OBJECTIVETo explore the neural dynamics during alternating task switching.

METHODSIn an alternating-runs paradigm, 23 healthy volunteers were asked to categorize Arabic numerals displayed on the screen into either even or odd numbers or judge if the number was greater than 5 according its color cues. The color of the numerals were regularly switched every three trials (switch, nested and pre-switch trials). ANOVA of repeated-measure and paired t-test were used for analysis of the behavioral performance and event-related potential (ERP) data of 19 channels, and statistical parametric mapping of F and t values was used to reveal the spatiotemporal patterns of ERP.

RESULTSSignificant switch costs (switch versus nested trial) were found in the mean reaction time (123.61∓83.84 ms, P<0.05) and the mean accuracy [(1.24∓3.30)%, P<0.05]. Statistical parametric mapping of t value of ERP suggested that the switch effects appeared in the right frontal-parietal network and then in the left one. The preparation effects appeared in the right frontal pole followed by the left one, both accompanied by the activation of the posterior regions.

CONCLUSIONSCognitive flexibility depends on the dynamic activation of the fronto-parietal network. The frontal poles are involved in the pre-switch preparatory process, the dorsal frontal areas are related with the actual switch process, and the left and right frontal regions play different roles.