Abstracts

Rationale: In the hippocampus, high frequency oscillations (HFOs) of 80-200 Hz play an important role in memory consolidation, whereas oscillations with higher spectral frequencies in the 200-500 Hz range may be biomarkers of epileptogenicity (pathological HFOs). It is not yet clear, however, whether standard macrocontacts or embedded microwires have a similar ability to detect HFOs in different distinct frequency bands. Methods: We addressed this question by examining wideband intrahippocampal ECoG recordings from readily available clinical depth electrodes containing embedded micro wires interspersed between macrocontacts, implanted in patients undergoing chronic intracranial monitoring for seizure mapping. HFOs were identified using a wavelet time-frequency decomposition-based automatic detection algorithm and subsequent visual confirmation. Results: As expected, the total number of the oscillations recorded by either contact type was enhanced in seizure onset-related brain areas compared to other areas. The number of HFOs and pHFOs recorded by any single microcontact was greater than those recorded by adjacent macrocontacts. pHFOs were detected by microcontacts at a significantly higher rate than by macrocontacts. The difference between the duration of HFOs and pHFOs recorded by either of the contact types was not significant. Conclusions: These data demonstrate that microcontacts are more effective than macrocontacts for detecting HFOs and especially pHFOs, suggesting that choice of depth-electrode type may determine the resolution with which pHFOs can be characterized and utilized as electrophysiological biomarkers. These data also inform hypotheses regarding the spatial extent of the neural substrate generating pHFOs.