Assessing transient cross-frequency coupling in EEG data

Synchronization of oscillatory EEG signals across different frequency bands is receiving waxing interest in cognitive neuroscience and neurophysiology, and cross-frequency coupling is being increasingly linked to cognitive and perceptual processes. Several methods exist to examine cross-frequency coupling, although each has its limitations, typically by being flexible only over time or over frequency. Here, a method for assessing transient cross-frequency coupling is presented, which allows one to test for the presence of multiple, dynamic, and flexible cross-frequency coupling structure over both time and frequency. The method is applied to intracranial EEG data, and strong coupling between gamma (similar to 40-80 Hz) and upper theta (similar to 7-9 Hz) was observed. This method might have useful applications in uncovering the electrophysiological correlates of cognitive processes. Q 2007 Elsevier B.V. All rights reserved.