P217 Disrupting cognitive control in dual-task situations by transcranial magnetic stimulation of the lateral prefrontal cortex

Abstract

Introduction Performance in dual-task situations is usually impaired compared to performance in single-task situations, which is reflected in prolonged reaction times as well as increased error rates. These dual-task costs can be explained by the requirement to recruit additional task-order control processes that are crucial for scheduling, monitoring and regulating the processing order of two temporally overlapping tasks. Recent neuroimaging studies with functional magnetic resonance imagery (fMRI) could show that the lateral prefrontal cortex (lPFC) may play an essential role for implementing these control processes. However, the association between prefrontal activity and task-order control remains only correlational due to the nature of the fMRI method. Objectives The aim of this study was to provide evidence for the causal involvement of prefrontal activity in dual-task processing by applying transcranial magnetic stimulation (TMS). Methods 16 Participants performed a dual-task consisting of two simple choice reaction tasks. Demands on task-order control processes were manipulated by introducing dual-task blocks with either fixed or random order of both tasks. We compared the effects of TMS over the lPFC to two control conditions. Results As a result, we could show that in the stimulation condition dual-task performance decreased compared to control conditions only if demands on task-order control processes where high. Conclusion This pattern of results supports the conclusion that the lPFC plays a causal role for the implementation of task-order control processes in situations with temporally overlapping tasks. More specifically, we argue that the lPFC is recruited for activating an internal order representation into working memory.