Numbers in action during cognitive flexibility - A neurophysiological approach on numerical operations underlying task switching.

Cognitive flexibility is a major competence to cope with daily life requirements and is usually investigated using task switching paradigms. Often, numerical stimuli are used to examine switching between task rules. Based upon functional neuroanatomical considerations we hypothesize that the ability to efficiently perform task switching varies depending on the cognitive operations performed with these numerical stimuli during task switching (magnitude vs parity judgments). We use a system-neurophysiological approach combining EEG and event-related potential (ERP) recordings with temporal data decomposition and source localization methods. We show that task switching processes are more demanding during parity judgments, compared to magnitude judgments. This, however, was only the case when task switching processes were triggered by external sensory stimuli, but not when memory-based processes had to be used during task switching. After accounting for intra-individual variability in the EEG data, the neurophysiological data showed that these effects were due to very specific subprocesses reflecting processes to update task sets and stimulus-response mappings during task switching. Source reconstructions show that left inferior and superior parietal areas (BA40 and BA7) were associated with these processes. The data show how different numerical operations differentially affect cognitive flexibility processes. Especially parity judgments exacerbate processes to update and reconfigure task sets during task switching in parietal areas. These findings are a valuable contribution to further reflections on the theories developed to date in task switching.