INTERICTAL SPIKE DIPOLES WITH HIGHER AMPLITUDES HAVE LOWER RESIDUALS
Abstract number :
2.225
Submission category :
Year :
2003
Submission ID :
3851
Source :
www.aesnet.org
Presentation date :
12/6/2003 12:00:00 AM
Published date :
Dec 1, 2003, 06:00 AM
Authors :
Warren S. Merrifield, Dinah Thyerlei, Matt L. Riggs, Nancy P. Lopez, Adam N. Mamelak, William W. Sutherling MEG Laboratory, Huntington Medical Research Institutes, Pasadena, CA; Epilepsy and Brain Mapping Program, Pasadena, CA; Department of Psychology, L
Understanding the characteristics of MEG interictal spike dipoles in the epileptic population enables clinicians to better diagnose patients and improve the likelihood of successful intervention. One method of determining the properties of MEG interictal spike dipoles is to utilize statistics to analyze potential correlations and differences. Through a retrospective analysis, we were able to identify two statistical parameters, amplitude and residual, that appear to be highly related. We analyzed spike dipoles to determine the correlation coefficient between amplitude and residual.
A total of 24 patients were studied (9 female, 15 male; mean age 29.4 years). All patients had medically intractable, socially disabling partial epilepsy and underwent evaluation for surgery.
Individual interictal spikes were modeled. Single equivalent current dipoles were calculated using the model of a moving current dipole in a homogeneous sphere (Stok, 1986, 1987) with the downhill simplex optimization algorithm of Nelder and Meade (Press et al, 1992) to obtain the least squares error between the data and the dipole model.
For each patient, the mean amplitude and mean residual were calculated for the single spike dipoles. Then the correlation coefficient was calculated between mean amplitude and mean residual.
There was a significant negative correlation between dipole amplitude and dipole residual (r=-0.67, p=.00002). Interictal spike dipoles with higher amplitudes had lower residuals. Amplitude had a mean of 379.84 nA with a range from 136.22 nA to 933.82 nA. Residual had a mean of 11.15% with a range from 6.3% to 17.03%.
Interictal spike dipoles with higher amplitudes had lower residuals or better goodness-of-fit values. One would expect this result given that a spike with higher amplitude would have a larger SNR. Since the single dipole model is dominated by the signal, a larger SNR would allow the dipole to fit more of the data, resulting in a lower residual. This analysis assigns a Pearson correlation coefficient and p value to amplitude versus residual in spikes. We are investigating if different brain regions yield different correlation coefficients, which may lead to a better understanding of the epileptic population and the properties of the human brain.[figure1]
[Supported by: NIH grants NINDS RO1-NS20806, NCRR S10RR13276, NIHM MH53213, and the Norris, Zeilstra and Bacon Foundations.]
