Stop-signal Performance Research Articles

Altered Impulse Control in Alcohol Dependence: Neural Measures of Stop Signal Performance

Altered impulse control has been implicated in the shaping of habitual alcohol use and eventual alcohol dependence. We sought to identify the neural correlates of altered impulse control in 24 abstinent patients with alcohol dependence (PAD), as compared to 24 demographics matched healthy control subjects (HC). In particular, we examined the processes of risk taking and cognitive control as the neural endophenotypes of alcohol dependence. To this end, functional magnetic resonance imaging (fMRI) was conducted during a stop signal task (SST), in which a procedure was used to elicit errors in the participants. The paradigm allowed trial-by-trial evaluation of response inhibition, error processing, and post-error behavioral adjustment. Furthermore, by imposing on the subjects to be both fast and accurate, the SST also introduced a distinct element of risk, which participants may or may not avert during the task. Brain imaging data were analyzed with Statistical Parametric Mapping in covariance analyses accounting for group disparity in general performance. The results showed that, compared to HC, PAD demonstrated longer go trial reaction time (RT) and higher stop success rate (SS%). HC and PAD were indistinguishable in stop signal reaction time (SSRT) and post-error slowing (PES). In a covariance analysis accounting for go trial RT and SS%, HC showed greater activity in the left dorsolateral prefrontal cortex than PAD, when subjects with short and long SSRT were contrasted. By comparing PAD and HC directly during stop errors (SE), as contrasted with SS, we observed greater activity in PAD in bilateral visual and frontal cortices. Compared to HC, PAD showed less activation of the right dorsolateral prefrontal cortex during PES, an index of post-error behavioral adjustment. Furthermore, PAD who showed higher alcohol urge at the time of the fMRI were particularly impaired in dorsolateral prefrontal activation, as compared to those with lower alcohol urge. Finally, compared to HC subjects, PAD showed less activity in cortical and subcortical structures including putamen, insula, and amygdala during risk-taking decisions in the SST. These preliminary results provided evidence for altered neural processing during impulse control in PAD. These findings may provide a useful neural signature in the evaluation of treatment outcomes and development of novel pharmacotherapy for alcohol dependence.

Neural Correlates of Speeded as Compared with Delayed Responses in a Stop Signal Task: An Indirect Analog of Risk Taking and Association with an Anxiety Trait

The stop signal task (SST) is widely used to explore neural processes involved in cognitive control. By randomly intermixing stop and go trials and imposing on participants to respond quickly to the go but not the stop signal, the SST also introduces an indirect element of risk, which participants may avert by slowing down or ignore by responding "as usual," during go trials. This "risk-taking" component of the SST has to our knowledge never been investigated. The current study took advantage of variability of go trial reaction time (RT) and compared the post-go go trials that showed a decrease in RT (risk-taking decision) and those post-go go trials that showed an increase in RT ("risk-aversive" decision) in 33 healthy individuals who underwent functional magnetic resonance imaging during the SST. This contrast revealed robust activation in bilateral visual cortices as well as left inferior parietal and posterior cingulate cortices, amygdala, and middle frontal gyrus (P < 0.05, family-wise error [FWE] corrected). Furthermore, we observed that the magnitude of amygdala activity is positively correlated with trait anxiety of the participants. These results thus delineated, for the first time, a neural analog of risk taking during stop signal performance, highlighting a novel aspect and broadening the utility of this behavioral paradigm.

ADHD and Behavioral Inhibition: A Re-examination of the Stop-signal Task

The current study investigates two recently identified threats to the construct validity of behavioral inhibition as a core deficit of attention-deficit/hyperactivity disorder (ADHD) based on the stop-signal task: calculation of mean reaction time from go-trials presented adjacent to intermittent stop-trials, and non-reporting of the stop-signal delay metric. Children with ADHD (n = 12) and typically developing (TD) children (n = 11) were administered the standard stop-signal task and three variant stop-signal conditions. These included a no-tone condition administered without the presentation of an auditory tone; an ignore-tone condition that presented a neutral (i.e., not associated with stopping) auditory tone; and a second ignore-tone condition that presented a neutral auditory tone after the tone had been previously paired with stopping. Children with ADHD exhibited significantly slower and more variable reaction times to go-stimuli, and slower stop-signal reaction times relative to TD controls. Stop-signal delay was not significantly different between groups, and both groups' go-trial reaction times slowed following meaningful tones. Collectively, these findings corroborate recent meta-analyses and indicate that previous findings of stop-signal performance deficits in ADHD reflect slower and more variable responding to visually presented stimuli and concurrent processing of a second stimulus, rather than deficits of motor behavioral inhibition.

Subcortical processes of motor response inhibition during a stop signal task

Previous studies have delineated the neural processes of motor response inhibition during a stop signal task, with most reports focusing on the cortical mechanisms. A recent study highlighted the importance of subcortical processes during stop signal inhibition in 13 individuals and suggested that the subthalamic nucleus (STN) may play a role in blocking response execution (Aron and Poldrack, 2006. Cortical and subcortical contributions to Stop signal response inhibition: role of the subthalamic nucleus. J Neurosci 26, 2424–2433). Here in a functional magnetic resonance imaging (fMRI) study we replicated the finding of greater activation in the STN during stop (success or error) trials, compared to go trials, in a larger sample of subjects (n=30). However, since a contrast between stop and go trials involved processes that could be distinguished from response inhibition, the role of subthalamic activity during stop signal inhibition remained to be specified. To this end we followed an alternative strategy to isolate the neural correlates of response inhibition (Li et al., 2006a. Imaging response inhibition in a stop signal task —– neural correlates independent of signal monitoring and post-response processing. J Neurosci 26, 186–192). We compared individuals with short and long stop signal reaction time (SSRT) as computed by the horse race model. The two groups of subjects did not differ in any other aspects of stop signal performance. We showed greater activity in the short than the long SSRT group in the caudate head during stop successes, as compared to stop errors. Caudate activity was positively correlated with medial prefrontal activity previously shown to mediate stop signal inhibition. Conversely, bilateral thalamic nuclei and other parts of the basal ganglia, including the STN, showed greater activation in subjects with long than short SSRT. Thus, fMRI delineated contrasting roles of the prefrontal-caudate and striato-thalamic activities in mediating motor response inhibition.

How does bilingualism improve executive control? A comparison of active and reactive inhibition mechanisms.

It has been claimed that bilingualism enhances inhibitory control, but the available evidence is equivocal. The authors evaluated several possible versions of the inhibition hypothesis by comparing monolinguals and bilinguals with regard to stop signal performance, inhibition of return, and the attentional blink. These three phenomena, it can be argued, tap into different aspects of inhibition. Monolinguals and bilinguals did not differ in stop signal reaction time and thus were comparable in terms of active-inhibitory efficiency. However, bilinguals showed no facilitation from spatial cues, showed a strong inhibition of return effect, and exhibited a more pronounced attentional blink. These results suggest that bilinguals do not differ from monolinguals in terms of active inhibition but have acquired a better ability to maintain action goals and to use them to bias goal-related information. Under some circumstances, this ability may indirectly lead to more pronounced reactive inhibition of irrelevant information.

Motor Response Inhibition and Execution in the Stop-Signal Task: Development and Relation to ADHD Behaviors

The main aim of this study was to investigate the developmental course of motor response inhibition and execution as measured by the stop-signal task in a population-based sample of 525 4- to 12-year-olds. A further aspiration of the study was to enhance the limited knowledge on how the various stop-signal measures relate to ADHD behaviors in a normal sample. We also wanted to contribute to the theoretical understanding of the various stop-signal measures by examining the relations between the stop-signal measures and performance on tasks reflecting other aspects of response inhibition and execution. Our results showed that the ability to inhibit as well as to execute a motor response as measured by the stop-signal task improved with age during childhood. Of specific interest are the findings suggesting that this task captures the development of motor response inhibition in the late preschool years (age 5 years). Both of the inhibition measures derived from the stop-signal task (i.e., SSRT and probability of inhibition) related significantly to teacher ratings of inattention as well as to performance on tasks tapping other aspects of inhibition. The data provided by this study have thus contributed to the scarce knowledge on early development of motor response inhibition, as well as suggested that the stop-signal task may be a valuable tool for capturing deficient motor response inhibition in ADHD behaviors in normal samples.

Neural Correlates of Impulse Control During Stop Signal Inhibition in Cocaine-Dependent Men

Altered impulse control is associated with substance use disorders, including cocaine dependence. We sought to identify the neural correlates of impulse control in abstinent male patients with cocaine dependence (PCD). Functional magnetic resonance imaging (fMRI) was conducted during a stop signal task that allowed trial-by-trial evaluation of response inhibition. Fifteen male PCD and 15 healthy control (HC) subjects, matched in age and years of education, were compared. Stop signal reaction time (SSRT) was derived on the basis of a horse race model. By comparing PCD and HC co-varied for stop success rate, task-related frustration rating, and post-error slowing, we isolated the neural substrates of response inhibition, independent of attentional monitoring (of the stop signal) and post-response processes including affective responses and error monitoring. Using region of interest analysis, we found no differences between HC and PCD who were matched in stop signal performance in the pre-supplementary motor area (pre-SMA) previously shown to be associated with SSRT. However, compared with HC, PCD demonstrated less activation of the rostral anterior cingulate cortex (rACC), an area thought to be involved in the control of stop signal inhibition. The magnitude of rACC activation also correlated negatively with the total score and the impulse control subscore of the Difficulty in Emotion Regulation Scale in PCD. The current study thus identified the neural correlates of altered impulse control in PCD independent of other cognitive processes that may influence stop signal performance. Relative hypoactivation of the rACC during response inhibition may represent a useful neural marker of difficulties in impulse control in abstinent cocaine-dependent men who are at risk of relapse.

Neural mechanisms underlying trait impulsivity in non-clinical adults: Stop-signal performance and event-related potentials

Impaired inhibitory processing has been implicated in clinical expressions of impulsivity, but it is unknown whether the same deficit underlies the personality trait in healthy, non-clinical populations. The present study examined performance and event-related potentials (ERPs) during a stop-signal task in non-clinical adults who scored in the top (“Low” n = 20) and bottom 15% (“High” n = 20) on Eysenck's Impulsiveness Questionnaire from a sample of 200 subjects. The stop-signal task consisted of a visual choice-RT task and auditory stop-signals presented on 30% of trials. While performance findings revealed no differences between groups, underlying ERPs revealed a number of quantitative differences. Lateralised readiness potential (LRP) amplitude on stop-signal trials was larger in the High than Low group, indicating greater response side-specific motor preparation in the primary motor cortex (PMC), while an N1/P3 complex was evoked on successful stop-signal trials and was also enhanced in the High than Low group. The centrally-maximal successful-stop P3 has previously been implicated as an index of inhibition in the PMC, suggesting enhanced inhibitory processing in the High group. Together these findings indicate that the High impulsivity group was able to counteract an impulsive response style on stop-signal trials with enhanced inhibitory activation, resulting in comparable overt performance to the Low group. These results provide a unique insight into the neural mechanisms underlying trait impulsivity in non-clinical adults.

Motor Response Inhibition in Children With Tourette's Disorder

Motor Response Inhibition in Children With Tourette's Disorder

Gender differences in the neural correlates of response inhibition during a stop signal task

We used functional magnetic resonance imaging to examine gender differences in the neural correlates of response inhibition during a stop signal task. The task has a frequent “go” signal to set up a pre-potent response tendency and a less frequent “stop” signal for subjects to withhold their response. A contrast in brain activation was made between successful and failed inhibitions for individual subjects. We compared 20 men and 20 women matched in age and years of education and in stop signal performance, with stop success rate, post-error slowing and task-related frustration ratings as covariates. The results showed greater activation in men, compared to women, in a wide array of cortical and subcortical areas, including the globus pallidus and motor thalamus during stop signal inhibition. In contrast, no brain regions demonstrated greater activation in women, even at a lower statistical threshold. Moreover, while men activated the medial superior frontal and anterior cingulate cortices, women activated the caudate tail to mediate response inhibition. These results extended gender differences in regional brain activation to response inhibition during a cognitive motor task. Men activated the motor circuitry while women appeared to involve visual association or habit learning during stop signal performance.