Neurophysiological signature of effective anticipatory task-set control: a task-switching investigation Aureliu Lavric, Guy A. Mizon and Stephen Monsell School of Psychology, Washington Singer Labs, University of Exeter, Exeter, UK Keywords: cognitive control, ERP, task switching Abstract Changing between cognitive tasks requires a reorganization of cognitive processes. Behavioural evidence suggests this can occur in advance of the stimulus. However, the existence or detectability of an anticipatory task-set reconfiguration process remains controversial, in part because several neuroimaging studies have not detected extra brain activity during preparation for a task switch relative to a task repeat. In contrast, electrophysiological studies have identified potential correlates of preparation for a task switch, but their interpretation is hindered by the scarcity of evidence on their relationship to performance. We aimed to: (i) identify the brain potential(s) reflecting effective preparation for a task-switch in a task-cuing paradigm that shows clear behavioural evidence for advance preparation, and (ii) characterize this activity by means of temporal segmentation and source analysis. Our results show that when advance preparation was effective (as indicated by fast responses), a protracted switch- related component, manifesting itself as widespread posterior positivity and concurrent right anterior negativity, preceded stimulus onset for 300 ms, with sources primarily in the left lateral frontal, right inferior frontal and temporal cortices. When advance preparation was ineffective (as implied by slow responses), or made impossible by a short cue–stimulus interval (CSI), a similar component, with lateral prefrontal generators, peaked 300 ms poststimulus. The protracted prestimulus component (which we show to be distinct from P3 or contingent negative variation, CNV) also correlated over subjects with a behavioural measure of preparation. Furthermore, its differential lateralization for word and picture cues was consistent with a role for verbal self-instruction in preparatory task-set reconfiguration. Introduction The cognitive processes and actions triggered by a stimulus depend on our current ‘task-set’. Although task-set is to some degree stimulus- driven (e.g. text evokes reading, even when this is unwanted and interferes with performance; Stroop, 1935), it is normally under voluntary control, and can seemingly be reconfigured at will to prepare to process an upcoming stimulus. To capture such executive preparation in the laboratory, researchers have used task-cuing (e.g. Meiran, 1996): each stimulus is preceded by a cue specifying one of two or more tasks. Changing the task typically prolongs reaction time (RT) relative to performing the same task on successive trials. This ‘switch cost’ can be substantially reduced by increasing the CSI available for preparation (for review see Monsell, 2003). A natural interpretation is that enabling a changed task-set (and suppressing the previous one) requires a control process: task-set reconfiguration. If time permits it can be accomplished before the stimulus onset, whereas later reconfiguration delays or prolongs response selection, increasing RT (Rogers & Monsell, 1995; Meiran, 1996). Studies using functional magnetic resonance imaging (fMRI; see Discussion) have found it difficult to distinguish prestimulus activa- tion reflecting preparation for a task change from poststimulus activation consequent upon a task change. In contrast, event-related potential (ERP) studies (see Discussion) have detected several prestimulus components that potentially reflect anticipatory reconfigu- ration on task-switch trials: a positive deflection 400 ms or more into the preparation interval, maximal over the posterior scalp (e.g. Karayanidis et al., 2003), an anterior negativity in the same latency range (e.g. Astle et al., 2006), a longer latency anterior–central negativity (Tieges et al., 2006, 2007) and an early anterior positivity (Rushworth et al., 2002b). However, important questions remain unanswered. First, do all (or any of) these effects reflect anticipatory task-set reconfiguration? We need evidence that they relate to effective preparation, as indexed by behavioural measures (e.g. reduction in switch cost). To date, no switch-related ERP deflection has been unequivocally associated with effective preparation. Second, the cortical generators of these components should be further explored. Third, the relationship between the posterior positivity and other well- documented ERP components in its time-range (P3, CNV) remains unclear; some authors identify the former with one of the latter (Kieffaber & Hetrick, 2005; Hsieh & Chen, 2006). Fourth, behavio- ural evidence suggests a critical role for linguistic self-instruction in task-set reconfiguration (e.g. Goschke, 2000), but relevant manipula- tions, such as verbal vs. non-verbal cues, have not yet been studied with ERPs. To establish which switch-induced ERP effects (if any) relate to effective anticipatory task-set reconfiguration, we assessed the relationship between ERPs and behavioural measures of performance using a task-cuing paradigm based on recent behavioural research (Monsell & Mizon, 2006). We examined the cortical correlates of the switch-related ERPs using distributed source Correspondence: Professor S. Monsell, as above. E-mail: s.monsell@ex.ac.uk Received 16 May 2007, revised 16 June 2008, accepted 19 June 2008 European Journal of Neuroscience, Vol. 28, pp. 1016–1029, 2008 doi:10.1111/j.1460-9568.2008.06372.x ª The Authors (2008). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd European Journal of Neuroscience