Computing Phase Amplitude Coupling in EEGLAB: PACTools

Phase-Amplitude Coupling (PAC) in electrophysiological signals refers to the transient interplay of activities in different frequency ranges, wherein phase in a low-frequency band and amplitude in a high-frequency band are in some way dependent. PAC phenomena have received increasing interest in neuroscience given the growing evidence of their apparent role in both normal and pathological brain processes. This interest has resulted in publication of a wave of methods for PAC estimation, each with its own advantages and drawbacks relative to others. Motivated by the widespread study of this phenomenon, most academic open source software environments for analyzing electrophysiological signals (e.g., Fieldtrip, Brainstorm, MNE) have implemented at least one method of PAC estimation. Here we describe an EEGLAB plug-in release, PACTools for MATLAB (The Mathworks, Inc.), that computes PAC in either continuous or event-related data using any of five methods for PAC estimation: Mean Vector Length Modulation Index, Kullback- Leibler Modulation Index, Phase-Locking Value, General Linear Model Modulation Index and Mutual Information PAC (MIPAC). PACTools uses parallelized code for efficient performance and offers built-in direct access to online high-performance computing resources made freely available for nonprofit research by the Neurosciences Gateway (nsgportal.org). PACTools features intuitive graphic user interfaces and equivalent command line calls that make its use straightforward and seamless in the EEGLAB environment. We discuss toolbox implementation, architecture, dependencies, and the implemented methods of PAC computation and visualization.