Fig. 9.
Normalized bispectrum at high speeds (𝑣 > 35 cm/s). Same organization as in Fig. 8, where columns (left to right) show the bicoherence |𝔟|, the real ℜ(𝔟) (skewness) and imaginary 𝔍(𝔟) (asymmetry) parts of the normalized bispectrum 𝔟, and the biphase arg(𝔟). Note the development of multiple regions of high bicoherence |𝔟|, notably 1) t theta (theta frequency fθ ≈ 8 Hz) and its harmonics (nfθ, with n = 2, 3, 4, …), with peaks detectable up to 48 Hz across all layers, and 2) theta and a wide gamma band spanning approximately the interval between 60 and 100 Hz. The lacunosum-moleculare (LM) exhibits the richest nonlinear structures of the 4 layers examined with gamma coupling to the first harmonic of theta. Or, oriens; CA1.Pyr, pyramidal layer; CA1.Rad, radiatum.