Timing of Task-Set Reconfiguration in Frontal and Parietal Cortices

Neuroimaging studies have shown that the inferior frontal junction area (IFJ, near the junction of inferior frontal and inferior precentral sulci) and the intraparietal sulcus are involved in task preparation. Theories based on animal research have assumed that the contribution of the prefrontal cortex is to bias processing in posterior brain regions. If this assumption holds true, one would expect prefrontal cortex activation preceding parietal activation. The present study tested this assumption by combining results from functional magnetic resonance imaging (fMRI) providing high spatial resolution and event-related potentials (ERP) to gain high temporal resolution. We collected ERP data in 19 participants performing a modified task-switching paradigm. In most trials two task cues with a preparation interval in between were presented before the task stimuli. Assigning two different cues to each task enabled us to isolate task-set reconfiguration in the preparation interval. This process was associated with a midline negative ERP deflection peaking around 470 ms after presentation of the task cue. We placed dipoles in regions activated in a previous fMRI study that used the same paradigm (left IFJ, right inferior frontal, right parietal) and fitted their directions and magnitudes to the ERP effect. The frontal dipoles contributed to the ERP effect earlier than the parietal dipole, providing support for the view that the prefrontal cortex is involved in updating of general task representations and biases relevant stimulus response associations in the parietal cortex.