIVE: To determine whether resection of areas with evidence of intense, synchronized neural firing during seizures is an accurate indicator of postoperative outcome. METHODS: Channels meeting phase-locked high gamma (PLHG) criteria were identified retrospectively from intracranial EEG recordings (102 seizures, 46 implantations, 45 patients). Extent of removal of both the seizure onset zone (SOZ) and PLHG was correlated with seizure outcome, classified as good (Engel class I or II, n = 32) or poor (Engel class III or IV, n = 13). RESULTS: Patients with good outcomes had significantly greater proportions of both SOZ and the first 4 (early) PLHG sites resected. Improved outcome classification was noted with early PLHG, as measured by the area under the receiver operating characteristic curves (PLHG 0.79, SOZ 0.68) and by odds ratios for resections including at least 75% of sites identified by each measure (PLHG 9.7 [95% CI: 2.3-41.5], SOZ 5.3 [95% CI: 1.2-23.3]). Among patients with resection of at least 75% of the SOZ, 78% (n = 30) had good outcomes, increasing to 91% when the resection also included at least 75% of early PLHG sites (n = 22). CONCLUSIONS: This study demonstrates the localizing value of early PLHG, which is comparable to that provided by the SOZ. Incorporation of PLHG into the clinical evaluation may improve surgical efficacy and help to focus resections on the most critical areas.

A new neurogenic vestibular evoked potential (N6) recorded with the use of air-conducted sound.

INTRODUCTION: Neurogenic vestibular evoked potentials that are recorded from the scalp have so far been recorded in the form of N3 (click air-conducted), N5 (tone air-conducted), and P10 (bone-conducted stimulus) waveforms. The purpose of this study is to find other vestibular waveforms obtained with air-conducted sound. METHODS: The experiments were organized into 4 parts: 1) topographic scalp mapping; 2) determining the consistency in appearance of candidate vestibular waveforms; 3) further characteristics such as their relationship to vestibular evoked myogenic potentials, sensitivity to 5-kHz tone, and threshold of activation; and (D) recording of the new vestibular waveforms in a case of hearing loss. RESULTS: A montage was discovered, O2-P3 and O1-P4 with left and right ear stimulation respectively, that yielded a negative wave at 6 milliseconds after stimulus onset and was labeled N6. It is not a vestibular evoked myogenic potential, disappears with 5-kHz tone stimuli, has a high threshold of stimulation, and is present in a case of hearing loss. DISCUSSION: A new vestibular waveform is discovered that probably originates at or near the midbrain based on its latency. Together with the previously mentioned waves, lesions along the vestibular pathway can now be localized further.