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.