Cerebral Cortex Advance Access originally published online on January 4, 2007
Cerebral Cortex 2007 17(11):2516-2525; doi:10.1093/cercor/bhl157
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Plastic Phase-Locking and Magnetic Mismatch Response to Auditory Deviants in Temporal Lobe Epilepsy
1 Institute of Physiology, 2 Department of Neurology, 3 Institute of Clinical Medicine, 4 Institute of Brain Science, 5 School of Medicine, National Yang-Ming University, Taipei, Taiwan, 6 Department of Medical Research and Education, 7 Neurological Institute, Taipei Veterans General Hospital, Taipei, Taiwan
Address correspondence to Dr Yung-Yang Lin, Institute of Physiology, National Yang-Ming University, No. 155, Sec. 2, Linong St., Beitou District, Taipei City 112, Taiwan. Email: yylin{at}vghtpe.gov.tw.
The magnetic equivalent (MMNm) of mismatch negativity may reflect auditory discrimination and sensory memory. To study whether temporal lobe epilepsy (TLE) affects automatic central auditory-change processing, we recorded magnetoencephalographic (MEG) responses to standard and duration-deviant sounds in 12 TLE patients and 12 age-matched controls, and repeated MEG measurement in 8 patients 6–30 months following epilepsy surgery and in 6 controls 3–8 months after their first measurement. We compared the MMNm between patients and controls, and also evaluated intertrial phase coherences as indexed by phase-locking factors (PLF) using wavelet-based analyses. We observed longer MMNm latencies for patients than for controls. Dipole modeling and minimum-current estimates together showed bi-frontotemporal sources for MMNm. The phase locking across trials was dominant at the 4- to 14-Hz band, and the main difference in PLF between deviant- and standard-evoked responses occurred in the time frame of 150–250 ms after stimulus onset. Notably, in the 5 patients who became seizure free after removal of right temporal epileptic focus, the phase-locking phenomena resulting from deviant stimuli were enhanced, and even more distributed in the frontotemporal regions. We conclude that mesial TLE might affect auditory-change detection, and a successful surgery causes a possible plastic change in phase locking of deviant-evoked signals.
Key Words: auditory MMNm magnetoencephalography neural plasticity phase-locking temporal lobe epilepsy