Fig. 5.

Breathing-phase coupling to gamma-amplitude oscillations. A: sample electrode in the olfactory bulb (OB) exhibiting bursts of broadband signal (40–150 Hz) at specific phases of the respiratory cycle, particularly during the beginning and end of exhalation during natural breathing. B: gamma-band amplitude at different phases of the breathing signal (18 bins of 20° width each) for this sample electrode averaged across an 8-min period. C: iEEG-breath coherence and cross-frequency coupling in GM, WM, and CSF. Pie chart shows the percentage of electrodes exhibiting large coherence values (>99th percentile; horizontal hatching) as well as cross-frequency coupling (cross-hatching), and cross-frequency coupling alone (black) across the population (n = 1,137 electrodes). D: distribution of modulation indexes (MIs) across the population of GM, WM, and CSF electrodes. Lines represent raw MIs after smoothing (window width = 0.02). MIs were smaller in electrodes located in the CSF and WM compared with electrodes in the GM. Only 138/1,137 (12.2%) of the electrodes showed MIs above the threshold, all located in the GM. The threshold (dark gray area) was the 99th percentile of the surrogate MI distribution derived from shifting the respiration signal with respect to the iEEG (as indicated by asterisk). The y-axis represents electrode percentages normalized with respect to each area (GM, WM, and CSF), separately. E: percentage of GM electrodes within each brain area that showed both MIs and coherence values above the threshold. Up to 40% of the electrodes that were in the amygdala, hippocampus, insula, motor, parietal, and primary olfactory cortices showed increased gamma-amplitude oscillations at specific phases of the respiratory cycle. cfc,  cross-frequency coupling; coh, coherence; PAC, phase-amplitude coupling; lat., lateral; med., medial; olfact., olfactory; occipital-cal, occipital-calcarine; sup. temp, superior temporal; mid. temp, middle temporal; inf, inferior.