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. 2014 Mar 12;34(11):3937–3946. doi: 10.1523/JNEUROSCI.3581-13.2014

Figure 3.

Figure 3.

Lack of neocortical and hippocampal coupling to the respiratory cycle under ketamine-xylazine anesthesia at matching fundamental frequencies. A, A representative example of simultaneously recorded LFP traces from nCTX, HPC, and PIRI sites, together with thermistor readings from the nostril (RESP, with inspiration shown as downward deflections). B, Overlaid power spectral plots from periods (including those shown in A) demonstrate matching peak frequencies (fundamentals) for SO and RESP signals. The arrow with the dotted line indicates the matching cortical and respiratory frequency. The logarithmic scale for brain LFP power is shown on the left side and the power of the respiratory signal is displayed on the linear scale to the right. Low-frequency, <0.33 Hz, near-DC frequencies were truncated from the respiratory plot for ease of visualization. C, Coherence spectra for brain-derived LFP signal pairs demonstrating high coupling across neocortical and hippocampal sites. D, Coherence spectra for the respiratory signal to each brain LFP recording demonstrating low coupling at the respiratory fundamental, while at the same shared frequency, which demonstrates that despite a common fundamental, the respiratory signal was only coherent with piriform activity. All spectra shown (B–D) are from the same 1 min sample that includes the raw sample shown in A. E, F, Average coherence (±SEM) for all signal pairs for data samples demonstrating matched peak frequency for SO and RESP signals. The SO, embodied by high nCTX and HPC coherence, emerges as separate process from respiratory activity, indicated by high RESP and PIRI coherence, even when cycling fundamentals are the same. Respiratory (circles) comparisons were separated from LFP (square) signal pairings for ease of visualization. The numbers of samples for averages are displayed above the symbols. The averages resulted from samples collected from a subset of five experiments incidentally all under ketamine-xylazine anesthesia. The horizontal dotted line indicates the threshold for significant coherence, >0.21.