Fig. 2.

Coherence between the intracranial EEG (iEEG) and the breathing during natural respiration. A: iEEG (red lines) and breathing signals (black lines) during a representative 30-s period during natural respiration for 2 sample electrodes: one in the hippocampus (top), which shows strong phase-locked signals, and another in the white matter (bottom) showing negligible phase locking. B, top: power spectrum of the manometric breathing signal (black line) and the hippocampal iEEG trace (red line), both with peaks at 0.28 Hz. The iEEG shows an additional peak at 1.33 Hz. Bottom, power spectrum for an electrode in the adjacent white matter showing no such peak at the breathing rate. C, top: coherence between respiration and hippocampal signals. The coherence value at the 0.28-Hz respiratory rate (dashed green lines) was significant (coherence value = 0.62, P = 0.0001). Significance (magenta dash line) was evaluated by performing bootstrap analysis shuffling iEEG and breathing signals (1,000 iterations, P < 0.01). Bottom: iEEG-breath coherence from an electrode in the white matter. The coherence value at the breathing frequency (dashed green line) was not significant (coherence value = 0.02, P = 0.44). abs., Absolute; a.u., arbitrary units; RR, respiratory rate.