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. 2018 Sep 25;9:1338. doi: 10.3389/fphys.2018.01338

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Copyright © 2018 Niizeki and Saitoh.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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(A) Auto-correlation functions (ACFs) of brain δ-wave, λ, normalized high-frequency component of HRV (HF_n), and amplitude of RSA (A_RSA), calculated from the entire night of sleep. Open red circles indicate peaks of ACF. (B) Normalized power spectral densities (PSDs) for the respective ACF. Open red circle, detected maximal peak; vertical dotted lines, ± 25% of the peak frequency. (C) Cross-correlation functions (CCFs) between δ-wave and λ, between δ-wave and HF_n, and between δ-wave and A_RSA. The lag time at which CCF attains its maximum is indicated by a red vertical bar in each CCF.