HEMISHERIC LANGUAGE DOMINANCE IN PATIENTS WITH FOCAL EPILEPSIES: DISTRIBUTED SOURCE VERSUS SINGLE DIPOLE MODEL FROM NEUROMAGNETIC FIELDS
Abstract number :
1.260
Submission category :
Year :
2004
Submission ID :
4288
Source :
www.aesnet.org
Presentation date :
12/2/2004 12:00:00 AM
Published date :
Dec 1, 2004, 06:00 AM
Authors :
1D. M. Foxe, 1S. Knake, 1K. Hara, 1S. Camposana, 1P. Grant, 2D. Schomer, 4E. B. Bromfield, 3B. Bourgeois, 1E. Halgren, and 1S. M. Stufflebeam
Previously, we described using magnetoencephalography (MEG) as a non-invasive tool for determination of hemispheric language dominance (HLD)using a single dipole model [1]. This study further investigated HLD with MEG in 24 right-handed pts with medically intractable focal epilepsies. We separately calculated the Laterality Index (LI) based on dipole counting and Dynamic Statistical Parametric Maps (dSPM) with a visual language paradigm. 24 pts aged 13-52 years were studied using 306-channel MEG and 70-channel EEG (Elekta-Neuromag). Some pts were included in a previous report [2]. Visual word stimuli were presented. Equivalent Current Dipoles (ECD) on a spherical head model were fitted using sequential single dipole fitting with a time range of 150ms[ndash]600ms and 1ms steps. Only dipoles with a goodness of fit (GOF) [gt]70% were displayed for analysis. The LI was calculated using for each pt using the formula: LI = (L-R)/(L+R).
Minimum norm estimates (MNE) and dSPM [3] were constrained to cortical surface, with loose orientation constraint and noise normalization. The LI was calculated using: LI=(L-R)/(L + R), where L [amp] R = area of activated cortex. ECD: 15/24 pts (62.5%) showed left HLD. Three pts showed right HLD (12.5%). 6 pts (25%) showed a Bilateral(LI= -0.1-+0.1) HLD. One pt with right HLD suffered from left HE and 2 suffered from right HE.
Using dSPM the results were comparable, but were highly dependent upon the thresholding used for the statistical analysis. 11/24 pts had the WADA test preformed 8 were left dominant result and 5 showed left HLD with MEG analysis.
Three of the Bilateral HLD pts had the WADA test preformed and the results were all left. One pt had a right WADA test result and the MEG was also Right HLD.
10/15 left HLD pts suffered from left hemisphere epilepsy (HE), five from right HE. 1/10 pts with Left HE and a Left LI with MEG showed an inconclusive WADA test result. ECD counting and dSPM current summation are promising methods in determination of HLD. The dSPM method requires the calculation of statistics with the use of a properly chosen statistical threshold.
LITERATURE
1. Foxe et al: Epilepsia 44 Suppl. 9:297(Abst. 2.354), 2003
2. Springer J et al: [italic]Brain[/italic] 1999;122:2033-46 3. Dale A.M et al: [italic]Neuron, [/italic]2000, 26: 55-67.[figure1] (Supported by MIND Institute)
