Modulations of theta frequency for cognitive control in behavior and in EEG
Neural oscillations at theta frequency (4-8 Hz) are thought to play an important role in guiding behaviour (Cavanagh & Frank, 2014), a phenomenon sometimes labeled as cognitive control. In particular, theta amplitude increases when an unexpected event happens or something goes wrong. However, the computational role of theta has remained unclear. We present a computational model of how theta guides faster (gamma) frequencies, thus to synchronize (functionally, attend to) specific neural modules. In this model, theta amplitude and theta frequency are two dimensions that can be controlled for optimal cognitive control. The model predicts that theta frequency decreases when a more difficult task is upcoming, because slower waves allow more time for competing representations to settle. This decreased frequency should be visible in both neurophysiology (measured via EEG) and behavior (measured via accuracy). In line with model simulations, we find empirically in the EEG spectrum that a cue predicting an upcoming difficult (relative to easy) stimulus, leads to an decreased theta frequency. Similarly, theta frequency measured at the behavioral level is slowed down on such difficult stimuli. This result demonstrates how different aspects of theta oscillations (amplitude and frequency) can be recruited for cognitive control, and how they can be manifested in EEG and behavior.