Authors :
Presenting Author: Sakar Rijal, MSc. – University Of Texas at Arlington
Calandra Jones, MS – Research Assistant, Neuroscience Research, Jane and John Justin Institute for Mind Health Neurosciences Center; Sabrina Shandley, Ph.D – Lab Manager, Neuroscience Research, Jane and John Justin Institute for Mind Health Neurosciences Center; M. Scott Perry, MD – Neuroscience Research – Jane and John Justin Institute for Mind Health Neurosciences Center; Christos Papadelis, Ph.D – Director, Neuroscience Research, Jane and John Justin Institute for Mind Health Neurosciences Center
Rationale:
High-frequency oscillations (HFOs) have emerged as promising electrophysiological biomarkers of epileptogenic tissue. Yet, a significant barrier in translating HFOs as a reliable biomarker into clinical practice is inherent difficulties distinguishing between pathological HFOs from high-frequency power associated with increased neuronal firing (i.e., physiological HFOs). Differentiating physiological from pathological HFOs is challenging due to overlapping properties in frequency, morphology, and spatial distribution. Our novel study examines induced (ongoing brain activity elicited by the processing of visual stimuli) and evoked (direct reflection of brain activity to visual stimulus) responses of cortical rhythmic activity (CRA) to differentiate between physiological and pathological HFOs in children with epilepsy and healthy controls. We hypothesize reduced ripple power in epilepsy patients' brain responses to visual stimuli compared to controls. Identifying consistent differences in CRA responses establishes markers for recognizing and differentiating pathological HFOs in clinical settings.
Methods:
We recruited nine children with epilepsy (mean age: 7 years ± 5.22; 4 females) and 22 healthy controls (mean age: 9 years ± 2.79; 8 females). Participants had simultaneous HD-EEG and MEG recordings with child-friendly visual stimuli (cartoons overlaid on flashing checkerboards; 340 trials) (Figure 1A). The data were filtered (DC offset, 4th order band-pass Butterworth filter: 1-100 Hz, 60 Hz notch filter) and inspected for artifacts. Time windows from -200 to 500 ms post-stimulus were averaged across trials. (Figure 1B and C). Cortical activity in the primary visual cortex (V1) was localized using dynamic Statistical Parametric Mapping (dSPM), and virtual sensors were reconstructed at V1 (Figure 1D). Time-frequency (TF) analysis maps estimated evoked and induced activity using reconstructed virtual sensors (Figure 1E). Statistical analysis (permutation t-test) compared TF maps between children with epilepsy and controls (corrected for multiple comparisons; significance at p=0.05).
Results:
Statistical analysis of evoked and induced responses, measured by EEG, revealed suppressed relative power in individuals with epilepsy compared to controls (at ~100 ms after stimulus onset) in beta, gamma, and low-ripples bands [evoked: beta: 250% ± 50 vs. 550% ± 37; p< 0.05; induced: high gamma (30-80 Hz) and low-ripples (80-100 Hz): 660% ± 70 vs. 1168% ± 85; p< 0.05) (Figure 2).