Functional dissociations between prefrontal and parietal cortex during task switching: A combined fMRI and TMS study

Preparatory control in task-switching has been suggested to rely upon a set of distributed regions within a frontoparietal network, with frontal and parietal cortical areas cooperating to implement switch-specific preparation processes. Although recent causal evidences using transcranial magnetic stimulation (TMS) have generally supported this model, alternative evidences from both functional neuroimaging and neurophysiological studies have questioned the switch-specific role of both frontal and parietal cortices. The aim of the present study was to clarify the role of prefrontal and parietal areas supporting preparatory cognitive control in task-switching. Within this purpose, an fMRI study during task-switching performance was conducted to identify the specific brain areas involved in preparatory control during performance of a task-switching paradigm. Then, TMS was applied over the specific coordinates previously identified through fMRI, that is, the anterior portion of the inferior frontal junction (aIFJ) and the intraparietal sulcus (IPS). Results revealed that TMS over the aIFJ disrupted performance in both switch and repeat trails in terms of delayed responses as compared to Sham condition. In contrast, TMS over the IPS selectively interfered performance in switch trials. These findings support a multicomponent model of executive control with the aIFJ being involved in more general switch-unspecific process such as the episodic retrieval of goals, and the IPS being related to the implementation of switch-specific preparation mechanisms for activating stimulus-response mappings. The results help conciliating preceding evidences about the role of a frontoparietal network during task-switching, and support current models about a hierarchical organization within prefrontal cortex. Significance Statement A combined fMRI and TMS study was conducted to clarify the brain areas involved in the executive control of attention during a cueing task-switching paradigm. Functional dissociations were observed during TMS stimulation, with prefrontal and parietal areas playing different roles during task-switching preparation. While the anterior portion of the inferior prefrontal junction seemed to be involved in a general mechanism of memory retrieval for goal identification, the intraparietal sulcus seemed to be engaged in a switch-specific mechanism for the translation of abstract task goals into action rules. The results help conciliating preceding evidences about the role of a frontoparietal network during task-switching, and support current models about a hierarchical organization within prefrontal cortex.