Related Experiment Video
Updated: Aug 18, 2026
Electromagnetic Source Imaging in Presurgical Evaluation of Children with Drug-Resistant Epilepsy
Published on: September 20, 2024
Source analysis of interictal spikes in polymicrogyria: loss of relevant cortical fissures requires simultaneous EEG
Thomas Bast1, Georgia Ramantani, Tobias Boppel
1Department of Pediatric Neurology, University Hospital, Im Neuenheimer Feld 150, D-69120 Heidelberg, Germany. Thomas_Bast@med.uni-heidelberg.de
Purpose:
Multiple source analysis of interictal EEG and MEG spikes was used to identify irritative zones in polymicrogyria (PMG). Spike onset times and source localization were compared between both modalities. PMG is characterized by a marked loss of deep cortical fissures. Hence, differences between EEG and MEG were expected since MEG signals are predominantly generated from tangentially orientated neurons in fissures.
Patients:
We studied 7 children and young adults (age 7.5 to 19 years) with localization-related epilepsy and unilateral polymicrogyria (PMG) as defined from anatomical MRI.
Methods:
122-channel whole-head MEG and 32-channel EEG were recorded simultaneously for 25 to 40 min. Using the BESA program, interictal spikes were identified visually and used as templates to search for similar spatio-temporal spike patterns throughout the recording. Detected similar spikes (r > 0.85) were averaged, high-pass filtered (5 Hz) to enhance spike onset, and subjected to multiple spatio-temporal source analysis. Source localization was visualized by superposition on T1-weighted MRI and compared to the lesion.
Results:
Nine spike types were identified in seven patients (2 types in 2 patients). Eight out of nine EEG sources and seven MEG sources modeling spike onset were localized within the visible lesion. EEG spike onset preceded MEG significantly in two spike types by 19 and 25 ms. This was related to radial onset activity in EEG while MEG localized propagated activity. In one case, the earliest MEG spike activity was localized to the normal hemisphere while the preceding radial EEG onset activity was localized within the lesion. Distances between EEG and MEG onset sources varied markedly between 9 and 51 mm in the eight spike types with concordant lateralization.
Conclusion:
Interictal irritative zones were localized within the lesion in PMG comparable to other malformations, e.g., FCD. Discrepancies in MEG and EEG were related to the lack of deep fissures in PMG. In two cases, MEG was blind to the onset of radial interictal spike activity and localized propagated spike activity. In two other cases, MEG localized to the more peripheral parts of the irritative zone. Simultaneous EEG recordings with MEG and multiple source analysis are required to avoid problems of MEG interpretation.
Insights
Comparing electroencephalography (EEG) and magnetoencephalography (MEG) for epilepsy in polymicrogyria (PMG), this study found EEG better detects early spike activity. Simultaneous recordings are crucial for accurate irritative zone localization in PMG.
Area of Science:
- Neuroscience
- Medical Imaging
- Epileptology
Background:
- Polymicrogyria (PMG) is a cortical malformation characterized by reduced fissures.
- This structural difference may affect the ability of electroencephalography (EEG) and magnetoencephalography (MEG) to localize epilepsy sources.
- Understanding these differences is crucial for accurate diagnosis and treatment of epilepsy in PMG patients.
Purpose of the Study:
- To compare the ability of simultaneous EEG and MEG, using multiple source analysis, to identify irritative zones in patients with polymicrogyria (PMG).
- To investigate discrepancies in spike onset times and source localization between EEG and MEG in PMG.
- To determine the clinical implications of these modality differences for epilepsy surgery planning.
Main Methods:
- Simultaneous 122-channel MEG and 32-channel EEG recordings were obtained from 7 patients with PMG and epilepsy.
- Interictal spikes were identified, averaged, and subjected to multiple spatio-temporal source analysis using BESA software.
- Source localizations were compared between EEG and MEG and correlated with anatomical MRI findings.
Main Results:
- Eight out of nine EEG sources and seven MEG sources were localized within the PMG lesion.
- EEG spike onset preceded MEG in two cases by 19-25 ms, attributed to radial vs. tangential activity.
- Significant discrepancies in source localization between EEG and MEG were observed, with MEG sometimes localizing to peripheral or normal hemisphere areas.
Conclusions:
- Interictal irritative zones in PMG can be localized to the lesion, similar to other malformations like focal cortical dysplasia (FCD).
- Discrepancies between EEG and MEG in PMG are linked to the malformation's lack of deep cortical fissures.
- Simultaneous EEG and MEG with multiple source analysis are essential for accurate interpretation and to avoid mislocalization of epileptic activity in PMG.
More Related Videos
10:22Interictal High Frequency Oscillations Detected with Simultaneous Magnetoencephalography and Electroencephalography as Biomarker of Pediatric Epilepsy
Published on: December 6, 2016
09:00Investigating the Function of Deep Cortical and Subcortical Structures Using Stereotactic Electroencephalography: Lessons from the Anterior Cingulate Cortex
Published on: April 15, 2015