Regulating action: alternating activation of midline frontal and motor cortical networks

Objectives: Focal electrical fields recorded over the midline prefrontal co rtex have been found to index rapid evaluative decisions, including the rec ognition of having made an error in a speeded response task. The nature of these electrical fields and how they are related to cortical areas involved in response execution remains to be clarified. Methods: As subjects performed a speeded response task the EEG was recorded with a 128-channel sensor array. By filtering out the large slow waves of the event-related potential, we found that the error-related negativity (Ne /ERN) arises from a midline frontal oscillation that alternates with oscill ations over lateral sensorimotor cortex. Electrical source analyses were us ed to determine the brain sources involved in the generation of these oscil lations. Results: The results show that the midline and lateral oscillations have a period of about 200 ms (theta), and they are present for both correct and e rror responses. When an error is made, the midline error oscillation is rec ruited strongly, and it becomes correlated with the motor oscillation. Sour ce analyses localized the midline error oscillation to centromedial frontal cortex and the lateral oscillation to sensorimotor cortices. Conclusions: Because of the similarity between the midline oscillation obse rved in the present study and frontal midline theta, the nature of the Ne/E RN may be clarified by the frontal midline theta literature. The correlatio n between the midline and sensorimotor oscillations suggests a possible mec hanism for how midline frontal evaluative and monitoring networks contribut e to action regulation. (C) 2001 Elsevier Science Ireland Ltd. All rights r eserved.