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Published on: August 15, 2025
Altered neural synchronization to pure tone stimulation in patients with mesial temporal lobe epilepsy: An MEG study
Teppei Matsubara1, Katsuya Ogata1, Naruhito Hironaga1
1Department of Clinical Neurophysiology, Neurological Institute, Faculty of Medicine, Graduate School of Medical Sciences, Kyushu University, Japan.
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.
Insights
This study shows that altered neural synchronization in auditory evoked magnetic fields (AEFs) can help diagnose and lateralize epileptic foci in mesial temporal lobe epilepsy (mTLE) patients. Monaural AEFs reveal functional deterioration and aid in understanding mTLE pathophysiology.
Area of Science:
- Neuroscience
- Epilepsy Research
- Auditory Neuroscience
Background:
- Mesial temporal lobe epilepsy (mTLE) significantly impacts auditory processing.
- Previous studies on monaural auditory evoked magnetic fields (AEFs) in mTLE were limited by small sample size and focus on M100 responses.
- Elucidating the lateralization of epileptic foci is crucial for effective treatment.
Purpose of the Study:
- To investigate if neural synchronization, measured by AEFs, provides diagnostic information for epileptic foci lateralization in unilateral mTLE.
- To expand upon previous findings with a larger patient cohort.
- To assess the utility of monaural pure tone stimulation in understanding mTLE pathophysiology.
Main Methods:
- Recruited 39 patients with unilateral mTLE (25 left, 14 right) and 32 healthy controls (HCs).
- Administered monaural 500-Hz tone burst stimuli and analyzed AEFs, focusing on M100 responses and neural synchronization (PLF, PLV) in auditory cortices (ACs).
- Utilized linear discriminant analysis for diagnosis and lateralization of epileptic foci.
Main Results:
- Right mTLE patients showed reduced M100 amplitude and decreased alpha-band PLF compared to left mTLE and HCs.
- Right hemispheric auditory cortex (AC) predominance was absent in right mTLE patients.
- Reduced functional connectivity (PLV) between bilateral ACs was observed in both left and right mTLE patients compared to HCs.
- Diagnosis and lateralization accuracy ranged from 80% to 90%.
Conclusions:
- Auditory cortex dysfunction is more pronounced in right mTLE patients.
- Monaural AEFs are valuable tools for revealing mTLE pathophysiology.
- Altered neural synchronization patterns offer significant insights into functional deterioration in unilateral mTLE.
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