Data from: On cross-frequency phase-phase coupling between theta and gamma oscillations in the hippocampus

Phase-amplitude coupling between theta and multiple gamma sub-bands is a hallmark of hippocampal activity and believed to take part in information routing. More recently, theta and gamma oscillations were also reported to exhibit phase-phase coupling, or n:m phase-locking, suggesting an important mechanism of neuronal coding that has long received theoretical support. However, by analyzing simulated and actual LFPs, here we question the existence of theta-gamma phase-phase coupling in the rat hippocampus. We show that the quasi-linear phase shifts introduced by filtering lead to spurious coupling levels in both white noise and hippocampal LFPs, which highly depend on epoch length, and that significant coupling may be falsely detected when employing improper surrogate methods. We also show that waveform asymmetry and frequency harmonics may generate artifactual n:m phase-locking. Studies investigating phase-phase coupling should rely on appropriate statistical controls and be aware of confounding factors; otherwise, they could easily fall into analysis pitfalls.θ节律与多个γ频段子带之间的相位振幅耦合（phase-amplitude coupling）是海马活动的标志性特征，且被认为参与信息路由过程。近年来，也有研究报道θ与γ振荡存在相位-相位耦合（phase-phase coupling），即n:m锁相，这提示了一种长期以来获得理论支持的重要神经元编码机制。然而，本研究通过分析模拟与实测的局部场电位（local field potentials, LFP），对大鼠海马中存在θ-γ相位-相位耦合这一观点提出质疑。本研究表明，滤波过程引入的准线性相移会在白噪声与海马LFP中产生虚假的耦合强度，且该效应高度依赖于数据时段长度；同时，若采用不当的替代检验方法，可能会误检出具有统计学显著性的耦合。此外，本研究还发现，波形不对称性与频率谐波也可能产生人工伪迹性n:m锁相。开展相位-相位耦合相关研究时，应采用恰当的统计控制手段，并警惕混杂因素的干扰，否则极易陷入分析误区。