P308 Cross-frequency coupling in the human epileptic hippocampus

Abstract

Background Cross-frequency coupling (CFC) of multiple neuronal rhythms could be a general mechanism used by the brain to perform network level dynamical computations underlying voluntary behaviour. It is known, in the hippocampus, theta phase modulates gamma and HFO amplitude. In the present study, we analysed for the first time in vivo, the general CFC characteristic in subregions of the human epileptic hippocampus (Hc) during electrically evoked potentials. Methods We used laminar multi-electrodes to record local field potential (LFP) by cortical electrical stimulation (0.2 ms; 5–15 mA; 0.5 Hz). Hippocampal regions were reconstructed based on histological assessment: Cornu Ammonis 2-3 (CA2-3), Dentate Gyrus (DG), Subiculum (Sub). Phase-amplitude coupling (PAC) was calculated based on modulation index (MI) on 1 s window for control and evoked ripples. Results We analysed the interaction of frequencies between 10 to 1000 Hz grouped by CA2-3, DG, Subiculum. The regions show a slightly different coupling pattern (modulating/modulated frequency): 10–35 Hz/15–320 Hz (CA2-3); 10–56 Hz/47–475 Hz (DG) and 10–35 Hz/46–500 Hz (Sub). The volume of this effect is the following based on maximal MI values: 0.4 (DG), 0.25 (Sub) and 0.14 (CA2-3). Statistical analysis ( p 0.01 ) resulted in a significant difference between active and background activity. Conclusion Our results demonstrate that phase-amplitude coupling is a prominent feature of the oscillatory LFP in epileptic hippocampus. These phase–amplitude modulations were distinct for different high-frequency bands modulated by slow gamma (10–50 Hz) and for different during evoked events and control, which similar to previous findings.