Optimal sustained attention is linked to the spectral content of background EEG activity: greater ongoing tonic alpha (10 Hz) power supports successful phasic goal activation Paul M. Dockree, 1,5 Simon P. Kelly, 2,3,5 John J. Foxe, 1,3,4,5 Richard B. Reilly 2,5 and Ian H. Robertson 1,5 1 Department of Psychology & Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin 2, Ireland 2 Department of Electronic and Electrical Engineering, University College Dublin, Dublin, Ireland 3 The Cognitive Neurophysiology Laboratory, Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, NY, USA 4 Program in Cognitive Neuroscience, Department of Psychology, The City College of the City University of New York, 138th St. & Convent Avenue, New York, USA 5 The Cognitive Neurophysiology Laboratory, St Vincent’s Hospital, Fairview, Dublin, Ireland Abstract Efficient executive control frequently requires the timely activation or re-activation of a task-goal to enable purposeful behaviour. Additionally, more generalized factors such as alertness or neurological health will influence the efficiency with which control can be implemented. Goal-directed processes have been investigated by examining event-related potentials (ERPs), but much less is known about the involvement of background or ‘tonic’ processes reflected in the ongoing electroencephalogram (EEG), and how these affect the phasic processes expressed in the broad-band ERP. Here, we investigate the relationship between a key attention- sensitive tonic process – the alpha rhythm – and relevant phasic processes observed during a sustained attention paradigm in neurologically healthy subjects. We report that subjects with relatively higher tonic alpha power (10 Hz) show a larger-amplitude late positive ERP component that is thought to index goal activation and has been found to predict good sustained attention performance as defined by correct response patterns. Source localization results suggest that the neural generators responsible for oscillatory alpha activity, which are found primarily in the parietal and occipital lobes, are distinct from those giving rise to the late positive component. The results are discussed in terms of increased alpha synchrony facilitating goal-directed behaviour. Introduction Goal-directed behaviour depends on the efficiency of executive control processes that select and manage goals in working memory (Posner & Peterson, 1990). Additionally, background factors such as circadian rhythms (Manly et al., 2002), age (Grigsby et al., 1995) or neurological health (Robertson et al., 1997) influence the degree to which behaviour can be controlled and purposeful. The consequences of breakdown in goal-directed behaviour can be dramatic, as seen in patients with frontal lobe damage or psychiatric illnesses such as schizophrenia. In support of goal-directed behaviour is an alertness or sustained attention system involving a right lateralised fronto-parietal network (Posner & Peterson, 1990; Sturm et al., 1999). This system is essential for maintaining an intrinsic goal-directed focus in otherwise unarousing contexts where exogenous stimuli are not present to increase alertness through novelty, demand or perceived difficulty (Robertson & Garavan, 2004). The aim of the current study is to examine the relationship between short-term ‘phasic’ neurophysio- logical processes at play during a test of sustained attention and longer-term ‘tonic’ neurophysiological signals. The former reflect moment-to-moment cognitive events whereas the latter are more stable and reflect characteristics or traits of normal individuals that change more slowly over time. Event-related potentials (ERPs) have been informative in under- standing phasic activity during goal-directed behaviour. We have previously charted the ERP components elicited during the fixed sequence sustained attention to response task (SART fixed ; Dockree et al., 2005). In this task a predictable series of single digits are presented (1–9) and subjects are required to make a response to each number (go-trials) with the exception of the number 3 (no-go trial). This task requires the activation and maintenance of a task goal, which is manifest in the ERP as a broadly distributed positivity over parieto- central areas. This goal activation component, termed late positive 1 (LP1) is observed 550–800 ms following stimulus onset on trial 2 (i.e. the digit ‘2’) and exhibits divergence between the conditions of correct and incorrect responding on the following target (no-go) trial 3. Specifically, it was found that preceding an error, the LP1 was attenuated. Thus on a grand average level this component is most clearly indicative of successful performance on the SART and so stands out as a component of interest. As exemplified by the aforementioned ERP component, neuro- physiological processes are most commonly examined with respect to event-related, phasic changes in electro-cortical signals that occur at a rapid rate. By contrast, tonic EEG processes vary at a much slower rate and can be influenced by daily changes in circadian rhythms (Aeschbach et al., 1999), fatigue (Borbely et al., 1981) and mood Correspondence: Dr Paul M. Dockree, 1 Department of Psychology & Trinity College Institute of Neuroscience, as above. E-mail: dockreep@tcd.i.e. Received 9 August 2006, revised 26 November 2006, accepted 28 November 2006 European Journal of Neuroscience, Vol. 25, pp. 900–907, 2007 doi:10.1111/j.1460-9568.2007.05324.x ª The Authors (2007). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd