Subcortical processes of motor response inhibition during a stop signal task

Involvement of Neurons in the Nonhuman Primate Anterior Striatum in Proactive Inhibition

Behaving as desired requires selecting the appropriate behavior and inhibiting the selection of inappropriate behavior. This inhibitory function involves multiple processes, such as reactive and proactive inhibition, instead of a single process. In this study, two male macaque monkeys were required to perform a task in which they had to sequentially select (accept) or refuse (reject) a choice. Neural activity was recorded from the anterior striatum, which is considered to be involved in behavioral inhibition, focusing on the distinction between proactive and reactive inhibitions. We identified neurons with significant activity changes during the rejection of bad objects. Cluster analysis revealed three distinct groups, of which only one showed increased activity during object rejection, suggesting its involvement in proactive inhibition. This activity pattern was consistent irrespective of the rejection method, indicating a role beyond saccadic suppression. Furthermore, minimal activity changes during the fixation task indicated that these neurons were not primarily involved in reactive inhibition. In conclusion, these findings suggest that the anterior striatum plays a crucial role in cognitive control and orchestrates goal-directed behavior through proactive inhibition, which may be critical in understanding the mechanisms of behavioral inhibition dysfunction that occur in patients with basal ganglia disease.

Multiple insular-prefrontal pathways underlie perception to execution during response inhibition in humans

Inhibiting prepotent responses in the face of external stop signals requires complex information processing, from perceptual to control processing. However, the cerebral circuits underlying these processes remain elusive. In this study, we used neuroimaging and brain stimulation to investigate the interplay between human brain regions during response inhibition at the whole-brain level. Magnetic resonance imaging suggested a sequential four-step processing pathway: initiating from the primary visual cortex (V1), progressing to the dorsal anterior insula (daINS), then involving two essential regions in the inferior frontal cortex (IFC), namely the ventral posterior IFC (vpIFC) and anterior IFC (aIFC), and reaching the basal ganglia (BG)/primary motor cortex (M1). A combination of ultrasound stimulation and time-resolved magnetic stimulation elucidated the causal influence of daINS on vpIFC and the unidirectional dependence of aIFC on vpIFC. These results unveil asymmetric pathways in the insular-prefrontal cortex and outline the macroscopic cerebral circuits for response inhibition: V1→daINS→vpIFC/aIFC→BG/M1.

Changes in Functional Connectivity Relate to Modulation of Cognitive Control by Subthalamic Stimulation

Subthalamic (STN) deep brain stimulation (DBS) in Parkinson's disease (PD) patients not only improves kinematic parameters of movement but also modulates cognitive control in the motor and non-motor domain, especially in situations of high conflict. The objective of this study was to investigate the relationship between DBS-induced changes in functional connectivity at rest and modulation of response- and movement inhibition by STN-DBS in a visuomotor task involving high conflict. During DBS ON and OFF conditions, we conducted a visuomotor task in 14 PD patients who previously underwent resting-state functional MRI (rs-fMRI) acquisitions DBS ON and OFF as part of a different study. In the task, participants had to move a cursor with a pen on a digital tablet either toward (automatic condition) or in the opposite direction (controlled condition) of a target. STN-DBS induced modulation of resting-state functional connectivity (RSFC) as a function of changes in behavior ON versus OFF DBS was estimated using link-wise network-based statistics. Behavioral results showed diminished reaction time adaptation and higher pen-to-target movement velocity under DBS. Reaction time reduction was associated with attenuated functional connectivity between cortical motor areas, basal ganglia, and thalamus. On the other hand, increased movement velocity ON DBS was associated with stronger pallido-thalamic connectivity. These findings suggest that decoupling of a motor cortico-basal ganglia network underlies impaired inhibitory control in PD patients undergoing subthalamic DBS and highlight the concept of functional network modulation through DBS.

Involvement of neurons in the non-human primate anterior striatum in proactive inhibition

Behaving as desired requires selecting the appropriate behavior and inhibiting the selection of inappropriate behavior. This inhibitory function involves multiple processes, such as reactive and proactive inhibition, instead of a single process. In this study, macaque monkeys were required to perform a task in which they had to sequentially select (accept) or refuse (reject) a choice. Neural activity was recorded from the anterior striatum, which is considered to be involved in behavioral inhibition, focusing on the distinction between proactive and reactive inhibitions. We identified neurons with significant activity changes during the rejection of bad objects. Cluster analysis revealed three distinct groups, of which one showed obviously increased activity during object rejection, suggesting its involvement in proactive inhibition. This activity pattern was consistent irrespective of the rejection method, indicating a role beyond mere saccadic suppression. Furthermore, minimal activity changes during the fixation task indicated that these neurons were not primarily involved in reactive inhibition. In conclusion, these findings suggest that the anterior striatum plays a crucial role in cognitive control and orchestrates goal-directed behavior through proactive inhibition, which may be critical in understanding the mechanisms of behavioral inhibition dysfunction that occur in patients with basal ganglia disease.

Subthalamic Activity for Motor Execution and Cancelation in Monkeys

The subthalamic nucleus (STN) receives cortical inputs via the hyperdirect and indirect pathways, projects to the output nuclei of the basal ganglia, and plays a critical role in the control of voluntary movements and movement disorders. STN neurons change their activity during execution of movements, while recent studies emphasize STN activity specific to cancelation of movements. To address the relationship between execution and cancelation functions, we examined STN activity in two Japanese monkeys (Macaca fuscata, both sexes) who performed a goal-directed reaching task with a delay that included Go, Cancel, and NoGo trials. We first examined responses to the stimulation of the forelimb regions in the primary motor cortex and/or supplementary motor area. STN neurons with motor cortical inputs were found in the dorsal somatomotor region of the STN. All these STN neurons showed activity changes in Go trials, suggesting their involvement in execution of movements. Part of them exhibited activity changes in Cancel trials and sustained activity during delay periods, suggesting their involvement in cancelation of planed movements and preparation of movements, respectively. The STN neurons rarely showed activity changes in NoGo trials. Go- and Cancel-related activity was selective to the direction of movements, and the selectivity was higher in Cancel trials than in Go trials. Changes in Go- and Cancel-related activity occurred early enough to initiate and cancel movements, respectively. These results suggest that the dorsal somatomotor region of the STN, which receives motor cortical inputs, is involved in preparation and execution of movements and cancelation of planned movements.

Cortical and subcortical contributions to non-motor inhibitory control: an fMRI study

Inhibition is a core executive cognitive function. However, the neural correlates of non-motor inhibitory control are not well understood. We investigated this question using functional Magnetic Resonance Imaging (fMRI) and a simple Count Go/NoGo task (n = 23), and further explored the causal relationships between activated brain regions. We found that the Count NoGo task activated a distinct pattern in the subcortical basal ganglia, including bilateral ventral anterior/lateral nucleus of thalamus (VA/VL), globus pallidus/putamen (GP/putamen), and subthalamic nucleus (STN). Stepwise regressions and mediation analyses revealed that activations in these region(s) were modulated differently by only 3 cortical regions i.e. the right inferior frontal gyrus/insula (rIFG/insula), along with left IFG/insula, and anterior cingulate cortex/supplementary motor area (ACC/SMA). The activations of bilateral VA/VL were modulated by both rSTN and rIFG/insula (with rGP/putamen as a mediator) independently, and the activation of rGP/putamen was modulated by ACC/SMA, with rIFG/insula as a mediator. Our findings provide the neural correlates of inhibitory control of counting and causal relationships between them, and strongly suggest that both indirect and hyperdirect pathways of the basal ganglia are involved in the Count NoGo condition.

The Pathogenesis of Disinhibition in Patients with Traumatic Brain Injury: A Two Patient Case Report

Higher brain dysfunction commonly occurs following traumatic brain injury (TBI), and may manifest in a social behavioral impairment which can significantly impede active social participation. We report two cases, one of voyeurism and the second of alcohol abuse, which might have been caused by TBI resulting in disinhibition, a type of social behavioral impairment. We discuss the underlying pathophysiological mechanisms to raise awareness of such cases and aid the development of effective interventions. Patient 1 suffered a TBI at 18 years of age, 2 years after which he presented repeated episodes of sexually deviant behavior (voyeurism). At 28, he committed suicide, since he was unable to control his aberrant behavior. Patient 2 suffered a TBI at the age of 13. He first displayed problematic behavior 7 years later, which included drinking excessive amounts of alcohol and stealing while inebriated. Despite both patients having sound moral judgment, they had irrational and uncontrollable impulses of desire. Imaging findings could explain the possible causes of impulse control impairments. Damage to the basal ganglia and limbic system, which are involved in social behavior, presumably led to desire-dominated behavior, leading to the patients conducting unlawful acts despite intact moral judgment. It is crucial to educate society about the prevalence of these disorders, explain how these disinhibitions start, and develop effective interventions.

Methylphenidate as a treatment option for substance use disorder: a transdiagnostic perspective

A transition in viewing mental disorders from conditions defined as a set of unique characteristics to one of the quantitative variations on a collection of dimensions allows overlap between disorders. The overlap can be utilized to extend to treatment approaches. Here, we consider the overlap between attention-deficit/hyperactivity disorder and substance use disorder to probe the suitability to use methylphenidate as a treatment for substance use disorder. Both disorders are characterized by maladaptive goal-directed behavior, impaired cognitive control, hyperactive phasic dopaminergic neurotransmission in the striatum, prefrontal hypoactivation, and reduced frontal cortex gray matter volume/density. In addition, methylphenidate has been shown to improve cognitive control and normalize associated brain activation in substance use disorder patients and clinical trials have found methylphenidate to improve clinical outcomes. Despite the theoretical basis and promising, but preliminary, outcomes, many questions remain unanswered. Most prominent is whether all patients who are addicted to different substances may equally profit from methylphenidate treatment.

The impact of emotional stimuli on response inhibition in an inpatient and day-hospital patient psychosomatic cohort

Objectives

To correctly recognize and respond to your counterpart's emotion is essential for a successful get-together. To ensure this, emotional processes and inhibitory control are linked and interact with each other. However, this interaction can be altered in several mental disorders. In a group of psychosomatic patients, we investigated possible differences in the response inhibition between neutral and emotional stimuli and whether a psychosomatic inpatient and day-hospital patient treatment influences response inhibition profiles.

Methods

One hundred and one patients, diagnosed with different psychiatric diagnoses (77 women, 41.43 ± 13.13 years), completed an emotional stop-signal task (ESST) and an impulsive behavior scale upon admission in an inpatient and day-hospital patient treatment on a psychosomatic ward (T0) and at discharge (T1). Patients with depressive disorders completed the test again after 1 year (follow-up measurement T2, n = 22). Emotional stimuli were angry and neutral faces. Stop-signal reaction time (SSRT) and stop-signal delay (SSD) were calculated as the main behavioral parameters.

Results

We found a significantly higher SSRT for neutral than angry faces at both admission (8.538 ms, p < 0.001) and discharge (11.142 ms, p < 0.001), with a matching higher SSD for angry than neutral faces at both timepoints (T0: 8.360 ms, p < 0.001, T1: (6.950 ms, p < 0.001). The SSRT for angry faces significantly decreased after treatment (-8.485 ms, p = 0.0110). For neutral faces, the decrease failed to reach significance (-5.881 ms, p = 0.250). A significant decrease in SSRT for neutral faces in patients with depressive disorders was found 1 year after discharge compared with admission (-19.040 ms, p = 0.0380).

Conclusion

Our data demonstrate a decreased response inhibition for neutral compared with emotional stimuli and an improved response inhibition for angry faces after discharge in a psychosomatic inpatient and day-hospital patient cohort. Additionally, patients with depressive disorders displayed a significantly better response inhibition for neutral faces 1 year after discharge compared with the baseline measurement. With this study, we provide more evidence for altered emotional response inhibition in different mental disorders and a hint that psychosomatic inpatient and day-hospital patient treatment may help to normalize it, even if the effects remained small and it needs further research to prove causality.

Cultural Differences in Inhibitory Control: An ALE Meta-Analysis

Culture greatly influences our attitudes, beliefs, and behaviors, affecting how we communicate and make decisions. There is an ongoing debate regarding the belief that people from Eastern cultures possess greater self-control abilities when compared to people from Western cultures. In this study, we conducted a meta-analysis using the Activation Likelihood Estimation (ALE) algorithm to compare 30 studies (719 subjects, 373 foci) that used fMRI to investigate the performance in Go-Nogo and Stop Signal Tasks of participants from Western and/or Eastern countries. Our meta-analysis found differences between the networks activated in Eastern and Western culture participants. The right prefrontal cortex showed distinct patterns, with the Inferior Frontal gyrus more active in the Eastern group and the middle and superior frontal gyri more active in the Western group. Our findings suggest that Eastern culture subjects have a higher tendency to activate brain regions involved in proactive inhibitory control, while Western culture subjects rely more on reactive inhibitory brain regions during cognitive control tasks. This implies that proactive inhibition may play a crucial role in promoting the collective and interdependent behavior typical of Eastern cultures, while reactive inhibition may be more important for efficient cognitive control in subjects of Western cultures that prioritize individualism and independence.

A circuit-based approach to modulate hypersexuality in Parkinson's disease

AIM

Impulse-control disorder is a common neuropsychiatric complication in Parkinson's disease (PD) under dopamine replacement therapy. Prior studies tested the balance between enhanced desire towards reward and cognitive control deficits, hypothesized to be biased towards the former in impulse control disorders. We provide evidence for this hypothesis by measuring behavioral and neural patterns behind the influence of sexual desire over response inhibition and tools towards functional restoration using repetitive transcranial stimulation in patients with hypersexuality as predominant impulsive disorder.

METHODS

The effect of sexual cues on inhibition was measured with a novel erotic stop-signal task under on and off dopaminergic medication. Task-related functional and anatomical connectivity models were estimated in 16 hypersexual and 17 nonhypersexual patients with PD as well as in 17 healthy controls. Additionally, excitatory neuromodulation using intermittent theta-burst stimulation (sham-controlled) was applied over the pre-supplementary motor area in 20 additional hypersexual patients with PD aiming to improve response inhibition.

RESULTS

Compared with their nonhypersexual peers, patients with hypersexuality recruited caudate, pre-supplementary motor area, ventral tegmental area, and anterior cingulate cortex while on medication. Reduced connectivity was found between pre-supplementary motor area and caudate nucleus in hypersexual compared with nonhypersexual patients (while medicated), a result paralleled by compensatory enhanced anatomical connectivity. Furthermore, stimulation over the pre-supplementary motor area improved response inhibition in hypersexual patients with PD when exposed to sexual cues.

CONCLUSION

This study, therefore, has identified a specific fronto-striatal and mesolimbic circuitry underlying uncontrolled sexual responses in medicated patients with PD where cortical neuromodulation halts its expression.

Is cortical inhibition in primary motor cortex related to executive control?

Recent research using paired-pulse transcranial magnetic stimulation (TMS) has shown that the speed with which people can stop an action is linked to GABAergic inhibitory activity in the motor system. Specifically, a significant proportion of the variance in stop signal reaction time (SSRT; a widely used measure of inhibitory control) is accounted for by short-interval cortical inhibition (SICI). It is still unclear whether this relationship reflects a broader link between GABAergic processes and executive functions, or a specific link between GABAergic processes and motor stopping ability. The current study sought to replicate the correlation between SSRT and SICI while investigating whether this association generalises to other measures of inhibitory control and working memory, and to long-interval cortical inhibition (LICI). Participants completed a battery of inhibition (Stop-Signal, Stroop, Flanker) and working memory (n-back, Digit Span, and Operation Span) tasks. We replicated the correlation between SICI and SSRT but found no other correlations between behavioural measures of executive control and the two cortical measures of inhibition. These findings indicate that the relationship between SSRT and SICI is specific to a particular property of response inhibition and likely reflects the function of local inhibitory networks mediated by GABA_A.

Effect of different sport environments on proactive and reactive motor inhibition: A study on open- and closed-skilled athletes via mouse-tracking procedure

This study aimed to investigate the effect of different sport environments (open-and closed-skill sports) on proactive and reactive inhibitory processes as two distinct components of motor inhibition. A mouse-tracking procedure was employed to compare behavioral performance among three groups of participants (tennis players, swimmers and non-athletes) in non-sport-specific cued Go/No-Go (GNG) and Stop Signal Task (SST), which mainly engage proactive and reactive inhibitory control, respectively. Reaction times (RTs), inhibitory failures, and Stop Signal Reaction Times (SSRTs) were measured. To investigate dynamic aspects of inhibitory control, movement trajectories classified as one-shot (absence of trajectory alteration reflected in a steep slope) or non-one-shot (non-linear/multipeaked trajectory, with one or multiple corrections) were analyzed and compared among groups. Results showed no group differences in RTs in Go/No-Go and Stop conditions. SSRTs were significant shorter for the athletes than non-athletes in SST, but no differences emerged for inhibitory failures in cued GNG. During inhibitory failures athletes showed higher proportion of non-one-shot movements than non-athletes. Higher proportion of non-one-shot profiles was observed in cued GNG compared to SST. Finally, no differences between open-and closed-skilled athletes were found in both tasks. Our findings suggest that both proactive and reactive inhibitory controls do benefit from sport practice, but open-and closed-skill sports do not differ in influencing inhibitory processes. Movement profile analysis could be a promising, complementary behavioral analysis to integrate for more fine-grained evaluation and differentiation of inhibitory motor control in athletes, specifically when using GNG tasks.

Unconscious Conflict Adaptation of Heroin Abstainers

Conflict adaptation is representative of the dynamic cognitive control process, which reflects the adaptability and flexibility of personal cognitive processing. Cognitive control plays an important role in drug use and relapse in addicts. Previous studies have identified conscious conflict adaptation in drug addicts. The present study examined unconscious conflict adaptation in persons with heroin use disorder using an arrow version meta-contrast masking task. The results found that persons with heroin use disorder had smaller unconscious conflict adaptation compared to the healthy control group. This may be a result of functional brain damage caused by long-term drug use.

Exploring stop signal reaction time over two sessions of the anticipatory response inhibition task

Various behavioural tasks measure response inhibition encompassing the ability to cancel unwanted actions, evaluated via stop signal reaction time (SSRT). It is unclear whether SSRT is an unchangeable inherent measure of inhibitory network integrity or whether it can improve with repetition. The current study explored if and how SSRT changed over two sessions for the Anticipatory Response Inhibition Task (ARIT), and how this compared with the Stop Signal Task (SST). Forty-four participants repeated the ARIT and SST over two sessions. SSRT and its constituent measures (Go trial reaction time, stop signal delay) were calculated. SSRT reflecting non-selective response inhibition was consistent between sessions in the ARIT and SST (both p > 0.293). Reaction time and stop signal delay also remained stable across sessions in the ARIT (all p > 0.063), whereas in the SST, reaction time (p = 0.013) and stop signal delay (p = 0.009) increased. SSRT reflecting behaviourally selective stopping on the ARIT improved (p < 0.001) over two sessions, which was underpinned by changes to reaction time (p < 0.001) and stop signal delay (p < 0.001). Overall, the maximal efficiency of non-selective inhibition remained stable across two sessions in the ARIT. Results of the SST confirmed that non-selective inhibition can, however, be affected by more than inhibitory network integrity. Behaviourally selective stopping on the ARIT changed across sessions, suggesting the sequential neural process captured by the SSRT occurred more quickly in session two. These findings have implications for future studies that necessitate behavioural measures over multiple sessions.

Comparing Stop Signal Reaction Times in Alzheimer's and Parkinson's Disease

BACKGROUND

To investigate the relative contributions of cerebral cortex and basal ganglia to movement stopping, we tested the optimum combination Stop Signal Reaction Time (ocSSRT) and median visual reaction time (RT) in patients with Alzheimer's disease (AD) and Parkinson's disease (PD) and compared values with data from healthy controls.

METHODS

Thirty-five PD patients, 22 AD patients, and 29 healthy controls were recruited to this study. RT and ocSSRT were measured using a hand-held battery-operated electronic box through a stop signal paradigm.

RESULT

The mean ocSSRT was found to be 309 ms, 368 ms, and 265 ms in AD, PD, and healthy controls, respectively, and significantly prolonged in PD compared to healthy controls (p = 0.001). The ocSSRT but not RT could separate AD from PD patients (p = 0.022).

CONCLUSION

Our data suggest that subcortical networks encompassing dopaminergic pathways in the basal ganglia play a more important role than cortical networks in movement-stopping. Combining ocSSRT with other putative indices or biomarkers of AD (and other dementias) could increase the accuracy of early diagnosis.

A causal role of anterior prefrontal-putamen circuit for response inhibition revealed by transcranial ultrasound stimulation in humans

Stopping an inappropriate response requires the involvement of the prefrontal-subthalamic hyperdirect pathway. However, how the prefrontal-striatal indirect pathway contributes to stopping is poorly understood. In this study, transcranial ultrasound stimulation is used to perform interventions in a task-related region in the striatum. Functional magnetic resonance imaging (MRI) reveals activation in the right anterior part of the putamen during response inhibition, and ultrasound stimulation to the anterior putamen, as well as the subthalamic nucleus, results in significant impairments in stopping performance. Diffusion imaging further reveals prominent structural connections between the anterior putamen and the right anterior part of the inferior frontal cortex (IFC), and ultrasound stimulation to the anterior IFC also shows significant impaired stopping performance. These results demonstrate that the right anterior putamen and right anterior IFC causally contribute to stopping and suggest that the anterior IFC-anterior putamen circuit in the indirect pathway serves as an essential route for stopping.

Motivation(s) from control: response-effect contingency and confirmation of sensorimotor predictions reinforce different levels of selection

Humans and other animals live in dynamic environments. To reliably manipulate the environment and attain their goals they would benefit from a constant modification of motor-responding based on responses' current effect on the current environment. It is argued that this is exactly what is achieved by a mechanism that reinforces responses which have led to accurate sensorimotor predictions. We further show that evaluations of a response's effectiveness can occur simultaneously, driven by at least two different processes, each relying on different statistical properties of the feedback and affecting a different level of responding. Specifically, we show the continuous effect of (a) a sensorimotor process sensitive only to the conditional probability of effects given that the agent acted on the environment (i.e., action-effects) and of (b) a more abstract judgement or inference that is also sensitive to the conditional probabilities of occurrence of feedback given no action by the agent (i.e., inaction-effects). The latter process seems to guide action selection (e.g., should I act?) while the former the manner of the action's execution. This study is the first to show that different evaluation processes of a response's effectiveness influence different levels of responding.

The motor inhibitory network in patients with asymmetrical Parkinson's disease: An fMRI study

Recent imaging studies with the stop-signal task in healthy individuals indicate that the subthalamic nucleus, the pre-supplementary motor area and the inferior frontal gyrus are key components of the right hemisphere “inhibitory network”. Limited information is available regarding neural substrates of inhibitory processing in patients with asymmetric Parkinson’s disease. The aim of the current fMRI study was to identify the neural changes underlying deficient inhibitory processing on the stop-signal task in patients with predominantly left-sided Parkinson’s disease. Fourteen patients and 23 healthy controls performed a stop-signal task with the left and right hands. Behaviorally, patients showed delayed response inhibition with either hand compared to controls. We found small imaging differences for the right hand, however for the more affected left hand when behavior was successfully inhibited we found reduced activation of the inferior frontal gyrus bilaterally and the insula. Using the stop-signal delay as regressor, contralateral underactivation in the right dorsolateral prefrontal cortex, inferior frontal and anterior putamen were found in patients. This finding indicates dysfunction of the right inhibitory network in left-sided Parkinson’s disease. Functional connectivity analysis of the left subthalamic nucleus showed a significant increase of connectivity with bilateral insula. In contrast, the right subthalamic nucleus showed increased connectivity with visuomotor and sensorimotor regions of the cerebellum. We conclude that altered inhibitory control in left-sided Parkinson’s disease is associated with reduced activation in regions dedicated to inhibition in healthy controls, which requires engagement of additional regions, not observed in controls, to successfully stop ongoing actions.

Gray matter structural plasticity in patients with basal ganglia germ cell tumors: A voxel-based morphometry study

BACKGROUND

Basal ganglia germ cell tumors (BGGCTs) are rare intracranial germ cell tumors (iGCTs) that often presents with cognitive impairment.

OBJECTIVE

To assess structural brain plasticity in the presence of unilateral basal ganglia germ cell tumors (BGGCTs), and the correlation between gray matter volume (GMV) changes and cognitive tests.

MATERIALS AND METHODS

We applied voxel-based morphometry (VBM) to structural magnetic resonance imaging (MRI) scans to compare a sample of 41 patients with BGGCTs in the left (n = 22) or right (n = 19) and a sample of 16 patients as control group using a two-sample t-test, correcting for family-wise-errors. A battery of cognitive tests was administered to all BGGCTs patients prior to MRI. We used Pearson correlation analysis to assess the correlation between cognitive test scores and GMV changes.

RESULTS

In patients with left BGGCTs, whole-brain VBM analysis revealed a large cluster of voxels reflecting an increase in GMV in the left parahippocampal region (k = 529 voxels, T = 4.18, p < 0.01), right middle cingulate cortex (k = 172 voxels, T = 3.96, p < 0.01), and a decrease in volume in the left thalamus (k = 527 voxels, T = -4.88, p < 0.01), right inferior frontal gyrus (k = 495 voxels, T = -4.29, p < 0.01). Pearson correlation analysis showed that the GMV were significantly correlated with the Integrated Visual and Auditory continuous performance test (IVA-CPT) scale (r = 0.637, P = 0.002), abstract reasoning (r = 0.597, P = 0.011), Self-rating Depression Scale (SAS) scale (r = -0.623, P = 0.004) and memory recall (r = 0.648, P = 0.003).

CONCLUSION

These results demonstrate that slow growing but destructive BGGCTs markedly and asymmetrically effect the GMV in left parahippocampal, left thalamus, right middle cingulate cortex, right inferior frontal gyrus and GMV changes were significantly associated with cognitive test.

Mapping local and long-distance resting connectivity markers of TMS-related inhibition reduction in schizophrenia

Short interval intracortical inhibition (SICI) is a biomarker for altered motor inhibition in schizophrenia, but the manner in which distant sites influence the inhibitory cortical-effector response remains elusive. Our study investigated local and long-distance resting state functional connectivity (rsFC) markers of SICI in a sample of N = 23 patients with schizophrenia and N = 29 controls. Local functional connectivity was quantified using regional homogeneity (ReHo) analysis and long-range connectivity was estimated using seed-based rsFC analysis. Direct and indirect effects of connectivity measures on SICI were modeled using mediation analysis. Higher SICI ratios (indicating reduced inhibition) in patients were associated with lower ReHo in the right insula. Follow-up rsFC analyses showed that higher SICI scores (indicating reduced inhibition) were associated with reduced connectivity between right insula and hubs of the corticospinal pathway: sensorimotor cortex and basal ganglia. Mediation analysis supported a model in which the direct effect of local insular connectivity strength on SICI is mediated by the interhemispheric connectivity between insula and left sensorimotor cortex. The broader clinical implications of these findings are discussed with emphasis on how these preliminary findings might inform novel interventions designed to restore or improve SICI in schizophrenia and deepen our understanding of motor inhibitory control and impact of abnormal signaling in motor-inhibitory pathways in schizophrenia.

The Human Basal Ganglia Mediate the Interplay between Reactive and Proactive Control of Response through Both Motor Inhibition and Sensory Modulation

The basal ganglia (BG) have long been known for contributing to the regulation of motor behaviour by means of a complex interplay between tonic and phasic inhibitory mechanisms. However, after having focused for a long time on phasic reactive mechanisms, it is only recently that psychological research in healthy humans has modelled tonic proactive mechanisms of control. Mutual calibration between anatomo-functional and psychological models is still needed to better understand the unclear role of the BG in the interplay between proactive and reactive mechanisms of control. Here, we implemented an event-related fMRI design allowing proper analysis of both the brain activity preceding the target-stimulus and the brain activity induced by the target-stimulus during a simple go/nogo task, with a particular interest in the ambiguous role of the basal ganglia. Post-stimulus activity was evoked in the left dorsal striatum, the subthalamus nucleus and internal globus pallidus by any stimulus when the situation was unpredictable, pinpointing its involvement in reactive, non-selective inhibitory mechanisms when action restraint is required. Pre-stimulus activity was detected in the ventral, not the dorsal, striatum, when the situation was unpredictable, and was associated with changes in functional connectivity with the early visual, not the motor, cortex. This suggests that the ventral striatum supports modulatory influence over sensory processing during proactive control.

Blunted prefrontal signature of proactive inhibitory control in cocaine use disorder

BACKGROUND

Impulsivity is an established risk factor for substance use disorder (SUD). Integral to SUD recovery is proactive control (leveraging information about a potential need for behavioral restraint to marshal increased cognitive resources toward inhibition) when cues for drug use are unavoidable. However, proactive control is little studied in SUD, and is merely inferred from post-error performance adjustments.

METHODS

We probed covert neurocircuit signatures of proactive control in persons with SUD, as well as the moderating effects of incentives for successfully exerting proactive control. We administered a Monetary Incentive Stop Task (MIST) during functional magnetic resonance imaging of adults with cocaine use disorder (CUD; n = 21) and healthy controls (n = 21). The MIST blended the reward and loss-anticipatory cues of the Monetary Incentive Delay (MID) Task with a variant of the Stop-Signal Task, in which target color signaled whether or not withholding a response might be necessary.

RESULTS

In controls, but not in CUD participants, targets that signaled a potential need to stop (as a contrast with targets that signaled no need to stop) activated portions of right operculum akin to activation commonly elicited by stop signals, despite no actual stop signal. Across all participants, this proactive control activation did not relate to task behavior or to questionnaire impulsivity. Anticipatory incentive cues did not recruit ventral striatum.

CONCLUSIONS

These data suggest that persons with CUD show blunted covert signatures of attention and proactive control. This potentially accounts in part for the role of poor executive function in relapse vulnerability.

Between-module functional connectivity of the salient ventral attention network and dorsal attention network is associated with motor inhibition

The ability to inhibit motor response is crucial for daily activities. However, whether brain networks connecting spatially distinct brain regions can explain individual differences in motor inhibition is not known. Therefore, we took a graph-theoretic perspective to examine the relationship between the properties of topological organization in functional brain networks and motor inhibition. We analyzed data from 141 healthy adults aged 20 to 78, who underwent resting-state functional magnetic resonance imaging and performed a stop-signal task along with neuropsychological assessments outside the scanner. The graph-theoretic properties of 17 functional brain networks were estimated, including within-network connectivity and between-network connectivity. We employed multiple linear regression to examine how these graph-theoretical properties were associated with motor inhibition. The results showed that between-network connectivity of the salient ventral attention network and dorsal attention network explained the highest and second highest variance of individual differences in motor inhibition. In addition, we also found those two networks span over brain regions in the frontal-cingulate-parietal network, suggesting that these network interactions are also important to motor inhibition.

Neurofunctional abnormalities in antisocial spectrum: A meta-analysis of fMRI studies on Five distinct neurocognitive research domains

Past functional magnetic resonance imaging on antisocial subjects have shown important inconsistencies and methodological problems (e.g. heterogeneity in fMRI tasks domain, small sample sizes, analyses on regions-of-interest). We aimed to conduct a meta-analysis of whole-brain fMRI studies on antisocial individuals based on distinct neurocognitive domains. A voxel-based meta-analysis via permutation of subject images (SDM-PSI) was performed on studies using fMRI tasks in the domains of acute threat response, cognitive control, social cognition, punishment and reward processing. Overall, 83 studies were retrieved. Using a liberal statistical threshold, several key regions were identified in the meta-analysis, principally during acute threat response, social cognition and cognitive control tasks. Additionally, we observed that the right amygdala was negatively associated with both callous-unemotional traits and severity of antisocial behaviors, in meta-analyses on region-of-interest and on dimensional studies, respectively. The findings show that the most prominent functional brain deficits arise during acute threat response, social cognitions and cognitive control neurocognitive domains. These results provide substantial insights for our understanding of aberrant neural processing across specific contexts.

Low-frequency transcranial stimulation of pre-supplementary motor area alleviates levodopa-induced dyskinesia in Parkinson's disease: a randomized cross-over trial

Levodopa-induced dyskinesia gradually emerges during long-term dopamine therapy, causing major disability in patients with Parkinson disease. Using pharmacodynamic functional MRI, we have previously shown that the intake of levodopa triggers an excessive activation of the pre-supplementary motor area in Parkinson disease patients with peak-of-dose dyskinesia. In this pre-registered, interventional study, we tested whether the abnormal responsiveness of the pre-supplementary motor area to levodopa may constitute a ‘stimulation target’ for treating dyskinesia. A gender-balanced group of 17 Parkinson disease patients with peak-of-dose dyskinesia received 30 min of robot-assisted repetitive transcranial magnetic stimulation, after they had paused their anti-Parkinson medication. Real-repetitive transcranial magnetic stimulation at 100% or sham-repetitive transcranial magnetic stimulation at 30% of individual resting corticomotor threshold of left first dorsal interosseous muscle was applied on separate days in counterbalanced order. Following repetitive transcranial magnetic stimulation, patients took 200 mg of oral levodopa and underwent functional MRI to map brain activity, while they performed the same go/no-go task as in our previous study. Blinded video assessment revealed that real-repetitive transcranial magnetic stimulation delayed the onset of dyskinesia and reduced its severity relative to sham-repetitive transcranial magnetic stimulation. Individual improvement in dyskinesia severity scaled linearly with the modulatory effect of real-repetitive transcranial magnetic stimulation on task-related activation in the pre-supplementary motor area. Stimulation-induced delay in dyskinesia onset correlated positively with the induced electrical field strength in the pre-supplementary motor area. Our results provide converging evidence that the levodopa-triggered increase in pre-supplementary motor area activity plays a causal role in the pathophysiology of peak-of-dose dyskinesia and constitutes a promising cortical target for brain stimulation therapy.

The personality dispositions and resting-state neural correlates associated with aggressive children

Despite aggression being detrimental to children's physical health, mental health and social development, the dispositional and neurological antecedents of aggression in the child are poorly understood. Here we examined the relationship between trait aggression as measured by Buss and Warren's Aggression Questionnaire and personality traits measured with Big Five Questionnaire for Children in 77 primary-school children and recorded resting-state brain activity (fractional amplitude of low-frequency fluctuations [fALFF]) and resting-state functional connectivity (rsFC) using functional magnetic resonance imaging. The present results showed that trait aggression was negatively correlated with agreeableness and positively correlated with neuroticism. The brain analyses showed that children with a higher propensity for aggression had a lower fALFF mainly in the left superior temporal gyrus, right parahippocampal gyrus and left supramarginal gyrus. Physical and total aggressions were negatively associated with rsFC between the right parahippocampal gyrus and the right putamen. Further analysis revealed that this rsFC could moderate the influence of neuroticism on total aggression. Moreover, the results suggest the presence of a sex difference in the neurodevelopmental mechanisms underlying aggression in middle childhood. Overall, our findings indicate that aggressive children have lower agreeableness and higher neuroticism, and the underlying neural systems are mainly implicated in social judgment and empathy.

Subthalamic Nucleus Subregion Stimulation Modulates Inhibitory Control

Patients with Parkinson's disease (PD) often experience reductions in the proficiency to inhibit actions. The motor symptoms of PD can be effectively treated with deep brain stimulation (DBS) of the subthalamic nucleus (STN), a key structure in the frontal-striatal network that may be directly involved in regulating inhibitory control. However, the precise role of the STN in stopping control is unclear. The STN consists of functional subterritories linked to dissociable cortical networks, although the boundaries of the subregions are still under debate. We investigated whether stimulating the dorsal and ventral subregions of the STN would show dissociable effects on ability to stop. We studied 12 PD patients with STN DBS. Patients with two adjacent contacts positioned within the bounds of the dorsal and ventral STN completed two testing sessions (OFF medication) with low amplitude stimulation (0.4 mA) at either the dorsal or ventral contacts bilaterally, while performing the stop task. Ventral, but not dorsal, DBS improved stopping latencies. Go reactions were similar between dorsal and ventral DBS STN. Stimulation in the ventral, but not dorsal, subregion of the STN improved stopping speed, confirming the involvement of the STN in stopping control and supporting the STN functional subregions.

Effects of Diazepam on Reaction Times to Stop and Go

Introduction: The ability to stop the execution of a movement in response to an external cue requires intact executive function. The effect of psychotropic drugs on movement inhibition is largely unknown. Movement stopping can be estimated by the Stop Signal Reaction Time (SSRT). In a recent publication, we validated an improved measure of SSRT (optimum combination SSRT, ocSSRT). Here we explored how diazepam, which enhances transmission at GABA_A receptors, affects ocSSRT.

Methods: Nine healthy individuals were randomized to receive placebo, 5 mg or 10 mg doses of diazepam. Each participant received both the dosage of drug and placebo orally on separate days with adequate washout. The ocSSRT and simple reaction time (RT) were estimated through a stop-signal task delivered via a battery-operated box incorporating green (Go) and red (Stop) light-emitting diodes. The task was performed just before and 1 h after dosing.

Result: The mean change in ocSSRT after 10 mg diazepam was significantly higher (+27 ms) than for placebo (−1 ms; p = 0.012). By contrast, the mean change in simple response time remained comparable in all three dosing groups (p = 0.419).

Conclusion: Our results confirm that a single therapeutic adult dose of diazepam can alter motor inhibition in drug naïve healthy individuals. The selective effect of diazepam on ocSSRT but not simple RT suggests that GABAergic neurons may play a critical role in movement-stopping.

Efficacy of inhibitory control depends on procrastination and deceleration in saccade planning

A goal-directed flexible behavior warrants our ability to timely inhibit impending movements deemed inappropriate due to an abrupt change in the context. Race model of countermanding rapid saccadic eye movement posits a competition between a preparatory GO process and an inhibitory STOP process rising to reach a fixed threshold. Stop-signal response time (SSRT), which is the average time STOP takes to rise to the threshold, is widely used as a metric to assess the ability to revoke a movement. A reliable estimation of SSRT critically depends on the assumption of independence between GO and STOP process, which has been violated in many studies. In addition, the physiological correlate of stochastic rise of STOP process to a threshold remains unsubstantiated thus far. Here, we introduce a method to estimate the efficacy of inhibitory control on the premise of an alternative model that assumes deceleration of GO process following the stop-signal onset. The average reaction time increased exponentially with the increase in the maximum duration available to attenuate GO process by the stop-signal. Our method estimates saccade procrastination in anticipation of the stop-signal, and the rate of increase in attenuation on GO process. Unlike SSRT, these new metrics are independent of how the stopping performance varies with the delay between go- and stop-signal onsets. We reckon that these metrics together qualify to be considered as an efficient alternative to SSRT for the estimation of individuals' ability to countermand saccades, especially in cases when the assumptions of race model are no longer valid.

Stop Signal Task Training Strengthens GABA-mediated Neurotransmission within the Primary Motor Cortex

We have recently shown that the efficiency in stopping a response, measured using the stop signal task, is related to GABAA-mediated short-interval intracortical inhibition (SICI) in the primary motor cortex. In this study, we conducted two experiments on humans to determine whether training participants in the stop signal task within one session (Experiment 1) and across multiple sessions (Experiment 2) would increase SICI strength. For each experiment, we obtained premeasures and postmeasures of stopping efficiency and resting-state SICI, that is, during relaxed muscle activity (Experiment 1, n = 45, 15 male participants) and SICI during the stop signal task (Experiment 2, n = 44, 21 male participants). In the middle blocks of Experiment 1 and the middle sessions of Experiment 2, participants in the experimental group completed stop signal task training, whereas control participants completed a similar task without the requirement to stop a response. After training, the experimental group showed increased resting-state SICI strength (Experiment 1) and increased SICI strength during the stop signal task (Experiment 2). Although there were no overall behavioral improvements in stopping efficiency, improvements at an individual level were correlated with increases in SICI strength at rest (Experiment 1) and during successful stopping (Experiment 2). These results provide evidence of neuroplasticity in resting-state and task-related GABAA-mediated SICI in the primary motor cortex after response inhibition training. These results also suggest that SICI and stopping efficiency are temporally linked, such that a change in SICI between time points is correlated with a change in stopping efficiency between time points.

Mouse Tracking to Explore Motor Inhibition Processes in Go/No-Go and Stop Signal Tasks

Response inhibition relies on both proactive and reactive mechanisms that exert a synergic control on goal-directed actions. It is typically evaluated by the go/no-go (GNG) and the stop signal task (SST) with response recording based on the key-press method. However, the analysis of discrete variables (i.e., present or absent responses) registered by key-press could be insufficient to capture dynamic aspects of inhibitory control. Trying to overcome this limitation, in the present study we used a mouse tracking procedure to characterize movement profiles related to proactive and reactive inhibition. A total of fifty-three participants performed a cued GNG and an SST. The cued GNG mainly involves proactive control whereas the reactive component is mainly engaged in the SST. We evaluated the velocity profile from mouse trajectories both for responses obtained in the Go conditions and for inhibitory failures. Movements were classified as one-shot when no corrections were observed. Multi-peaked velocity profiles were classified as non-one-shot. A higher proportion of one-shot movements was found in the SST compared to the cued GNG when subjects failed to inhibit responses. This result suggests that proactive control may be responsible for unsmooth profiles in inhibition failures, supporting a differentiation between these tasks.

Cross-Task Contributions of Frontobasal Ganglia Circuitry in Response Inhibition and Conflict-Induced Slowing

Why are we so slow in choosing the lesser of 2 evils? We considered whether such slowing relates to uncertainty about the value of these options, which arises from the tendency to avoid them during learning, and whether such slowing relates to frontosubthalamic inhibitory control mechanisms. In total, 49 participants performed a reinforcement-learning task and a stop-signal task while fMRI was recorded. A reinforcement-learning model was used to quantify learning strategies. Individual differences in lose-lose slowing related to information uncertainty due to sampling, and independently, to less efficient response inhibition in the stop-signal task. Neuroimaging analysis revealed an analogous dissociation: subthalamic nucleus (STN) BOLD activity related to variability in stopping latencies, whereas weaker frontosubthalamic connectivity related to slowing and information sampling. Across tasks, fast inhibitors increased STN activity for successfully canceled responses in the stop task, but decreased activity for lose-lose choices. These data support the notion that fronto-STN communication implements a rapid but transient brake on response execution, and that slowing due to decision uncertainty could result from an inefficient release of this "hold your horses" mechanism.

Functional Organization for Response Inhibition in the Right Inferior Frontal Cortex of Individual Human Brains

The right inferior frontal cortex (IFC) is critical to response inhibition. The right IFC referred in the human studies of response inhibition is located in the posterior part of the inferior frontal gyrus and the surrounding regions and consists of multiple areas that implement distinct functions. Recent studies using resting-state functional connectivity have parcellated the cerebral cortex and revealed across-subject variability of parcel-based cerebrocortical networks. However, how the right IFC of individual brains is functionally organized and what functional properties the IFC parcels possess regarding response inhibition remain elusive. In the present functional magnetic resonance imaging study, precision functional mapping of individual human brains was adopted to the parcels in the right IFC to evaluate their functional properties related to response inhibition. The right IFC consisted of six modules or subsets of subregions, and the spatial organization of the modules varied considerably across subjects. Each module revealed unique characteristics of brain activity and its correlation to behavior related to response inhibition. These results provide updated functional features of the IFC and demonstrate the importance of individual-focused approaches in studying response inhibition in the right IFC.

Neural correlates of enhanced response inhibition in the aftermath of stress

Life stress has been shown to impact cognitive functions, including inhibitory control. However, the immediate effects of acute stress on inhibitory control and the underlying neural mechanisms remain unclear. In a behavioral pilot study (N = 30) and a within-subject functional magnetic resonance imaging study (N = 30), we examined how acute stress induced by Trier Social Stress Test influenced inhibitory control in a stop signal task. Behavioral results across two studies showed that stress consistently improved inhibitory control. Shorter stop signal reaction time (SSRT) in stress as compared with control condition was associated with stronger connectivity between the superior/middle frontal gyrus (SFG/MFG) and striatum. Dynamic causal modeling revealed distinct best models under stress and control condition, with an enhanced interaction between the SFG/MFG and the striatum after stress exposure. This research identified the SFG/MFG-striatum network as a key circuit underlying acute stress-elicited enhancement of inhibitory control in a stop signal task.

Aftereffect and Reproducibility of Three Excitatory Repetitive TMS Protocols for a Response Inhibition Task

A number of repetitive transcranial magnetic stimulation (rTMS) protocols have been developed for modulating brain function non-invasively. To identify the most powerful one, these protocols have been compared in the context of the motor system. However, to what extent the conclusions could be generalized to high-level functions is largely unknown. In this study, we compared the modulatory effect of three excitatory rTMS protocols on high-level cognition represented by response inhibition ability. Our first experiment revealed that intermittent theta-burst stimulation (iTBS) could significantly improve reaction time in a stop signal task, while 5-Hz and 25-Hz stimuli were ineffective. This iTBS effect was significantly higher than that for the sham simulation and only occurred in the second session of the stop signal task after iTBS in the first experiment. However, this aftereffect of iTBS was not reproduced in the second experiment, indicating high variability across subjects. Thus, on the one hand, our findings indicate that iTBS on the pre-SMA could improve inhibitory control, but on the other hand, the reliability and reproducibility of this effect needs further investigation.

Hyperdirect insula-basal-ganglia pathway and adult-like maturity of global brain responses predict inhibitory control in children

Inhibitory control is fundamental to children's self-regulation and cognitive development. Here we investigate cortical-basal ganglia pathways underlying inhibitory control in children and their adult-like maturity. We first conduct a comprehensive meta-analysis of extant neurodevelopmental studies of inhibitory control and highlight important gaps in the literature. Second, we examine cortical-basal ganglia activation during inhibitory control in children ages 9-12 and demonstrate the formation of an adult-like inhibitory control network by late childhood. Third, we develop a neural maturation index (NMI), which assesses the similarity of brain activation patterns between children and adults, and demonstrate that higher NMI in children predicts better inhibitory control. Fourth, we show that activity in the subthalamic nucleus and its effective connectivity with the right anterior insula predicts children's inhibitory control. Fifth, we replicate our findings across multiple cohorts. Our findings provide insights into cortical-basal ganglia circuits and global brain organization underlying the development of inhibitory control.

Individual differences in the effect of menstrual cycle on basal ganglia inhibitory control

Basal ganglia (BG) are involved in inhibitory control (IC) and known to change in structure and activation along the menstrual cycle. Therefore, we investigated BG activation and connectivity patterns related to IC during different cycle phases. Thirty-six naturally cycling women were scanned three times performing a Stop Signal Task and hormonal levels analysed from saliva samples. We found an impaired Stop signal reaction time (SSRT) during pre-ovulatory compared to menses the higher the baseline IC of women. Blood oxygen level dependent (BOLD)-response in bilateral putamen significantly decreased during the luteal phase. Connectivity strength from the left putamen displayed an interactive effect of cycle and IC. During pre-ovulatory the connectivity with anterior cingulate cortex and left inferior parietal lobe was significantly stronger the higher the IC, and during luteal with left supplementary motor area. Right putamen's activation and left hemisphere's connectivity predicted the SSRT across participants. Therefore, we propose a compensatory mechanism for the hormonal changes across the menstrual cycle based on a lateralized pattern.

Oscillatory brain mechanisms supporting response cancellation in selective stopping strategies

Although considerable progress has been made in understanding the neural substrates of simple or global stopping, the neural mechanisms supporting selective stopping remain less understood. The selectivity of the stop process is often required in our everyday life in situations where responses must be suppressed to certain signals but not others. Here, we examined the oscillatory brain mechanisms of response cancellation in selective stopping by controlling for the different strategies adopted by participants (n = 54) to accomplish a stimulus selective stop-signal task. We found that successfully cancelling an initiated response was specifically associated with increased oscillatory activity in the high-beta frequency range in the strategy characterized by stopping selectively (the so called dependent Discriminate then Stop, dDtS), but not in the strategy characterized by stopping non-selectively (Stop then Discriminate, StD). Beamforming source reconstruction suggests that this high-beta activity was mainly generated in the superior frontal gyrus (including the pre-supplementary motor area) and the middle frontal gyrus. Present findings provide neural support for the existence of different strategies for solving selective stopping tasks. Specifically, differences between strategies were observed in the oscillatory activity associated with the stop process and were restricted to the high-beta frequency range. Moreover, current results provide important evidence suggesting that high-beta oscillations in superior and middle frontal cortices play an essential role in cancelling an initiated motor response.

Strategies of selective changing: Preparatory neural processes seem to be responsible for differences in complex inhibition

Selective inhibition describes the stopping of an action while other actions are further executed. It can be differentiated between two strategies to stop selectively: the fast but global stop all, then discriminate strategy and the slower but more selective first discriminate, then stop strategy. It is assumed that the first discriminate, then stop strategy is especially used when information regarding which action might have to be stopped is already available beforehand. Moreover, it is supposed that both strategies differ in matters of basal ganglia pathways used for their execution. Aim of the present study was to investigate the use of the two strategies in situations requiring selective changing of an action. Eighteen healthy male participants performed a selective stop-change task with informative and uninformative cues during fMRI. Behavioral results show that informative cues led to a benefit in both inhibition times and selectivity. FMRI data revealed that the same cortico-subcortical pathway was used with informative and uninformative cues. Behavioral and neuronal results indicate that participants used the first discriminate, then stop strategy for selective inhibition irrespective of the amount of previously available information. Moreover, the neural activity data indicate that the benefit in the informed condition was produced by an efficient preparation for the concrete change process. Possible factors that might affect which strategy is used for selective stopping are the level of previously available information (foreknowledge) and the experimental set-up, as e.g. task complexity.

Structural connectivity of right frontal hyperactive areas scales with stuttering severity

A neuronal sign of persistent developmental stuttering is the magnified coactivation of right frontal brain regions during speech production. Whether and how stuttering severity relates to the connection strength of these hyperactive right frontal areas to other brain areas is an open question. Scrutinizing such brain–behaviour and structure–function relationships aims at disentangling suspected underlying neuronal mechanisms of stuttering. Here, we acquired diffusion-weighted and functional images from 31 adults who stutter and 34 matched control participants. Using a newly developed structural connectivity measure, we calculated voxel-wise correlations between connection strength and stuttering severity within tract volumes that originated from functionally hyperactive right frontal regions. Correlation analyses revealed that with increasing speech motor deficits the connection strength increased in the right frontal aslant tract, the right anterior thalamic radiation, and in U-shaped projections underneath the right precentral sulcus. In contrast, with decreasing speech motor deficits connection strength increased in the right uncinate fasciculus. Additional group comparisons of whole-brain white matter skeletons replicated the previously reported reduction of fractional anisotropy in the left and right superior longitudinal fasciculus as well as at the junction of right frontal aslant tract and right superior longitudinal fasciculus in adults who stutter compared to control participants. Overall, our investigation suggests that right fronto-temporal networks play a compensatory role as a fluency enhancing mechanism. In contrast, the increased connection strength within subcortical-cortical pathways may be implied in an overly active global response suppression mechanism in stuttering. Altogether, this combined functional MRI–diffusion tensor imaging study disentangles different networks involved in the neuronal underpinnings of the speech motor deficit in persistent developmental stuttering.

Response inhibition in borderline personality disorder: Neural and behavioral correlates

Although response inhibition is thought to be important in borderline personality disorder (BPD), little is known about its neurophysiological basis. This study aimed to provide insight into this issue by capitalizaing on the high temporal resolution of electroencephalography and information provided by source localization methods. To this end, twenty unmedicated patients with BPD and 20 healthy control subjects performed a modified go/no-go task designed to better isolate the brain activity specifically associated with response inhibition. Event-related potentials (ERP) were measured and further analyzed at the scalp and source levels. Patients with BPD made more commission errors (failed inhibitions) than control subjects. Scalp ERP data showed that both groups displayed greater frontocentral P3 amplitude for no-go (response inhbition) than for go trials (response execution). However, source reconstruction data revealed that patients with BPD activated posterior parietal regions (precuneus) to inhibit their responses, whereas controls activated prefrontal regions (presupplementary motor area, preSMA). This dissociation was supported by a significant Region (precuneus, preSMA) x Trial Type (no-go, go) x Group (BPD, control) interaction. These findings extend our understanding of the neurophysiological basis of abnormal response inhibition in BPD, suggesting that patients with BPD recruit different brain regions for inhibiting prepotent responses compared to controls. Future research in larger, medication-naïve samples of patients with BPD is required to confirm and extend these findings.

Unilateral Stimulation of Subthalamic Nucleus Does Not Affect Inhibitory Control

Despite the relevance of inhibitory control in shaping our behavior its neural substrates are still hotly debated. In this regard, it has been suggested that inhibitory control relies upon a right-lateralized network which involves the right subthalamic nucleus (STN). To assess the role of STN, we took advantage of a relatively rare model, i.e., advanced Parkinson's patients who received unilateral deep-brain stimulation (DBS) of the STN either of the left (n = 10) or of the right (n = 10) hemisphere. We gave them a stop-signal reaching task, and we compared patients' performance in two experimental conditions, DBS-ON and DBS-OFF. In addition, we also tested 22 age-matched healthy participants. As expected, we found that inhibitory control is impaired in Parkinson's patients with respect to healthy participants. However, neither reactive nor proactive inhibition is improved when either the right or the left DBS is active. We interpreted these findings in light of the fact that previous studies, exploiting exactly the same task, have shown that only bilateral STN DBS restores a near-normal inhibitory control. Thus, although null results have to be interpreted with caution, our current findings confirm that the right STN does not play a key role in suppressing pending actions. However, on the ground of previous studies, it is very likely that this subcortical structure is part of the brain network subserving inhibition but to implement this executive function both subthalamic nuclei must be simultaneously active. Our findings are of significance to other researchers studying the effects of STN DBS on key executive functions, such as impulsivity and inhibition and they are also of clinical relevance for determining the therapeutic benefits of STN DBS as they suggest that, at least as far as inhibitory control is concerned, it is better to implant DBS bilaterally than unilaterally.

Subthalamic Nucleus Activation Occurs Early during Stopping and Is Associated with Trait Impulsivity

The subthalamic nucleus (STN) is thought to be a central regulator of behavioral inhibition, which is thought to be a major determinant of impulsivity. Thus, it would be reasonable to hypothesize that STN function is related to impulsivity. However, it has been difficult to test this hypothesis because of the challenges in noninvasively and accurately measuring this structure's signal in humans. We utilized a novel approach for STN signal localization that entails identifying this structure directly on fMRI images for each individual participant in native space. Using this approach, we measured STN responses during the stop signal task in a sample of healthy adult participants. We confirmed that the STN exhibited selective activation during "Stop" trials. Furthermore, the magnitude of STN activation during successful Stop trials inversely correlated with individual differences in trait impulsivity as measured by a personality inventory. Time course analysis revealed that early STN activation differentiated successful from unsuccessful Stop trials, and individual differences in the magnitude of STN activation inversely correlated with stop signal RT, an estimate of time required to stop. These results are consistent with the STN playing a central role in inhibition and related behavioral proclivities, with implications for both normal range function and clinical syndromes of inhibitory dyscontrol. Moreover, the methods utilized in this study for measuring STN fMRI signal in humans may be gainfully applied in future studies to further our understanding of the role of the STN in regulating behavior and neuropsychiatric conditions.