The effect of Parkinson's disease on interference control during action selection

Dopamine activity in the nigrostriatal pathway alters cue-induced risky choice patterns in female rats

Deficits in cost/benefit decision making is a critical risk factor for gambling disorder. Reward-paired cues may play an important role, as these stimuli can enhance risk preference in rats. Despite extensive research implicating the dorsal striatum in the compulsive aspects of addiction, the role of nigrostriatal dopaminergic activity in cue-induced risk preference remains unclear, particularly in females. Accordingly, we examined the effects of manipulating the dopaminergic nigrostriatal pathway on cue-induced risky choice in female rats. TH:Cre rats were trained on the cued version of the rat Gambling Task. This task was designed such that maximal reward is attained by avoiding the high-risk, high-reward options and instead favouring the options associated with lower per-trial gains, as they feature less frequent and shorter time-out penalties. Adding reward-paired audiovisual cues to the task leads to greater risky choice on average. To assess the role of the nigrostriatal pathway, a viral vector carrying either Cre-dependent inhibitory or excitatory DREADD was infused into the substantia nigra. Rats then received clozapine-N-oxide either during task acquisition or after a stable performance baseline was reached. Inhibition of this pathway accelerated the development of risk preference in early sessions and increased risky choice during performance, but long-term inhibition actually improved decision making. Activation of this pathway had minimal effects. These results provide evidence for the involvement of the dopaminergic nigrostriatal pathway in cue-induced risk preference in females, therefore shedding light on its role in cost/benefit decision-making deficits and expanding our knowledge of the female dopaminergic system.

Easy to process, hard to control: Transient and sustained processing fluency impairs cognitive control adjustments to conflict

Recent research suggests that the cognitive monitoring system of control could be using negative affective cues intrinsic to changes in information processing to initiate top-down regulatory mechanisms. Here, we propose that positive feelings of ease-of-processing could be picked up by the monitoring system as a cue indicating that control is not necessary, leading to maladaptive control adjustments. We simultaneously target control adjustments driven by task context and on a trial-by-trial level, macro-, and micro-adjustments. This hypothesis was tested using a Stroop-like task comprised trials varying in congruence and perceptual fluency. A pseudo randomisation procedure within different proportion of congruence conditions was used to maximise discrepancy and fluency effects. Results suggest that in a mostly congruent context participants committed more fast errors when incongruent trials were easy-to-read. Moreover, within the mostly incongruent condition, we also found more errors on incongruent trials after experiencing the facilitation effect of repeated congruent trials. These results suggest that transient and sustained feelings of processing fluency can downregulate control mechanisms, leading to failed adaptive adjustments to conflict.

Mechanisms and neuroanatomy of response selection in tool and non-tool action tasks: Evidence from left-hemisphere stroke

The ability to select between potential actions is central to the complex process of tool use. After left hemisphere stroke, individuals with limb apraxia make more hand action errors when gesturing the use of tools with conflicting hand actions for grasping-to-move and use (e.g., screwdriver) relative to tools that are grasped-to-move and used with the same hand action (e.g., hammer). Prior research indicates that this grasp-use interference effect is driven by abnormalities in the competitive action selection process. The goal of this project was to determine whether common mechanisms and neural substrates support the competitive selection of task-appropriate responses in both tool and non-tool domains. If so, the grasp-use interference effect in a tool use gesturing task should be correlated with response interference effects in the classic Eriksen flanker and Simon tasks, and at least partly overlapping neural regions should subserve the 3 tasks. Sixty-four left hemisphere stroke survivors (33 with apraxia) participated in the tool- and non-tool interference tasks and underwent T1 anatomical MRI. There were robust grasp-use interference effects (grasp-use conflict test) and response interference effects (Eriksen flanker and Simon tasks), but these effects were not correlated. Lesion-symptom mapping analyses showed that lesions to the left inferior parietal lobule, ventral premotor cortex, and insula were associated with grasp-use interference. Lesions to the left inferior parietal lobule, postcentral gyrus, insula, caudate, and putamen were associated with response interference in the Eriksen flanker task. Lesions to the left caudate and putamen were also associated with response interference in the Simon task. Our results suggest that the selection of hand posture for tool use is mediated by distinct cognitive mechanisms and partly distinct neuroanatomic substrates from those mapping a stimulus to an appropriate motor response in non-tool domains.

Parkinson Disease Recognition Using a Gamified Website: Machine Learning Development and Usability Study

BACKGROUND

Parkinson disease (PD) affects millions globally, causing motor function impairments. Early detection is vital, and diverse data sources aid diagnosis. We focus on lower arm movements during keyboard and trackpad or touchscreen interactions, which serve as reliable indicators of PD. Previous works explore keyboard tapping and unstructured device monitoring; we attempt to further these works with structured tests taking into account 2D hand movement in addition to finger tapping. Our feasibility study uses keystroke and mouse movement data from a remotely conducted, structured, web-based test combined with self-reported PD status to create a predictive model for detecting the presence of PD.

OBJECTIVE

Analysis of finger tapping speed and accuracy through keyboard input and analysis of 2D hand movement through mouse input allowed differentiation between participants with and without PD. This comparative analysis enables us to establish clear distinctions between the two groups and explore the feasibility of using motor behavior to predict the presence of the disease.

METHODS

Participants were recruited via email by the Hawaii Parkinson Association (HPA) and directed to a web application for the tests. The 2023 HPA symposium was also used as a forum to recruit participants and spread information about our study. The application recorded participant demographics, including age, gender, and race, as well as PD status. We conducted a series of tests to assess finger tapping, using on-screen prompts to request key presses of constant and random keys. Response times, accuracy, and unintended movements resulting in accidental presses were recorded. Participants performed a hand movement test consisting of tracing straight and curved on-screen ribbons using a trackpad or mouse, allowing us to evaluate stability and precision of 2D hand movement. From this tracing, the test collected and stored insights concerning lower arm motor movement.

RESULTS

Our formative study included 31 participants, 18 without PD and 13 with PD, and analyzed their lower limb movement data collected from keyboards and computer mice. From the data set, we extracted 28 features and evaluated their significances using an extra tree classifier predictor. A random forest model was trained using the 6 most important features identified by the predictor. These selected features provided insights into precision and movement speed derived from keyboard tapping and mouse tracing tests. This final model achieved an average F1-score of 0.7311 (SD 0.1663) and an average accuracy of 0.7429 (SD 0.1400) over 20 runs for predicting the presence of PD.

CONCLUSIONS

This preliminary feasibility study suggests the possibility of using technology-based limb movement data to predict the presence of PD, demonstrating the practicality of implementing this approach in a cost-effective and accessible manner. In addition, this study demonstrates that structured mouse movement tests can be used in combination with finger tapping to detect PD.

Huntington disease exacerbates action impulses

Background

Impulsivity is a common clinical feature of Huntington disease (HD), but the underlying cognitive dynamics of impulse control in this population have not been well-studied.

Objective

To investigate the temporal dynamics of action impulse control in HD patients using an inhibitory action control task.

Methods

Sixteen motor manifest HD patients and seventeen age-matched healthy controls (HC) completed the action control task. We applied the activation-suppression theoretical model and distributional analytic techniques to differentiate the strength of fast impulses from their top-down suppression.

Results

Overall, HD patients produced slower and less accurate reactions than HCs. HD patients also exhibited an exacerbated interference effect, as evidenced by a greater slowing of RT on non-corresponding compared to corresponding trials. HD patients made more fast, impulsive errors than HC, evidenced by significantly lower accuracy on their fastest reaction time trials. The slope reduction of interference effects as reactions slowed was similar between HD and controls, indicating preserved impulse suppression.

Conclusion

Our results indicate that patients with HD show a greater susceptibility to act rapidly on incorrect motor impulses but preserved proficiency of top-down suppression. Further research is needed to determine how these findings relate to clinical behavioral symptoms.

Effects of deep brain stimulation target on the activation and suppression of action impulses

OBJECTIVE

Deep brain stimulation (DBS) is an effective treatment to improve motor symptoms in Parkinson's disease (PD). The Globus Pallidus (GPi) and the Subthalamic Nucleus (STN) are the most targeted brain regions for stimulation and produce similar improvements in PD motor symptoms. However, our understanding of stimulation effects across targets on inhibitory action control processes is limited. We compared the effects of STN (n = 20) and GPi (n = 13) DBS on inhibitory control in PD patients.

METHODS

We recruited PD patients undergoing DBS at the Vanderbilt Movement Disorders Clinic and measured their performance on an inhibitory action control task (Simon task) before surgery (optimally treated medication state) and after surgery in their optimally treated state (medication plus their DBS device turned on).

RESULTS

DBS to both STN and GPi targets induced an increase in fast impulsive errors while simultaneously producing more proficient reactive suppression of interference from action impulses.

CONCLUSIONS

Stimulation in GPi produced similar effects as STN DBS, indicating that stimulation to either target increases the initial susceptibility to act on strong action impulses while concomitantly improving the ability to suppress ongoing interference from activated impulses.

SIGNIFICANCE

Action impulse control processes are similarly impacted by stimulating dissociable nodes in frontal-basal ganglia circuitry.

A neurocomputational theory of action regulation predicts motor behavior in neurotypical individuals and patients with Parkinson’s disease

Surviving in an uncertain environment requires not only the ability to select the best action, but also the flexibility to withhold inappropriate actions when the environmental conditions change. Although selecting and withholding actions have been extensively studied in both human and animals, there is still lack of consensus on the mechanism underlying these action regulation functions, and more importantly, how they inter-relate. A critical gap impeding progress is the lack of a computational theory that will integrate the mechanisms of action regulation into a unified framework. The current study aims to advance our understanding by developing a neurodynamical computational theory that models the mechanism of action regulation that involves suppressing responses, and predicts how disruption of this mechanism can lead to motor deficits in Parkinson’s disease (PD) patients. We tested the model predictions in neurotypical individuals and PD patients in three behavioral tasks that involve free action selection between two opposed directions, action selection in the presence of conflicting information and abandoning an ongoing action when a stop signal is presented. Our results and theory suggest an integrated mechanism of action regulation that affects both action initiation and inhibition. When this mechanism is disrupted, motor behavior is affected, leading to longer reaction times and higher error rates in action inhibition.

Essential tremor impairs the ability to suppress involuntary action impulses

Essential tremor (ET) is a movement disorder characterized primarily by action tremor which affects the regulation of movements. Disruptions in cerebello-thalamocortical networks could interfere with cognitive control over actions in ET, for example, the ability to suppress a strong automatic impulse over a more appropriate action (conflict control). The current study investigated whether ET impacts conflict control proficiency. Forty-one ET patients and 29 age-matched healthy controls (HCs) performed a conflict control task (Simon task). Participants were instructed to give a left or right response to a spatially lateralized arrow (direction of the arrow). When the action signaled by the spatial location and direction of the arrow were non-corresponding (induced conflict), the inappropriate action impulse required suppression. Overall, ET patients responded slower and less accurately compared to HCs. ET patients were especially less accurate on non-corresponding conflict (Nc) versus corresponding (Cs) trials. A focused analysis on fast impulsive response rates (based on the accuracy rate at the fastest reaction times on Nc trials) showed that ET patients made more fast errors compared to HCs. Results suggest impaired conflict control in ET compared to HCs. The increased impulsive errors seen in the ET population may be a symptom of deficiencies in the cerebello-thalamocortical networks, or, be caused by indirect effects on the cortico-striatal pathways. Future studies into the functional networks impacted by ET (cortico-striatal and cerebello-thalamocortical pathways) could advance our understanding of inhibitory control in general and the cognitive deficits in ET.

Better Executive Functions Are Associated With More Efficient Cognitive Pain Modulation in Older Adults: An fMRI Study

Growing evidence suggests that aging is associated with less efficient endogenous pain modulation as demonstrated by reduced conditioned pain modulation, and that these changes may be mediated by differences in frontal functioning. Yet, little is known about potential age-related changes in cognitive pain modulation, such as distraction from pain. In a first session, 30 healthy young (19-35 years) and 30 healthy older (59-82 years) adults completed a battery of neuropsychological tests. In a second session, we acquired functional brain images while participants completed a working memory task with two levels of cognitive load (high vs. low) and concurrently received individually adjusted heat stimuli (warm vs. painful). In both age groups, completing the high load task was associated with a significant reduction in the perceived intensity and unpleasantness of painful stimuli and a reduction in activation of brain regions involved in pain processing. Group comparisons revealed that young adults showed a stronger de-activation of brain regions involved in pain processing during the high load vs. the low load task, such as the right insula, right mid cingulate cortex and left supramarginal gyrus, compared to older adults. Older adults, on the other hand, showed an increased activation in the anterior cingulate cortex during the high load vs. low load task, when compared to young adults. Covariate analyses indicated that executive functions significantly predicted neural pain modulation in older adults: Better executive functions were associated with a more pronounced de-activation of the insula, thalamus and primary somatosensory cortex and increased activation of prefrontal regions during the high vs. low load task. These findings suggest that cognitive pain modulation is altered in older age and that the preservation of executive functions may have beneficial effects on the efficacy of distraction from pain.

Spatio-temporal dynamics of large-scale electrophysiological networks during cognitive action control in healthy controls and Parkinson's disease patients

Among the cognitive symptoms that are associated with Parkinson's disease (PD), alterations in cognitive action control (CAC) are commonly reported in patients. CAC enables the suppression of an automatic action, in favor of a goal-directed one. The implementation of CAC is time-resolved and arguably associated with dynamic changes in functional brain networks. However, the electrophysiological functional networks involved, their dynamic changes, and how these changes are affected by PD, still remain unknown. In this study, to address this gap of knowledge, 10 PD patients and 10 healthy controls (HC) underwent a Simon task while high-density electroencephalography (HD-EEG) was recorded. Source-level dynamic connectivity matrices were estimated using the phase-locking value in the beta (12-25 Hz) and gamma (30-45 Hz) frequency bands. Temporal independent component analyses were used as a dimension reduction tool to isolate the task-related brain network states. Typical microstate metrics were quantified to investigate the presence of these states at the subject-level. Our results first confirmed that PD patients experienced difficulties in inhibiting automatic responses during the task. At the group-level, we found three functional network states in the beta band that involved fronto-temporal, temporo-cingulate and fronto-frontal connections with typical CAC-related prefrontal and cingulate nodes (e.g., inferior frontal cortex). The presence of these networks did not differ between PD patients and HC when analyzing microstates metrics, and no robust correlations with behavior were found. In the gamma band, five networks were found, including one fronto-temporal network that was identical to the one found in the beta band. These networks also included CAC-related nodes previously identified in different neuroimaging modalities. Similarly to the beta networks, no subject-level differences were found between PD patients and HC. Interestingly, in both frequency bands, the dominant network at the subject-level was never the one that was the most durably modulated by the task. Altogether, this study identified the dynamic functional brain networks observed during CAC, but did not highlight PD-related changes in these networks that might explain behavioral changes. Although other new methods might be needed to investigate the presence of task-related networks at the subject-level, this study still highlights that task-based dynamic functional connectivity is a promising approach in understanding the cognitive dysfunctions observed in PD and beyond.

Two sides of the same coin: ADHD affects reactive but not proactive inhibition in children

Children with attention-deficit/hyperactivity disorder (ADHD) present a deficit in inhibitory control. Still, it remains unclear whether it comes from a deficit in reactive inhibition (ability to stop the action in progress), proactive inhibition (ability to exert preparatory control), or both.We compared the performance of 39 children with ADHD and 42 typically developing children performing a Simon choice reaction time task. The Simon task is a conflict task that is well-adapted to dissociate proactive and reactive inhibition. Beyond classical global measures (mean reaction time, accuracy rate, and interference effect), we used more sophisticated dynamic analyses of the interference effect and accuracy rate to investigate reactive inhibition. We studied proactive inhibition through the congruency sequence effect (CSE).Our results showed that children with ADHD had impaired reactive but not proactive inhibition. Moreover, the deficit found in reactive inhibition seems to be due to both a stronger impulse capture and more difficulties in inhibiting impulsive responses. These findings contribute to a better understanding of how ADHD affects inhibitory control in children.

Dorsal visual stream is preferentially engaged during externally guided action selection in Parkinson Disease

OBJECTIVE

In patients with Parkinson Disease (PD), self-imitated or internally cued (IC) actions are thought to be compromised by the disease process, as exemplified by impairments in action initiation. In contrast, externally-cued (EC) actions which are made in response to sensory prompts can restore a remarkable degree of movement capability in PD, particularly alleviating freezing-of-gait. This study investigates the electrophysiological underpinnings of movement facilitation in PD through visuospatial cuing, with particular attention to the dynamics within the posterior parietal cortex (PPC) and lateral premotor cortex (LPMC) axis of the dorsal visual stream.

METHODS

Invasive cortical recordings over the PPC and LPMC were obtained during deep brain stimulation lead implantation surgery. Thirteen PD subjects performed an action selection task, which was constituted by left or right joystick movement with directional visual cuing in the EC condition and internally generated direction selection in the IC condition. Time-resolved neural activities within and between the PPC and LPMC were compared between EC and IC conditions.

RESULTS

Reaction times (RT) were significantly faster in the EC condition relative to the IC condition (paired t-test, p = 0.0015). PPC-LPMC inter-site phase synchrony within the β-band (13-35 Hz) was significantly greater in the EC relative to the IC condition. Greater PPC-LPMC β debiased phase lag index (dwPLI) prior to movement onset was correlated with faster reaction times only in the EC condition. Multivariate granger causality (GC) was greater in the EC condition relative to the IC condition, prior to and during movement.

CONCLUSION

Relative to IC actions, we report relative increase in inter-site phase synchrony and directional PPC to LPMC connectivity in the β-band during preparation and execution of EC actions. Furthermore, increased strength of connectivity is predictive of faster RT, which are pathologically slow in PD patients. Stronger engagement of the PPC-LPMC cortical network by an EC specifically through the channel of β-modulation is implicated in correcting the pathological slowing of action initiation seen in Parkinson's patients.

SIGNIFICANCE

These findings shed light on the electrophysiological mechanisms that underlie motor facilitation in PD patients through visuospatial cuing.

Functional brain imaging of speeded decision processing in Parkinson's disease and comparison with Schizophrenia

This study examined whether Parkinson's disease (PD¹) and schizophrenia (SCZ²) share a hypo dopaminergic dysfunction of the prefrontal cortex leading to cognitive impairments in decision processing. 24 medicated PD patients and 28 matched controls performed the Eriksen flanker two-choice reaction time (RT³) task while brain activity was measured throughout, using functional Magnetic Resonance Imaging (fMRI⁴). Results were directly compared to those of 30 SCZ patients and 30 matched controls. Significant differences between SCZ and PD were found, through directly comparing the z-score deviations from healthy controls across all behavioral measures, where only SCZ patients showed deviances from controls. Similarly a direct comparison of z-score activation deviations from controls indicated significant differences in prefrontal and cingulate cortical activation between SCZ and PD, where only SCZ patients showed hypo-activation of these areas compared to controls. The hypo-activation of the dorsolateral prefrontal cortex was related to larger RT variability (ex-Gaussian tau) in SCZ but not PD patients. Overall, the concluding evidence does not support a shared neural substrate of cognitive dysfunction, since the deficit in speeded decision processing and the related cortical hypo-activation observed in SCZ were absent in PD.

Long-Term Wu Qin Xi Exercise on Response Inhibition and Cortical Connectivity in Parkinson's Disease: Design and Implementation of a Randomized Controlled Clinical Trial

Background: Motor symptom disorders in patients with Parkinson disease (PD) are closely related to reduced inhibitory ability. Although exercise has been shown to improve this ability in patients with PD, its effects on proactive and reactive inhibition have not been determined. Most previous studies of inhibitory control disorder in people with PD have been behavioral, and little attention has been paid to functional cortical connectivity. Wu Qin Xi, a low–medium-intensity qigong exercise that is safe and easy to do for elderly individuals, can support physical well-being and help prevent and alleviate disease. In this study, our aims were to explore the effects of a long-term Wu Qin Xi intervention on response inhibition and to examine how improved inhibition control relates to cortical connectivity using dual-site paired-pulse transcranial magnetic stimulation (ppTMS), in patients with mild–moderate PD.

Methods: A single-blind randomized controlled trial will be conducted. A total of 90 elderly subjects will be recruited and allocated randomly to Wu Qin Xi, balance exercise, and healthy control groups. The exercise interventions will be implemented in three 90-min sessions per week for 24 weeks; the healthy control group will receive no intervention. The primary assessments will be response inhibition metrics and task-based ppTMS. The secondary outcomes will include motor symptom severity, mobility, balance, emotional state, and quality of life. Assessments will be conducted at baseline, at the conclusion of the intervention period (week 24), and a few months after the intervention (week 36 follow-up).

Discussion: This study is designed to provide insights into the effects of practicing Wu Qin Xi on response inhibition function in people with PD. The results will provide evidence on the value of traditional Chinese exercise as a therapeutic rehabilitation option for these patients. They will also provide data addressing how brain function–related cortical connectivity is related to reactive vs. proactive inhibition in people with PD participating in an exercise intervention.

Clinical Trial Registration: This study has been registered prospectively in the Chinese Clinical Trial Registry (ChiCTR2000038517, 18 January 2021).

The role of dopamine in action control: Insights from medication effects in Parkinson's disease

Parkinson's disease (PD) is a neurological disorder associated primarily with overt motor symptoms. Several studies show that PD is additionally accompanied by impairments in covert cognitive processes underlying goal-directed motor functioning (e.g., action planning, conflict adaptation, inhibition), and that dopaminergic medication may modulate these action control components. In this review we aim to leverage findings from studies in this domain to elucidate the role of dopamine (DA) in action control. A qualitative review of studies that investigated the effects of medication status (on vs. off) on action control in PD suggests a component-specific role for DA in action control, although the expression of medication effects depends on characteristics of both the patients and experimental tasks used to measure action control. We discuss these results in the light of findings from other research lines examining the role of DA in action control (e.g., animal research, pharmacology), and recommend that future studies use multi-method, within-subject approaches to model DA effects on action control across different components as well as underlying striatal pathways (ventral vs. dorsal).

The arrow of time: Advancing insights into action control from the arrow version of the Eriksen flanker task

Since its introduction by B. A. Eriksen and C. W. Eriksen (Perception & Psychophysics, 16, 143-49, 1974), the flanker task has emerged as one of the most important experimental tasks in the history of cognitive psychology. The impact of a seemingly simple task design involving a target stimulus flanked on each side by a few task-irrelevant stimuli is astounding. It has inspired research across the fields of cognitive neuroscience, psychophysiology, neurology, psychiatry, and sports science. In our tribute to Charles W. ("Erik") Eriksen, we (1) review the seminal papers originating from his lab in the 1970s that launched the paradigmatic task and laid the foundation for studies of action control, (2) describe the inception of the arrow version of the Eriksen flanker task, (3) articulate the conceptual and neural models of action control that emerged from studies of the arrows flanker task, and (4) illustrate the influential role of the arrows flanker task in disclosing developmental trends in action control, fundamental deficits in action control due to neuropsychiatric disorders, and enhanced action control among elite athletes.

Control of response interference: caudate nucleus contributes to selective inhibition

While the role of cortical regions in cognitive control processes is well accepted, the contribution of subcortical structures (e.g., the striatum), especially to the control of response interference, remains controversial. Therefore, the present study aimed to investigate the cortical and particularly subcortical neural mechanisms of response interference control (including selective inhibition). Thirteen healthy young participants underwent event-related functional magnetic resonance imaging while performing a unimanual version of the Simon task. In this task, successful performance required the resolution of stimulus–response conflicts in incongruent trials by selectively inhibiting interfering response tendencies. The behavioral results show an asymmetrical Simon effect that was more pronounced in the contralateral hemifield. Contrasting incongruent trials with congruent trials (i.e., the overall Simon effect) significantly activated clusters in the right anterior cingulate cortex, the right posterior insula, and the caudate nucleus bilaterally. Furthermore, a region of interest analysis based on previous patient studies revealed that activation in the bilateral caudate nucleus significantly co-varied with a parameter of selective inhibition derived from distributional analyses of response times. Our results corroborate the notion that the cognitive control of response interference is supported by a fronto-striatal circuitry, with a functional contribution of the caudate nucleus to the selective inhibition of interfering response tendencies.

Eriksen flanker delta plot shapes depend on the stimulus

Several experimental paradigms are purported to measure response conflict, including the Stroop, Simon, and Eriksen flanker tasks. Although these tasks are often treated as being similar, delta plot analyses of response time distributions have revealed marked differences across them. Several theories have been proposed to explain these differences, however, assessing their veracity is difficult given the numerous differences across tasks. To explore what might cause delta plots to differ in a more controlled manner, here stimulus materials were manipulated across four Eriksen flanker tasks. The results reveal substantially different delta plot shapes for different stimuli: positive-going functions when color or motion served as the target and flankers, and delta plots with negative-going components when stimuli were arrows or orientated gratings. These results cast doubt on the proposal that negative-going delta plots occur only when spatial location serves as the interfering stimulus dimension. Moreover, because targets and flankers were always of the same stimulus type, the results also suggest that differences in materials across the relevant and irrelevant dimensions do not determine delta plot shapes. Instead, we propose that the delta plot shape is determined by several factors, including how early the interfering information is processed in the visual cortex.

Response mode modulates the congruency sequence effect in spatial conflict tasks: evidence from aimed-movement responses

The present study investigated how response mode determines the specificity of control responsible for the congruency sequence effect (CSE), especially when conflict arises from spatial dimensions. Horizontal and vertical Simon tasks were presented in turn, while response mode (Experiment 1) or task-relevant stimulus dimension (Experiment 2) was manipulated. All responses were made by aimed movements to make the relative salience of the horizontal and vertical dimensions equivalent regardless of response mode. The confound-minimized CSEs were significant only when the two tasks shared the same response mode, which did not vary as a function of task-relevant stimulus dimension. This result suggests that response mode determines the scope of control, as it reconfigures the representations of the task-irrelevant spatial dimensions (i.e., the horizontal and vertical dimensions), which is corroborated by distributional analyses. This response mode-specific control was also consistently found for the horizontal and vertical arrow versions of flanker-compatibility tasks in Experiment 3, in which conflict does not directly arise from the response dimension. Furthermore, the current findings revealed that the CSEs were more evident in movement times than in initiation times, which provides new insight on how control inhibits the response activated by a task-irrelevant stimulus dimension, especially at a motor level.

Flanker Task-Elicited Event-Related Potential Sources Reflect Human Recombinant Erythropoietin Differential Effects on Parkinson's Patients

We used EEG source analysis to identify which cortical areas were involved in the automatic and controlled processes of inhibitory control on a flanker task and compared the potential efficacy of recombinant-human erythropoietin (rHuEPO) on the performance of Parkinson's Disease patients. The samples were 18 medicated PD patients (nine of them received rHuEPO in addition to their usual anti-PD medication through random allocation and the other nine patients were on their regular anti-PD medication only) and 9 age and education-matched healthy controls (HCs) who completed the flanker task with simultaneous EEG recordings. N1 and N2 event-related potential (ERP) components were identified and a low resolution tomography (LORETA) inverse solution was employed to localize the neural generators. Reaction times and errors were increased for the incongruent flankers for PD patients compared to controls. EEG source analysis identified an effect of rHuEPO on the lingual gyri for the early N1 component. N2-related sources in middle cingulate and precuneus were associated with the inhibition of automatic responses evoked by incongruent stimuli differentiated PD and HCs. From our results rHuEPO seems to mediate an effect on N1 sources in lingual gyri but not on behavioural performance. N2-related sources in middle cingulate and precuneus were evoked by incongruent stimuli differentiated PD and HCs.

Continuous force measurements reveal no inhibitory control deficits in Parkinson's disease

Suppression of unwanted motor responses can be disrupted by Parkinson’s disease. People with Parkinson’s (PwP) can show maladaptive reward-driven behaviours in the form of impulse control behaviours, which are associated with the use of the dopaminergic treatments used to alleviate the motor symptoms of the disease. However, the effects of Parkinson’s itself on impulsive behaviour and control are unclear—empirical studies have yielded mixed findings, and some imaging studies have shown a functional deficit in the absence of a measurable change in behaviour. Here, we investigated the effects of Parkinson’s on response activation and control by studying the dynamics of response in standard inhibitory control tasks—the Stop Signal and Simon tasks—using a continuous measure of response force. Our results are largely in favour of the conclusion that response inhibition appears to be intact in PwP, even when using a more sensitive measure of behavioural control relative to traditional button-press measures. Our findings provide some clarity as to the effects of Parkinson’s on response inhibition and show continuous response force measurement can provide a sensitive means of detecting erroneous response activity in PwP, which could also be generalised to studying related processes in other populations.

Multiple expectancies underlie the congruency sequence effect in confound-minimized tasks

The congruency sequence effect (CSE) occurs when the congruency effect observed in tasks such as the Eriksen flanker task is smaller on trials preceded by an incongruent trial relative to trials preceded by a congruent trial. The CSE has been attributed to a range of factors including repetition expectancy, conflict monitoring, feature integration, and contingency learning. To clarify the debate surrounding the CSE and the mechanisms underlying its occurrence, researchers have developed confound-minimized congruency tasks designed to control for feature-integration and contingency-learning effects. A CSE is often observed in confound-minimized tasks, indicating that the effect is driven by repetition expectancy, conflict monitoring, or a combination of the two. Here, we propose and test a variant of the repetition expectancy account that emphasizes how multiple expectations can be formed simultaneously based upon the congruency type (congruent vs. incongruent) and the congruency repetition type (congruency repetition vs. congruency alternation) of the most recent trial. Data from confound-minimized versions of the prime-probe task were found to support this novel account. Data from confound-minimized versions of the Eriksen flanker, Simon, and Stroop tasks indicate that feature-integration confounds often remain in these tasks, potentially undermining the conclusions of previous work. We discuss the implications of these findings for ongoing theoretical debates surrounding the CSE.

Sensorimotor Control in Dystonia

This is an overview of the sensorimotor impairments in dystonia, a syndrome characterized by sustained or intermittent aberrant movement patterns leading to abnormal movements and/or postures with or without a tremulous component. Dystonia can affect the entire body or specific body regions and results from a plethora of etiologies, including subtle changes in gray and white matter in several brain regions. Research over the last 25 years addressing topics of sensorimotor control has shown functional sensorimotor impairments related to sensorimotor integration, timing, oculomotor and head control, as well as upper and lower limb control. In the context of efforts to update the classification of dystonia, sensorimotor research is highly relevant for a better understanding of the underlying pathology, and potential mechanisms contributing to global and regional dysfunction within the central nervous system. This overview of relevant research regarding sensorimotor control in humans with idiopathic dystonia attempts to frame the dysfunction with respect to what is known regarding motor control in patients and healthy individuals. We also highlight promising avenues for the future study of neuromotor control that may help to further elucidate dystonia etiology, pathology, and functional characteristics.

Fast Intracortical Sensory-Motor Integration: A Window Into the Pathophysiology of Parkinson's Disease

Parkinson's Disease (PD) is a prototypical basal ganglia disorder. Nigrostriatal dopaminergic denervation leads to progressive dysfunction of the cortico-basal ganglia-thalamo-cortical sensorimotor loops, causing the classical motor symptoms. Although the basal ganglia do not receive direct sensory input, they are important for sensorimotor integration. Therefore, the basal ganglia dysfunction in PD may profoundly affect sensory-motor interaction in the cortex. Cortical sensorimotor integration can be probed with transcranial magnetic stimulation (TMS) using a well-established conditioning-test paradigm, called short-latency afferent inhibition (SAI). SAI probes the fast-inhibitory effect of a conditioning peripheral electrical stimulus on the motor response evoked by a TMS test pulse given to the contralateral primary motor cortex (M1). Since SAI occurs at latencies that match the peaks of early cortical somatosensory potentials, the cortical circuitry generating SAI may play an important role in rapid online adjustments of cortical motor output to changes in somatosensory inputs. Here we review the existing studies that have used SAI to examine how PD affects fast cortical sensory-motor integration. Studies of SAI in PD have yielded variable results, showing reduced, normal or even enhanced levels of SAI. This variability may be attributed to the fact that the strength of SAI is influenced by several factors, such as differences in dopaminergic treatment or the clinical phenotype of PD. Inter-individual differences in the expression of SAI has been shown to scale with individual motor impairment as revealed by UPDRS motor score and thus, may reflect the magnitude of dopaminergic neurodegeneration. The magnitude of SAI has also been linked to cognitive dysfunction, and it has been suggested that SAI also reflects cholinergic denervation at the cortical level. Together, the results indicate that SAI is a useful marker of disease-related alterations in fast cortical sensory-motor integration driven by subcortical changes in the dopaminergic and cholinergic system. Since a multitude of neurobiological factors contribute to the magnitude of inhibition, any mechanistic interpretation of SAI changes in PD needs to consider the group characteristics in terms of phenotypical spectrum, disease stage, and medication.

Impaired conflict monitoring in cognitive decline

Resolving conflicts is an important cognitive ability of executive function, and it may decrease with cognitive decline. The flanker task is a practical test used to assess the ability to suppress responses that are inappropriate in a particular context. The aims of the present study were to investigate conflict monitoring of cognitive control in subjects with different levels of cognitive impairment, and clarify the usefulness of the flanker task in screening cognitive decline. We recruited 50 subjects with mild cognitive impairment (MCI) and 34 patients with Alzheimer's disease (AD), and 44 mentally healthy elderly subjects as a control group. To evaluate cognitive performance, each participant underwent a neuropsychological assessment using the Cognitive Abilities Screening Instrument and a modified flanker task. Compared with the normal controls and those with MCI, the patients with AD had a significantly lower accuracy rate and longer reaction time in both congruent and incongruent trials. The diagnosis of AD predicted significantly poorer performances on the flanker tasks. Furthermore, behavioral data of the patients with AD were significantly correlated with the results of neuropsychological tests. Our results indicated that executive cognitive deficits in conflict monitoring as detected by the flanker task were significantly impaired in the patients with AD. The flanker task could be a quick and easier alternative tool for screening AD among elderly people with suspicious cognitive impairment.

Low and variable correlation between reaction time costs and accuracy costs explained by accumulation models: Meta-analysis and simulations

The underpinning assumption of much research on cognitive individual differences (or group differences) is that task performance indexes cognitive ability in that domain. In many tasks performance is measured by differences (costs) between conditions, which are widely assumed to index a psychological process of interest rather than extraneous factors such as speed-accuracy trade-offs (e.g., Stroop, implicit association task, lexical decision, antisaccade, Simon, Navon, flanker, and task switching). Relatedly, reaction time (RT) costs or error costs are interpreted similarly and used interchangeably in the literature. All of this assumes a strong correlation between RT-costs and error-costs from the same psychological effect. We conducted a meta-analysis to test this, with 114 effects across a range of well-known tasks. Counterintuitively, we found a general pattern of weak, and often no, association between RT and error costs (mean r = .17, range -.45 to .78). This general problem is accounted for by the theoretical framework of evidence accumulation models, which capture individual differences in (at least) 2 distinct ways. Differences affecting accumulation rate produce positive correlation. But this is cancelled out if individuals also differ in response threshold, which produces negative correlations. In the models, subtractions between conditions do not isolate processing costs from caution. To demonstrate the explanatory power of synthesizing the traditional subtraction method within a broader decision model framework, we confirm 2 predictions with new data. Thus, using error costs or RT costs is more than a pragmatic choice; the decision carries theoretical consequence that can be understood through the accumulation model framework. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Roles for globus pallidus externa revealed in a computational model of action selection in the basal ganglia

The basal ganglia are considered vital to action selection - a hypothesis supported by several biologically plausible computational models. Of the several subnuclei of the basal ganglia, the globus pallidus externa (GPe) has been thought of largely as a relay nucleus, and its intrinsic connectivity has not been incorporated in significant detail, in any model thus far. Here, we incorporate newly revealed subgroups of neurons within the GPe into an existing computational model of the basal ganglia, and investigate their role in action selection. Three main results ensued. First, using previously used metrics for selection, the new extended connectivity improved the action selection performance of the model. Second, low frequency theta oscillations were observed in the subpopulation of the GPe (the TA or 'arkypallidal' neurons) which project exclusively to the striatum. These oscillations were suppressed by increased dopamine activity - revealing a possible link with symptoms of Parkinson's disease. Third, a new phenomenon was observed in which the usual monotonic relationship between input to the basal ganglia and its output within an action 'channel' was, under some circumstances, reversed. Thus, at high levels of input, further increase of this input to the channel could cause an increase of the corresponding output rather than the more usually observed decrease. Moreover, this phenomenon was associated with the prevention of multiple channel selection, thereby assisting in optimal action selection. Examination of the mechanistic origin of our results showed the so-called 'prototypical' GPe neurons to be the principal subpopulation influencing action selection. They control the striatum via the arkypallidal neurons and are also able to regulate the output nuclei directly. Taken together, our results highlight the role of the GPe as a major control hub of the basal ganglia, and provide a mechanistic account for its control function.

Preserved but Less Efficient Control of Response Interference After Unilateral Lesions of the Striatum

Previous research on the neural basis of cognitive control processes has mainly focused on cortical areas, while the role of subcortical structures in cognitive control is less clear. Models of basal ganglia function as well as clinical studies in neurodegenerative diseases suggest that the striatum (putamen and caudate nucleus) modulates the inhibition of interfering responses and thereby contributes to an important aspect of cognitive control, namely response interference control. To further investigate the putative role of the striatum in the control of response interference, 23 patients with stroke-induced lesions of the striatum and 32 age-matched neurologically healthy controls performed a unimanual version of the Simon task. In the Simon task, the correspondence between stimulus location and response location is manipulated so that control over response interference can be inferred from the reaction time costs in incongruent trials. Results showed that stroke patients responded overall slower and more erroneous than controls. The difference in response times (RTs) between incongruent and congruent trials (known as the Simon effect) was smaller in the ipsilesional/-lateral hemifield, but did not differ significantly between groups. However, in contrast to controls, stroke patients exhibited an abnormally stable Simon effect across the reaction time distribution indicating a reduced efficiency of the inhibition process. Thus, in stroke patients unilateral lesions of the striatum did not significantly impair the general ability to control response interference, but led to less efficient selective inhibition of interfering responses.

A model-based quantification of action control deficits in Parkinson's disease

Basal ganglia dysfunction in Parkinson's disease (PD) is thought to generate deficits in action control, but the characterization of these deficits have been qualitative rather than quantitative. Patients with PD typically show prolonged response times on tasks that instantiate a conflict between goal-directed processing and automatic response tendencies. In the Simon task, for example, the irrelevant location of the stimulus automatically activates a corresponding lateralized response, generating a potential conflict with goal-directed choices. We applied a new computational model of conflict processing to two sets of behavioral data from the Simon task to quantify the effects of PD and dopaminergic (DA) medication on action control mechanisms. Compared to healthy controls (HC) matched in age gender and education, patients with PD showed a deficit in goal-directed processing, and the magnitude of this deficit positively correlated with cognitive symptoms. Analyses of the time-course of the location-based automatic activation yielded mixed findings. In both datasets, we found that the peak amplitude of the automatic activation was similar between PD and HC, demonstrating a similar degree of response capture. However, PD patients showed a prolonged automatic activation in only one dataset. This discrepancy was resolved by theoretical analyses of conflict resolution in the Simon task. The reduction of interference generated by the automatic activation appears to be driven by a mixture of passive decay and top-down inhibitory control, the contribution of each component being modulated by task demands. Our results suggest that PD selectively impairs the inhibitory control component, a deficit likely remediated by DA medication. This work advances our understanding of action control deficits in PD, and illustrates the benefit of using computational models to quantitatively measure cognitive processes in clinical populations.

Exposing an "Intangible" Cognitive Skill among Collegiate Football Players: Enhanced Interference Control

American football is played in a chaotic visual environment filled with relevant and distracting information. We investigated the hypothesis that collegiate football players show exceptional skill at shielding their response execution from the interfering effects of distraction (interference control). The performances of 280 football players from National Collegiate Athletic Association Division I football programs were compared to age-matched controls in a variant of the Eriksen flanker task (Eriksen and Eriksen, 1974). This task quantifies the magnitude of interference produced by visual distraction on split-second response execution. Overall, football athletes and age controls showed similar mean reaction times (RTs) and accuracy rates. However, football athletes were more proficient at shielding their response execution speed from the interfering effects of distraction (i.e., smaller flanker effect costs on RT). Offensive and defensive players showed smaller interference costs compared to controls, but defensive players showed the smallest costs. All defensive positions and one offensive position showed statistically smaller interference effects when compared directly to age controls. These data reveal a clear cognitive advantage among football athletes at executing motor responses in the face of distraction, the existence and magnitude of which vary by position. Individual differences in cognitive control may have important implications for both player selection and development to improve interference control capabilities during play.

Testing the validity of conflict drift-diffusion models for use in estimating cognitive processes: A parameter-recovery study

Researchers and clinicians are interested in estimating individual differences in the ability to process conflicting information. Conflict processing is typically assessed by comparing behavioral measures like RTs or error rates from conflict tasks. However, these measures are hard to interpret because they can be influenced by additional processes like response caution or bias. This limitation can be circumvented by employing cognitive models to decompose behavioral data into components of underlying decision processes, providing better specificity for investigating individual differences. A new class of drift-diffusion models has been developed for conflict tasks, presenting a potential tool to improve analysis of individual differences in conflict processing. However, measures from these models have not been validated for use in experiments with limited data collection. The present study assessed the validity of these models with a parameter-recovery study to determine whether and under what circumstances the models provide valid measures of cognitive processing. Three models were tested: the dual-stage two-phase model (Hübner, Steinhauser, & Lehle, Psychological Review, 117(3), 759-784, 2010), the shrinking spotlight model (White, Ratcliff, & Starns, Cognitive Psychology, 63(4), 210-238, 2011), and the diffusion model for conflict tasks (Ulrich, Schröter, Leuthold, & Birngruber, Cogntive Psychology, 78, 148-174, 2015). The validity of the model parameters was assessed using different methods of fitting the data and different numbers of trials. The results show that each model has limitations in recovering valid parameters, but they can be mitigated by adding constraints to the model. Practical recommendations are provided for when and how each model can be used to analyze data and provide measures of processing in conflict tasks.

Motivational Sensitivities Linked to Impulsive Motor Errors in Parkinson's Disease

OBJECTIVES

We investigated how broad motivational tendencies are related to the expression and suppression of action impulses in Parkinson's disease (PD).

METHODS

Sixty-nine participants with PD completed a Simon response conflict task and Behavioral Inhibition System (BIS) and Behavioral Activation System (BAS) scales based on Gray's (1987) reinforcement sensitivity theory. Analyses determined relationships between BIS, BAS, and the susceptibility to making impulsive action errors and the proficiency of inhibiting interference from action impulses.

RESULTS

BIS scores correlated positively with rates of impulsive action errors, indicating that participants endorsing low BIS tendencies were much more susceptible to acting on strong motor impulses. Analyses of subgroups with high versus low BIS scores confirmed this pattern and ruled out alternative explanations in terms of group differences in speed-accuracy tradeoffs. None of the scores on the BIS or BAS scales correlated with reactive inhibitory control.

CONCLUSIONS

PD participants who endorse diminished predilection toward monitoring and avoiding aversive experiences (low BIS) show much greater difficulty restraining fast, impulsive motor errors. Establishing relationships between motivational sensitivities and cognitive control processes may have important implications for treatment strategies and positive health outcomes in participants with PD, particularly those at risk for falling and driving difficulties related to impulsive reactions. (JINS, 2018, 24, 128-138).

Continuous subcutaneous apomorphine infusion does not impair the dynamics of cognitive action control in mild to moderate Parkinson's disease

INTRODUCTION

Continuous subcutaneous apomorphine infusion (CSAI) is increasingly used in Parkinson's disease (PD), notably in patients contraindicated for subthalamic deep brain stimulation. Although it has been suggested that CSAI is safe regarding cognition, few studies have actually investigated its effect, especially on cognitive control which is a crucial process for goal-directed behavior. More specifically, its impact on the dynamics of cognitive action control, as reflected by the activation and suppression of impulsive responses, has yet to be investigated, which is the objective of the present study.

METHODS

We compared cognitive action control between baseline (M0) and 6 months (M6) after the start of add-on CSAI by administering an oculomotor Simon task to 20 patients with mild to moderate PD. We used the activation-suppression model to determine whether CSAI had an effect on either the impulsive errors made in conflict situations or the suppression of these responses.

RESULTS

We found no difference between M0 and M6 in the congruence effect regarding either reaction time or accuracy, indicating that overall conflict resolution was not influenced by CSAI. Furthermore, the rate of fast errors in the conflict situation and the last slope of the delta plots (reflecting the strength of impulsive response suppression) were unaffected by the treatment. The 95% confidence intervals calculated for the treatment effect on both of these measures fell below the range of usual meaningful effects.

CONCLUSION

We found no difference between M0 and M6, which strongly suggests that CSAI does not impair the dynamics of cognitive action control.

Stepping reaction time and gait adaptability are significantly impaired in people with Parkinson's disease: Implications for fall risk

BACKGROUND

Decline in the ability to take effective steps and to adapt gait, particularly under challenging conditions, may be important reasons why people with Parkinson's disease (PD) have an increased risk of falling. This study aimed to determine the extent of stepping and gait adaptability impairments in PD individuals as well as their associations with PD symptoms, cognitive function and previous falls.

METHODS

Thirty-three older people with PD and 33 controls were assessed in choice stepping reaction time, Stroop stepping and gait adaptability tests; measurements identified as fall risk factors in older adults.

RESULTS

People with PD had similar mean choice stepping reaction times to healthy controls, but had significantly greater intra-individual variability. In the Stroop stepping test, the PD participants were more likely to make an error (48 vs 18%), took 715 ms longer to react (2312 vs 1517 ms) and had significantly greater response variability (536 vs 329 ms) than the healthy controls. People with PD also had more difficulties adapting their gait in response to targets (poorer stepping accuracy) and obstacles (increased number of steps) appearing at short notice on a walkway. Within the PD group, higher disease severity, reduced cognition and previous falls were associated with poorer stepping and gait adaptability performances.

CONCLUSIONS

People with PD have reduced ability to adapt gait to unexpected targets and obstacles and exhibit poorer stepping responses, particularly in a test condition involving conflict resolution. Such impaired stepping responses in Parkinson's disease are associated with disease severity, cognitive impairment and falls.

Neurophysiological mechanisms of circadian cognitive control in RLS patients - an EEG source localization study

The circadian variation of sensory and motor symptoms with increasing severity in the evening and at night is a key diagnostic feature/symptom of the restless legs syndrome (RLS). Even though many neurological diseases have shown a strong nexus between motor and cognitive symptoms, it has remained unclear whether cognitive performance of RLS patients declines in the evening and which neurophysiological mechanisms are affected by the circadian variation. In the current study, we examined daytime effects (morning vs. evening) on cognitive performance in RLS patients (n = 33) compared to healthy controls (n = 29) by analyzing flanker interference effects in combination with EEG and source localization techniques. RLS patients showed larger flanker interference effects in the evening than in the morning (p = .023), while healthy controls did not display a comparable circadian variation. In line with this, the neurophysiological data showed smaller N1 amplitudes in RLS patients compared to controls in the interfering task condition in the evening (p = .042), but not in the morning. The results demonstrate diurnal cognitive changes in RLS patients with intensified impairments in the evening. It seems that not all dopamine-regulated cognitive processes are altered in RLS and thus show daytime-dependent impairments. Instead, the daytime-related cognitive impairment emerges from attentional selection processes within the extra-striate visual cortex, but not from later cognitive processes such as conflict monitoring and response selection.

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RLS patients have larger flanker interference effect in the evening.

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RLS patients have enhanced impairment of attentional selection in the evening.

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Nocturnal attentional impairment relies on the extra-striate visual cortex.

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Conflict monitoring and response selection are not affected by RLS.

Focused stimulation of dorsal subthalamic nucleus improves reactive inhibitory control of action impulses

Frontal-basal ganglia circuitry dysfunction caused by Parkinson's disease impairs important executive cognitive processes, such as the ability to inhibit impulsive action tendencies. Subthalamic Nucleus Deep Brain Stimulation in Parkinson's disease improves the reactive inhibition of impulsive actions that interfere with goal-directed behavior. An unresolved question is whether this effect depends on stimulation of a particular Subthalamic Nucleus subregion. The current study aimed to 1) replicate previous findings and additionally investigate the effect of chronic versus acute Subthalamic Nucleus stimulation on inhibitory control in Parkinson's disease patients off dopaminergic medication 2) test whether stimulating Subthalamic Nucleus subregions differentially modulate proactive response control and the proficiency of reactive inhibitory control. In the first experiment, twelve Parkinson's disease patients completed three sessions of the Simon task, Off Deep brain stimulation and medication, on acute Deep Brain Stimulation and on chronic Deep Brain Stimulation. Experiment 2 consisted of 11 Parkinson's disease patients with Subthalamic Nucleus Deep Brain Stimulation (off medication) who completed two testing sessions involving of a Simon task either with stimulation of the dorsal or the ventral contact in the Subthalamic Nucleus. Our findings show that Deep Brain Stimulation improves reactive inhibitory control, regardless of medication and regardless of whether it concerns chronic or acute Subthalamic Nucleus stimulation. More importantly, selective stimulation of dorsal and ventral subregions of the Subthalamic Nucleus indicates that especially the dorsal Subthalamic Nucleus circuitries are crucial for modulating the reactive inhibitory control of motor actions.

Focused and Sustained Attention Is Modified by a Goal-Based Rehabilitation in Parkinsonian Patients

Rehabilitation for patients with Parkinson’s disease (PD) is based on cognitive strategies that exploit attention. Parkinsonians exhibit impairments in divided attention and interference control. Nevertheless, the effectiveness of specific rehabilitation treatments based on attention suggests that other attentional functions are preserved. Data about attention are conflicting in PD, and it is not clear whether rehabilitative treatments that entail attentional strategies affect attention itself. Reaction times (RTs) represent an instrument to explore attention and investigate whether changes in attentional performances parallel rehabilitation induced-gains. RTs of 103 parkinsonian patients in “on” state, without cognitive deficits, were compared with those of a population of 34 healthy controls. We studied those attentional networks that subtend the use of cognitive strategies in motor rehabilitation: alertness and focused and sustained attention, which is a component of the executive system. We used visual and auditory RTs to evaluate alertness and multiple choices RTs (MC RTs) to explore focused and sustained attention. Parkinsonian patients underwent these tasks before and after a 4-week multidisciplinary, intensive and goal-based rehabilitation treatment (MIRT). Unified Parkinson’s Disease Rating Scale (UPDRS) III and Timed Up and Go test (TUG) were assessed at the enrollment and at the end of MIRT to evaluate the motor-functional effectiveness of treatment. We did not find differences in RTs between parkinsonian patients and controls. Further, we found that improvements in motor-functional outcome measures after MIRT (p < 0.0001) paralleled a reduction in MC RTs (p = 0.014). No changes were found for visual and auditory RTs. Correlation analysis revealed no association between changes in MC RTs and improvements in UPDRS-III and TUG. These findings indicate that alertness, as well as focused and sustained attention, are preserved in “on” state. This explains why Parkinsonians benefit from a goal-based rehabilitation that entails the use of attention. The reduction in MC RTs suggests a positive effect of MIRT on the executive component of attention and indicates that this type of rehabilitation provides benefits by exploiting executive functions. This ensues from different training approaches aimed at bypassing the dysfunctional basal ganglia circuit, allowing the voluntary execution of the defective movements. These data suggest that the effectiveness of a motor rehabilitation tailored for PD lies on cognitive engagement.

Dopamine Selectively Modulates the Outcome of Learning Unnatural Action-Valence Associations

Learning the contingencies between stimulus, action, and outcomes is disrupted in disorders associated with altered dopamine (DA) function in the BG, such as Parkinson disease (PD). Although the role of DA in learning to act has been extensively investigated in PD, the role of DA in "learning to withhold" (or inhibit) action to influence outcomes is not as well understood. The current study investigated the role of DA in learning to act or to withhold action to receive rewarding, or avoid punishing outcomes, in patients with PD tested "off" and "on" dopaminergic medication (n = 19) versus healthy controls (n = 30). Participants performed a reward-based learning task that orthogonalized action and outcome valence (action-reward, inaction-reward, action-punishment, inaction-punishment). We tested whether DA would bias learning toward action, toward reward, or to particular action-outcome interactions. All participants demonstrated inherent learning biases preferring action with reward and inaction to avoid punishment, and this was unaffected by medication. Instead, DA produced a complex modulation of learning less natural action-outcome associations. "Off" DA medication, patients demonstrated impairments in learning to withhold action to gain reward, suggesting a difficulty to overcome a bias toward associating inaction with punishment avoidance. On DA medication, these patterns changed, and patients showed a reduced ability to learn to act to avoid punishment, indicating a bias toward action and reward. The current findings suggest that DA in PD has a complex influence on the formation of action-outcome associations, particularly those involving less natural linkages between action and outcome valence.

Dopaminergic modulation of performance monitoring in Parkinson's disease: An event-related potential study

Monitoring one’s actions is essential for goal-directed performance. In the event-related potential (ERP), errors are followed by fronto-centrally distributed negativities. These error(-related) negativity (N_e/ERN) amplitudes are often found to be attenuated in patients with Parkinson’s disease (PD) compared to healthy controls (HC). Although N_e/ERN has been proposed to be related to dopaminergic neuronal activity, previous research did not find evidence for effects of dopaminergic medication on N_e/ERN amplitudes in PD. We examined 13 PD patients “on” and “off” dopaminergic medication. Their response-locked ERP amplitudes (obtained on correct [N_c/CRN] and error [N_e/ERN] trials of a flanker task) were compared to those of 13 HC who were tested twice as well, without receiving dopaminergic medication. While PD patients committed more errors than HC, error rates were not significantly modulated by dopaminergic medication. PD patients showed reduced N_e/ERN amplitudes relative to HC; however, this attenuation of response-locked ERP amplitudes was not specific to errors in this study. PD-related attenuation of response-locked ERP amplitudes was most pronounced when PD patients were on medication. These results suggest overdosing of dopaminergic pathways that are relatively spared in PD, but that are related to the generation of the N_e/ERN, notably pathways targeted on the medial prefrontal cortex.

Impulsive oculomotor action selection in Parkinson's disease

The effects of Parkinson's disease (PD) on the dynamics of impulsive action selection and suppression have recently been studied using distributional analyses, but with mixed results, especially for selection. Furthermore, some authors have suggested that impulsivity, regarded as a personality trait, shares common features with behavioral tasks' measures. The current study was designed to clarify the impact of PD on impulsive action selection and suppression, and investigate the link between cognitive action control and self-reported impulsivity. We administered an oculomotor version of the Simon task to 32 patients with PD and 32 matched healthy controls (HC), and conducted distributional analyses in accordance with the activation-suppression model. Patients and HC also filled out the Barratt Impulsiveness Scale (BIS) questionnaire. Results showed that patients with PD were faster overall and exhibited a greater congruence effect than HC. They also displayed enhanced impulsive action selection. By contrast, the suppression of impulsive responses was similar across both groups. Furthermore, patients had higher impulsivity scores, which were correlated with higher impulsive action selection and higher suppression. Our study yielded two interesting findings. First, PD resulted in a higher number of fast errors. The activation-suppression model suggests that patients with PD are more susceptible to the impulsive action selection induced by the irrelevant stimulus dimension. Second, impulsive action selection and suppression were both associated with trait impulsivity, as measured by the BIS, indicating that these two aspects of impulsivity share common features.

Influence of subthalamic deep-brain stimulation on cognitive action control in incentive context

Subthalamic nucleus deep-brain stimulation (STN-DBS) is an effective treatment in Parkinson's disease (PD), but can have cognitive side effects, such as increasing the difficulty of producing appropriate responses when a habitual but inappropriate responses represent strong alternatives. STN-DBS also appears to modulate representations of incentives such as monetary rewards. Furthermore, conflict resolution can be modulated by incentive context. We therefore used a rewarded Simon Task to assess the influence of promised rewards on cognitive action control in 50 patients with PD, half of whom were being treated with STN-DBS. Results were analyzed according to the activation-suppression model. We showed that STN-DBS (i) favored the expression of motor impulsivity, as measured with the Barratt Impulsiveness Scale, (ii) facilitated the expression of incentive actions as observed with a greater increase in speed according to promised reward in patients with versus without DBS and (iii) may increase impulsive action selection in an incentive context. In addition, analysis of subgroups of implanted patients suggested that those who exhibited the most impulsive action selection had the least severe disease. This may indicate that patients with less marked disease are more at risk of developing impulsivity postoperatively. Finally, in these patients, incentive context increased the difficulty of resolving conflict situations. As a whole, the current study revealed that in patients with PD, STN-DBS affects the cognitive processes involved in conflict resolution, reward processing and the influence of promised rewards on conflict resolution.

Dopamine and temporal attention: An attentional blink study in Parkinson's disease patients on and off medication

The current study aimed to shed more light on the role of dopamine in temporal attention. To this end, we pharmacologically manipulated dopamine levels in a large sample of Parkinson's disease patients (n=63) while they performed an attentional blink (AB) task in which they had to identify two targets (T1 and T2) presented in close temporal proximity among distractors. We specifically examined 1) differences in the magnitude of the AB between unmedicated Parkinson patients, who have depleted levels of striatal dopamine, and healthy controls, and 2) effects of two dopaminergic medications (l-DOPA and dopamine agonists) on the AB in the Parkinson patients at the group level and as a function of individual baseline performance. In line with the notion that relatively low levels of striatal dopamine may impair target detection in general, Parkinson patients OFF medications displayed overall poor target perception compared to healthy controls. Moreover, as predicted, effects of dopaminergic medication on AB performance critically depended on individual baseline AB size, although this effect was only observed for l-DOPA. l-DOPA generally decreased the size of the AB in patients with a large baseline AB (i.e., OFF medications), while l-DOPA generally increased the AB in patients with a small baseline AB. These findings may support a role for dopamine in the AB and temporal attention, more generally and corroborate the notion that there is an optimum dopamine level for cognitive function. They also emphasize the need for more studies that examine the separate effects of DA agonists and l-DOPA on cognitive functioning.