Past studies show beneficial as well as detrimental effects of subthalamic nucleus deep-brain stimulation on impulsive behaviour. We address this paradox by investigating individuals with Parkinson's disease treated with subthalamic nucleus stimulation (n = 17) and healthy controls without Parkinson's disease (n = 17) on performance in a Simon task. In this reaction time task, conflict between premature response impulses and goal-directed action selection is manipulated. We applied distributional analytic methods to separate the strength of the initial response impulse from the proficiency of inhibitory control engaged subsequently to suppress the impulse. Patients with Parkinson's disease were tested when stimulation was either turned on or off. Mean conflict interference effects did not differ between controls and patients, or within patients when stimulation was on versus off. In contrast, distributional analyses revealed two dissociable effects of subthalamic nucleus stimulation. Fast response errors indicated that stimulation increased impulsive, premature responding in high conflict situations. Later in the reaction process, however, stimulation improved the proficiency with which inhibitory control was engaged to suppress these impulses selectively, thereby facilitating selection of the correct action. This temporal dissociation supports a conceptual framework for resolving past paradoxical findings and further highlights that dynamic aspects of impulse and inhibitory control underlying goal-directed behaviour rely in part on neural circuitry inclusive of the subthalamic nucleus.

The ability to interact with a constantly changing environment requires a balance between maintaining the currently relevant working memory content and being sensitive to potentially relevant new information that should be given priority access to working memory. Mesocortical dopamine projections to frontal brain areas modulate working memory maintenance and flexibility. Recent neurocognitive and neurocomputational work suggests that dopamine release is transiently enhanced by induced positive affect. This ERP study investigated the role of positive affect in different aspects of information processing: in proactive control (context maintenance and updating), reactive control (flexible adaptation to incoming task-relevant information), and evaluative control in an AX-CPT task. Subjects responded to a target probe if it was preceded by a specific cue. Induced positive affect influenced the reactive and evaluative components of control (indexed by the N2 elicited by the target and by the error-related negativity elicited after incorrect responses, respectively), whereas cue-induced proactive preparation and maintenance processes remained largely unaffected (as reflected in the P3b and the contingent negative variation components of the ERP).

The inhibitory control of actions has been claimed to rely on dopaminergic pathways. Given that this hypothesis is mainly based on patient and drug studies, some authors have questioned its validity and suggested that beneWcial eVects of dopaminergic stimulants on response inhibition may be limited to cases of suboptimal inhibitory functioning. We present evidence that, in carefully selected healthy adults, spontaneous eyeblink rate, a marker of central dopaminergic functioning, reliably predicts the eYciency in inhibiting unwanted action tendencies in a stop-signal task. These Wndings support the assumption of a modulatory role for dopamine in inhibitory action control.

Dopamine plays a key role in a range of action control processes. Here, we investigate how dopamine depletion caused by Parkinson disease (PD) and how dopamine restoring medication modulate the expression and suppression of unintended action impulses. Fifty-five PD patients and 56 healthy controls (HCs) performed an action control task (Simon task). PD patients completed the task twice, once withdrawn from dopamine medications and once while taking their medications. PD patients experienced similar susceptibility to making fast errors in conflict trials as HCs, but PD patients were less proficient compared with HCs at suppressing incorrect responses. Administration of dopaminergic medications had no effect on impulsive error rates but significantly improved the proficiency of inhibitory control in PD patients. We found no evidence that dopamine precursors and agonists affected action control in PD differently. Additionally, there was no clear evidence that individual differences in baseline action control (off dopamine medications) differentially responded to dopamine medications (i.e., no evidence for an inverted U-shaped performance curve). Together, these results indicate that dopamine depletion and restoration therapies directly modulate the reactive inhibitory control processes engaged to suppress interference from the spontaneously activated response impulses but exert no effect on an individual's susceptibility to act on impulses.

People integrate the features of perceived events and of action plans, as well as of episodic stimulusresponse relations, into event files. We investigated whether the management of event files, and particularly the speed of updating the binding between the task-relevant stimulus feature and the response, correlates with fluid intelligence. Indeed, the performance of participants scoring high on Raven's Standard Progressive Matrices test was less impaired by a mismatch between the stimulus-response relation in the current and the previous trial. This result suggests that high intelligence is accompanied by a higher degree of flexibility in handling event files-that is, by higher efficiency in updating episodic representations.One of the most discussed issues in cognitive psychology is what has become known as the binding problem (Treisman, 1996)-that is, the question of how the human (or primate) brain is able to properly integrate all information about a particular event. In perception, there must be a mechanism that functionally links the features of an object to what Kahneman, Treisman, and Gibbs (1992) have called an object file-that is, a temporary cognitive structure containing all the perceptual information about an object, and perhaps even episodic and semantic information. Since comparable binding problems exist in action planning (Stoet & Hommel, 1999) and in coordinating perceptual codes and action plans (Hommel, 1998;Hommel, Müsseler, Aschersleben, & Prinz, 2001), it makes sense to assume that perceiving and acting require the creation of all sorts of event files (Hommel, 1998(Hommel, , 2004. In this article, we address the question of whether and how the cognitive management of event files is correlated with fluid intelligence, as measured by Spearman's g. There are three lines of reasoning that motivated us to consider a link between intelligence and event file handling.First, event files are temporary structures that must be held and updated in working memory-a system whose flexibility has been shown to correlate with fluid intelligence (Duncan et al., 2000). To see how intelligence may relate to event files, let us consider the task from Hommel (1998), which we adopted for the present study (see Figure 1). In this task, participants are cued to prepare a left-or right-hand keypress (RI), which they carry out as soon as a first stimulus (S 1) appears. The identity of S I Correspondence relating to this article may be sent to L. S. Colzato, Leiden University, Department of Psychology, Cognitive Psychology Unit, Postbus 9555, 2300 RB Leiden, The Netherlands (e-mail: colzato@ fsw.leidennniv. nl).does not matter for the response, but it varies in shape, location, and color. One second later a second stimulus (S2) appears, signaling Response 2 (R2), a binary-choice response to the shape of S2 (S2 color and location are entirely irrelevant to this version of the task). Performance in such a task reveals interesting interactions between repetition effects: Performance is impaired in partialrepetition tri...