Altered neural synchronization to pure tone stimulation in patients with mesial temporal lobe epilepsy: An MEG study.

OBJECTIVE: Our previous study of monaural auditory evoked magnetic fields (AEFs) demonstrated that hippocampal sclerosis significantly modulated auditory processing in patients with mesial temporal lobe epilepsy (mTLE). However, the small sample size (n = 17) and focus on the M100 response were insufficient to elucidate the lateralization of the epileptic focus. Therefore, we increased the number of patients with mTLE (n = 39) to examine whether neural synchronization induced by monaural pure tone stimulation provides useful diagnostic information about epileptic foci in patients with unilateral mTLE. METHODS: Twenty-five patients with left mTLE, 14 patients with right mTLE, and 32 healthy controls (HCs) were recruited. Auditory stimuli of 500-Hz tone burst were monaurally presented to subjects. The AEF data were analyzed with source estimation of M100 responses in bilateral auditory cortices (ACs). Neural synchronization within ACs and between ACs was evaluated with phase-locking factor (PLF) and phase-locking value (PLV), respectively. Linear discriminant analysis was performed for diagnosis and lateralization of epileptic focus. RESULTS: The M100 amplitude revealed that patients with right mTLE exhibited smaller M100 amplitude than patients with left mTLE and HCs. Interestingly, PLF was able to differentiate the groups with mTLE, with decreased PLFs in the alpha band observed in patients with right mTLE compared with those (PLFs) in patients with left mTLE. Right hemispheric predominance was confirmed in both HCs and patients with left mTLE while patients with right mTLE showed a lack of right hemispheric predominance. Functional connectivity between bilateral ACs (PLV) was reduced in both patients with right and left mTLE compared with that of HCs. The accuracy of diagnosis and lateralization was 80%-90%. CONCLUSION: Auditory cortex subnormal function was more pronounced in patients with right mTLE compared with that in patients with left mTLE as well as HCs. Monaural AEFs can be used to reveal the pathophysiology of mTLE. Overall, our results indicate that altered neural synchronization may provide useful information about possible functional deterioration in patients with unilateral mTLE.

The hemispheric lateralization of the auditory cortex after being stimulated by pure tone: a 1H-MRS study / 中华行为医学与脑科学杂志

Objective To explore the asymmetry of metabolic products of the auditory cortex in normal human brain after being stimulated by the pure tone with the proton magnetic resonance spectroscopy(1 H-MRS). Methods Twelve healthy volunteers, including 7 males and 5 females, were performed MRS tests before and after the stimulation of the pure tone of 90 dB in intensity and 1000 Hz in frequency. The the metabolites peak of the N-acetylaspartate (NAA) ,creatine(Cr) ,choline( Cho) , glutamine/glutamate ( Glx) and GABA in auditory cortex were investigated, The content of metabolic products were conducted with half-quantitative analysis. The differences of the NAA/( Cho + Cr) ,Glx/Cr and GABA/ Cr ratios before and after pure tone stimulation in the bilateral auditory cortex were analyzed. The difference of distribution of the metabolic products between the left and right auditory cortex was also analyzed to explore the asymmetry of the auditory cortex. Results The NAA/( Cho + Cr) and GABA/Cr ratios increased,the Glx/Cr ratio decreased in the left auditory cortex after being stimulated by the pure tone. There were significant differences in the NAA/( Cho + Cr) , Glx/Cr and GABA/Cr ratios before and after pure tone stimulation (P0.05). There were statistically significant differences in the Glx/Cr ratio of the auditory cortex between two sides after being stimulated by the pure tone. Conclusion The metabolic lateralization exists in auditory cortex of normal human brain after being stimulated by the pure tone, which may be the bases of the functional asymmetry.