A psychophysiological analysis of inhibitory motor control in the stop-signal paradigm

EEG signatures associated with stopping are sensitive to preparation

Preparing to stop may "prime" the neural mechanism for stopping and alter brain activity at the time of stopping. Much electroencephalography (EEG) research has studied the N2/P3 complex over frontocentral electrodes during outright stopping. Here, we used differential reward of the stop and go processes in a stop signal task to study the sensitivity of these EEG components to preparation. We found that (a) stopping was faster when it was rewarded; (b) the P3 amplitude was larger for successful versus failed stopping, and this difference was greater when stopping was rewarded over going; (c) the N2 component was observed only on failed stop trials; and (d) there was greater EEG coherence between frontocentral and occipitoparietal electrodes at 12 Hz during the initiation of a go response when stopping was rewarded over going. We propose that frontocentral cortical mechanisms active before and at the time of stopping are sensitive to preparation.

Developmental change in intentional action and inhibition: a heart rate analysis

The ability to inhibit is a major developmental dimension. Previous studies examined developmental change in instructed inhibition. The current study, however, focused on intentional inhibition. We examined heart rate responses to intentional action and inhibition, with a focus on developmental differences. Three age groups (8-10, 11-12, and 18-26 years) performed a child-friendly marble paradigm in which they had to choose between intentionally acting on, or inhibiting, a prepotent response. As instructed, all age groups chose to intentionally inhibit on approximately 50 percent of the intentional trials. A pronounced heart rate deceleration was observed during both intentional action and intentional inhibition, but this deceleration was most pronounced for intentional inhibition. Heart rate responses did not differentiate between age groups, suggesting that intentional action and inhibition reach mature levels early in childhood.

The Contingent Negative Variation Laterality and Dynamics in Antisaccade Task in Normal and Unmedicated Schizophrenic Subjects

Contingent negative variation (CNV) topography, hemispheric asymmetry and time-course were investigated in healthy subjects and non-medicated paranoid schizophrenic patients in two antisaccade paradigms with the short (800-1000 ms) and long (1200-1400 ms) durations of the fixation period. EEG and electrooculogram (EOG) were recorded. Saccade characteristics and mean amplitudes of slow cortical potentials time-locked to peripheral target were analyzed in 23 healthy volunteers and 19 schizophrenic patients. Compared to healthy control subjects, schizophrenic patients had significantly slower antisaccades and committed significantly more erroneous saccades in the both antisaccade tasks. The prolongation of the fixation period resulted in noticeable decrease of error percent in patients group. The analysis of CNV time-course has revealed two distinct stages in both groups. The early CNV stage was represented by a negative wave with the maximal amplitude over midline fronto-central area, and the late stage was characterized by increased CNV amplitude at the midline and left parietal electrode sites. In healthy subjects the simultaneous activation of frontal and parietal areas was observed in the paradigm with the shorter fixation interval; the increase of the fixation period produced consecutive activation of these areas. Schizophrenic patients' CNV amplitude was generally smaller than that of healthy subjects. The most pronounced between-group differences of the negative shift amplitude were revealed at frontal electrode sites during the early CNV stage in both modifications of the antisaccade task. The deficit of frontal activation revealed in patients at the early stage of antisaccade preparatory set in both antisaccadic paradigms may be related to pathogenesis of paranoid schizophrenia.

N1 and N2 ERPs reflect the regulation of automatic approach tendencies to positive stimuli

The Approach-Avoidance Task (AAT) measures automatic approach-avoidance tendencies and their regulation: compatible reactions (approach positive, avoid negative) are faster than incompatible ones (approach negative, avoid positive). The present study assessed event-related potentials (ERPs) in 15 healthy persons for depicting neuropsychological sub-processes of such stimulus-response compatibility (SRC) effects. Early attention allocation preparing efficient stimulus classification (N1 ERP) and response inhibition on the level of response representations (N2 ERP) were found to underlie the solution of the AAT-conflict. For positive stimuli, these processes were enhanced during the incompatible condition avoid positive compared to the compatible condition approach positive. Source localization analysis revealed activity in right occipital areas (N1 ERP), and in left DLPFC and insula (N2 ERP) to be neuronal generators of these electrophysiological SRC effects. This neuronal regulation resulted in no influence of incompatibility at the behavioural level. For negative pictures, we found the reversed pattern: there were no electrophysiological SRC effects, but clear behavioural SRC effects in both RTs and error frequency, i.e. participants were faster and made fewer errors during avoiding than approaching negative pictures. These valence-specific differences are in line with previous studies indicating negative stimuli - probably due to higher importance for survival - to more strongly influence behaviour.

Validation of a within-trial measure of the oculomotor stop process

The countermanding (or stop signal) task requires subjects try to withhold a planned movement upon the infrequent presentation of a stop signal. We have previously proposed a within-trial measure of movement cancellation based on neck muscle recruitment during the cancellation of eye-head gaze shifts. Here, we examined such activity after either a bright or dim stop signal, a manipulation known to prolong the stop signal reaction time (SSRT). Regardless of stop signal intensity, subjects generated an appreciable number of head-only errors during successfully cancelled gaze shifts (compensatory eye-in-head motion ensured gaze stability), wherein subtle head motion toward a peripheral target was ultimately stopped by a braking pulse of antagonist neck muscle activity. Both the SSRT and timing of antagonist muscle recruitment relative to the stop signal increased for dim stop signals and decreased for longer stop signal delays. Moreover, we observed substantial variation in the distribution of antagonist muscle recruitment latencies across our sample. The magnitude and variance of the SSRTs and antagonist muscle recruitment latencies correlated positively across subjects, as did the within-subject changes across bright and dim stop signals. Finally, we fitted our behavioral data with a race model architecture that incorporated a lower threshold for initiating head movements. This model allowed us to estimate the efferent delay between the completion of a central stop process and the recruitment of antagonist neck muscles; the estimated efferent delay remained consistent within subjects across stop signal intensity. Overall, these results are consistent with the hypothesis that neck muscle recruitment during a specific subset of cancelled trials provides a peripheral expression of oculomotor cancellation on a single trial. In the discussion, we briefly speculate on the potential value of this measure for research in basic or clinical domains and consider current issues that limit more widespread use.

When bilinguals choose a single word to speak: Electrophysiological evidence for inhibition of the native language

Behavioral and event-related potential (ERP) measures are reported for a study in which relatively proficient Chinese-English bilinguals named identical pictures in each of their two languages. Production occurred only in Chinese (the first language, L1) or only in English (the second language, L2) in a given block with the order counterbalanced across participants. The repetition of pictures across blocks was expected to produce facilitation in the form of faster responses and more positive ERPs. However, we hypothesized that if both languages are activated when naming one language alone, there might be evidence of inhibition of the stronger L1 to enable naming in the weaker L2. Behavioral data revealed the dominance of Chinese relative to English, with overall faster and more accurate naming performance in L1 than L2. However, reaction times for naming in L1 after naming in L2 showed no repetition advantage and the ERP data showed greater negativity when pictures were named in L1 following L2. This greater negativity for repeated items suggests the presence of inhibition rather than facilitation alone. Critically, the asymmetric negativity associated with the L1 when it followed the L2 endured beyond the immediate switch of language, implying long-lasting inhibition of the L1. In contrast, when L2 naming followed L1, both behavioral and ERP evidence produced a facilitatory pattern, consistent with repetition priming. Taken together, the results support a model of bilingual lexical production in which candidates in both languages compete for selection, with inhibition of the more dominant L1 when planning speech in the less dominant L2. We discuss the implications for modeling the scope and time course of inhibitory processes.

The impact of depression heterogeneity on inhibitory control

OBJECTIVE

Major depressive disorder (MDD) is associated with deficits in executive cognitive function, including inhibitory control. However, inconsistencies have been found across studies. Depression is a heterogeneous disorder and these inconsistencies may therefore relate to heterogeneity in relatively small samples.

METHOD

Here we sought to examine event-related potentials (ERPs) during a cognitive Go/No-Go task in melancholic (n = 60) and non-melancholic depressed patients (n = 54) relative to controls (n = 114).

RESULTS

Behavioural responses indicate that inhibitory control processes are differentially affected by subtypes of depression such that melancholic patients exhibit a greater number of commission errors and more variable response rates in comparison to non-melancholic patients and controls respectively. However, ERPs do not differ during a cognitive Go/No-Go task when ERPs associated with correct responses are examined.

CONCLUSIONS

These findings indicate that while patients with melancholia differ from patients without melancholia and controls, no neurophysiological differences are observed when controlling for observable behavioural impairment.

Dissociable components of cognitive control: an event-related potential (ERP) study of response inhibition and interference suppression

Background

Cognitive control refers to the ability to selectively attend and respond to task-relevant events while resisting interference from distracting stimuli or prepotent automatic responses. The current study aimed to determine whether interference suppression and response inhibition are separable component processes of cognitive control.

Methodology/Principal Findings

Fourteen young adults completed a hybrid Go/Nogo flanker task and continuous EEG data were recorded concurrently. The incongruous flanker condition (that required interference suppression) elicited a more centrally distributed topography with a later N2 peak than the Nogo condition (that required response inhibition).

Conclusions/Significance

These results provide evidence for the dissociability of interference suppression and response inhibition, indicating that taxonomy of inhibition is warranted with the integration of research evidence from neuroscience.

Inhibitory Control Differentiates Rare Target Search Performance in Children

Age-related differences in rare-target search are primarily explained by the speed-accuracy trade-off, primed responses, or decision making. The goal was to examine how motor inhibition influences visual search. Children pressed a key when a rare target was detected. On no-target trials, children withheld reactions. Response time (RT), hits, misses, correct rejection, and false alarms were measured. Tapping tests assessed motor control. Older children tapped faster, were more sensitive to rare targets (higher d'), and reacted more slowly than younger ones. Girls outperformed boys in search sensitivity but not in RT. Motor speed was closely associated with hit rate and RT. Results suggest that development of inhibitory control plays a key role in visual detection. The potential implications for cognitive-motor development and individual differences are discussed.

One action system or two? Evidence for common central preparatory mechanisms in voluntary and stimulus-driven actions

Human behavior is comprised of an interaction between intentionally driven actions and reactions to changes in the environment. Existing data are equivocal concerning the question of whether these two action systems are independent, involve different brain regions, or overlap. To address this question we investigated whether the degree to which the voluntary action system is activated at the time of stimulus onset predicts reaction times to external stimuli. We recorded event-related potentials while participants prepared and executed left- or right-hand voluntary actions, which were occasionally interrupted by a stimulus requiring either a left- or right-hand response. In trials where participants successfully performed the stimulus-driven response, increased voluntary motor preparation was associated with faster responses on congruent trials (where participants were preparing a voluntary action with the same hand that was then required by the target stimulus), and slower responses on incongruent trials. This suggests that early hand-specific activity in medial frontal cortex for voluntary action trials can be used by the stimulus-driven system to speed responding. This finding questions the clear distinction between voluntary and stimulus-driven action systems.

Towards a cognitive and neurobiological model of motivated forgetting

Historically, research on forgetting has been dominated by the assumption that forgetting is passive, reflecting decay, interference, and changes in context. This emphasis arises from the pervasive assumption that forgetting is a negative outcome. Here, we present a functional view of forgetting in which the fate of experience in memory is determined as much by motivational forces that dictate the focus of attention as it is by passive factors. A central tool of motivated forgetting is retrieval suppression, a process whereby people shut down episodic retrieval to control awareness. We review behavioral, neurobiological, and clinical research and show that retrieval suppression leads us to forget suppressed experiences. We discuss key questions necessary to address to develop this model, relationships to other forgetting phenomena, and the implications of this research for understanding recovered memories. This work provides a foundation for understanding how motivational forces influence what we remember of life experience.

Lifespan changes in global and selective stopping and performance adjustments

This study examined stopping and performance adjustments in four age groups (M ages: 8, 12, 21, and 76 years). All participants performed on three tasks, a standard two-choice task and the same task in which stop-signal trials were inserted requiring either the suppression of the response activated by the choice stimulus (global stop task) or the suppression of the response when one stop-signal was presented but not when the other stop-signal occurred (selective stop task). The results showed that global stopping was faster than selective stopping in all age groups. Global stopping matured more rapidly than selective stopping. The developmental gain in stopping was considerably more pronounced compared to the loss observed during senescence. All age groups slowed the response on trials without a stop-signal in the stop task compared to trials in the choice task, the elderly in particular. In addition, all age groups slowed on trials following stop-signal trials, except the elderly who did not slow following successful inhibits. By contrast, the slowing following failed inhibits was disproportionally larger in the elderly compared to young adults. Finally, sequential effects did not alter the pattern of performance adjustments. The results were interpreted in terms of developmental change in the balance between proactive and reactive control.

Dissociation of motor and sensory inhibition processes in normal aging

OBJECTIVE

Age-related cognitive impairments have been attributed to deficits in inhibitory processes that mediate both motor restraint and sensory filtering. However, behavioral studies have failed to show an association between tasks that measure these distinct types of inhibition. In the present study, we hypothesized neural markers reflecting each type of inhibition may reveal a relationship across inhibitory domains in older adults.

METHODS

Electroencephalography (EEG) and behavioral measures were used to explore whether there was an across-participant correlation between sensory suppression and motor inhibition. Sixteen healthy older adult participants (65-80 years) engaged in two separate experimental paradigms: a selective attention, delayed-recognition task and a stop-signal task.

RESULTS

Findings revealed no significant relationship existed between neural markers of sensory suppression (P1 amplitude; N170 latency) and markers of motor inhibition (N2 and P3 amplitude and latency) in older adults.

CONCLUSIONS

These distinct inhibitory domains are differentially impacted in normal aging, as evidenced by previous behavioral work and the current neural findings. Thus a generalized inhibitory deficit may not be a common impairment in cognitive aging.

SIGNIFICANCE

Given that some theories of cognitive aging suggest age-related failure of inhibitory mechanisms may span different modalities, the present findings contribute to an alternative view where age-related declines within each inhibitory modality are unrelated.

Electrophysiological Evidence for Different Inhibitory Mechanisms When Stopping or Changing a Planned Response

People are able to adapt their behavior to changing environmental contingencies by rapidly inhibiting or modifying their actions. Response inhibition is often studied in the stop-signal paradigm that requires the suppression of an already prepared motor response. Less is known about situations calling for a change of motor plans such that the prepared response has to be withheld but another has to be executed instead. In the present study, we investigated whether electrophysiological data can provide evidence for distinct inhibitory mechanisms when stopping or changing a response. Participants were instructed to perform in a choice RT task with two classes of embedded critical trials: Stop signals called for the inhibition of any response, whereas change signals required participants to inhibit the prepared response and execute another one instead. Under both conditions, we observed differences in go-stimulus processing, suggesting a faster response preparation in failed compared with successful inhibitions. In contrast to stop-signal trials, changing a response did not elicit the inhibition-related frontal N2 and did not modulate the parietal mu power decrease. The results suggest that compared with changing a response, additional frontal and parietal regions are engaged when having to inhibit a response.

P300 deficits in adults with attention deficit hyperactivity disorder: a meta-analysis

BACKGROUND

The P300 (P3) event-related potential (ERP) component, a possible endophenotype for attention deficit hyperactivity disorder (ADHD), has been widely examined in children, but received little attention in adults. Our objective was to conduct a meta-analysis of P3 studies in adults with ADHD.

METHOD

We searched the Medline and PsycINFO databases for controlled studies examining both adult ADHD and matched healthy controls. Six relevant publications were identified for the meta-analysis, which had comparable data across studies with regard to the amplitude of ERP components related to target detection (P3, P3b). Pooled effect size (ES) for P3 amplitude as well as the association of the ES with age and gender were investigated using meta-regression.

RESULTS

Comparing the ADHD group versus controls, the pooled effect size for a decrease in P3 amplitude was in the medium range (Cohen's d=-0.55, p=0.0006). Additionally, meta-regression revealed that decrease in P3 amplitude significantly varied with the mean age of ADHD patients (p=0.0087), with a gradual increasing of the difference at higher ages. Results also showed a significant association between the ES and gender, indicating a more pronounced reduction of P3 amplitude in the ADHD group versus controls when females were predominantly represented in the sample.

CONCLUSIONS

To our knowledge, this is the first meta-analysis of P3 characteristics in adults with ADHD. It reveals a significantly decreased P3 amplitude during target detection. Our result that the reduction in P3 amplitude increases with age is interpreted in a neurodevelopmental context.

Measurement of the extraocular spike potential during saccade countermanding

The stop signal task is used to investigate motor inhibition. Several groups have reported partial electromyogram (EMG) activation when subjects successfully withhold manual responses and have used this finding to define the nature of response inhibition properties in the spinal motor system. It is unknown whether subthreshold EMG activation from extraocular muscles can be detected in the saccadic response version of the stop signal task. The saccadic spike potential provides a way to examine extraocular EMG activation associated with eye movements in electroencephalogram (EEG) recordings. We used several techniques to isolate extraocular EMG activation from anterior electrode locations of EEG recorded from macaque monkeys. Robust EMG activation was present when eye movements were made, but no activation was detected when saccades were deemed canceled. This work highlights a key difference between the spinal motor system and the saccade system.

Dissociable Brain Mechanisms Underlying the Conscious and Unconscious Control of Behavior

Cognitive control allows humans to overrule and inhibit habitual responses to optimize performance in challenging situations. Contradicting traditional views, recent studies suggest that cognitive control processes can be initiated unconsciously. To further capture the relation between consciousness and cognitive control, we studied the dynamics of inhibitory control processes when triggered consciously versus unconsciously in a modified version of the stop task. Attempts to inhibit an imminent response were often successful after unmasked (visible) stop signals. Masked (invisible) stop signals rarely succeeded in instigating overt inhibition but did trigger slowing down of response times. Masked stop signals elicited a sequence of distinct ERP components that were also observed on unmasked stop signals. The N2 component correlated with the efficiency of inhibitory control when elicited by unmasked stop signals and with the magnitude of slowdown when elicited by masked stop signals. Thus, the N2 likely reflects the initiation of inhibitory control, irrespective of conscious awareness. The P3 component was much reduced in amplitude and duration on masked versus unmasked stop trials. These patterns of differences and similarities between conscious and unconscious cognitive control processes are discussed in a framework that differentiates between feedforward and feedback connections in yielding conscious experience.

Processing of global and selective stop signals: application of Donders' subtraction method to stop-signal task performance

This paper applied Donders' subtraction method to examine the processing of global and selective stop signals in the stop-signal paradigm. Participants performed on three different versions of the stop task: a global task and two selective tasks. A global task required participants to inhibit their response to a go signal whenever a stop signal was presented (Stop-a task). A selective stop task required participants to inhibit to one stop signal but not to the other (Stop-c task). Another selective stop task required them to inhibit when the response indicated by go and stop signals was the same but not when they were different (Stop-b task). Stop-signal reaction time (SSRT) was shortest for Stop-a and longest for Stop-b, with intermediate values for the Stop-c task. Additional control experiments that manipulated stop probability confirmed the robustness of global and selective stopping latencies even when the stop-signal probability varied. The current findings contribute to the conclusion that Donders' subtraction method provides a useful tool for estimating the durations of subprocesses that together comprise SSRT.

Performance monitoring local field potentials in the medial frontal cortex of primates: supplementary eye field

We describe intracranial local field potentials (LFPs) recorded in the supplementary eye field (SEF) of macaque monkeys performing a saccade countermanding task. The most prominent feature at 90% of the sites was a negative-going polarization evoked by a contralateral visual target. At roughly 50% of sites a negative-going polarization was observed preceding saccades, but in stop signal trials this polarization was not modulated in a manner sufficient to control saccade initiation. When saccades were canceled in stop signal trials, LFP modulation increased with the inferred magnitude of response conflict derived from the coactivation of gaze-shifting and gaze-holding neurons. At 30% of sites, a pronounced negative-going polarization occurred after errors. This negative polarity did not appear in unrewarded correct trials. Variations of response time with trial history were not related to any features of the LFP. The results provide new evidence that error-related and conflict-related but not feedback-related signals are conveyed by the LFP in the macaque SEF and are important for identifying the generator of the error-related negativity.

A combined rTMS and ERP investigation of dorsolateral prefrontal cortex involvement in response inhibition

The stop signal task is used to investigate inhibition of an initiated response. Converging evidence suggests that right inferior prefrontal cortex is involved in this behavior, although other regions in the prefrontal cortex have also been implicated. One technique used to determine the contribution of specific cortical regions to behavior is repetitive transcranial magnetic stimulation (rTMS). In the present study, fourteen subjects performed the stop signal task before and after receiving a train of rTMS to the left and right dorsolateral prefrontal cortex (DLPFC). The effects of rTMS were determined using event-related potential (ERP) measures that have been associated with response inhibition in previous studies. Stimulation of left and right DLPFC did not affect ERP measures of response inhibition. This negative finding is interpreted with caution, but is consistent with a recent study which found that stimulation of the same region had no effect on a behavioral measure of response inhibition.

Movement initiation and inhibition are impaired in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) features central and peripheral paresis owing to the degeneration of upper and lower motor neurons. Here, we asked whether motor preparation and inhibition are also affected. Thirteen ALS patients and thirteen matched controls participated in an event-related brain potentials (ERP) experiment in which a cue stimulus indicated whether the following target stimulus was to be responded to by the left or the right hand by a speeded button press. In 25% of the trials a stop-signal followed the target stimulus (onset asynchrony 150 ms) indicating that participants had to abort the already initiated motor response. ERPs indicated deficits of the ALS patients in the preparation and inhibition of motor responses: The lateralized readiness potential indicating motor preparation had a grossly reduced amplitude. A right frontal negative component following about 200 ms after the stop-signal and known to indicate inhibitory processes was diminished in amplitude and prolonged in latency in ALS. Finally, a later negative component associated with error processing was also reduced in amplitude in ALS. These electrophysiological changes were accompanied by behavioral deficits in the patient group (less efficient stopping of movements, no reaction time adaptation after stop trials). In conclusion, ALS patients showed deficits in both, movement initiation and inhibition, with the latter associated with prefrontal dysfunction.

Voluntary Control of Multisaccade Gaze Shifts During Movement Preparation and Execution

Although the nature of gaze control regulating single saccades is relatively well documented, how such control is implemented to regulate multisaccade gaze shifts is not known. We used highly eccentric targets to elicit multisaccade gaze shifts and tested the ability of subjects to control the saccade sequence by presenting a second target on random trials. Their response allowed us to test the nature of control at many levels: before, during, and between saccades. Although the saccade sequence could be inhibited before it began, we observed clear signs of truncation of the first saccade, which confirmed that it could be inhibited in midflight as well. Using a race model that explains the control of single saccades, we estimated that it took about 100 ms to inhibit a planned saccade but took about 150 ms to inhibit a saccade during its execution. Although the time taken to inhibit was different, the high subject-wise correlation suggests a unitary inhibitory control acting at different levels in the oculomotor system. We also frequently observed responses that consisted of hypometric initial saccades, followed by secondary saccades to the initial target. Given the estimates of the inhibitory process provided by the model that also took into account the variances of the processes as well, the secondary saccades (average latency ∼215 ms) should have been inhibited. Failure to inhibit the secondary saccade suggests that the intersaccadic interval in a multisaccade response is a ballistic stage. Collectively, these data indicate that the oculomotor system can control a response until a very late stage in its execution. However, if the response consists of multiple movements then the preparation of the second movement becomes refractory to new visual input, either because it is part of a preprogrammed sequence or as a consequence of being a corrective response to a motor error.

Somatosensory effects of action inhibition: a study with the stop-signal paradigm

When a weak shock is delivered to the finger immediately before a voluntary movement, or during a delay interval where subjects are prepared to make the movement, shock detection rates worsen progressively as the movement approaches. Further, we previously showed that shock detection improves again if a NoGo signal produces inhibition of a prepared response. Here, we used a somatosensory version of the stop-signal paradigm to investigate inhibitory processing during the 'horserace' period when motor excitation and inhibition processes may be simultaneously active. When subjects made a rapid keypress response to a go-signal, shock detection deteriorated in a time-dependent manner, replicating sensory suppression. However, when go-signals were followed by adaptively delayed stop-signals so that subjects could not inhibit the prepared movement, and made errors of commission, we found a paradoxical brief increase in shock detection performance just after the stop-signal, as if in a NoGo trial. During this brief window, the somatosensory system showed a pattern consistent with motor inhibition, even though the motor system itself was too far advanced in movement execution for action to be inhibited. Most models of stop-signal processing propose a two-horse race between excitation and inhibition, with a winner-takes-all solution. We show that there may be distinct motor and somatosensory races. Moreover, inhibitory processes may lead in the somatosensory race, at least briefly, even when excitatory processes win the motor race.

Neural correlates of successful and partial inhibitions in children: an ERP study

This experiment used event-related potentials (ERPs) to investigate the neural processes underlying the development of response inhibition in a modified version of the go/no-go paradigm [Cragg and Nation [2008] Developmental Science 11(6): 819-827]. N2 and P3 ERP components on correct go trials and partial and successful inhibitions were compared in 7- and 9-year-old children. A larger N2 effect on successful inhibitions was found in 9-year-olds compared to 7-year-olds at fronto-central electrodes. N2 amplitude was positively related to behavioral performance in the 7-year-olds suggesting it may reflect inhibitory processes; however, this relationship was not present in the 9-year-olds. Age differences were also apparent in the go P3, perhaps indicating differences in stimulus processing. The no-go P3 component was larger on successful than partial inhibitions. In contrast, there was no difference in N2 amplitude between partial and successful inhibitions. A significant difference was found in N2 latency however. This suggests that inhibitory processes are similar in both cases but initiated earlier on successful inhibitions. N2 latency was also shorter in 9-year-olds than 7-year-olds supporting an increase in the efficiency of response inhibition with age.

The role of the right inferior frontal gyrus: inhibition and attentional control

There is growing interest regarding the role of the right inferior frontal gyrus (RIFG) during a particular form of executive control referred to as response inhibition. However, tasks used to examine neural activity at the point of response inhibition have rarely controlled for the potentially confounding effects of attentional demand. In particular, it is unclear whether the RIFG is specifically involved in inhibitory control, or is involved more generally in the detection of salient or task relevant cues. The current fMRI study sought to clarify the role of the RIFG in executive control by holding the stimulus conditions of one of the most popular response inhibition tasks–the Stop Signal Task–constant, whilst varying the response that was required on reception of the stop signal cue. Our results reveal that the RIFG is recruited when important cues are detected, regardless of whether that detection is followed by the inhibition of a motor response, the generation of a motor response, or no external response at all.

Models of response inhibition in the stop-signal and stop-change paradigms

The stop-signal paradigm is very useful for the study of response inhibition. Stop-signal performance is typically described as a race between a go process, triggered by a go stimulus, and a stop process, triggered by the stop signal. Response inhibition depends on the relative finishing time of these two processes. Numerous studies have shown that the independent horse-race model of Logan and Cowan [Logan, G.D., Cowan, W.B., 1984. On the ability to inhibit thought and action: a theory of an act of control. Psychological Review 91, 295-327] accounts for the data very well. In the present article, we review the independent horse-race model and related models, such as the interactive horse-race model [Boucher, L., Palmeri, T.J., Logan, G.D., Schall, J.D., 2007. Inhibitory control in mind and brain: an interactive race model of countermanding saccades. Psychological Review 114, 376-397]. We present evidence that favors the independent horse-race model but also some evidence that challenges the model. We end with a discussion of recent models that elaborate the role of a stop process in inhibiting a response.

Performance monitoring in children following traumatic brain injury

BACKGROUND

Executive control deficits are common sequelae of childhood traumatic brain injury (TBI). The goal of the current study was to assess a specific executive control function, performance monitoring, in children following TBI.

METHODS

Thirty-one children with mild-moderate TBI, 18 with severe TBI, and 37 control children without TBI, of comparable age and sex, performed the stop signal task, a speeded choice reaction time task. On occasion, they were presented with a signal to stop their responses. Performance monitoring was defined as the extent of slowing in go-task reaction time following failure to stop responses.

RESULTS

The TBI group as a whole demonstrated less post-error slowing than did controls. This finding suggested impaired error monitoring performance. In addition, time since injury and socioeconomic status predicted less slowing after stopped responses.

CONCLUSIONS

We suggest that alterations in performance monitoring expressed as the inability to notice, regulate and adjust behavior to changing situations are an effect of TBI in children.

The presence of visual gap affects the duration of stopping process

A milestone on which relies the voluntary control of behavior is the ability to shape our motor output to meet the needs of the context which we are continuously facing. Even though it is solidly established that contextual information influence movement generation few studies have so far explored their effects on inhibitory processes. We compared the inhibitory control of arm movements of ten healthy right-handed volunteers in a countermanding reaching paradigm with and without the presence of a temporal gap between the offset of the central target and the peripheral target appearance. We found that this perceptual gap reduces the reaction times of hand movements and, at the same time, increases the duration of the stop process, the stop signal reaction time. The two effects are not correlated implying that inhibition and execution of reaching movement are two independent processes influenced by a common factor: the disengagement of selective attention from the central target. Therefore our results support the idea of the existence of a link between spatial selective attention and inhibitory processes.