Sander Nieuwenhuis

Electrophysiological correlates of anterior cingulate function in a go/no-go task: effects of response conflict and trial type frequency.

Neuroimaging and computational modeling studies have led to the suggestion that response conflict monitoring by the anterior cingulate cortex plays a key role in cognitive control. For example, response conflict is high when a response must be withheld (no-go) in contexts in which there is a prepotent tendency to make an overt (go) response. An event-related brain potential (ERP) component, the N2, is more pronounced on no-go than on go trials and was previously thought to reflect the need to inhibit the go response. However, the N2 may instead reflect the high degree of response conflict on no-go trials. If so, an N2 should also be apparent when subjects make a go response in conditions in which nogo events are more common. To test this hypothesis, we collected high-density ERP data from subjects performing a go/no-go task, in which the relative frequency of go versus no-go stimuli was varied. Consistent with our hypothesis, an N2 was apparent on both go and no-go trials and showed the properties expected of an ERP measure of conflict detection on correct trials: (1) It was enhanced for low-frequency stimuli, irrespective of whether these stimuli were associated with generating or suppressing a response, and (2) it was localized to the anterior cingulate cortex. This suggests that previous conceptions of the no-go N2 as indexing response inhibition may be in need of revision. Instead, the results are consistent with the view that the N2 in go/no-go tasks reflects conflict arising from competition between the execution and the inhibition of a single response.

Error-related brain potentials are differentially related to awareness of response errors : Evidence from an antisaccade task

The error negativity (Ne/ERN) and error positivity (Pe) are two components of the event-related brain potential (ERP) that are associated with action monitoring and error detection. To investigate the relation between error processing and conscious self-monitoring of behavior, the present experiment examined whether an Ne and Pe are observed after response errors of which participants are unaware. Ne and Pe measures, behavioral accuracy, and trial-to-trial subjective accuracy judgments were obtained from participants performing an antisaccade task, which elicits many unperceived, incorrect reflex-like saccades. Consistent with previous research, subjectively unperceived saccade errors were almost always immediately corrected, and were associated with faster correction times and smaller saccade sizes than perceived errors. Importantly, irrespective of whether the participant was aware of the error or not, erroneous saccades were followed by a sizable Ne. In contrast, the Pe was much more pronounced for perceived than for unperceived errors. Unperceived errors were characterized by the absence of posterror slowing. These and other results are consistent with the view that the Ne and Pe reflect the activity of two separate error monitoring processes, of which only the later process, reflected by the Pe, is associated with conscious error recognition and remedial action.

Dorsal anterior cingulate cortex shows fMRI response to internal and external error signals.

In our event-related functional magnetic resonance imaging (fMRI) experiment, participants learned to select between two response options by trial-and-error, using feedback stimuli that indicated monetary gains and losses. The results of the experiment indicate that error responses and error feedback activate the same region of dorsal anterior cingulate cortex, suggesting that this region is sensitive to both internal and external sources of error information.

Errors in reward prediction are reflected in the event-related brain potential.

The error-related negativity (ERN) is a negative deflection in the event-related brain potential associated with error processing. A recent theory holds that the ERN is elicited by the impact of a reward prediction error signal carried by the mesencephalic dopamine system on anterior cingulate cortex. The theory predicts that larger ERNs should be elicited by unexpected unfavorable outcomes than by expected unfavorable outcomes. We tested the theory in an experiment in which the frequency of occurrence of reward was varied by condition, reasoning that the system that produces the ERN would come to expect non-reward when rewards were infrequent. Consistent with the theory, we found that larger ERNs were elicited by unexpected absences of reward.

A computational account of altered error processing in older age: Dopamine and the error-related negativity

When participants commit errors or receive feedback signaling that they have made an error, a negative brain potential is elicited. According to Holroyd and Coles’s (in press) neurocomputational model of error processing, this error-related negativity (ERN) is elicited when the brain first detects that the consequences of an action are worse than expected. To study age-related changes in error processing, we obtained performance and ERN measures of younger and high-functioning older adults. Experiment 1 demonstrated reduced ERN amplitudes in older adults in the context of otherwise intact brain potentials. This result could not be attributed to uncertainty about the required response in older adults. Experiment 2 revealed impaired performance and reduced response- and feedback-related ERNs of older adults in a probabilistic learning task. These age changes could be simulated by manipulation of a single parameter of the neurocomputational model, this manipulation corresponding to weakened phasic activity of the mesencephalic dopamine system.

Residual costs in task switching: testing the failure-to-engage hypothesis

Reaction time is typically longer on trials on which the task changes. Thisswitch cost is reduced by the opportunity to prepare for the change before the stimulus onset, but there remains aresidual cost that resists reduction by further opportunity for preparation. De Jong (2000) proposed a model for evaluating the contribution to the residual cost of (1) failure to achieve endogenous task-set reconfiguration on a proportion of trials, and (2) limitations to the completeness of reconfiguration attainable by endogenous means. We report good fits of the model to the data from one previous and one new task-switching experiment, suggesting that the residual switch cost may indeed be attributable to a probabilistic failure to complete advance preparation. But strong incentives for preparation only marginally increased the estimated preparation probability, suggesting some intrinsic limitation to the ability to achieve endogenous preparation for a task switch on every trial.

Errors are foreshadowed in brain potentials associated with action monitoring in cingulate cortex in humans.

Previous studies have reported electrophysiological brain activity that is modulated when subjects commit errors in speeded reaction time tasks. This activity is thought to index an action monitoring system in anterior cingulate cortex that signals the need for performance adjustments to minimize the risk of future errors. Consistent with this view, we report here that performance errors are foreshadowed in a modulation of this brain activity on the immediately preceding trial. We propose that this modulation reflects fluctuations in the efficiency of the action monitoring system, which may occasionally compromise subsequent performance and thus comprise a prelude to performance errors.

Dissociating Response Conflict and Error Likelihood in Anterior Cingulate Cortex

Neuroimaging studies consistently report activity in anterior cingulate cortex (ACC) in conditions of high cognitive demand, leading to the view that ACC plays a crucial role in the control of cognitive processes. According to one prominent theory, the sensitivity of ACC to task difficulty reflects its role in monitoring for the occurrence of competition, or “conflict,” between responses to signal the need for increased cognitive control. However, a contrasting theory proposes that ACC is the recipient rather than source of monitoring signals, and that ACC activity observed in relation to task demand reflects the role of this region in learning about the likelihood of errors. Response conflict and error likelihood are typically confounded, making the theories difficult to distinguish empirically. The present research therefore used detailed computational simulations to derive contrasting predictions regarding ACC activity and error rate as a function of response speed. The simulations demonstrated a clear dissociation between conflict and error likelihood: fast response trials are associated with low conflict but high error likelihood, whereas slow response trials show the opposite pattern. Using the N2 component as an index of ACC activity, an EEG study demonstrated that when conflict and error likelihood are dissociated in this way, ACC activity tracks conflict and is negatively correlated with error likelihood. These findings support the conflict-monitoring theory and suggest that, in speeded decision tasks, ACC activity reflects current task demands rather than the retrospective coding of past performance.

A goal activation approach to the study of executive function: An application to antisaccade tasks

We argue that a general control process, responsible for the activation and maintenance of task goals, is central to the concept of executive function. Failures of this process can become manifest as goal neglect: disregard of a task requirement even though it has been understood (Duncan, 1995). We discuss the results of several published and new experiments using various versions of the antisaccade task in order to investigate the circumstances under which goal neglect is likely to occur. Potentially conflicting results in the literature on adaptive control of saccadic eye movements are argued to be attributable to the extent to which different task versions elicit goal neglect. The results suggest an increased susceptibility to goal neglect of high-functioning older adults (Experiment 1) and of first-episode schizophrenia patients (Experiment 2), but not of patients with obsessive-compulsive disorder (Experiment 3). However, the degree to which such differences in susceptibility become manifest in task performance, is shown to be strongly influenced by manipulations of the relative saliency of task requirements. Theoretical and methodological implications for the study of executive function are discussed.

Neural mechanisms of attention and control: losing our inhibitions?

How are we able to focus our attention on the task at hand while ignoring myriad distractions? An elegant neuroimaging study in this issue finds that, contrary to a widely held view, the prefrontal cortex implements attentional control by amplifying task-relevant information, rather than by inhibiting distracting stimuli.