Success versus failure in cognitive control: meta-analytic evidence from neuroimaging studies on error processing

Brain mechanisms of error processing have often been investigated using response interference tasks and focusing on the posterior medial frontal cortex, which is also implicated in resolving response conflict in general. Thereby, the role other brain regions may play has remained undervalued. Here, activation likelihood estimation meta-analyses were used to synthesize the neuroimaging literature on brain activity related to committing errors versus responding successfully in interference tasks and to test for commonalities and differences. The salience network and the temporoparietal junction were commonly recruited irrespective of whether responses were correct or incorrect, pointing towards a general involvement in coping with situations that call for increased cognitive control. The dorsal posterior cingulate cortex, posterior thalamus, and left superior frontal gyrus showed error-specific convergence, which underscores their consistent involvement when performance goals are not met. In contrast, successful responding revealed stronger convergence in the dorsal attention network and lateral prefrontal regions. Underrecruiting these regions in error trials may reflect failures in activating the task-appropriate stimulus-response contingencies necessary for successful response execution.

Relation of BOLD response to food-specific and generic motor response inhibition tasks to body fat gain in adults with overweight and obesity

BACKGROUND

Low inhibitory control has been theorized to contribute to the development and maintenance of obesity. Knowledge on the neurobiological indicators of inhibitory control deficits predicting future weight gain is limited. The current study examined if individual differences in blood-oxygenation-level-dependent (BOLD) activity associated with food-specific and general motor response inhibition predict future body fat change in adults with overweight or obesity.

METHODS

BOLD activity and behavioral responses of adults with overweight or obesity (N = 160) were recorded while performing a food-specific stop signal task (n = 92) or a generic stop signal task (n = 68). Percent body fat was measured at baseline, posttest, 3-month, and 6-month follow-up.

RESULTS

Elevated BOLD activity in somatosensory (postcentral gyrus), and attention (precuneus) regions during successful inhibition in the food-specific stop signal task and elevated BOLD activity in a motor region (anterior cerebellar lobe) in the generic stop signal task predicted greater body fat gain over 6-month follow-up. Elevated BOLD activity in inhibitory control regions (inferior-, middle-, superior frontal gyri) and error monitoring regions (anterior cingulate cortex, insula) during erroneous responses in the generic stop signal task predicted body fat loss.

CONCLUSIONS

Results suggest that improving motor response inhibition and error monitoring may facilitate weight loss in adults with overweight and obesity.

An inhibitory signal associated with danger reduces honeybee dopamine levels

Positive and negative experiences can alter animal brain dopamine levels.¹ When first arriving at a rewarding food source or beginning to waggle dance and recruit nestmates to food, honeybees have increased brain dopamine levels, indicating a desire for food.² We provide the first evidence that an inhibitory signal, the stop signal, which counters waggle dancing and is triggered by negative events at the food source, can decrease head dopamine levels and dancing, independent of the dancer having any negative experiences. The hedonic value of food can therefore be depressed simply by the receipt of an inhibitory signal. Increasing the brain dopamine levels reduced the aversive effects of an attack, increasing the time that bees spent subsequently feeding and waggle dancing and decreasing their stop signaling and time spent in the hive. Because honeybees regulate food recruitment and its inhibition at the colony level, these results highlight the complex integration of colony information with a basic and highly conserved neural mechanism in mammals and insects.² VIDEO ABSTRACT.

Response Inhibition in Youth Undergoing Intensive Treatment for Obsessive Compulsive Disorder

Response Inhibition (RI) is the ability to suppress behaviors that are inappropriate for a given context. Obsessive-compulsive disorder (OCD) has been associated with impaired RI in adults as measured by the Stop Signal Task (SST). Conflicting results have been found in terms of the relationship between OCD severity and SST performance, and no studies to date have examined the relationship between SST and response to OCD treatment. Also relatively unknown is whether RI performance in OCD is associated with developmental or gender differences. This naturalistic study examined the relationship between SST performance, OCD severity, and OCD treatment response in a pediatric sample undergoing intensive treatment involving exposure and response prevention and medication management (n = 36). The SST and Children's Yale-Brown Obsessive Compulsive Scale (CYBOCS) were administered at admission and program discharge. OCD severity was not significantly related to stop signal reaction time (SSRT) in the whole sample and among subgroups divided by age and gender. Baseline SSRT and SSRT change did not predict CYBOCS change across treatment in the whole sample, but exploratory analyses indicated both were significant predictors among female adolescents. Results suggest there may be developmental gender differences in the relationship between RI and clinical improvement in pediatric OCD.

Responsiveness to inhibitory signals changes as a function of colony size in honeybees (Apis mellifera)

Biological collectives, like honeybee colonies, can make intelligent decisions and robustly adapt to changing conditions via intricate systems of excitatory and inhibitory signals. In this study, we explore the role of behavioural plasticity and its relationship to network size by manipulating honeybee colony exposure to an artificial inhibitory signal. As predicted, inhibition was strongest in large colonies and weakest in small colonies. This is ecologically relevant for honeybees, for which reduced inhibitory effects may increase robustness in small colonies that must maintain a minimum level of foraging and food stores. We discuss evidence for size-dependent plasticity in other types of biological networks.

Stopping a Response When You Really Care about the Action: Considerations from a Clinical Perspective

Response inhibition, whether reactive or proactive, is mostly investigated in a narrow cognitive framework. We argue that it be viewed within a broader frame than the action being inhibited, i.e., in the context of emotion and motivation of the individual at large. This is particularly important in the clinical domain, where the motivational strength of an action can be driven by threat avoidance or reward seeking. The cognitive response inhibition literature has focused on stopping reactively with responses in anticipation of clearly delineated external signals, or proactively in limited contexts, largely independent of clinical phenomena. Moreover, the focus has often been on stopping efficiency and its correlates rather than on inhibition failures. Currently, the cognitive and clinical perspectives are incommensurable. A broader context may explain the apparent paradox where individuals with disorders characterised by maladaptive action control have difficulty inhibiting their actions only in specific circumstances. Using Obsessive Compulsive Disorder as a case study, clinical theorising has focused largely on compulsions as failures of inhibition in relation to specific internal or external triggers. We propose that the concept of action tendencies may constitute a useful common denominator bridging research into motor, emotional, motivational, and contextual aspects of action control failure. The success of action control may depend on the interaction between the strength of action tendencies, the ability to withhold urges, and contextual factors.

A meta-analytic investigation of the role of reward on inhibitory control

Contemporary theories predict that inhibitory control (IC) can be improved when rewards are available for successfully inhibiting. In non-clinical samples empirical research has demonstrated some support; however, "null" findings have also been published. The aim of this meta-analysis was to clarify the magnitude of the effect of reward on IC and identify potential moderators. A total of 73 articles (contributing k = 80 studies) were identified from PubMed, PsycInfo, and Scopus, published between 1997 and 2020, using a systematic search strategy. A random effects meta-analysis was performed on effect sizes generated from IC tasks, which included rewarded and non-rewarded inhibition trials. Moderator analyses were conducted on clinical samples (vs "healthy controls"), task type (go/no-go vs stop signal vs Flanker vs Simon vs Stroop vs Anti-saccade), reward type (monetary vs points vs other), and age (adults vs children). The prospect of reward for successful inhibition significantly improved IC (SMD = 0.429, 95% CI = 0.288, 0.570, I² = 96.7%) compared with no reward conditions/groups. This finding was robust against influential cases and outliers. The significant effect was present across all IC tasks. There was no evidence of the effect moderated by type of reward, age, or clinical samples. Moderator analyses did not resolve the considerable heterogeneity. The findings suggest that IC is a transient state that fluctuates in response to motivations driven by reward. Future research might examine the potential of improving IC through rewards as a behavioural intervention.

Dissociation of Medial Frontal β-Bursts and Executive Control

The neural mechanisms of executive and motor control concern both basic researchers and clinicians. In human studies, preparation and cancellation of movements are accompanied by changes in the β-frequency band (15-29 Hz) of electroencephalogram (EEG). Previous studies with human participants performing stop signal (countermanding) tasks have described reduced frequency of transient β-bursts over sensorimotor cortical areas before movement initiation and increased β-bursting over medial frontal areas with movement cancellation. This modulation has been interpreted as contributing to the trial-by-trial control of behavior. We performed identical analyses of EEG recorded over the frontal lobe of macaque monkeys (one male, one female) performing a saccade countermanding task. While we replicate the occurrence and modulation of β-bursts associated with initiation and cancellation of saccades, we found that β-bursts occur too infrequently to account for the observed stopping behavior. We also found β-bursts were more common after errors, but their incidence was unrelated to response time (RT) adaptation. These results demonstrate the homology of this EEG signature between humans and macaques but raise questions about the current interpretation of β band functional significance.SIGNIFICANCE STATEMENT The finding of increased β-bursting over medial frontal cortex with movement cancellation in humans is difficult to reconcile with the finding of modulation too late to contribute to movement cancellation in medial frontal cortex of macaque monkeys. To obtain comparable measurement scales, we recorded electroencephalogram (EEG) over medial frontal cortex of macaques performing a stop signal (countermanding) task. We replicated the occurrence and modulation of β-bursts associated with the cancellation of movements, but we found that β-bursts occur too infrequently to account for observed stopping behavior. Unfortunately, this finding raises doubts whether β-bursts can be a causal mechanism of response inhibition, which impacts future applications in devices such as brain-machine interfaces.

Anxious arousal alters prefrontal cortical control of stopping

Anxiety heightens vigilance and stimulus-driven attention to the environment, which may in turn disrupt cognitive control processes such as response inhibition. How this unfolds at the neural level is unclear. Previous evidence implicates the right inferior frontal gyrus (IFG) as an important cortical node in both stimulus-driven attention and inhibitory control. Here we used magnetoencephalography (MEG) to investigate the neural mechanisms involved in the relationship between threat-induced anxiety and stopping during a stop-signal task, where a visual go signal was occasionally followed by an auditory stop signal. Healthy individuals (N = 18) performed the task during the threat of unpredictable shocks and safety to modulate anxious arousal. Behaviorally, we observed that stopping was impaired during threat (i.e. slower estimated stop-signal reaction times), indicating that anxious arousal weakens inhibitory control. MEG source analyses revealed that bilateral IFG and right dorsal prefrontal cortex showed increased beta-band activity (14-30 Hz) to the stop signal that varied as a function of successful stopping during nonanxious (safe) conditions only. Moreover, peak beta-band responses from right IFG were inversely correlated with stopping efficiency during nonanxious conditions. These findings support theoretical claims that beta oscillations function to maintain the current sensorimotor state, and that the lack of differential beta-band activity in prefrontal cortices underlies anxiety-related deficits in inhibitory control. We specifically argue that altered right IFG functioning might directly link impaired cognitive control to heightened stimulus-driven responding in anxiety states.

Preventing a Thought from Coming to Mind Elicits Increased Right Frontal Beta Just as Stopping Action Does

In the stop-signal task, an electrophysiological signature of action-stopping is increased early right frontal beta band power for successful vs. failed stop trials. Here we tested whether the requirement to stop an unwanted thought from coming to mind also elicits this signature. We recorded scalp EEG during a Think/No-Think task and a subsequent stop signal task in 42 participants. In the Think/No-Think task, participants first learned word pairs. In a second phase, they received the left-hand word as a reminder and were cued either to retrieve the associated right-hand word ("Think") or to stop retrieval ("No-Think"). At the end of each trial, participants reported whether they had experienced an intrusion of the associated memory. Finally, they received the left-hand reminder word and were asked to recall its associated target. Behaviorally, there was worse final recall for items in the No-Think condition, and decreased intrusions with practice for No-Think trials. For EEG, we reproduced increased early right frontal beta power for successful vs. failed action stopping. Critically, No-Think trials also elicited increased early right frontal beta power and this was stronger for trials without intrusion. These results suggest that preventing a thought from coming to mind also recruits fast prefrontal stopping.

Neural Signals in Red Nucleus during Reactive and Proactive Adjustments in Behavior

The ability to adjust behavior is an essential component of cognitive control. Much is known about frontal and striatal processes that support cognitive control, but few studies have investigated how motor signals change during reactive and proactive adjustments in motor output. To address this, we characterized neural signals in red nucleus (RN), a brain region linked to motor control, as male and female rats performed a novel variant of the stop-signal task. We found that activity in RN represented the direction of movement and was strongly correlated with movement speed. Additionally, we found that directional movement signals were amplified on STOP trials before completion of the response and that the strength of RN signals was modulated when rats exhibited cognitive control. These results provide the first evidence that neural signals in RN integrate cognitive control signals to reshape motor outcomes reactively within trials and proactivity across them.SIGNIFICANCE STATEMENT Healthy human behavior requires the suppression or inhibition of errant or maladaptive motor responses, often called cognitive control. While much is known about how frontal brain regions facilitate cognitive control, less is known about how motor regions respond to rapid and unexpected changes in action selection. To address this, we recorded from neurons in the red nucleus, a motor region thought to be important for initiating movement in rats performing a cognitive control task. We show that red nucleus tracks motor plans and that selectivity was modulated on trials that required shifting from one motor response to another. Collectively, these findings suggest that red nucleus contributes to modulating motor behavior during cognitive control.

Effects of Ten Sessions of High Frequency Repetitive Transcranial Magnetic Stimulation (HF-rTMS) Add-on Treatment on Impulsivity in Alcohol Use Disorder

Introduction

Alcohol use disorder (AUD) is characterized by increased impulsivity, which is multifactorial and can be assessed by tests like the delay discounting, Go-Nogo, and stop signal task (SST). Impulsivity has been related to poor treatment outcomes in substance use disorders, including AUD. In order to decrease impulsivity or improve inhibitory control, high frequency transcranial magnetic stimulation (HF-rTMS) has gained interest. Studies applying HF-rTMS over the DLPFC of individuals suffering from AUD assessing its effects on impulsivity measures are scarce, and results are inconclusive.

Methods

The current study (registered in Netherlands Trial Register with trial number 5291: https://www.trialregister.nl/trial/5151) applied 10 sessions of HF-rTMS [sixty 10 Hz trains of 5 s at 110% motor threshold (MT)] over the right DLPFC of 80 alcohol dependent patients in clinical treatment on 10 consecutive workdays. At baseline, halfway and after the HF-rTMS treatment, the delay discounting, Go-NoGo, and SST were assessed.

Results

Ten sessions of HF-rTMS over the right DLPFC versus sham HF-rTMS did not affect performance on the delay discounting, Go-NoGo, and SSTs. A significant effect of age was found for the Go-NoGo task, with higher age associated with better performance. Furthermore, no significant correlations were found between difference scores of task performance and baseline impulsivity or severity of AUD.

Discussion

Results of this study, in combination with other studies using HF-rTMS studies in alcohol and substance use disorder, indicate mixed and inconclusive findings of HF-rTMS on impulsivity. Future studies within patient groups hospitalized at the same department are recommended to consider using a sham coil that mimics the sensations on the scalp of active HF-rTMS and to measure motivation across test sessions.

Mid-Frontal Theta Modulates Response Inhibition and Decision Making Processes in Emotional Contexts

Inhibitory control is an integral part of executive functions. In this study, we report event-related spectral perturbation (ERSP) results from 15 healthy adults performing an emotional stop-signal task with the use of happy, disgusted, and neutral emotional faces. Our ERSP results at the group level suggest that changes in low frequency oscillatory power for emotional and neutral conditions start at as early as 200 ms after stimulus onset and 300 ms before button press for successful go trials. To quantify the dynamics of trial-by-trial theta power, we applied the hierarchical drift diffusion model to single-trial ERSP at the mid-frontal electrode site for the go condition. Hierarchical drift diffusion modeling (HDDM) assigned higher frontal low-frequency oscillatory power for evidence accumulation in emotional contexts as compared to a neutral setting. Our results provide new evidence for dynamic modulation of sensory processing of go stimuli in inhibition and extend our knowledge for processing of response inhibition in emotional contexts.

Firing of Putative Dopamine Neurons in Ventral Tegmental Area Is Modulated by Probability of Success during Performance of a Stop-Change Task

Response inhibition, the ability to refrain from unwanted actions, is an essential component of complex behavior and is often impaired across numerous neuropsychiatric disorders such as addiction, attention-deficit hyperactivity disorder (ADHD), schizophrenia, and obsessive-compulsive disorder. Accordingly, much research has been devoted to characterizing brain regions responsible for the regulation of response inhibition. The stop-signal task, a task in which animals are required to inhibit a prepotent response in the presence of a STOP cue, is one of the most well-studied tasks of response inhibition. While pharmacological evidence suggests that dopamine (DA) contributes to the regulation of response inhibition, what is exactly encoded by DA neurons during performance of response inhibition tasks is unknown. To address this issue, we recorded from single units in the ventral tegmental area (VTA), while rats performed a stop-change task. We found that putative DA neurons fired less and higher to cues and reward on STOP trials relative to GO trials, respectively, and that firing was reduced during errors. These results suggest that DA neurons in VTA encode the uncertainty associated with the probability of obtaining reward on difficult trials instead of the saliency associated with STOP cues or the need to resolve conflict between competing responses during response inhibition.

Subthalamic nucleus gamma activity increases not only during movement but also during movement inhibition

Gamma activity in the subthalamic nucleus (STN) is widely viewed as a pro-kinetic rhythm. Here we test the hypothesis that rather than being specifically linked to movement execution, gamma activity reflects dynamic processing in this nucleus. We investigated the role of gamma during fast stopping and recorded scalp electroencephalogram and local field potentials from deep brain stimulation electrodes in 9 Parkinson’s disease patients. Patients interrupted finger tapping (paced by a metronome) in response to a stop-signal sound, which was timed such that successful stopping would occur only in ~50% of all trials. STN gamma (60–90 Hz) increased most strongly when the tap was successfully stopped, whereas phase-based connectivity between the contralateral STN and motor cortex decreased. Beta or theta power seemed less directly related to stopping. In summary, STN gamma activity may support flexible motor control as it did not only increase during movement execution but also during rapid action-stopping.

DOI:http://dx.doi.org/10.7554/eLife.23947.001

Being able to stop walking to allow a car to pass is one example of how terminating a movement midway through can be essential for surviving in an ever-changing world. However, people with Parkinson’s disease sometimes struggle to stop performing a repetitive movement. Also, they may find themselves stopping despite having intended to keep moving. This inability to control stopping and starting can play havoc with everyday activities such as walking.

Some people with Parkinson’s disease find that their symptoms improve after a treatment called deep brain stimulation. Surgeons lower electrodes into specific regions of the brain and use them to block the abnormal electrical activity that causes problems with movement. One of the main brain regions targeted is an area called the subthalamic nucleus. Whenever people initiate a movement, nerve cells in the subthalamic nucleus start to become activated at the same time. This synchronization generates rhythmic waves of activity in the subthalamic nucleus, which are called gamma waves.

To find out whether gamma waves are also involved in stopping a movement, Fischer et al. measured activity in the subthalamic nucleus of nine patients with Parkinson’s disease as they performed a finger tapping exercise. The patients had to tap their finger in time with a metronome, but refrain from tapping whenever they heard a high pitched noise. As expected, a burst of gamma waves accompanied the start of each finger tap. However, Fischer et al. showed that an increase in gamma waves also occurred whenever patients successfully stopped a finger tap midway. Gamma waves may thus help people to interact flexibly with the world around them.

Techniques like deep brain stimulation have the potential to manipulate gamma waves. In order to treat symptoms without causing side effects, we need to work out how to target brain waves that are altered in patients, without disrupting other processes. A key step towards achieving this is to understand how brain waves change during essential behaviours such as stopping an on-going movement.

DOI:http://dx.doi.org/10.7554/eLife.23947.002

Models of inhibitory control

We survey models of response inhibition having different degrees of mathematical, computational and neurobiological specificity and generality. The independent race model accounts for performance of the stop-signal or countermanding task in terms of a race between GO and STOP processes with stochastic finishing times. This model affords insights into neurophysiological mechanisms that are reviewed by other authors in this volume. The formal link between the abstract GO and STOP processes and instantiating neural processes is articulated through interactive race models consisting of stochastic accumulator GO and STOP units. This class of model provides quantitative accounts of countermanding performance and replicates the dynamics of neural activity producing that performance. The interactive race can be instantiated in a network of biophysically plausible spiking excitatory and inhibitory units. Other models seek to account for interactions between units in frontal cortex, basal ganglia and superior colliculus. The strengths, weaknesses and relationships of the different models will be considered. We will conclude with a brief survey of alternative modelling approaches and a summary of problems to be addressed including accounting for differences across effectors, species, individuals, task conditions and clinical deficits.This article is part of the themed issue 'Movement suppression: brain mechanisms for stopping and stillness'.

The Role of Response Inhibition in Medicated and Unmedicated Obsessive-Compulsive Disorder Patients: Evidence from the Stop-Signal Task

BACKGROUND

Numerous studies have investigated response inhibition (RI) in obsessive-compulsive disorder (OCD), with many reporting that OCD patients demonstrate deficits in RI as compared to controls. However, reported effect sizes tend to be modest and results have been inconsistent, with some studies finding intact RI in OCD. To date, no study has examined the effect of medications on RI in OCD patients.

METHODS

We analyzed results from a stop-signal task to probe RI in 65 OCD patients (32 of whom were medicated) and 58 healthy controls (HCs).

RESULTS

There was no statistically significant difference in stop-signal reaction time between the OCD group and the HC group, or between the medicated and unmedicated OCD patients. However, variability was significantly greater in the medicated OCD group compared to the unmedicated group.

CONCLUSIONS

These results indicate that some samples of OCD patients do not have deficits in RI, making it unlikely that deficient RI underlies repetitive behaviors in all OCD patients. Future research is needed to fully elucidate the impact of medication use on stop-signal performance. Implications for future research on the cognitive processes underlying repetitive thoughts and behaviors are discussed.

GABRB1 Single Nucleotide Polymorphism Associated with Altered Brain Responses (but not Performance) during Measures of Impulsivity and Reward Sensitivity in Human Adolescents

Variations in genes encoding several GABA_A receptors have been associated with human drug and alcohol abuse. Among these, a number of human studies have suggested an association between GABRB1, the gene encoding GABA_A receptor β1 subunits, with Alcohol dependence (AD), both on its own and comorbid with other substance dependence and psychiatric illnesses. In the present study, we hypothesized that the GABRB1 genetically-associated increased risk for developing alcoholism may be associated with impaired behavioral control and altered sensitivity to reward, as a consequence of altered brain function. Exploiting the IMAGEN database (Schumann et al., 2010), we explored in a human adolescent population whether possession of the minor (T) variant of the single nucleotide polymorphism (SNP) rs2044081 is associated with performance of tasks measuring aspects of impulsivity, and reward sensitivity that are implicated in drug and alcohol abuse. Allelic variation did not associate with altered performance in either a stop-signal task (SST), measuring one aspect of impulsivity, or a monetary incentive delay (MID) task assessing reward anticipation. However, increased functional magnetic resonance imaging (fMRI) blood-oxygen-level dependent (BOLD) response in the right hemisphere inferior frontal gyrus (IFG), left hemisphere caudate/insula and left hemisphere inferior temporal gyrus (ITG) during MID performance was higher in the minor (T) allelic group. In contrast, during SST performance, the BOLD response found in the right hemisphere supramarginal gyrus, right hemisphere lingual and left hemisphere inferior parietal gyrus indicated reduced responses in the minor genotype. We suggest that β1-containing GABA_A receptors may play a role in excitability of brain regions important in controlling reward-related behavior, which may contribute to susceptibility to addictive behavior.

High post-movement parietal low-beta power during rhythmic tapping facilitates performance in a stop task

Voluntary movements are followed by a post-movement electroencephalography (EEG) beta rebound, which increases with practice and confidence in a task. We hypothesized that greater beta modulation reflects less load on cognitive resources and may thus be associated with faster reactions to new stimuli. EEG was recorded in 17 healthy subjects during rhythmically paced index finger tapping. In a STOP condition, participants had to interrupt the upcoming tap in response to an auditory cue, which was timed such that stopping was successful only in ~ 50% of all trials. In a second condition, participants carried on tapping twice after the stop signal (CONTINUE condition). Thus the conditions were distinct in whether abrupt stopping was required as a second task. Modulation of 12-20 Hz power over motor and parietal areas developed with time on each trial and more so in the CONTINUE condition. Reduced modulation in the STOP condition went along with reduced negative mean asynchronies suggesting less confident anticipation of the timing of the next tap. Yet participants were more likely to stop when beta modulation prior to the stop cue was more pronounced. In the STOP condition, expectancy of the stop signal may have increased cognitive load during movement execution given that the task might have to be stopped abruptly. However, within this condition, stopping ability was increased if the preceding tap was followed by a relatively larger beta increase. Significant, albeit weak, correlations confirmed that increased post-movement beta power was associated with faster reactions to new stimuli, consistent with reduced cognitive load.

Independent component analysis of functional networks for response inhibition: Inter-subject variation in stop signal reaction time

Cognitive control is a critical executive function. Many studies have combined general linear modeling and the stop signal task (SST) to delineate the component processes of cognitive control. For instance, by contrasting stop success (SS) and stop error (SE) trials in the SST, investigators examined regional responses to stop signal inhibition. In contrast to this parameterized approach, independent component analysis (ICA) elucidates brain networks subserving cognitive control. In our earlier work of 59 adults performing the SST during fMRI, we characterized six independent components (ICs). However, none of these ICs correlated with stop signal performance, raising questions about their behavioral validity. Here, in a larger sample (n = 100), we identified and explored 23 ICs for correlation with the stop signal reaction time (SSRT), a measure of the efficiency of response inhibition. At a corrected threshold (P < 0.0005), a paracentral lobule-midcingulate network and a left inferior parietal-supplementary motor-somatomotor network showed a positive correlation between SE beta weight and SSRT. In contrast, a midline cerebellum-thalamus-pallidum network showed a negative correlation between SE beta weight and SSRT. These findings suggest that motor preparation and execution prolongs the SSRT, likely via an interaction between the go and stop processes as suggested by the race model. Behaviorally, consistent with this hypothesis, the difference in G and SE reaction times is positively correlated with SSRT across subjects. These new results highlight the importance of cognitive motor regions in response inhibition and support the utility of ICA in uncovering functional networks for cognitive control in the SST.

Executive control signals in orbitofrontal cortex during response inhibition

Orbitofrontal cortex (OFC) lesions produce deficits in response inhibition and imaging studies suggest that activity in OFC is stronger on trials that require suppression of behavior, yet few studies have examined neural correlates at the single-unit level in a behavioral task that probes response inhibition without varying other factors, such as anticipated outcomes. Here we recorded from single neurons in lateral OFC in a task that required animals in the minority of trials to STOP or inhibit an ongoing movement and respond in the opposite direction. We found that population and single-unit firing was modulated primarily by response direction and movement speed, and that very few OFC neurons exhibited a response independent inhibition signal. Remarkably, the strength of the directional signal was not diminished on STOP trials and was actually stronger on STOP trials during conflict adaptation. Finally, directional signals were stronger during sessions in which rats had the most difficulty inhibiting behavior. These results suggest that "inhibition" deficits observed with OFC interference studies reflect deficits unrelated to signaling the need to inhibit behavior, but instead support a role for OFC in executive functions related to dissociating between two perceptually similar actions during response conflict.

Guanfacine enhances inhibitory control and attentional shifting in early abstinent cocaine-dependent individuals

OBJECTIVES

Attenuation of adrenergic drive and cognitive enhancement, via stimulation of alpha2 pre- and post-synaptic receptors, may selectively enhance executive performance in early abstinent cocaine-dependent individuals. As these cognitive processes underpin important treatment-related behaviors, the alpha2 agonist, guanfacine HCl, may represent an effective pharmaco-therapeutic intervention.

METHODS

Twenty-five early abstinent cocaine-dependent individuals were administered a battery of neurocognitive tasks on entry into treatment (baseline) and again following 3 weeks of either placebo or guanfacine treatment (up to 3 mg). Tasks included: Stop Signal, Stroop, 3-Dimentional Intra-dimensional/Extra-dimensional (IDED) task, Spatial Working Memory (SWM), Paired Associates Learning (PAL), Verbal Fluency and the Rey Auditory Verbal Learning Test (RAVLT).

RESULTS

Compared with placebo, the guanfacine group demonstrated attenuated anxiety and negative affect as well as improved performance on selective executive tests. This included fewer directional errors on the stop signal task, fewer errors on the extra-dimensional shift component of the IDED task and better attentional switching during verbal fluency. Guanfacine did not improve strategic working memory or peripheral memory.

CONCLUSION

Guanfacine improves selective cognitive processes which may underlie salient treatment-related regulatory behaviors. Alpha2 agonists may therefore represent important agents for cocaine dependence.

Functional Brain Activation Associated with Inhibitory Control Deficits in Older Adults

In young adults, canceling an initiated action depends on the right inferior frontal cortex (IFC), presupplementary motor area (preSMA), and the basal ganglia. Older adults show response inhibition deficits, but how this relates to functional brain activation remains unclear. Using event-related functional magnetic resonance imaging, we tested whether older adults (N = 20) exhibit overactivation during stop-signal inhibition as shown for attentional control tasks, or reduced activity compared with young adults (N = 20). We used a modified stop-signal task involving coupled bimanual responses and manipulated whether both or just one hand was cued to stop. Stop-task difficulty was matched across groups. We found a group by condition interaction in supramarginal gyrus, anterior insula, rIFC, and preSMA, with activation increasing for successful Stop versus Go trials in the young adults only. Comparing the groups on Stop trials revealed preSMA and striatum hypoactivity for older adults. White matter tracts connecting rIFC, preSMA, and the subthalamic nuclei were associated with stronger activation of preSMA in older adults, suggesting that maintenance of the brain's structure has positive implications for brain function.

A dual role of EphB1/ephrin-B3 reverse signaling on migrating striatal and cortical neurons originating in the preoptic area: should I stay or go away?

During embryonic development the preoptic area (POA) gives rise to two populations of neurons which are generated at the same time, cortical interneurons and striatal cells. POA-derived cortical interneurons take a superficial path and avoid the developing striatum (Str) when they migrate to their target region. We found that EphB1, which is expressed in the striatal anlage, prevents cortical interneurons from entering the Str via ephrin-B3 reverse signaling. In contrast, for striatal neurons which also express ephrin-B3, EphB1 acts as a stop signal. This dual role of EphB1 is due to differences in ephrin-B3 reverse signaling cascades. For striatal neurons, binding of EphB1 to ephrin-B3 reduces endogenously high levels of pSrc and pFAK, which then causes the cells to stop migration. In contrast, in cortical interneurons EphB1-ephrin-B3 reverse signaling leads to phosphorylation of Src and focal adhesion kinase (FAK) which then mediates repulsion. Consistent with these in vitro findings, in an ephrin-B3 knockout mouse line, we discovered misrouted cortical interneurons in the Str and an over-migration of striatal neurons in their target region. Thus, EphB1/ephrin-B3 reverse signaling has a different impact on two sets of neurons which are generated at the same time and place: it can act as a repulsive cue for migrating neurons or it can terminate neuronal migration, a novel role of the Eph/ephrin system.

Effect of Bhramari Pranayama on response inhibition: Evidence from the stop signal task

Context:

Response inhibition is a key executive control processes. An inability to inhibit inappropriate actions has been linked to a large range of neurologic and neuropsychiatric disorders.

Aims:

Examine the effect of Bhramari Pranayama (Bhpr) on response inhibition in healthy individuals.

Settings and Design:

Thirty-one male students age ranged from 19-31 years from a residential Yoga University, Bengaluru, India were recruited for this study. We used a randomized self as control within-subjects design. Participants were counterbalanced randomly into two different experimental conditions (Bhpr and deep breathing (DB)).

Materials and Methods:

Response inhibition has been measured using a standard tool Stop Signal Task (SST). Each session lasted for 50 min with 10 min for the experimental conditions, preceded and followed by 20 min of assessment. The primary outcome measure was stop signal reaction time (SSRT), an estimate of the subject's capacity for inhibiting prepotent motor responses. Additional measures of interest were the probability of responding on stop signal trials, P (r | s) and mean RT to go stimuli.

Results:

The mean probability of responding on stop signal trials (P (r | s)) during Bhpr and DB are close to 50%, indicating reliable SSRT. Paired sample t-tests showed a significant decrease (P = 0.024) in SSRT after Bhpr session, while the DB group did not show any significant change. Further, t-tests show that the go RT increased significantly after Bhpr (P = 0.007) and no other changes/differences were observed.

Conclusions:

Bhpr enhanced response inhibition and cognitive control in nonclinical participants.

Proactive and reactive inhibitory control in rats

Inhibiting actions inappropriate for the behavioral context, or inhibitory control, is essential for survival and involves both reactively stopping the current prepared action and proactively adjusting behavioral tendencies to increase future performance. A powerful paradigm widely used in basic and clinical research to study inhibitory control is the stop signal task (SST). Recent years have seen a surging interest in translating the SST to rodents to study the neural mechanisms underlying inhibitory control. However, significant differences in task designs and behavioral strategies between rodent and primate studies have made it difficult to directly compare the two literatures. In this study, we developed a rodent-appropriate SST and characterized both reactive and proactive control in rats. For reactive inhibitory control, we found that, unlike in primates, incorrect stop trials in rodents result from two independent types of errors: an initial failure-to-stop error or, after successful stopping, a subsequent failure-to-wait error. Conflating failure-to-stop and failure-to-wait errors systematically overestimates the covert latency of reactive inhibition, the stop signal reaction time (SSRT). To correctly estimate SSRT, we developed and validated a new method that provides an unbiased SSRT estimate independent of the ability to wait. For proactive inhibitory control, we found that rodents adjust both their reaction time and the ability to stop following failure-to-wait errors and successful stop trials, but not after failure-to-stop errors. Together, these results establish a valid rodent model that utilizes proactive and reactive inhibitory control strategies similar to primates, and highlight the importance of dissociating initial stopping from subsequent waiting in studying mechanisms of inhibitory control using rodents.

Stopping eyes and hands: evidence for non-independence of stop and go processes and for a separation of central and peripheral inhibition

In the stop-signal paradigm, participants perform a primary reaction task, for example a visual or auditory discrimination task, and have to react to a go stimulus as quickly as possible with a specified motor response. In a certain percentage of trials, after presentation of the stimulus (go signal), another stimulus (stop signal) is presented with a variable stop-signal delay. Whenever a stop signal occurs, the participant is asked to inhibit the execution of the response. Here, an extended test of the popular horse race model for this task (Logan and Cowan, 1984) is presented. Responses for eye and hand movements in both single-task and dual-task conditions were collected. Saccadic reaction times revealed some significant violations of the model's basic assumption of independent go and inhibition processes for all six participants. Saccades that escaped an early stop signal were systematically slower and had smaller amplitudes compared to saccades without a stop signal. Moreover, the analysis of concomitant electromyographic responses recorded from the upper arm suggests the existence of two separate inhibitory mechanisms: a slow, selective, central inhibitory mechanism and a faster, highly efficient, peripheral one, which is probably ineffective for saccades.

Reconciling the influence of task-set switching and motor inhibition processes on stop signal after-effects

Executive response functions can be affected by preceding events, even if they are no longer associated with the current task at hand. For example, studies utilizing the stop signal task have reported slower response times to “GO” stimuli when the preceding trial involved the presentation of a “STOP” signal. However, the neural mechanisms that underlie this behavioral after-effect are unclear. To address this, behavioral and electroencephalography (EEG) measures were examined in 18 young adults (18–30 years) on “GO” trials following a previously “Successful Inhibition” trial (pSI), a previously “Failed Inhibition” trial (pFI), and a previous “GO” trial (pGO). Like previous research, slower response times were observed during both pSI and pFI trials (i.e., “GO” trials that were preceded by a successful and unsuccessful inhibition trial, respectively) compared to pGO trials (i.e., “GO” trials that were preceded by another “GO” trial). Interestingly, response time slowing was greater during pSI trials compared to pFI trials, suggesting executive control is influenced by both task set switching and persisting motor inhibition processes. Follow-up behavioral analyses indicated that these effects resulted from between-trial control adjustments rather than repetition priming effects. Analyses of inter-electrode coherence (IEC) and inter-trial coherence (ITC) indicated that both pSI and pFI trials showed greater phase synchrony during the inter-trial interval compared to pGO trials. Unlike the IEC findings, differential ITC was present within the beta and alpha frequency bands in line with the observed behavior (pSI > pFI > pGO), suggestive of more consistent phase synchrony involving motor inhibition processes during the ITI at a regional level. These findings suggest that between-trial control adjustments involved with task-set switching and motor inhibition processes influence subsequent performance, providing new insights into the dynamic nature of executive control.

Working memory and response inhibition as one integral phenotype of adult ADHD? A behavioral and imaging correlational investigation

OBJECTIVE

It is an open question whether working memory (WM) and response inhibition (RI) constitute one integral phenotype in attention deficit hyperactivity disorder (ADHD).

METHOD

The authors investigated 45 adult ADHD patients and 41 controls comparable for age, gender, intelligence, and education during a letter n-back and a stop-signal task, and measured prefrontal oxygenation by means of functional near-infrared spectroscopy.

RESULTS

The authors replicated behavioral and cortical activation deficits in patients compared with controls for both tasks and also for performance in both control conditions. In the patient group, 2-back performance was correlated with stop-signal reaction time. This correlation did not seem to be specific for WM and RI as 1-back performance was correlated with go reaction time. No significant correlations of prefrontal oxygenation between WM and RI were found.

CONCLUSION

The authors' findings do not support the hypothesis of WM and RI representing one integral phenotype of ADHD mediated by the prefrontal cortex.

Family history of alcoholism interacts with alcohol to affect brain regions involved in behavioral inhibition

RATIONALE

Impulsive behavior is associated with both alcohol use disorders and a family history of alcoholism (FHA). One operational definition of impulsive behavior is the stop-signal task (SST) which measures the time needed to stop a ballistic hand movement.

OBJECTIVE

Employ functional magnetic resonance imaging (fMRI) to study right frontal responses to stop signals in heavy drinking subjects with and without FHA, and as a function of alcohol exposure.

METHODS

Twenty-two family history-positive (FHP; age = 22.7 years, SD = 1.9) and 18 family history-negative (FHN; age = 23.7, SD = 1.8) subjects performed the SST in fMRI in two randomized visits: once during intravenous infusion of alcohol, clamped at a steady-state breath alcohol (BrAC) concentration of 60 mg/dL, and once during infusion of placebo saline. An independent reference group (n = 13, age = 23.7, SD = 1.8) was used to identify a priori right prefrontal regions activated by successful inhibition (Inh) trials, relative to "Go" trials that carried no need for inhibition [Inh > Go].

RESULTS

FHA interacted with alcohol exposure in right prefrontal cortex, where alcohol reduced [Inh > Go] activation in FHN subjects but not in FHP subjects. Within this right frontal cortical region, stop-signal reaction time also correlated negatively with [Inh > Go] activation, suggesting that the [Inh > Go] activity was related to inhibitory behavior.

CONCLUSIONS

The results are consistent with the low level of response theory (Schuckit, J Stud Alcohol 55:149-158, 1980; Quinn and Fromme, Alcohol Clin Exp Res 35:1759-1770, 2011), with FHP being less sensitive to alcohol's effects.

Stop feeling: inhibition of emotional interference following stop-signal trials

Although a great deal of literature has been dedicated to the mutual links between emotion and the selective attention component of executive control, there is very little data regarding the links between emotion and the inhibitory component of executive control. In the current study we employed an emotional stop-signal task in order to examine whether emotion modulates and is modulated by inhibitory control. Results replicated previous findings showing reduced inhibitory control [longer stop-signal reaction time (SSRT)] following negative, compared to neutral pictures. Most importantly, results show decreased emotional interference following stop-signal trials. These results show that the inhibitory control component of executive control can serve to decrease emotional effects. We suggest that inhibitory control and emotion have a two-way connection in which emotion disrupts inhibitory control and activation of inhibitory control disrupts emotion.

Reelin acts as a stop signal for radially migrating neurons by inducing phosphorylation of n-cofilin at the leading edge

The extracellular matrix protein Reelin, secreted by Cajal-Retzius (CR) cells in the marginal zone (MZ) of the cerebral cortex, is important for neuronal migration during development. Two lipoprotein receptors for Reelin have been identified, apolipoprotein E receptor 2 (ApoER2) and the very low-density lipoprotein receptor (VLDLR). The binding of Reelin to these receptors induces tyrosine phosphorylation of an adapter protein, disabled 1 (Dab1) by src family kinases (SFKs). In the Reelin-deficient mutant reeler, cortical lamination is inverted with many neurons invading the marginal zone and others that are unable to migrate to their destinations and accumulate underneath their predecessors, suggesting a role for Reelin signaling in dynamic cytoskeletal reorganization. At present these effects of Reelin are poorly understood. In our recent study, we showed that Reelin induces serine3 phosphorylation of n-cofilin, an actin-depolymerizing protein promoting the disassembly of F-actin. Phosphorylation of cofilin renders it unable to depolymerize F-actin, thus stabilizing the cytoskeleton. We provided evidence for ApoER2, Dab1, SFKs and phosphatidylinositol-3-kinase (PI3K) to be involved in Reelin-induced cofilin phosphorylation. We found that phosphorylation of cofilin occurs in the leading processes of radially migrating neurons as they grow towards the Reelin-containing marginal zone. By cofilin phosphorylation, Reelin may act as a stop signal for radially migrating neurons.

NOS1 ex1f-VNTR polymorphism affects prefrontal oxygenation during response inhibition tasks

Impulsivity is a trait shared by many psychiatric disorders and therefore a suitable intermediate phenotype for their underlying biological mechanisms. One of the molecular determinants involved is the NOS1 ex1f-VNTR, whose short variants are associated with a variety of impulsive behaviors. Fifty-six healthy controls were stratified into homozygous long (LL) (30 probands) and short (SS) (26 probands) allele groups. Subjects completed a combined stop-signal go/nogo task, while the oxygenation in the prefrontal cortex was measured with functional near-infrared spectroscopy. Electromyography was recorded to control for differences in muscle activity in the two inhibition tasks. Two questionnaires on impulsive traits were completed. Differences between the two tasks are shown by distinct activation patterns within the prefrontal cortex. The nogo task resulted mainly in the activation of the dorsolateral prefrontal cortex (dlPFC), whereas successful and unsuccessful inhibition in the stop-signal task elicited the predicted activity in the inferior frontal cortex (IFC). Although significant differences were found in neither the scores obtained on impulsivity-related questionnaires nor the behavioral data, the LL group displayed increased dlPFC activity during nogo trials and the predicted activation in the IFC during successful inhibition in the stop-signal task, while no significant activation was found in the SS group. Our data confirm an influence of NOS1 ex1f-VNTR on impulsivity, as carriers of the short risk allele exhibited diminished activity of (pre-)frontal brain regions during the inhibition in a stop-signal task. Impairment of prefrontal control with consecutive failure of inhibitory processes might underlie association findings reported previously.

Response inhibition and response monitoring in a saccadic countermanding task in schizophrenia

BACKGROUND

Cognitive control deficits are pervasive in individuals with schizophrenia (SZ) and are reliable predictors of functional outcome, but the specificity of these deficits and their underlying neural mechanisms have not been fully elucidated. The objective of the present study was to determine the nature of response inhibition and response monitoring deficits in SZ and their relationship to symptoms and social and occupational functioning with a behavioral paradigm that provides a translational approach to investigating cognitive control.

METHODS

Seventeen patients with SZ and 16 demographically matched healthy control subjects participated in a saccadic countermanding task. Performance on this task is approximated as a race between movement generation and inhibition processes; this race model provides an estimate of the time needed to cancel a planned movement. Response monitoring can be assessed by reaction time adjustments on the basis of trial history.

RESULTS

Saccadic reaction time was normal, but patients required more time to inhibit a planned saccade. The latency of the inhibitory process was associated with the severity of negative symptoms and poorer occupational functioning. Both groups slowed down significantly after correctly cancelled and erroneously noncancelled stop signal trials, but patients slowed down more than control subjects after correctly inhibited saccades.

CONCLUSIONS

These results suggest that SZ is associated with a difficulty in inhibiting planned movements and an inflated response adjustment effect after inhibiting a saccade. Furthermore, behavioral results are consistent with potential abnormalities in frontal and supplementary eye fields in patients with SZ.

Stress and alcohol cues exert conjoint effects on go and stop signal responding in male problem drinkers

Stress, cues, and pharmacological priming are linked with relapse to addictive behavior. Increased salience and decreased inhibitory control are thought to mediate the effects of relapse-related stimuli. However, the functional relationship between these two processes is unclear. To address this issue, a modified Stop Signal Task was employed, which used Alcohol, Neutral, and Non-Words as Go stimuli, and lexical decision as the Go response. Subjects were 38 male problem drinkers (mean Alcohol Dependence Scale (ADS) score: 18.0). Uncontrollable noise (∼ 10 min at 110 dB) was the stressor; nonalcoholic placebo beer (P-Beer) was the cue manipulation, and alcohol (0.7 g/kg), the pharmacological prime. Half the sample received alcohol, and half P-Beer. Stress and beverage (test drink vs soft drink) were manipulated within subjects on two sessions, with half the sample receiving active manipulations together and half receiving them separately. Go response time (RT) and Stop Signal RT (SSRT) were slower to Alcohol than Neutral words. Stress augmented this bias. Alcohol and P-Beer impaired overall SSRT. Stress impaired neither overall SSRT nor Go RT. SSRT to Neutral words and Non-Words correlated inversely with Go RT to Alcohol and Neutral words, and Non-Words. ADS correlated directly with SSRT to Alcohol words. A resource allocation account was proposed, whereby diversion of limited resources to salient cues effectively yoked otherwise independent Go and Stop processes. Disturbances of prefrontal norepinephrine and dopamine were cited as possibly accounting for these effects. Treatments that optimize prefrontal catecholamine transmission may deter relapse by reducing disinhibitory effects of salient eliciting stimuli.

Calpain inhibition impairs TNF-alpha-mediated neutrophil adhesion, arrest and oxidative burst

Proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-alpha), are increased in many chronic inflammatory disorders, including rheumatoid arthritis, and contribute to recruitment of neutrophils into areas of inflammation. TNF-alpha induces a stop signal that promotes neutrophil firm adhesion and inhibits neutrophil polarization and chemotaxis. Calpain is a calcium-dependent protease that mediates cytoskeletal reorganization during cell migration. Here, we show that calpain inhibition impairs TNF-alpha-induced neutrophil firm adhesion to fibrinogen-coated surfaces and the formation of vinculin-containing focal complexes. Calpain inhibition induces random migration in TNF-alpha-stimulated cells and prevents the generation of reactive oxygen species, but does not alter TNF-alpha-mediated activation of p38 MAPK and ERK MAPK. These findings suggest that the TNF-alpha-induced neutrophil arrest requires the activity of calpain independent of p38 MAPK and ERK signaling seen after TNF-alpha stimulation. Together, our data suggest that therapeutic inhibition of calpain may be beneficial for limiting TNF-alpha-induced inflammatory responses.

Methylphenidate improves response inhibition but not reflection-impulsivity in children with attention deficit hyperactivity disorder (ADHD)

RATIONALE

Impulsivity is a cardinal feature of attention deficit hyperactivity disorder (ADHD), which is thought to underlie many of the cognitive and behavioural symptoms associated with the disorder. Impairments on some measures of impulsivity have been shown to be responsive to pharmacotherapy. However, impulsivity is a multi-factorial construct and the degree to which different forms of impulsivity contribute to impairments in ADHD or respond to pharmacological treatments remains unclear.

OBJECTIVES

The aims of the study were to assess the effects of methylphenidate (MPH) on the performance of children with ADHD on measures of reflection-impulsivity and response inhibition and to compare with the performance of healthy volunteers.

METHODS

Twenty-one boys (aged 7-13 years) diagnosed with ADHD underwent a double-blind, placebo-controlled trial of MPH (0.5 mg/kg) during which they performed the Information Sampling Task (IST) and the Stop Signal Task. A healthy age- and education-matched control group was tested on the same measures without medication.

RESULTS

Children with ADHD were impaired on measures of response inhibition, but did not demonstrate reflection-impulsivity on the IST. However, despite sampling a similar amount of information as their peers, the ADHD group made more poor decisions. MPH improved performance on measures of response inhibition and variability of response, but did not affect measures of reflection-impulsivity or quality of decision-making.

CONCLUSIONS

MPH differentially affected two forms of impulsivity in children with ADHD and failed to ameliorate their poor decision-making on the information sampling test.

N-cadherin regulates ingrowth and laminar targeting of thalamocortical axons

Thalamocortical axons are precisely targeted to cortical layer IV, but the identity of specific molecules that govern the establishment of laminar specificity in the thalamocortical projection has been elusive. In this study, we test the role of N-cadherin, a homophilic cell adhesion molecule, in laminar targeting of thalamocortical axons using cocultured thalamic and cortical slice explants exposed to N-cadherin function-blocking antibodies or inhibitory peptides. In untreated cocultures, labeled thalamocortical axons normally grow to and stop in layer IV, forming terminal-like arbors. In the N-cadherin-blocked cocultures, thalamic axons reach layer IV by growing through deep layers at the same rate as those in the untreated cocultures, but instead of terminating in layer IV, they continue growing uninterruptedly through layer IV and extend into supragranular layers to reach the outermost cortical edge, where some form terminal-like arbors in this aberrant laminar position. In cocultures in which the cortical slice is taken at an earlier maturational stage, one that corresponds to a time when thalamic axons are normally growing through deep layers before the emergence of layer IV from the cortical plate, thalamic axon ingrowth through deep layers is significantly attenuated by N-cadherin blocking reagents. These data indicate that N-cadherin has multifaceted roles in establishing the thalamocortical projection, governing aspects of both thalamic axon ingrowth and laminar targeting by acting as a layer IV stop signal, which progressively change in parallel with the maturational state of the cortex.