Epileptic scalp ripples are associated with corticothalamic BOLD changes
Firas Fahoum1, Federico Melani, Luciana Andrade-Valença
1Montreal Neurological Institute, McGill University, Montréal, Québec, Canada.
Epilepsia
|August 30, 2014
Summary
High-rate epileptic ripples, not gamma oscillations, detected via EEG-fMRI, indicate greater brain activity and thalamic involvement in focal epilepsy patients. This suggests a more active pathological network.
Area of Science:
- Neuroscience
- Epileptology
- Medical Imaging
Background:
- Interictal high-frequency oscillations (HFOs) in the 40-200 Hz range are biomarkers for focal epilepsy.
- HFOs, including gamma (40-80 Hz) and ripples (80-200 Hz), often co-occur with interictal epileptiform discharges (IEDs).
- The precise brain regions generating HFOs remain largely unknown.
Purpose of the Study:
- To investigate the brain regions involved in HFO generation using combined EEG-fMRI.
- To differentiate the BOLD signal characteristics associated with gamma and ripple HFOs.
- To explore the relationship between HFO rates and brain metabolic activity.
Main Methods:
- Combined EEG-fMRI was performed on 22 focal epilepsy patients.
- Patients were grouped based on high versus low co-occurrence of gamma or ripples with IEDs.
- Blood oxygenation level-dependent (BOLD) signal changes were analyzed in relation to HFOs.
Main Results:
- No significant BOLD changes distinguished high versus low gamma groups.
- High ripple (HR) patients showed larger IED-concordant BOLD clusters compared to low ripple (LR) patients.
- HR patients exhibited significantly more thalamic BOLD changes (activation/deactivation) than LR patients, lateralized to the cortical ripple side.
Conclusions:
- Frequent epileptic ripples, unlike gamma oscillations, are linked to increased cortical metabolic response and thalamic involvement in focal epilepsy.
- Thalamic BOLD changes lateralize with cortical ripples, suggesting a connected network.
- A high rate of epileptic ripples may indicate a more active pathological cortico-thalamocortical network.
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