Unconscious Learning of Automatic Inhibition is Reflected in Frontal Theta and Sensorimotor Oscillations.

The cognitive control of action is thought to be mediated by conscious effort as reflected by changes in frontal theta activity. We measured frontal theta during a response inhibition task in 16 healthy adults who implicitly learned repeated patterns of go/switch cues, resulting in unaware differences in cognitive demand for different cues. Learning was reflected by reduced reaction times (RT) to probable compared to unexpected switch cues. In the rare absence of behavioural (RT) differences, concurrent measures of pupil diameter revealed changes in effort with stimulus probability, while effort was accompanied by parametric increases in theta. Additionally, theta predicted pre-response sensorimotor gamma, suggesting interactions between frontal and sensorimotor cortex during cognitive control. These results provide further evidence for a functional role of theta in cognitive effort during response preparation, inhibition and execution, even in the absence of conscious awareness.