Stimulation of the Pre-SMA Influences Cerebral Blood Flow in Frontal Areas Involved with Inhibitory Control of Action

Transcranial Magnetic Stimulation-Induced Plasticity Improving Cognitive Control in Obsessive-Compulsive Disorder, Part I: Clinical and Neuroimaging Outcomes From a Randomized Trial

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is an emerging treatment for obsessive-compulsive disorder (OCD). The neurobiological mechanisms of rTMS in OCD have been incompletely characterized. We compared clinical outcomes and changes in task-based brain activation following 3 different rTMS protocols, all combined with exposure and response prevention.

METHODS

In this 3-arm proof-of-concept randomized trial, 61 treatment-refractory adult patients with OCD received 16 sessions of rTMS immediately before exposure and response prevention over 8 weeks, with task-based functional magnetic resonance imaging scans and clinical assessments before and after treatment. Patients received high-frequency rTMS to the left dorsolateral prefrontal cortex (n = 19 [13 women/6 men]), high-frequency rTMS to the left presupplementary motor area (preSMA) (n = 23 [13 women/10 men]), or control rTMS to the vertex (n = 19 [13 women/6 men]). Changes in task-based functional magnetic resonance imaging activation before/after treatment were compared using both a Bayesian region of interest and a general linear model whole-brain approach.

RESULTS

Mean OCD symptom severity decreased significantly in all treatment groups (Δ = -10.836, p < .001, 95% CI -12.504 to -9.168), with no differences between groups. Response rate in the entire sample was 57.4%. The dorsolateral prefrontal cortex rTMS group showed decreased planning-related activation after treatment that was associated with greater symptom improvement. No group-level activation changes were observed for the preSMA and vertex rTMS groups. Participants in the preSMA group with greater symptom improvement showed decreased error-related activation, and symptom improvement in the vertex group was associated with increased inhibition-related activation.

CONCLUSIONS

rTMS to preSMA and dorsolateral prefrontal cortex combined with exposure and response prevention led to activation decreases in targeted task networks in individuals showing greater symptom improvement, although we observed no differences in symptom reduction between groups.

Cortical Oscillatory Activity and Motor Control in Pediatric Stroke Patients With Hemidystonia

Dystonia is a movement disorder characterized by repetitive muscle contractions, twisting movements, and abnormal posture, affecting 20% of pediatric arterial ischemic stroke (AIS) survivors. Recent studies have reported that children with dystonia are at higher risk of cognitive deficits. The connection between impaired motor outcomes and cognitive impairment in dystonia is not fully understood; dystonia might affect motor control alone, or it could also contribute to cognitive impairment through disruptions in higher-order motor processes. To assess the functional correlates underlying motor control in children with dystonia, we used magnetoencephalography (MEG) to measure frontal theta (4-8 Hz), motor beta (15-30 Hz), and sensorimotor gamma (60-90 Hz) activity during a "go"/"no-go" task. Beamformer-based source analysis was carried out on 19 post-stroke patients: nine with dystonia (mean age = 13.78, SD = 2.82, 8 females), 10 without dystonia (mean age = 12.90, SD = 3.54, 4 females), and 17 healthy controls (mean age = 12.82, SD = 2.72, 8 females). To evaluate inhibitory control, frontal theta activity was analyzed during correct "no-go" (successful withhold) trials. To assess motor execution and sensorimotor integration, movement time-locked beta and sensorimotor gamma activity were analyzed during correct "go" trials. Additionally, the Delis-Kaplan Executive Function System (DKEFS) color-word interference task was used as a non-motor, inhibitory control task to evaluate general cognitive inhibition abilities. During affected hand use, dystonia patients had higher "no-go" error rates (failed withhold) compared to all other groups. Dystonia patients also exhibited higher frontal theta power during correct withhold responses for both affected and unaffected hands compared to healthy controls. Furthermore, dystonia patients exhibited decreased movement-evoked gamma power and gamma peak frequency compared to non-dystonia patients and healthy controls. Movement-related beta desynchronization (ERD) activity was increased in non-dystonia patients for both hands compared to healthy participants. These results confirm that post-stroke dystonia is associated with impaired frontally mediated inhibitory control, as reflected by increased frontal theta power. Post-stroke dystonia patients also exhibited reduced motor gamma activity during movement, reflecting altered sensorimotor integration. The increased beta ERD activity in non-dystonia patients may suggest compensatory sensorimotor plasticity not observed in dystonia patients. These findings suggest that differences in motor outcomes in childhood stroke result from a combination of cognitive and motor deficits.

Effects of repetitive transcranial magnetic stimulation combined with cognitive training for improving response inhibition: A proof-of-concept, single-blind randomised controlled study

BACKGROUND

Impaired response inhibition is a common characteristic of various psychiatric disorders. Cognitive training (CT) can improve cognitive function, but the benefits may be limited. Repetitive transcranial magnetic stimulation (rTMS) is a promising tool to enhance neuroplasticity, and thereby augment the effects of CT. We aimed to investigate the augmentation effects of rTMS on CT for response inhibition in healthy participants.

METHODS

Sixty healthy participants were randomly assigned to two experimental groups: one with prolonged intermittent theta burst stimulation (iTBS) + CT and the other with sham iTBS + CT over four experimental sessions. Prolonged iTBS (1800 pulses) was used to stimulate the right inferior frontal cortex (rIFC) and pre-supplementary motor area (pre-SMA) in a counterbalanced order. Participants completed a Stop Signal training task following iTBS over one brain region, followed by the Go/No-Go training task after iTBS over the other brain region. The Stroop task with concomitant electroencephalography was conducted before and immediately after the intervention.

RESULTS

There were no significant differences between groups in behavioural outcomes on the Stop Signal task, Go/No-Go task, Stroop task or Behavior Rating Inventory of Executive Functioning for Adults. Similarly, analysis of event-related potentials (ERPs) from the Stroop task (N200 and N400) and exploratory cluster-based permutation analysis did not reveal any significant differences between groups. Subgroup analyses revealed that individuals with higher baseline impulsivity exhibited better learning effects in the active group.

CONCLUSIONS

This first proof of concept study did not find evidence that four sessions of active rTMS + CT could induce cognitive or neurophysiological effects on response inhibition in healthy participants. However, subgroup analyses suggests that rTMS combined with CT could be useful in improving response inhibition in individuals with high impulsivity. It is recommended that future proof of concept studies examine its potential in this clinical population.

Role of right dorsolateral prefrontal cortex-left primary motor cortex interaction in motor inhibition in Parkinson's disease

Background

Impaired motor inhibition in Parkinson's disease (PD) is associated with functional alterations in the frontal-basal ganglia (BG) neural circuits. The right dorsolateral prefrontal cortex (DLPFC), pre-supplementary motor area (pre-SMA), and primary motor cortex (M1) play key roles in regulating this inhibition. However, the changes in interhemispheric interactions during motor inhibition in PD have not been clearly defined.

Methods

We used dual-site paired-pulse transcranial magnetic stimulation (ppTMS) to examine the interactions between the right DLPFC and pre-SMA and the left M1 in 30 patients with early-stage PD and 30 age-matched healthy controls (HC) during both resting and active conditions, specifically while performing a stop-signal task (SST).

Results

Stop-signal reaction times (SSRT) were significantly longer in PD patients compared to HC. The right DLPFC-left M1 interaction, at both short- and long-latency intervals, showed enhanced inhibition in PD following the stop-signal. In PD patients, SSRT was correlated with the inhibition of the right DLPFC-left M1 interaction, with stronger inhibition associated with shorter SSRT.

Conclusion

The deficit in reactive inhibition observed in PD is linked to an abnormal modulation of the right DLPFC-left M1 interaction during the stopping process.

Repetitive Transcranial Magnetic Stimulation on Individualized Spots Based on Task functional Magnetic Resonance Imaging Improves Swallowing Function in Poststroke Dysphagia

Background: Functional magnetic resonance imaging (fMRI) has not previously been used to localize the swallowing functional area in repetitive transcranial magnetic stimulation (rTMS) treatment for poststroke dysphagia; Traditionally, the target area for rTMS is the hotspot, which is defined as the specific region of the brain identified as the optimal location for transcranial magnetic stimulation (TMS). This study aims to compare the network differences between the TMS hotspot and the saliva swallowing fMRI activation to determine the better rTMS treatment site and investigate changes in functional connectivity related to poststroke dysphagia using resting-state fMRI. Methods: Using an information-based approach, we conducted a single case study to explore neural functional connectivity in a patient with poststroke dysphagia before, immediately after rTMS, and 4 weeks after rTMS intervention. A total of 20 healthy participants underwent fMRI and TMS hotspot localization as a control group. Neural network alterations were assessed, and functional connections related to poststroke dysphagia were examined using resting-state fMRI. Results: Compared to the TMS-induced hotspots, the fMRI activation peaks were located significantly more posteriorly and exhibited stronger functional connectivity with bilateral postcentral gyri. Following rTMS treatment, this patient developed functional connection between the brainstem and the bilateral insula, caudate, anterior cingulate cortex, and cerebellum. Conclusion: The saliva swallowing fMRI activation peaks show more intense functional connectivity with bilateral postcentral gyri compared to the TMS hotspots. Activation peak-guided rTMS treatment improves swallowing function in poststroke dysphagia. This study proposes a novel and potentially more efficacious therapeutic target for rTMS, expanding its therapeutic options for treating poststroke dysphagia.

The causal role of the subthalamic nucleus in the inhibitory network

The neural network mediating successful response inhibition mainly includes right hemisphere activation of the pre-supplementary motor area, inferior frontal gyrus (IFG), subthalamic nucleus (STN), and caudate nucleus. However, the causal role of these regions in the inhibitory network is undefined. Five patients with Parkinson's disease were assessed prior to and after therapeutic thermal ablation of the right STN in two separate functional magnetic resonance imaging (fMRI) sessions while performing a stop-signal task. Initiation times were faster but motor inhibition with the left hand (contralateral to the lesion) was significantly impaired as evident in prolonged stop-signal reaction times. Reduced inhibition after right subthalamotomy was associated (during successful inhibition) with the recruitment of basal ganglia regions outside the established inhibitory network. They included the putamen and caudate together with the anterior cingulate cortex and IFG of the left hemisphere. Subsequent network connectivity analysis (with the seed over the nonlesioned left STN) revealed a new inhibitory network after right subthalamotomies. Our results highlight the causal role of the right STN in the neural network for motor inhibition and the possible basal ganglia mechanisms for compensation upon losing a key node of the inhibition network.

Causal computations of supplementary motor area on spatial impulsivity

Spatial proximity to important stimuli often induces impulsive behaviour. How we overcome impulsive tendencies is what determines behaviour to be adaptive. Here, we used virtual reality to investigate whether the spatial proximity of stimuli is causally related to the supplementary motor area (SMA) functions. In two experiments, we set out to investigate these processes using a virtual environment that recreates close and distant spaces to test the causal contributions of the SMA in spatial impulsivity. In an online first experiment (N = 93) we validated and measured the influence of distant stimuli using a go/no-go task with close (21 cm) or distant stimuli (360 cm). In experiment 2 (N = 28), we applied transcranial static magnetic stimulation (tSMS) over the SMA (double-blind, crossover, sham-controlled design) to test its computations in controlling impulsive tendencies towards close vs distant stimuli. Reaction times and error rates (omission and commission) were analysed. In addition, the EZ Model parameters (a, v, Ter and MDT) were computed. Close stimuli elicited faster responses compared to distant stimuli but also exhibited higher error rates, specifically in commission errors (experiment 1). Real stimulation over SMA slowed response latencies (experiment 2), an effect mediated by an increase in decision thresholds (a). Current findings suggest that impulsivity might be modulated by spatial proximity, resulting in accelerated actions that may lead to an increase of inaccurate responses to nearby objects. Our study also provides a first starting point on the role of the SMA in regulating spatial impulsivity.

The role of pre-supplementary motor cortex in action control with emotional stimuli: A repetitive transcranial magnetic stimulation study

Swiftly halting ongoing motor actions is essential to react to unforeseen and potentially perilous circumstances. However, the neural bases subtending the complex interplay between emotions and motor control have been scarcely investigated. Here, we used an emotional stop signal task (SST) to investigate whether specific neural circuits engaged by action suppression are differently modulated by emotional signals with respect to neutral ones. Participants performed an SST before and after the administration of one session of repetitive transcranial magnetic stimulation (rTMS) over the pre-supplementary motor cortex (pre-SMA), the right inferior frontal gyrus (rIFG), and the left primary motor cortex (lM1). Results show that rTMS over the pre-SMA improved the ability to inhibit prepotent action (i.e., better action control) when emotional stimuli were presented. In contrast, action control in a neutral context was fostered by rTMS over the rIFG. No changes were observed after lM1 stimulation. Intriguingly, individuals with higher impulsivity traits exhibited enhanced motor control when facing neutral stimuli following rIFG stimulation. These results further our understanding of the interplay between emotions and motor functions, shedding light on the selective modulation of neural pathways underpinning these processes.

A modified neural circuit framework for semantic memory retrieval with implications for circuit modulation to treat verbal retrieval deficits

Word finding difficulty is a frequent complaint in older age and disease states, but treatment options are lacking for such verbal retrieval deficits. Better understanding of the neurophysiological and neuroanatomical basis of verbal retrieval function may inform effective interventions. In this article, we review the current evidence of a neural retrieval circuit central to verbal production, including words and semantic memory, that involves the pre-supplementary motor area (pre-SMA), striatum (particularly caudate nucleus), and thalamus. We aim to offer a modified neural circuit framework expanded upon a memory retrieval model proposed in 2013 by Hart et al., as evidence from electrophysiological, functional brain imaging, and noninvasive electrical brain stimulation studies have provided additional pieces of information that converge on a shared neural circuit for retrieval of memory and words. We propose that both the left inferior frontal gyrus and fronto-polar regions should be included in the expanded circuit. All these regions have their respective functional roles during verbal retrieval, such as selection and inhibition during search, initiation and termination of search, maintenance of co-activation across cortical regions, as well as final activation of the retrieved information. We will also highlight the structural connectivity from and to the pre-SMA (e.g., frontal aslant tract and fronto-striatal tract) that facilitates communication between the regions within this circuit. Finally, we will discuss how this circuit and its correlated activity may be affected by disease states and how this circuit may serve as a novel target engagement for neuromodulatory treatment of verbal retrieval deficits.

The resting-state brain activity signatures for addictive disorders

BACKGROUND

Addiction is a chronic and relapsing brain disorder. Despite numerous neuroimaging and neurophysiological studies on individuals with substance use disorder (SUD) or behavioral addiction (BEA), currently a clear neural activity signature for the addicted brain is lacking.

METHODS

We first performed systemic coordinate-based meta-analysis and partial least-squares regression to identify shared or distinct brain regions across multiple addictive disorders, with abnormal resting-state activity in SUD and BEA based on 46 studies (55 contrasts), including regional homogeneity (ReHo) and low-frequency fluctuation amplitude (ALFF) or fractional ALFF. We then combined Neurosynth, postmortem gene expression, and receptor/transporter distribution data to uncover the potential molecular mechanisms underlying these neural activity signatures.

FINDINGS

The overall comparison between addiction cohorts and healthy subjects indicated significantly increased ReHo and ALFF in the right striatum (putamen) and bilateral supplementary motor area, as well as decreased ReHo and ALFF in the bilateral anterior cingulate cortex and ventral medial prefrontal cortex, in the addiction group. On the other hand, neural activity in cingulate cortex, ventral medial prefrontal cortex, and orbitofrontal cortex differed between SUD and BEA subjects. Using molecular analyses, the altered resting activity recapitulated the spatial distribution of dopaminergic, GABAergic, and acetylcholine system in SUD, while this also includes the serotonergic system in BEA.

CONCLUSIONS

These results indicate both common and distinctive neural substrates underlying SUD and BEA, which validates and supports targeted neuromodulation against addiction.

FUNDING

This work was supported by the National Natural Science Foundation of China and Intramural Research Program of the National Institute on Drug Abuse, National Institutes of Health.

Effects of transcranial magnetic stimulation on reactive response inhibition

Reactive response inhibition cancels impending actions to enable adaptive behavior in ever-changing environments and has wide neuropsychiatric implications. A canonical paradigm to measure the covert inhibition latency is the stop-signal task (SST). To probe the cortico-subcortical network underlying motor inhibition, transcranial magnetic stimulation (TMS) has been applied over central nodes to modulate SST performance, especially to the right inferior frontal cortex and the presupplementary motor area. Since the vast parameter spaces of SST and TMS enabled diverse implementations, the insights delivered by emerging TMS-SST studies remain inconclusive. Therefore, a systematic review was conducted to account for variability and synthesize converging evidence. Results indicate certain protocol specificity through the consistent perturbations induced by online TMS, whereas offline protocols show paradoxical effects on different target regions besides numerous null effects. Ancillary neuroimaging findings have verified and dissociated the underpinning network dynamics. Sources of heterogeneity in designs and risk of bias are highlighted. Finally, we outline best-practice recommendations to bridge methodological gaps and subserve the validity as well as replicability of future work.

TMS-induced plasticity improving cognitive control in OCD I: Clinical and neuroimaging outcomes from a randomised trial of rTMS for OCD

Background

Repetitive transcranial magnetic stimulation (rTMS) is an emerging treatment option for obsessive-compulsive disorder (OCD). The neurobiological mechanisms of rTMS in OCD have, however, been incompletely characterized. We compared clinical outcomes and changes in task-based brain activation following three different rTMS stimulation protocols, all combined with exposure and response prevention (ERP).

Methods

In this three-arm proof-of-concept randomized controlled clinical trial, 61 treatment-refractory adult OCD patients received 16 sessions of rTMS immediately prior to ERP over 8 weeks, with task-based functional MRI (tb-fMRI) scans and clinical assessments pre- and post-treatment. Patients received either: high frequency (HF) rTMS to the left dorsolateral prefrontal cortex (DLPFC) (n=19 (6M/13F)); HF rTMS to the left pre-supplementary motor area (preSMA) (n=23 (10M/13F)); or control rTMS to the vertex (n=19 (6M/13F)). Changes in tb-fMRI activation pre-post treatment were compared using both a Bayesian region-of-interest and a general linear model whole-brain approach.

Results

Mean OCD symptom severity decreased significantly in all treatment groups (delta=- 10.836, p<0.001, 95% CI [-12.504, -9.168]), with no differences between groups. Response rate in the entire sample was 57.4%. Groups receiving DLPFC or preSMA rTMS showed, respectively, a decrease in planning and error processing task-related activation after treatment that was associated with symptom improvement, while individuals in the vertex rTMS group with greater symptom improvement showed an increase in inhibition-related activation.

Conclusions

PreSMA and DLPFC rTMS combined with ERP led to significant symptom improvement related to activation decreases in targeted task networks, although we observed no differences in symptom reduction between groups. This trial was registered at clinicaltrials.gov ( NCT03667807 ).

Impact of combination of intermittent theta burst stimulation and methadone maintenance treatment in individuals with opioid use disorder: A comparative study

Prior studies indicate that subjects undergoing methadone maintenance therapy (MMT) may experience anxiety, depression and cravings. This study aimed to explore the impact of intermittent theta burst stimulation (iTBS)-MMT combination on craving and emotional symptoms of opioid use disorder. This comparative study included subjects with opioid use disorder at the Methadone Maintenance Clinic of Pudong New Area between September 2019 and March 2020. The subjects were divided into two groups: those who received iTBS-MMT combination treatment (iTBS-MMT) and those who received MMT treatment and sham stimulation treatment (MMT). Outcomes were reduction rate of anxiety, depression and craving. Anxiety was measured by Hamilton Anxiety (HAMA) scale, depression was determined by Hamilton Depression (HAMD) scale and craving was analyzed using visual analog scale. A total of 76 subjects completed the treatment, with 38 subjects in each group. Twenty days after treatment, subjects in the iTBS-MMT group had significant improvement of anxiety (HAMA reduction rate), depression (HAMD reduction rate) and craving (Craving reduction rate) reduction rate compared with MMT group. iTBS-MMT combination treatment may produce better drug craving reduction and emotional improvement than MMT alone.

Offline 20 Hz transcranial alternating current stimulation over the right inferior frontal gyrus increases theta activity during a motor response inhibition task

OBJECTIVES

Previous studies have shown that the right inferior frontal gyrus (rIFG) and the pre-supplementary motor area (preSMA) play an important role in motor inhibitory control. The aim of the study was to use theta frequency transcranial alternating current stimulation (tACS) to modulate brain activity in the rIFG and preSMA and to test the effects of stimulation using a motor response inhibition task.

METHODS

In four sessions, 20 healthy participants received tACS at 6 Hz over preSMA or rIFG, or 20 Hz over rIFG (to test frequency specificity), or sham stimulation before task processing. After each type of stimulation, the participants performed the Go/NoGo task with simultaneous electroencephalogram (EEG) recording.

RESULTS

By stimulating rIFG and preSMA with 6 Hz tACS, we were not able to modulate either behavioral performance nor the EEG correlate. Interestingly, 20 Hz tACS over the rIFG significantly increased theta activity, however without behavioral effects. This increased theta activity did not coincide with the stimulation area and was localized in the fronto-central and centro-parietal areas.

CONCLUSIONS

The inclusion of a control frequency is crucial to test for frequency specificity. Our findings are in accordance with previous studies showing that after effects of tACS are not restricted to the stimulation frequency but can also occur in other frequency bands.

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.

The Supplementary Motor Area and Automatic Cognitive Control: Lack of Evidence from Two Neuromodulation Techniques

The SMA is fundamental in planning voluntary movements and execution of some cognitive control operations. Specifically, the SMA has been known to play a dominant role in controlling goal-directed actions as well as those that are highly predicted (i.e., automatic). Yet, the essential contribution of SMA in goal-directed or automatic control of behavior is scarce. Our objective was to test the possible direct role of SMA in automatic and voluntary response inhibition. We separately applied two noninvasive brain stimulation (NIBS) inhibitory techniques over SMA: either continuous theta-burst stimulation using repetitive transcranial magnetic stimulation or transcranial static magnetic field stimulation. Each NIBS technique was performed in a randomized, crossover, sham-controlled design. Before applying NIBS, participants practiced a go/no-go learning task where associations between stimulus and stopping behaviors were created (initiation and inhibition). After applying each NIBS, participants performed a go/no-go task with reversed associations (automatic control) and the stop signal task (voluntary control). Learning associations between stimuli and response initiation/inhibition was achieved by participants and therefore automatized during training. However, no significant differences between real and sham NIBS were found in either automatic (go/no-go learning task) or voluntary inhibition (stop signal task), with Bayesian statistics providing moderate evidence of absence. In conclusion, our results are compatible with a nondirect involvement of SMA in automatic control of behavior. Further studies are needed to prove a noncausal link between prior neuroimaging findings relative to SMA controlling functions and the observed behavior.

Changing Cerebral Blood Flow, Glucose Metabolism, and Dopamine Binding Through Transcranial Magnetic Stimulation: A Systematic Review of Transcranial Magnetic Stimulation-Positron Emission Tomography Literature

Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation tool currently used as a treatment in multiple psychiatric and neurologic disorders. Despite its widespread use, we have an incomplete understanding of the way in which acute and chronic sessions of TMS affect various neural and vascular systems. This systematic review summarizes the state of our knowledge regarding the effects TMS may be having on cerebral blood flow, glucose metabolism, and neurotransmitter release. Forty-five studies were identified. Several key themes emerged: 1) TMS transiently increases cerebral blood flow in the area under the coil; 2) TMS to the prefrontal cortex increases glucose metabolism in the anterior cingulate cortex of patients with depression; and 3) TMS to the motor cortex and prefrontal cortex decreases dopamine receptor availability in the ipsilateral putamen and caudate respectively. There is, however, a paucity of literature regarding the effects TMS may have on other neurotransmitter and neuropeptide systems of interest, all of which may shed vital light on existing biologic mechanisms and future therapeutic development. SIGNIFICANCE STATEMENT: Transcranial magnetic stimulation (TMS) is a noninvasive neuromodulation tool currently used as a treatment in multiple psychiatric and neurologic disorders. This systematic review summarizes the state of our knowledge regarding the effects TMS on cerebral blood flow, glucose metabolism, and neurotransmitter release.

Glutamate-Weighted Magnetic Resonance Imaging (GluCEST) Detects Effects of Transcranial Magnetic Stimulation to the Motor Cortex

Transcranial magnetic stimulation (TMS) is used in several FDA-approved treatments and, increasingly, to treat neurological disorders in off-label uses. However, the mechanism by which TMS causes physiological change is unclear, as are the origins of response variability in the general population. Ideally, objective in vivo biomarkers could shed light on these unknowns and eventually inform personalized interventions. Continuous theta-burst stimulation (cTBS) is a form of TMS observed to reduce motor evoked potentials (MEPs) for 60 min or longer post-stimulation, although the consistency of this effect and its mechanism continue to be under debate. Here, we use glutamate-weighted chemical exchange saturation transfer (gluCEST) magnetic resonance imaging (MRI) at ultra-high magnetic field (7T) to measure changes in glutamate concentration at the site of cTBS. We find that the gluCEST signal in the ipsilateral hemisphere of the brain generally decreases in response to cTBS, whereas consistent changes were not detected in the contralateral region of interest (ROI) or in subjects receiving sham stimulation.

Functional correlates of response inhibition in impulse control disorders in Parkinson's disease

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PD patients with ICD behave like controls in proactive and reactive inhibition.

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PD patients with ICD recruit different mechanisms depending on the inhibition type.

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Proactive inhibition is executed hyperactivating the stopping network bilaterally.

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Restrained inhibition is accomplished with the coactivation of attentional areas.

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In restrained inhibition, connectivity between right STN and precuneus is reduced.

Impulse control disorder is a prevalent side-effect of Parkinson’s disease (PD) medication, with a strong negative impact on the quality of life of those affected. Although impulsivity has classically been associated with response inhibition deficits, previous evidence from PD patients with impulse control disorder (ICD) has not revealed behavioral dysfunction in response inhibition. In this study, 18 PD patients with ICD, 17 PD patients without this complication, and 15 healthy controls performed a version of the conditional Stop Signal Task during functional magnetic resonance imaging. Whole-brain contrasts, regions of interest, and functional connectivity analyses were conducted. Our aim was to investigate the neural underpinnings of two aspects of response inhibition: proactive inhibition, inhibition that has been prepared beforehand, and restrained inhibition, inhibition of an invalid inhibitory tendency. We observed that, in respect to the other two groups, PD patients with ICD exhibited hyperactivation of the stopping network bilaterally while performing proactive inhibition. When engaged in restrained inhibition, they showed hyperactivation of the left inferior frontal gyrus, an area linked to action monitoring. Restrained inhibition also resulted in changes to the functional co-activation between inhibitory regions and left inferior parietal cortex and right supramarginal gyrus. Our findings indicate that PD patients with ICD completed the inhibition task correctly, showing altered engagement of inhibitory and attentional areas. During proactive inhibition they showed bilateral hyperactivation of two inhibitory regions, while during restrained inhibition they showed additional involvement of attentional areas responsible for alerting and orienting.

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.

Lateral Prefrontal Cortex Is a Hub for Music Production from Structural Rules to Movements

Complex sequential behaviors, such as speaking or playing music, entail flexible rule-based chaining of single acts. However, it remains unclear how the brain translates abstract structural rules into movements. We combined music production with multimodal neuroimaging to dissociate high-level structural and low-level motor planning. Pianists played novel musical chord sequences on a muted MR-compatible piano by imitating a model hand on screen. Chord sequences were manipulated in terms of musical harmony and context length to assess structural planning, and in terms of fingers used for playing to assess motor planning. A model of probabilistic sequence processing confirmed temporally extended dependencies between chords, as opposed to local dependencies between movements. Violations of structural plans activated the left inferior frontal and middle temporal gyrus, and the fractional anisotropy of the ventral pathway connecting these two regions positively predicted behavioral measures of structural planning. A bilateral frontoparietal network was instead activated by violations of motor plans. Both structural and motor networks converged in lateral prefrontal cortex, with anterior regions contributing to musical structure building, and posterior areas to movement planning. These results establish a promising approach to study sequence production at different levels of action representation.

Decoupling countermands nonselective response inhibition during selective stopping

Response inhibition is essential for goal-directed behavior within dynamic environments. Selective stopping is a complex form of response inhibition where only part of a multi-effector response must be cancelled. A substantial response delay emerges on unstopped effectors when a cued effector is successfully stopped. This stopping-interference effect is indicative of nonselective response inhibition during selective stopping which may, in-part, be a consequence of functional coupling. The present study examined selective stopping of (de)coupled bimanual responses in healthy human participants of either sex. Participants performed synchronous and asynchronous versions of an anticipatory stop-signal paradigm across two sessions while mu (µ) and beta (β) rhythm were measured with electroencephalography. Results showed that responses were behaviorally decoupled during asynchronous go trials and the extent of response asynchrony was associated with lateralized sensorimotor µ and β desynchronization during response preparation. Selective stopping produced a stopping-interference effect and was marked by a nonselective increase and subsequent rebound in prefrontal and sensorimotor β. In support of the coupling account, stopping-interference was smaller during selective stopping of asynchronous responses, and negatively associated with the magnitude of decoupling. However, the increase in sensorimotor β during selective stopping was equivalent between the stopped and unstopped hand irrespective of response synchrony. Overall, the findings demonstrate that decoupling facilitates selective stopping after a global pause process and emphasizes the importance of considering the influence of both the go and stop context when investigating response inhibition.

Causal Prefrontal Contributions to Stop-Signal Task Performance in Humans

The frontal lobes have long been implicated in inhibitory control, but a full understanding of the underlying mechanisms remains elusive. The stop-signal task has been widely used to probe instructed response inhibition in cognitive neuroscience. The processes involved have been modeled and related to putative brain substrates. However, there has been surprisingly little human lesion research using this task, with the few existing studies implicating different prefrontal regions. Here, we tested the effects of focal prefrontal damage on stop-signal task performance in a large sample of people with chronic focal damage affecting the frontal lobes (n = 42) and demographically matched healthy individuals (n = 60). Patients with damage to the left lateral, right lateral, dorsomedial, or ventromedial frontal lobe had slower stop-signal RT compared to healthy controls. There were systematic differences in the patterns of impairment across frontal subgroups: Those with damage to the left or right lateral and dorsomedial frontal lobes, but not those with ventromedial frontal damage, were slower than controls to "go" as well as to stop. These findings suggest that multiple prefrontal regions make necessary but distinct contributions to stop-signal task performance. As a consequence, stop-signal RT slowing is not strongly localizing within the frontal lobes.

Repetitive Transcranial Magnetic Stimulation on the Supplementary Motor Area Changes Brain Connectivity in Functional Dysphagia

Background: Previous studies arguing that functional dysphagia could be explained by underlying neurobiological mechanisms are insufficient to explain brain regions that functionally interact in patients with functional dysphagia. Therefore, we investigated functional connectivity changes associated with functional dysphagia after applying facilitatory repetitive transcranial magnetic stimulation (rTMS) on the supplementary motor area (SMA). Materials and Methods: A patient with severe long-lasting functional dysphagia and 15 healthy controls participated in this study. A facilitatory 5 Hz rTMS protocol was applied to the patient's SMA. We performed functional magnetic resonance imaging (fMRI) using volitional swallowing tasks to investigate neural network changes before rTMS (pre-rTMS), immediately after rTMS, and 3 months later. Results: The pre-rTMS fMRI results of the patient showed extensive overactivation in the left-lateralized regions related to volitional swallowing compared with the healthy controls. Following rTMS, dysphagia symptoms partially improved. The patient showed positive connectivity with the bilateral cerebellum in the bilateral SMA seeds before rTMS treatment. Furthermore, left-lateralized overactivation was washed out immediately after completion of rTMS, and connectivity between the left SMA and left precentral gyrus recovered 3 months after rTMS treatment. Conclusion: Our findings confirm that functional dysphagia might be a neurobiological manifestation caused by maladaptive functional connectivity changes in brain structures related to swallowing. Furthermore, noninvasive brain modulation with rTMS over the SMA may facilitate functional connectivity changes between the cortical and subcortical regions. Accordingly, these changes will allow control of the movements related to swallowing and may lead to improved clinical symptoms.

Out with the Old and in with the New: the Contribution of Prefrontal and Cerebellar Areas to Backward Inhibition

The inhibitory mechanism named backward inhibition (BI) counteracts interference of previous tasks supporting task switching. For instance, if task set A is inhibited when switching to task B, then it should take longer to immediately return to task set A (as occurring in an ABA sequence), as compared to a task set that has not been just inhibited (as occurring in a CBA sequence), because extra time will be needed to overcome the inhibition of task set A.The evidenced prefrontal and cerebellar role in inhibitory control suggests their involvement even in BI. Here, for the first time, we modulated the excitability of multiple brain sites (right presupplementary motor area (pre-SMA), left and right cerebellar hemispheres) through continuous theta burst stimulation (cTBS) in a valuable sham-controlled order-balanced within-subject experimental design in healthy individuals performing two domain-selective (verbal and spatial) task-switching paradigms. Verbal BI was abolished by prefrontal or cerebellar stimulations through opposite alterations of the basal pattern: cTBS on pre-SMA increased CBA reaction times, disclosing the current prefrontal inhibition of any interfering old task. Conversely, cerebellar cTBS decreased ABA reaction times, disclosing the current cerebellar recognition of sequences in which it is necessary to overcome previously inhibited events.

Adjustments to Proactive Motor Inhibition without Effector-Specific Foreknowledge Are Reflected in a Bilateral Upregulation of Sensorimotor β-Burst Rates

Classic work using the stop-signal task has shown that humans can use inhibitory control to cancel already initiated movements. Subsequent work revealed that inhibitory control can be proactively recruited in anticipation of a potential stop-signal, thereby increasing the likelihood of successful movement cancellation. However, the exact neurophysiological effects of proactive inhibitory control on the motor system are still unclear. On the basis of classic views of sensorimotor β-band activity, as well as recent findings demonstrating the burst-like nature of this signal, we recently proposed that proactive inhibitory control is implemented by influencing the rate of sensorimotor β-bursts during movement initiation. Here, we directly tested this hypothesis using scalp EEG recordings of β-band activity in 41 healthy human adults during a bimanual RT task. By comparing motor responses made in two different contexts-during blocks with or without stop-signals-we found that premovement β-burst rates over both contralateral and ipsilateral sensorimotor areas were increased in stop-signal blocks compared to pure-go blocks. Moreover, the degree of this burst rate difference indexed the behavioral implementation of proactive inhibition (i.e., the degree of anticipatory response slowing in the stop-signal blocks). Finally, exploratory analyses showed that these condition differences were explained by a significant increase in β bursting that was already present during the premovement baseline period in stop blocks. Together, this suggests that the strategic deployment of proactive inhibitory motor control is implemented by upregulating the tonic inhibition of the motor system, signified by increased sensorimotor β-bursting both before and after signals to initiate a movement.

Please, don't do it! Fifteen years of progress of non-invasive brain stimulation in action inhibition

The ability to inhibit prepotent responses is critical for survival. Action inhibition can be investigated using a stop-signal task (SST), designed to provide a reliable measure of the time taken by the brain to suppress motor responses. Here we review the major research advances using the combination of this paradigm with the use of non-invasive brain stimulation techniques in the last fifteen years. We highlight new methodological approaches to understanding and exploiting several processes underlying action control, which is critically impaired in several psychiatric disorders. In this review we present and discuss existing literature demonstrating i) the importance of the use of non-invasive brain stimulation in studying human action inhibition, unveiling the neural network involved ii) the critical role of prefrontal areas, including the pre-supplementary motor area (pre-SMA) and the inferior frontal gyrus (IFG), in inhibitory control iii) the neural and behavioral evidence of proactive and reactive action inhibition. As the main result of this review, the specific literature demonstrated the crucial role of pre-SMA and IFG as evidenced from the field of noninvasive brain stimulation studies. Finally, we discuss the critical questions that remain unanswered about how such non-invasive brain stimulation protocols can be translated to therapeutic treatments.

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.

Static magnetic field stimulation of the supplementary motor area modulates resting-state activity and motor behavior

Focal application of a strong static magnetic field over the human scalp induces measurable local changes in brain function. Whether it also induces distant effects across the brain and how these local and distant effects collectively affect motor behavior remains unclear. Here we applied transcranial static magnetic field stimulation (tSMS) over the supplementary motor area (SMA) in healthy subjects. At a behavioral level, tSMS increased the time to initiate movement while decreasing errors in choice reaction-time tasks. At a functional level, tSMS increased SMA resting-state fMRI activity and bilateral functional connectivity between the SMA and both the paracentral lobule and the lateral frontotemporal cortex, including the inferior frontal gyrus. These results suggest that tSMS over the SMA can induce behavioral aftereffects associated with modulation of both local and distant functionally-connected cortical circuits involved in the control of speed-accuracy tradeoffs, thus offering a promising protocol for cognitive and clinical research.

Sparse Principal Component based High-Dimensional Mediation Analysis

Causal mediation analysis aims to quantify the intermediate effect of a mediator on the causal pathway from treatment to outcome. When dealing with multiple mediators, which are potentially causally dependent, the possible decomposition of pathway effects grows exponentially with the number of mediators. An existing approach incorporated the principal component analysis (PCA) to address this challenge based on the fact that the transformed mediators are conditionally independent given the orthogonality of the principal components (PCs). However, the transformed mediator PCs, which are linear combinations of original mediators, can be difficult to interpret. A sparse high-dimensional mediation analysis approach is proposed which adopts the sparse PCA method to the mediation setting. The proposed approach is applied to a task-based functional magnetic resonance imaging study, illustrating its ability to detect biologically meaningful results related to an identified mediator.

Reduced premovement positivity during the stimulus-response interval precedes errors: Using single-trial and regression ERPs to understand performance deficits in ADHD

Brain mechanisms linked to incorrect response selections made under time pressure during cognitive task performance are poorly understood, particularly in adolescents with attention-deficit hyperactivity disorder (ADHD). Using subject-specific multimodal imaging (electroencephalogram, magnetic resonance imaging, behavior) during flanker task performance by a sample of 94 human adolescents (mean age = 15.5 years, 50% female) with varying degrees of ADHD symptomatology, we examined the degree to which amplitude features of source-resolved event-related potentials (ERPs) from brain-independent component processes within a critical (but often ignored) period in the action selection process, the stimulus-response interval, were associated with motor response errors (across trials) and error rates (across individuals). Response errors were typically preceded by two smaller peaks in both trial-level and trial-averaged ERP projections from posterior medial frontal cortex (pMFC): a frontocentral P3 peaking about 390 ms after stimulus onset, and a premovement positivity (PMP) peaking about 110 ms before the motor response. Separating overlapping stimulus-locked and response-locked ERP contributions using a "regression ERP" approach showed that trial errors and participant error rates were primarily associated with smaller PMP, and not with frontocentral P3. Moreover, smaller PMP mediated the association between larger numbers of errors and ADHD symptoms, suggesting the possible value of using PMP as an intervention target to remediate performance deficits in ADHD.

Modulation of Resting Connectivity Between the Mesial Frontal Cortex and Basal Ganglia

Background: The mesial prefrontal cortex, cingulate cortex, and the ventral striatum are key nodes of the human mesial fronto-striatal circuit involved in decision-making and executive function and pathological disorders. Here we ask whether deep wide-field repetitive transcranial magnetic stimulation (rTMS) targeting the mesial prefrontal cortex (MPFC) influences resting state functional connectivity. Methods: In Study 1, we examined functional connectivity using resting state multi-echo and independent components analysis in 154 healthy subjects to characterize default connectivity in the MPFC and mid-cingulate cortex (MCC). In Study 2, we used inhibitory, 1 Hz deep rTMS with the H7-coil targeting MPFC and dorsal anterior cingulate (dACC) in a separate group of 20 healthy volunteers and examined pre- and post-TMS functional connectivity using seed-based and independent components analysis. Results: In Study 1, we show that MPFC and MCC have distinct patterns of functional connectivity with MPFC-ventral striatum showing negative, whereas MCC-ventral striatum showing positive functional connectivity. Low-frequency rTMS decreased functional connectivity of MPFC and dACC with the ventral striatum. We further showed enhanced connectivity between MCC and ventral striatum. Conclusions: These findings emphasize how deep inhibitory rTMS using the H7-coil can influence underlying network functional connectivity by decreasing connectivity of the targeted MPFC regions, thus potentially enhancing response inhibition and decreasing drug-cue reactivity processes relevant to addictions. The unexpected finding of enhanced default connectivity between MCC and ventral striatum may be related to the decreased influence and connectivity between the MPFC and MCC. These findings are highly relevant to the treatment of disorders relying on the mesio-prefrontal-cingulo-striatal circuit.

Granger mediation analysis of multiple time series with an application to functional magnetic resonance imaging

This paper presents Granger mediation analysis, a new framework for causal mediation analysis of multiple time series. This framework is motivated by a functional magnetic resonance imaging (fMRI) experiment where we are interested in estimating the mediation effects between a randomized stimulus time series and brain activity time series from two brain regions. The independent observation assumption is thus unrealistic for this type of time-series data. To address this challenge, our framework integrates two types of models: causal mediation analysis across the mediation variables, and vector autoregressive (VAR) models across the temporal observations. We use "Granger" to refer to VAR correlations modeled in this paper. We further extend this framework to handle multilevel data, in order to model individual variability and correlated errors between the mediator and the outcome variables. Using Rubin's potential outcome framework, we show that the causal mediation effects are identifiable under our time-series model. We further develop computationally efficient algorithms to maximize our likelihood-based estimation criteria. Simulation studies show that our method reduces the estimation bias and improves statistical power, compared with existing approaches. On a real fMRI data set, our approach quantifies the causal effects through a brain pathway, while capturing the dynamic dependence between two brain regions.

Linking brain activation to topological organization in the frontal lobe as a synergistic indicator to characterize the difference between various cognitive processes of executive functions

Executive functions (EFs) associated with the frontal lobe are vital for goal-orientated behavior. To date, limited efforts have been made to examine the relationships among the behavior, brain activation, and topological organization of functional networks in the frontal lobe underlying various EF tasks, including inhibition, working memory, and cognitive flexibility. In this study, functional near-infrared spectroscopy neuroimaging technique was used to systematically inspect the differences in the brain activation and the topological organization of brain networks between various EF tasks in the frontal lobe. In addition, the relationships between brain activation/network properties and task performances and the relationships between brain activation and network properties were, respectively, examined for different EF tasks. Consequently, we have discovered that the nodal and global properties of the resting-state and task-evoked networks, respectively, exhibited significant correlations with the activation of various brain regions during various EF tasks. In particular, the measure that links the neural activation to the topological organization of the brain networks in the frontal lobe can serve as a synergistic indicator to examine the difference between various EF tasks, which paves a way toward a comprehensive understanding of the neural mechanism underlying EFs.

Dopamine effects on frontal cortical blood flow and motor inhibition in Parkinson's disease

Parkinson's disease (PD) is characterized by dysfunction in frontal cortical and striatal networks that regulate action control. We investigated the pharmacological effect of dopamine agonist replacement therapy on frontal cortical activity and motor inhibition. Using Arterial Spin Labeling MRI, we examined 26 PD patients in the off- and on-dopamine agonist medication states to assess the effect of dopamine agonists on frontal cortical regional cerebral blood flow. Motor inhibition was measured by the Simon task in both medication states. We applied the dual process activation suppression model to dissociate fast response impulses from motor inhibition of incorrect responses. General linear regression model analyses determined the medication effect on regional cerebral blood flow and motor inhibition, and the relationship between regional cerebral blood flow and motor inhibitory proficiency. We show that dopamine agonist administration increases frontal cerebral blood flow, particularly in the pre-supplementary motor area (pre-SMA) and the dorsolateral prefrontal cortex (DLPFC). Higher regional blood flow in the pre-SMA, DLPFC and motor cortex was associated with better inhibitory control, suggesting that treatments which improve frontal cortical activity could ameliorate motor inhibition deficiency in PD patients.

Modulating functional connectivity with non-invasive brain stimulation for the investigation and alleviation of age-associated declines in response inhibition: A narrative review

Response inhibition, the ability to withhold a dominant and prepotent response following a change in circumstance or sensory stimuli, declines with advancing age. While non-invasive brain stimulation (NiBS) has shown promise in alleviating some cognitive and motor functions in healthy older individuals, NiBS research focusing on response inhibition has mostly been conducted on younger adults. These extant studies have primarily focused on modulating the activity of distinct neural regions known to be critical for response inhibition, including the right inferior frontal gyrus (rIFG) and the pre-supplementary motor area (pre-SMA). However, given that changes in structural and functional connectivity have been associated with healthy aging, this review proposes that NiBS protocols aimed at modulating the functional connectivity between the rIFG and pre-SMA may be the most efficacious approach to investigate-and perhaps even alleviate-age-related deficits in inhibitory control.

Exploring the effects of anodal and cathodal high definition transcranial direct current stimulation targeting the dorsal anterior cingulate cortex

The dorsal anterior cingulate cortex (dACC) has been identified as a core region affected by many disorders, representing a promising target for neuromodulation. High Definition-transcranial Direct Current Stimulation (HD-tDCS) is a non-invasive neuromodulation technique that has already shown promising outcomes and has been tested to engage deeper structures. This study investigates whether it is possible to modulate dACC activity using anodal and cathodal HD-tDCS. Furthermore, it examines what effects anodal and cathodal HD-tDCS targeting dACC have on cognitive and emotional processing. Forty-five healthy subjects were randomly assigned to 1 of 3 groups: anodal, cathodal, and sham. Resting-state electroencephalography (rsEEG) and a cognitive and emotional Counting Stroop task were administered before and after HD-tDCS. RsEEG showed changes: anodal HD-tDCS showed significant increase in beta frequency band activity in dACC, while cathodal HD-tDCS led to significant increase in activity at dorsal and rostral ACC in the theta frequency band. Behavioral changes were also found after anodal HD-tDCS in the cognitive Counting Stroop for incongruent trials and after cathodal HD-tDCS in the emotional Counting Stroop for emotional trials. This study demonstrated that HD-tDCS is able to modulate dACC activity, suggesting that it has the potential to be used as a treatment tool.

Sensitivity to perception level differentiates two subnetworks within the mirror neuron system

Mirror neurons are a subset of brain cells that discharge during action execution and passive observation of similar actions. An open question concerns the functional role of their ability to match observed and executed actions. Since understanding of goals requires conscious perception of actions, we expect that mirror neurons potentially involved in action goal coding, will be modulated by changes in action perception level. Here, we manipulated perception level of action videos depicting short hand movements and measured the corresponding fMRI BOLD responses in mirror regions. Our results show that activity levels within a network of regions, including the sensorimotor cortex, primary motor cortex, dorsal premotor cortex and posterior superior temporal sulcus, are sensitive to changes in action perception level, whereas activity levels in the inferior frontal gyrus, ventral premotor cortex, supplementary motor area and superior parietal lobule are invariant to such changes. In addition, this parcellation to two sub-networks manifest as smaller functional distances within each group of regions during task and resting state. Our results point to functional differences between regions within the mirror neurons system which may have implications with respect to their possible role in action understanding.

Online Transcranial Magnetic Stimulation Protocol for Measuring Cortical Physiology Associated with Response Inhibition

We describe the development of a reproducible, child-friendly motor response inhibition task suitable for online Transcranial Magnetic Stimulation (TMS) characterization of primary motor cortex (M1) excitability and inhibition. Motor response inhibition prevents unwanted actions and is abnormal in several neuropsychiatric conditions. TMS is a non-invasive technology that can quantify M1 excitability and inhibition using single- and paired-pulse protocols and can be precisely timed to study cortical physiology with high temporal resolution. We modified the original Slater-Hammel (S-H) stop signal task to create a "racecar" version with TMS pulses time-locked to intra-trial events. This task is self-paced, with each trial initiating after a button push to move the racecar towards the 800 ms target. GO trials require a finger-lift to stop the racecar just before this target. Interspersed randomly are STOP trials (25%) during which the dynamically adjusted stop signal prompts subjects to prevent finger-lift. For GO trials, TMS pulses were delivered at 650 ms after trial onset; whereas, for STOP trials, the TMS pulses occurred 150 ms after the stop signal. The timings of the TMS pulses were decided based on electroencephalography (EEG) studies showing event-related changes in these time ranges during stop signal tasks. This task was studied in 3 blocks at two study sites (n=38) and we recorded behavioral performance and event-related motor-evoked potentials (MEP). Regression modelling was used to analyze MEP amplitudes using age as a covariate with multiple independent variables (sex, study site, block, TMS pulse condition [single- vs. paired-pulse], trial condition [GO, successful STOP, failed STOP]). The analysis showed that TMS pulse condition (p<0.0001) and its interaction with trial condition (p=0.009) were significant. Future applications for this online S-H/TMS paradigm include the addition of simultaneous EEG acquisition to measure TMS-evoked EEG potentials. A potential limitation is that in children, the TMS pulse sound could affect behavioral task performance.

Loss of inhibition in sensorimotor networks in focal hand dystonia

Objective

To investigate GABA-ergic receptor density and associated brain functional and grey matter changes in focal hand dystonia (FHD).

Methods

18 patients with FHD of the right hand and 18 age and gender matched healthy volunteers (HV) participated in this study. We measured the density of GABA-A receptors using [¹¹C] Flumazenil and perfusion using [¹⁵O] H₂O. Anatomical images were also used to measure grey matter volume with voxel-based morphometry (VBM).

Results

In FHD patients compared to HV, the vermis VI of the right cerebellum and the left sensorimotor cortex had a decrease of Flumazenil binding potential (FMZ-BP), whereas the striatum and the lateral cerebellum did not show significant change. Bilateral inferior prefrontal cortex had increased FMZ-BP and an increase of perfusion, which correlated negatively with disease duration. Only the left sensorimotor cortex showed a decrease of grey matter volume.

Interpretation

Impairments of GABAergic neurotransmission in the cerebellum and the sensorimotor cortical areas could explain different aspects of loss of inhibitory control in FHD, the former being involved in maladaptive plasticity, the latter in surround inhibition. Reorganization of the inferior prefrontal cortices, part of the associative network, might be compensatory for the loss of inhibitory control in sensorimotor circuits. These findings suggest that cerebellar and cerebral GABAergic abnormalities could play a role in the functional imbalance of striato-cerebello-cortical loops in dystonia.

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We tested GABAergic deficiency to explain inhibitory control loss in focal dystonia.

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The right cerebellar vermis and left sensorimotor cortex had GABAergic deficiencies.

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Bilateral prefrontal cortex had an increase of GABAergic potential and activity.

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Prefrontal changes correlated with cerebellar deficiency and disease duration.

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We highlighted the importance of the cerebellum for the pathophysiology of dystonia.

Contribution of transcranial magnetic stimulation to assessment of brain connectivity and networks

The goal of this review is to show how transcranial magnetic stimulation (TMS) techniques can make a contribution to the study of brain networks. Brain networks are fundamental in understanding how the brain operates. Effects on remote areas can be directly observed or identified after a period of stimulation, and each section of this review will discuss one method. EEG analyzed following TMS is called TMS-evoked potentials (TEPs). A conditioning TMS can influence the effect of a test TMS given over the motor cortex. A disynaptic connection can be tested also by assessing the effect of a pre-conditioning stimulus on the conditioning-test pair. Basal ganglia-cortical relationships can be assessed using electrodes placed in the process of deep brain stimulation therapy. Cerebellar-cortical relationships can be determined using TMS over the cerebellum. Remote effects of TMS on the brain can be found as well using neuroimaging, including both positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). The methods complement each other since they give different views of brain networks, and it is often valuable to use more than one technique to achieve converging evidence. The final product of this type of work is to show how information is processed and transmitted in the brain.

Subthalamic deep brain stimulation sweet spots and hyperdirect cortical connectivity in Parkinson's disease

OBJECTIVES

Firstly, to identify subthalamic region stimulation clusters that predict maximum improvement in rigidity, bradykinesia and tremor, or emergence of side-effects; and secondly, to map-out the cortical fingerprint, mediated by the hyperdirect pathways which predict maximum efficacy.

METHODS

High angular resolution diffusion imaging in twenty patients with advanced Parkinson's disease was acquired prior to bilateral subthalamic nucleus deep brain stimulation. All contacts were screened one-year from surgery for efficacy and side-effects at different amplitudes. Voxel-based statistical analysis of volumes of tissue activated models was used to identify significant treatment clusters. Probabilistic tractography was employed to identify cortical connectivity patterns associated with treatment efficacy.

RESULTS

All patients responded well to treatment (46% mean improvement off medication UPDRS-III [p < 0.0001]) without significant adverse events. Cluster corresponding to maximum improvement in tremor was in the posterior, superior and lateral portion of the nucleus. Clusters corresponding to improvement in bradykinesia and rigidity were nearer the superior border in a further medial and posterior location. The rigidity cluster extended beyond the superior border to the area of the zona incerta and Forel-H₂ field. When the clusters where averaged, the coordinates of the area with maximum overall efficacy was X = -10(-9.5), Y = -13(-1) and Z = -7(-3) in MNI(AC-PC) space. Cortical connectivity to primary motor area was predictive of higher improvement in tremor; whilst that to supplementary motor area was predictive of improvement in bradykinesia and rigidity; and connectivity to prefrontal cortex was predictive of improvement in rigidity.

INTERPRETATION

These findings support the presence of overlapping stimulation sites within the subthalamic nucleus and its superior border, with different cortical connectivity patterns, associated with maximum improvement in tremor, rigidity and bradykinesia.

High frequency repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex for methamphetamine use disorders: A randomised clinical trial

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a brain stimulation and modulation electrophysiological technique, it can change cortical excitability of target brain region, modulate neuron plasticity and brain connections. Previous researches indicated that rTMS could reduce cue-induced craving in drug addiction.

OBJECTIVE

In this study, we employed real and sham rTMS of the left dorsolateral prefrontal cortex (DLPFC) to test whether it could reduce cue-induced craving for methamphetamine (MA) and influence cognitive function in a randomised clinical trial.

METHODS

Thirty MA-addicted patients were randomized to receive 5 sessions of 8min sham or 10Hz rTMS to the left DLPFC. Subjects rated their craving at baseline, after exposed to MA-associated cues and after rTMS sessions.

RESULTS

Real rTMS over the left DLPFC reduced craving significantly after 5 sessions of rTMS as compared to sham stimulation. Furthermore, real rTMS improved verbal learning and memory and social cognition in MA-addicted patients.

CONCLUSIONS

The present study suggests that 10Hz rTMS of the left DLPFC may reduce craving and have no negative effects on cognitive function in MA-addicted patients, supporting the safety of rTMS in treating MA addiction.

The critical role of the dorsal fronto-median cortex in voluntary action inhibition: A TMS study

BACKGROUND

Action inhibition is a complex decision process that can be triggered by external factors (exogenous) or internal decisions (endogenous). While the neuronal underpinnings of exogenous action inhibition have been extensively investigated, less is known about the brain areas responsible for endogenous action inhibition.

OBJECTIVE

We used inhibitory repetitive transcranial magnetic stimulation (rTMS) to test the causal role of two brain areas, the left dorsal fronto-median Cortex (dFMC) and the right Inferior Frontal Cortex (rIFC) in exogenous and endogenous action inhibition.

METHODS

The exogenous condition was a modified version of the Go/NoGo paradigm, where a green stimulus served as a cue to perform an action (a button press, Exogenous-Go), while a magenta stimulus indicated that action should be withhold (Exogenous-NoGo). Crucially, for the endogenous condition we psychophysically generated a shade of colour that participants randomly categorized as green or magenta. This unique stimulus, randomly intermixed with green and magenta stimuli, forced participants to perform an endogenous (internally-driven) choice to either execute or inhibit the action.

RESULTS

In the endogenous condition, at baseline participants executed the action on half the trials; however, after 1-Hz rTMS over the dFMC they responded significantly more frequently, indicating a reduced response inhibition. The effect was selective for the dFMC stimulation and sustained in time. Moreover, no significant effects were found in the exogenous condition.

CONCLUSIONS

These results support the causal role of the left dFMC in endogenous action inhibition and, more generally, the notion of separate brain circuits for endogenous and exogenous action inhibition.