The role of sustained posterior brain activity in the serial chaining of two cognitive operations: a MEG study

A fundamental necessity in human cognition is to link sequential mental operations where appropriate execution of the second task requires input from the first. The present study explores the neural basis of such "chaining" using a novel psychological refractory period (PRP) task. Participants were required to make speeded responses to two sequential visual tasks that were chained or independent. Magnetoencephalography (MEG) signals were recorded simultaneously to reveal the brain's response to these similar but fundamentally different conditions. RTs to Task 1 and 2 were slower in the Chained condition, and their temporal coupling weakened, relative to the Independent condition. MEG analysis of the accompanying event-related fields (ERFs) revealed an increased sustained posterior component in the Chained condition beginning approximately 350 ms after Task 2 onset and lasting for 450 ms. Beamformer localization of this ERF effect revealed a left hemisphere source near the junction of the temporal, parietal, and occipital lobes. These results extend our understanding of the behavioral and corresponding neural mechanisms required by everyday decision making.