Frontal theta and alpha power and coherence changes are modulated by semantic complexity in Go/NoGo tasks

To study the interactions between semantic processing and motor response inhibition, we recorded scalp EEG as subjects performed a series of Go/NoGo response inhibition tasks whose response criteria depended on different levels of semantic processing. Three different tasks were used. The first required the subject to make a Go/NoGo decision based on pictures of one particular car or one particular dog. The second used pictures of different types of cars and of dogs, and the final task used stimuli that ranged across multiple types of objects and animals. We found that the theta-band EEG power recorded during the NoGo response was attenuated as a function of semantic complexity while the peak latency was delayed in only the most complex category task. Further, frontal alpha-band desynchronization was strongest for the simplest task and remained close to baseline for the other tasks. Finally, there was significant theta-band coherence between the frontal pole and pre-SMA for the NoGo conditions across tasks, which was not found in the Go trials. These findings provide information about how more rostral frontal regions interact with the pre-SMA during response inhibition across different stimuli and task demands: specifically, level of processing affects latency, difficulty affects amplitude, and coherence is affected by whether the decision is Go or NoGo.