DIFFERENCES IN AUDITORY EVOKED FIELD AS A LATERALIZING FINDING IN TEMPORAL LOBE EPILEPSY - A PROSPECTIVE MEG STUDY
Abstract number :
1.139
Submission category :
Year :
2003
Submission ID :
4066
Source :
www.aesnet.org
Presentation date :
12/6/2003 12:00:00 AM
Published date :
Dec 1, 2003, 06:00 AM
Authors :
Keiko Hara, Susanne Knake, Hideaki Shiraishi, Valerie A. Carr, Deirdre M. Foxe, P. Ellen Grant, Eric Halgren, Steven M. Stufflebeam Martinos Center for Biomedical Imaging, MGH/Harvard Medical School, Charlestown, MA; Department of Pediatrics, Teine Keijin
Focal epilepsy may cause a dysfunction or reorganization of the adjacent eloquent cortex. Due to such reorganization, temporal lobe epilepsy (TLE) may have an effect on auditory response patterns. The influence of TLE on auditory evoked fields (AEF) has not been investigated yet. Here we report the use of MEG to evaluate with precise temporal resolution the influence of TLE on AEF components.
9 consecutive patients (all above 20 years of age, mean age 30) who were diagnosed with unilateral TLE were investigated between 3 March 2002 and 2 April 2003 at the MGH NMR-Center during pre-surgical evaluation. Six left TLE patients and 3 right TLE patients were analyzed. Five patients were excluded from our analyses: 3 whose diagnosis changed after our examination and 2 with prior operations for epilepsy. All patients were suffering from daily-monthly intractable seizures for a period ranging from 6 to 31 years.
MEG was collected with a 306-channel helmet-shaped system (Vectorview system; Neuromag Inc., Helsinki, Finland) with simultaneous 64-channel EEG.
Stimuli (1000Hz tones, 100ms duration) were presented to the ears alternatively at 60-75dB above hearing threshold, inter-stimulus intervals was varied between 0.8 and 1.2 second, and 70-161 trials were collected for each ear. After stimulation, each patient[rsquo]s averaged AEF and corresponding equivalent current dipole (ECD) was calculated by Neuromag software.
In all patients, the AEF showed interhemispheric differences between the hemispheres ipsi- and contralateral to the seizure focus. 1 of 9 patients showed disappearance of AEF on the ipsilateral hemisphere, but a clear AEF was present on the contralateral side. In other patients, Q value decreases and goodness of fit (GOF) increases were highly observed especially for the N100m component of the AEF in the ipsilatral hemisphere compared with the contralateral hemisphere.
In the N100m component in the contralateral hemisphere, 6 of 8 patients showed a Q value decrease (mean: 20.0(ipsi) vs. 26.3nAm(contra)), 6 of 8 patients showed a lower GOF (mean: 83.0 vs. 86.0 %). (See Table1).
Changing of the AEF could be observed in all patients suffering from TLE. These findings suggest that the function of the eloquent cortex might be disturbed by interictal activity. Interhemispheric differences of AEF might be used as a lateralizing sign in patients with TLE. [table1]
[Supported by: The MIND Institute]