Transient Reduction of Frontal Midline Theta Activity During Attentional Shifts in Healthy Young Adults

The prefrontal cortex, well-developed in humans, plays a crucial role in various behavioural outcomes. Neuronal resources are limited, however, and must be appropriately allocated. A specific type of theta activity, known as frontal midline theta (Fmθ), is intermittently observed in the frontal midline region during intense concentration to tasks. Meanwhile, the power of Fmθ activity is stronger in individuals with excessive concentration than in those who are not engaged in such state. Fmθ activity in healthy young adults is therefore speculated to be reduced when shifting attention from one target to another. However, the neuronal mechanisms of Fmθ reduction are largely unknown. In this study, 20 healthy young male adults performed 2-back cognitive tasks including two pieces of information (colour and position). Participants initially pay attention to one of them at the start of the task, and then to shift attention to the other when the screen's background colour was changed. Transient reduction of theta activity was observed with the attentional shift, and high current source density was observed in the medial prefrontal and the anterior cingulate regions. Reduction of alpha activity in the left inferior parietal lobe was simultaneously observed during the attentional shift. Moreover, there was a significant positive correlation between the reduction of Fmθ and alpha activity in the left parietal area. The reduction of Fmθ activity and the change in activity of the inferior parietal lobe may play an essential role in disengaging from intense concentration and the appropriate attentional shift. Trial Registration: UMIN000051023.