Abstracts

Rationale: Limitations in the spatial resolution and frequency bandwidth of clinical intracranial EEG (IEEG) has motivated investigations using wide bandwidth recordings from more physiologically appropriate hybrid electrodes containing both microwires and clinical macroelectrodes. Here we investigate the spectral range of ictal IEEG activity recorded from hybrid depth electrodes implanted in the mesial temporal lobe. Methods: Five patients undergoing evaluation for intractable temporal lobe epilepsy gave informed consent for implantation with hybrid depth electrodes containing clinical macroelectrodes and microwire arrays. Multiple seizures were recorded from these 5 patients using wide bandwidth intracranial EEG (IEEG: DC - 1000 Hz). A custom software tool for calculating and visualizing statistical spatial maps of spectral power was developed. The tool was initially tested in two patients, and average spectral power across multiple high frequency bands (gamma, ripple, and fast ripple) at seizure onset was compared to baseline interictal records. Results: Maps of high frequency energy recorded from microwire electrodes show significant increases in the ripple frequency range (80 - 250 Hz) at seizure onset within the seizure onset zone. Interestingly, there are intermittent periods within the baseline record also showing significant increases in high frequency energy. Recordings from microwire electrodes within the seizure onset zone demonstrated more significant increases in the high frequency energy compared to clinical macroelectrodes. Conclusions: The limitations in spatiotemporal resolution of clinical IEEG are addressed here with wide bandwidth recordings from hybrid temporal depth electrodes. Analysis from two initial patients demonstrates a significant increase in HFO energy in the ripple frequency band at seizure onset. This finding was most pronounced with microwire electrodes in the ripple frequency range.