Behavioral models of impulsivity in relation to ADHD: translation between clinical and preclinical studies

EAAT2 Activation Regulates Glutamate Excitotoxicity and Reduces Impulsivity in a Rodent Model of Parkinson's Disease

Parkinson's disease (PD) is a systemic disease characterized by motor and nonmotor impairments. Loss of dopaminergic neurons in the substantia nigra pars compacta region in PD disrupts dopamine-glutamate homeostasis in the corticostriatal circuit, contributing to cognitive impairment. In addition, excitatory amino acid transporter-2 (EAAT2), localized predominantly to astrocytes and responsible for > 80% of synaptic glutamate clearance, is downregulated in PD, causing glutamate spillover and excitotoxicity. This altered dopamine-glutamate homeostasis and excitotoxicity may affect reward-mediated decision-making behaviors and promote impulsive behaviors in PD. In this study, we hypothesized that GTS467, a small-molecule activator of EAAT2, could effectively reduce excitotoxicity and treat cognitive impairment without promoting impulsive behavior in PD. Rats that were unilaterally lesioned with the 6-OHDA toxin to produce Parkinsonian symptoms were referred to as lesioned rats. Lesioned rats were trained to meet baseline criteria in a 5-choice serial reaction time task, and the chronic effects of GTS467 were assessed after 3 weeks of treatment. The results showed that chronic treatment with GTS467 significantly improved correct responses and reduced premature impulsive responses and omissions compared with saline treatment. This improvement in performance correlated with a reduction in glutamate levels, an increase in EAAT2 expression, and normalization of NMDA receptor subunit expression and signaling. Furthermore, transcriptomic studies on the prefrontal cortex tissue have shown the differential expression of genes involved in neuroprotection, neuroinflammation, learning, and memory. These results validate the role of glutamate excitotoxicity in promoting impulsive behaviors and suggest that GTS467 can be developed as a therapeutic agent to reduce cognitive impairment and impulsive behaviors in PD.

The consistency of categorization-consistency in speech perception

Listeners generally map continuous acoustic information onto categories in a gradient manner with varying individual differences. Typically, such individual differences in speech categorization have been characterized by the mean slope of the response function, as quantified through the visual analog scaling (VAS) task. However, recent evidence suggests that categorization consistency (trial-by-trial response variability) may be a more robust predictor of real-world outcomes than the mean slope. Despite this, the extent to which these VAS indices represent reliable and stable traits relevant to speech perception remains uncertain. This study investigates the stability and trait-like nature of VAS indices by analyzing VAS responses across a diverse range of speech continua. We also examine the potential associations between differences in speech categorization and broader cognitive differences. American English-speaking adults (n = 68) completed the VAS task, alongside three questionnaires assessing autistic traits, anxiety, and impulsivity. We found that categorization consistency showed stronger correlations across continuum types than the categorization slope. Furthermore, no significant correlations were observed between the VAS indices and broader cognitive factors. These results suggest categorization consistency is a more stable property of individuals over the mean slope, and importantly, it is not an artifact due to higher cognitive factors. Thus, the extent to which listeners are consistent in their speech categorization may provide a more accurate characterization of individual differences in speech perception.

The effects of oral gestational particulate matter 10 exposure: Insights into neurodevelopmental milestones, inhibitory control, adult sociability, and object recognition

Air pollutants have been associated with various neurodevelopmental disorders, with several studies specifically linking Particulate Matter (PM) exposure to attentional and social deficits. This link is even more pronounced when exposure occurs during the prenatal period, as it can disrupt normal brain development. However, while social deficits have been extensively studied during adolescence, their impact on adult social behaviors remains largely unexplored. To investigate these effects, pregnant Wistar rats were exposed throughout gestation (GD1-GD21) to PM10 at a dosage of 200 μg/Kg/day diluted in PBS that was freely drunk. After birth, the pups were evaluated on developmental milestones such as weight progression, ocular opening, and muscular strength. In adulthood, inhibitory control was assessed using the Five Choice Serial Reaction Time Task (5-CSRTT), social behavior using the Three-Chambered Crawley's Test (3-CT), and object recognition using the Novelty Object Recognition test (NOR). The results indicated that prenatal PM10 exposure is associated with higher birth weight and poorer performance in neuromuscular tests. However, no significant differences were observed in inhibitory control (5-CSRTT) or social behavior (3-CT). Interestingly, prenatally exposed rodents showed heightened novelty responses in the NOR test. In conclusion, gestational exposure to PM10 is related to differences in neurodevelopmental milestones, including weight and muscular strength. While it does not impact adult inhibitory control or social behavior, it influences novelty recognition in later life.

Behavioural and physiological effects of binge eating: A systematic review and meta-analysis of animal models

Binge eating is defined as eating abnormally large amounts in a brief period of time. Many animal studies have examined the behavioural and physiological effects of binge eating of high-fat, high-sugar foods to model the consequences of human binge eating. The present systematic review of 199 rodent studies sought to identify the behavioural and physiological consequences of binge eating and determine whether changes were specific to binge eating or to general effects of exposure to a palatable diet. A meta-analysis of 18 rodent studies revealed that binge eating produces greater anxiety-like behaviour on the Elevated Plus-Maze with a small effect size and significant funnel plot asymmetry, suggesting that the true effect size is overestimated. A history of binge-like access generally increases progressive ratio breakpoint for the binged food, without altering 'liking' as measured by lick microstructure, suggesting that dissociable effects on 'wanting' but not 'liking' accompany binge eating behaviour and contribute to its persistence. Binge eating appears to enhance compulsive food-seeking behaviour and prevent stress-induced reductions in intake but does not appear to alter depression-like behaviour or locomotor activity. Notably, binge eating may produce comparable metabolic impairments to those observed after extended continuous exposure to a palatable diet despite no overall effects on body weight outcomes in most studies.

Environmental enrichment reverses prenatal ethanol exposure-induced attention-deficits in rats

Introduction

There is a high prevalence of fetal alcohol spectrum disorders (FASD) in the US and the world, which is caused by prenatal ethanol exposure (PE). Most individuals with FASD show attention deficit hyperactivity disorder (ADHD) -like symptoms. Using a rat model of FASD, we have successfully demonstrated that moderate and heavy PE leads to persistent attention deficits, including augmented impulsivity and impaired sustained attention. Anxiety is another primary symptom of FASD. Anxiety and ADHD are closely associated in clinical studies. However, the causal relationship between anxiety and ADHD is not clear. In the present study, we used the strategy of environmental enrichment to reduce anxiety after PE in rats and investigated if attention deficits could be ameliorated.

Methods

A 2nd-trimester binge-drinking pattern of heavy PE was used. Environmental enrichment consisted of neonatal handling and postweaning complex housing. Action impulsivity and sustained attention were tested in adult males and females using the 2-choice reaction time task.

Results

The results show environmental enrichment effectively ameliorated action impulsivity and improved sustained attention in male and female PE rats. Action impulsivity was also improved in control rats with environmental enrichment. In addition, environmental enrichment improved the efficiency of obtaining rewards in male and female control but not PE rats. Environmental enrichment altered the pattern of reaction time components, favoring slower movement initiation but faster movement.

Discussion

These observations support that environmental enrichment could be an effective strategy in ameliorating ADHD-like symptoms in FASD. The reduced anxiety could contribute to such an effect.

Breaking New Ground With Endoxifen: Augmentation Strategies in OCD Management-A Case Series

Obsessive-compulsive (OC) disorder (OCD) is a common and potentially disabling illness with a waxing and waning course. OCD significantly disrupts the quality of life. Selective serotonin reuptake inhibitors (SSRIs) are first-line pharmacological treatments for OCD and benefit up to half of the patients. Augmentation with low-dose antipsychotics is an evidence-based second-line strategy. Psychotherapy, including cognitive behavior therapy (CBT), is used both as first and second-line treatment. A significant portion of patients, however, do not respond to conventional treatments. We present a case series on the use of Endoxifen as an augmenting agent in patients with OCD and multiple psychiatric comorbidities who did not respond well to conventional pharmacotherapy.

Cocaine Self-Administration Increases Impulsive Decision-Making in Low-Impulsive Rats Associated with Impaired Functional Connectivity in the Mesocorticolimbic System

Impulsivity is often considered a risk factor for drug addiction; however, not all evidence supports this view. In the present study, we used a food reward delay-discounting task (DDT) to categorize rats as low-, middle-, and high-impulsive but failed to find any difference among these groups in the acquisition and maintenance of cocaine self-administration (SA), regardless of electrical footshock punishment. Additionally, there were no group differences in locomotor responses to acute cocaine in rats with or without a history of cocaine SA. Unexpectedly, chronic cocaine SA selectively increased impulsive choice in low-impulsive rats. Resting-state fMRI analysis revealed a positive correlation between impulsivity and cerebral blood volume in the midbrain, thalamus, and auditory cortex. Using these three regions as seeds, we observed a negative correlation between impulsivity and functional connectivity between the midbrain and frontal cortex, as well as between the thalamus and frontal cortex (including the orbitofrontal, primary, and parietal cortices) in low-impulsive rats. These correlations were attenuated following chronic cocaine SA. RNAscope in situ hybridization assays revealed a significant reduction in dopamine (DA) D1, D2, and D3 receptor mRNA expression in the corticostriatal regions of low-impulsive rats after cocaine SA. Our findings challenge the widely held view that impulsivity is a vulnerability factor for cocaine use disorder. Instead, chronic cocaine use appears to selectively increase impulsive choice decision-making in normally low-impulsive rats, associated with reduced functional connectivity and DA receptor expression in the mesocorticolimbic DA network.

Neural Correlates and Sex-Specific Effects of Affectively Driven Processes Underlying Decision-Making in Adult ADHD

AIMS

Adults with attention-deficit/hyperactivity disorder (ADHD) often exhibit heightened risk-taking behavior due to disadvantageous decision-making. This study investigates the influence of preceding unconscious and affectively driven processes on this behavior, with a focus on sex-specific effects.

METHODS

Functional magnetic resonance imaging was used to examine neural activity during the anticipation phase of decision-making in 18 individuals with ADHD (10 females and 8 males) and 20 healthy controls (10 females and 10 males) using a modified version of the Balloon Analogue Risk Task.

RESULTS

During the anticipation of decision-making, individuals with ADHD exhibited reduced activation in the right precuneus and the right superior frontal gyrus compared to healthy controls. Sex-specific effects were exclusively observed within the ADHD group, showing increased neural activity in females compared to males in areas including the dorsolateral prefrontal cortex, left insula, right caudate, right cuneus, and precuneus.

CONCLUSION

These findings indicate altered neural activity in adult patients with ADHD with sex-specific differences during the anticipation of a risky decision. The study underscores the importance of the right precuneus and superior frontal gyrus in relation to metacognitive functioning and interoceptive awareness. However, further research is needed to explore the interplay of unconscious processes during decision-making in ADHD.

A Prospective Study on Postmethylphenidate Treatment Changes in Premature Ejaculation Among Adults With Attention-Deficit/Hyperactivity Disorder

Background:

Methylphenidate is widely used to treat attention-deficit/hyperactivity disorder (ADHD), but its impact on comorbid conditions such as premature ejaculation (PE) and impulsivity in adult patients with ADHD is underexplored.

Study Question:

How does methylphenidate treatment affect impulsivity and PE symptoms in adults with ADHD?

Study Design:

A prospective cohort study at Erzurum City Hospital included 53 adult patients with ADHD diagnosed through the Structured Clinical Interview for DSM-5 Disorders. Of these, 34 had comorbid PE and 19 did not.

Measures and Outcomes:

Primary outcomes were changes in ADHD symptoms, impulsivity, and PE, measured by the Adult ADHD Self-Report Scale (ASRS), Urgency, Premeditation, Perseverance, and Sensation Seeking Impulsive Behavior Scale, and the Arabic Index of Premature Ejaculation (AIPE). Secondary outcomes included the correlation between methylphenidate dosage and symptom improvement and predictors of changes in PE symptoms.

Results:

A significant reduction was observed in the ASRS total score, which decreased from 51.7 ± 9.0 (mean ± SD) to 32.5 ± 8.4 (P < 0.001). Urgency, Premeditation, Perseverance, and Sensation Seeking Impulsive Behavior Scale scores also showed a significant decrease from 125.1 ± 14.3 to 97.0 ± 5.0 (P < 0.001). The AIPE scores, measured in points, increased from 22.4 ± 9.3 to 32.5 ± 8.4 (P < 0.001), suggesting improved control over ejaculation. Correlation analysis revealed a significant positive correlation between the immediate-release methylphenidate dose and improvements in ASRS total scores (r = 0.485, P < 0.001). Regression analysis indicated that the pretreatment AIPE score (β = −0.529, P < 0.001) was a significant predictor of posttreatment changes.

Conclusions:

Treatment with methylphenidate was associated with a decrease in both impulsivity and PE symptoms in adults with ADHD, particularly with immediate-release formulations. These findings highlight the importance of considering comorbid conditions in ADHD treatment.

Social context and dopamine signaling converge in the mushroom body to drive impulsivity

Organisms adapt their behaviors flexibly in response to various internal and environmental factors. However, how and where these factors converge in the brain to alter behavior is not well understood. In this study, we examine how social context interacts with dopamine activity to influence inhibitory control in Drosophila . We found that, regardless of social context-whether isolated or in groups-wild-type flies consistently showed strong movement suppression in a go/no-go task that measures action restraint. In contrast, flies with enhanced dopamine activity suppressed their movements when tested alone or with potential mates but exhibited impulsive behaviors when exposed to same-sex peers. This social-context-dependent impulsivity was shown to rely on dopamine-D1 receptor-cAMP signaling in mushroom body (MB) neurons. Remarkably, activating the MB was sufficient to induce impulsivity, even without dopamine input or a social context. Our findings highlight MB as a critical hub where social context and dopamine signaling converge to regulate impulsive behavior in Drosophila .

Signficance statement

This study demonstrates that impulsivity results from the interplay between elevated dopamine levels and social context, rather than dopamine alone, with the mushroom body (MB) serving as a key neural hub for integrating these signals in Drosophila . Social stimuli, such as the presence of same-sex peers, disrupt inhibitory control in a context-dependent manner, highlighting the importance of multimodal sensory inputs and MB activity. These findings challenge the isolation-focused approach in traditional impulsivity research and underscore the need to account for social influences when investigating cognitive processes and disorders like ADHD, autism, and substance use, where social settings often amplify symptoms.

Classification

Genetics / Neuroscience.

The Effect of Transcranial Direct Current Stimulation (TDCS) on Cognitive Functioning in Individuals with Attention Deficit/Hyperactivity Disorder (ADHD)

Objective

Attention deficit/hyperactivity disorder (ADHD) is among the most prevalent neurodevelopmental disorders in children, often persisting into adulthood. It is characterized by two symptom domains: impulsivity and inattention, both associated with underlying neural and cognitive deficiencies. This study is the first toinvestigate the potential effects of transcranial direct current stimulation (tDCS) targeting the left DLPFC on cognitive functions related to both symptom domains in adults with ADHD compared to typically developed controls.

Method

This pre-registered clinical trial enrolled 55 participants, 25 of whom were diagnosed with ADHD. Participants completed a series of cognitive tasks before and after receiving either tDCS or sham treatment.

Results

In the ADHD group, tDCS treatment improved measures associated with inattention,but not measures related to impulsivity. In the control group, tDCS treatment had no benefits.

Conclusions

The discrepancy in treatment response observed between inattentive and impulsivesymptoms has implications for understanding the neurobiological mechanisms of ADHD. Our findings offer new evidence supporting the positive impact of tDCS on cognitive functions linked to inattention.

Impulse control in Parkinson's disease: Distinct effects between action and choice

Aside from typical motor symptoms, impulse control issues related to engaging in actions or decision-making can manifest in Parkinson's disease (PD). The lack of direct comparisons between impulsive action and impulsive choice domains hinders a comprehensive understanding of impaired impulse control in this population. Therefore, the current review integrates findings across behavioural measures of impulsive action and choice in PD samples, both on and off dopaminergic medication. The qualitative review of studies revealed a distinction between the two impulsivity domains in the context of PD. While impulsive action impairments present in early, non-medicated PD and persist throughout the disease, impulsive choice deficits may only emerge after time on medication. Research on impulsive choice, especially in non-medicated PD, is limited, and the impact of medication status and disease progression on both domains remains inconclusive. We recommend that future studies integrate impulsive action and choice task types within the same sample and employ longitudinal designs to monitor how disease progression and corresponding medication changes affect impulse control over time.

Deep Brain Stimulation in Pediatric Populations: A Scoping Review of the Clinical Trial Landscape

INTRODUCTION

There has been rapid advancement in the development of deep brain stimulation (DBS) as a treatment option for adults for neurological and neuropsychiatric conditions. Here, we present a scoping review of completed and ongoing clinical trials focused on DBS in pediatric populations, highlighting key knowledge gaps.

METHODS

Three databases (PubMed, OVID, and Embase) and the clinicaltrials.gov registry were queried to identify clinical trials for DBS in pediatric cohorts (age ≤18 years). Prospective and retrospective case series were excluded. No restrictions were placed on the diagnoses or measured clinical outcomes. Individual patient demographics, diagnosis, DBS target, and primary endpoints were extracted and summarized.

RESULTS

A total of 13 clinical trials were included in the final review, consisting of 9 completed trials (357 screened) and 4 ongoing trials (82 screened). Of the completed trials, 6 studied dystonia (both inherited and acquired; participants aged 4-18 years) and 3 studied drug-resistant epilepsy (participants aged 4-17 years). Among the 6 trials for dystonia, 5 used the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) as the primary endpoint. There were a total of 18 adverse events documented across 63 participants, with 5 of 9 studies reporting adverse events. Ongoing clinical trials are evaluating DBS for dystonia (N = 2), epilepsy (N = 1), and self-injurious behavior (N = 1).

CONCLUSIONS

This scoping review summarizes the landscape of clinical trials for DBS in children and youth. In dystonia, further research is warranted with more relevant pediatric outcome measures and for understudied patient subgroups and targets. There are also significant gaps in our understanding of evaluating the role of DBS in other neurological and neurodevelopmental disorders in pediatric populations.

INTRODUCTION

There has been rapid advancement in the development of deep brain stimulation (DBS) as a treatment option for adults for neurological and neuropsychiatric conditions. Here, we present a scoping review of completed and ongoing clinical trials focused on DBS in pediatric populations, highlighting key knowledge gaps.

METHODS

Three databases (PubMed, OVID, and Embase) and the clinicaltrials.gov registry were queried to identify clinical trials for DBS in pediatric cohorts (age ≤18 years). Prospective and retrospective case series were excluded. No restrictions were placed on the diagnoses or measured clinical outcomes. Individual patient demographics, diagnosis, DBS target, and primary endpoints were extracted and summarized.

RESULTS

A total of 13 clinical trials were included in the final review, consisting of 9 completed trials (357 screened) and 4 ongoing trials (82 screened). Of the completed trials, 6 studied dystonia (both inherited and acquired; participants aged 4-18 years) and 3 studied drug-resistant epilepsy (participants aged 4-17 years). Among the 6 trials for dystonia, 5 used the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) as the primary endpoint. There were a total of 18 adverse events documented across 63 participants, with 5 of 9 studies reporting adverse events. Ongoing clinical trials are evaluating DBS for dystonia (N = 2), epilepsy (N = 1), and self-injurious behavior (N = 1).

CONCLUSIONS

This scoping review summarizes the landscape of clinical trials for DBS in children and youth. In dystonia, further research is warranted with more relevant pediatric outcome measures and for understudied patient subgroups and targets. There are also significant gaps in our understanding of evaluating the role of DBS in other neurological and neurodevelopmental disorders in pediatric populations.

Adolescents with Elevated Psychopathic Traits are Associated with an Increased Risk for Premature Mortality

The mortality rate among adolescents has been steadily increasing in recent years. Researchers have previously identified forms of externalizing psychopathology measured during adolescence associated with an increased risk for premature mortality, including attention-deficit/hyperactivity disorder (ADHD), substance use disorders (SUDs), oppositional defiant disorder (ODD), and conduct disorder (CD). The current study investigated whether additional personality traits (i.e., adolescent psychopathic traits, assessed via the Hare Psychopathy Checklist: Youth Version [PCL:YV]) were also associated with premature mortality risk among maximum-security incarcerated adolescents (N = 332). During a follow-up period ranging from 10 to 14 years, premature mortality was observed in n = 33 participants (9.94%), a mortality rate nearly ten times higher than population norms. We observed that adolescents scoring the highest on PCL:YV total scores exhibited significantly higher rates of premature mortality compared to adolescents scoring lower on PCL:YV total scores via Fisher's exact tests. Additionally, through univariate Cox proportional hazard regression analyses, PCL:YV total, Factor 2 (measuring lifestyle/behavioral and antisocial/developmental psychopathic traits), Facet 1 (measuring interpersonal psychopathic traits), and Facet 3 (measuring lifestyle/behavioral psychopathic traits) scores were associated with faster time to premature mortality. In supplemental analyses performed, we observed that adolescents meeting criteria for externalizing psychopathology (i.e., ADHD, SUDs, ODD, and CD) did not exhibit higher rates of premature mortality compared to control participants. The current study therefore identifies additional maladaptive personality traits to consider in relation to premature mortality risk (i.e., psychopathic traits) among a high-risk sample of incarcerated adolescents.

Important Mechanisms in the Development of Anxiety in Children with ADHD: The Role of Associated Features of ADHD and Interpersonal Functioning

Over a quarter of children with Attention-deficit/hyperactivity disorder (ADHD) meet diagnostic criteria for an anxiety disorder as well. The goals of this paper are (a) to examine what is currently known about co-occurring ADHD and anxiety in children, (b) propose and outline underlying factors relevant to the development of anxiety in children with ADHD, and (c) discuss future directions and clinical implications for the prevention and identification of anxiety development in children with ADHD. It is proposed that certain associated features of ADHD (i.e., low effortful control and emotion dysregulation) as well as various interpersonal factors related to ADHD (i.e., poor parent, teacher, and peer relationships) form a negative feedback loop that increases susceptibility to anxiety in a subset of children with ADHD. The literature supports interrelations between and across the associated features and interpersonal factors. Additional research is needed to test the validity of the proposed process. Obtaining further insight into the interplay between these different factors can help identify a subset of children with ADHD who are at risk for developing anxiety, which can enhance the precision of prevention, assessment, and treatment efforts for these children.

A study of impulsivity and adverse childhood experiences in a population health setting

As complex mental health traits and life histories are often poorly captured in hospital systems, the utility of using the Barratt Impulsivity Scale (BIS) and Adverse Childhood Experiences (ACEs) for assessing adult disease risks is unknown. Here, we use participants from the Healthy Nevada Project (HNP) to determine if two standard self-assessments could predict the incidence and onset of disease. We conducted a retrospective cohort study involving adult participants who completed the Behavioral and Mental Health Self-Assessment (HDSA) between September 2018 and March 2024. Impulsivity levels were measured using the BIS-15, and retrospective self-reports of ACEs were collected through a standardized questionnaire. In total, 17,482 HNP participants completed the HDSA. Our findings indicate that ACEs were significantly associated with impulsivity. Disease associations with impulsivity and ACEs were evaluated using a phenome-wide association study, identifying 230 significant associations with impulsivity. Among these, 44 were related to mental health diagnoses, including major depressive disorder (MDD). Kaplan-Meier survival estimates characterized the differences in the lifetime predicted probability between high and low impulsivity for major depressive disorder and essential hypertension. This analysis showed that having both high ACEs and high impulsivity confer substantial risk of MDD diagnosis (hazard ratios 2.81, 2.17, respectively). Additionally, lifetime predicted probability of MDD was approximately 40% higher for high ACEs and high impulsivity compared to no ACEs and low impulsivity. Essential hypertension demonstrated similar trends, with an approximate 20% increase in predicted lifetime probability of diagnosis. These results demonstrate that high ACES and elevated impulsivity scores are associated with a range of negative health outcomes and a simple self-assessment of complex traits and life history may significantly impact clinical risk assessments.

Inhibition of Indirect Pathway Activity Causes Abnormal Decision-Making In a Mouse Model of Impulse Control Disorder in Parkinson's Disease

Healthy action selection relies on the coordinated activity of striatal direct and indirect pathway neurons. In Parkinson's disease (PD), in which loss of midbrain dopamine neurons is associated with progressive motor and cognitive deficits, this coordination is disrupted. Dopamine replacement therapy can remediate motor symptoms, but can also cause impulse control disorder (ICD), which is characterized by pathological gambling, hypersexuality, and/or compulsive shopping. The cellular and circuit mechanisms of ICD remain unknown. Here we developed a mouse model of PD/ICD, in which ICD-like behavior was assayed with a delay discounting task. We found that in parkinsonian mice, the dopamine agonist pramipexole drove more pronounced delay discounting, as well as disrupted firing in both direct and indirect pathway neurons. We found that chemogenetic inhibition of indirect pathway neurons in parkinsonian mice drove similar phenotypes. Together, these findings provide a new mouse model and insights into ICD pathophysiology.

Effects of chronic stress on cognitive function - From neurobiology to intervention

Exposure to chronic stress contributes considerably to the development of cognitive impairments in psychiatric disorders such as depression, generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and addictive behavior. Unfortunately, unlike mood-related symptoms, cognitive impairments are not effectively treated by available therapies, a situation in part resulting from a still incomplete knowledge of the neurobiological substrates that underly cognitive domains and the difficulty in generating interventions that are both efficacious and safe. In this review, we will present an overview of the cognitive domains affected by stress with a specific focus on cognitive flexibility, behavioral inhibition, and working memory. We will then consider the effects of stress on neuronal correlates of cognitive function and the factors which may modulate the interaction of stress and cognition. Finally, we will discuss intervention strategies for treatment of stress-related disorders and gaps in knowledge with emerging new treatments under development. Understanding how cognitive impairment occurs during exposure to chronic stress is crucial to make progress towards the development of new and effective therapeutic approaches.

Associations Between Intertemporal Food Choice and BMI in Adult Women: An fMRI Study Using a Quasi-realistic Design

BACKGROUND

Impulsivity resulting in unrestrained eating has been implicated as a contributing factor for obesity. Delay discounting (DD) tasks where individuals choose between a smaller immediate reward and a larger delayed reward provide useful data to describe impulsive decision-making and to determine the extent to which delayed rewards are discounted.

OBJECTIVE

To study the association between body mass index(BMI) and delay discounting for food and money in adult women.

METHODS

We used a DD task with real food rewards to investigate impulsive decision-making as related to BMI in participants who self-identified as women. Participants in group A had a mean BMI of 21.4 (n = 14), and participants in group B had a mean BMI of 32.2 (n = 14). Each group was tested in a hungry state during a single session. We performed fMRI during a DD task requiring participants to choose between a food item (one sandwich) constituting a smaller immediate reward and multiple food items (two, three, or four sandwiches) constituting a series of larger delayed rewards available at different intervals. The steepness of the discounting curve for food was determined from these decisions. Participants then completed a monetary discounting task to facilitate a comparison of the discounting of food and monetary rewards.

RESULTS

Participants in group B discounted food rewards more steeply than monetary rewards. Decisions for delayed rewards led to increased activations of brain areas related to executive control on fMRI, such as the head of the caudate nucleus and the anterior cingulate cortex (ACC) in group A, but not group B participants.

CONCLUSION

Our findings suggest that group B had difficulty deciding against the immediate food rewards due to insufficient recruitment of cortical control areas. Therefore, impulsivity is an important target for behavioral interventions in individuals with obesity.

HPA activity mediates the link between trait impulsivity and boredom

Boredom, a complex emotional state with implications for mental health and well-being, has garnered attention across disciplines, yet remains relatively understudied in psychiatric research. Here, we explored the intricate relationship between trait-impulsivity, stress, and boredom across two studies. Participants completed self-report measures of trait-impulsivity and boredom and boredom-inducing tasks. Study 1, involving 80 participants (42 women and 38 men, aged 20-63), replicates previous findings, by demonstrating that impulsive individuals report greater boredom following a boring task. Study 2 then extends this, using 20 participants (9 women and 12 men, aged 18-24), to show that hypothalamic-pituitary-adrenal (HPA) axis activity, specifically heightened salivary cortisol responses, mediate the link between impulsivity and boredom following a boring task. Collectively, these results demonstrate that HPA axis activity may underline the relationship between trait-impulsivity and boredom by extending previous work and offering a novel insight into potential mechanisms. These findings offer promise for personalised interventions, designed for high impulsivity individuals, to alleviate the negative impacts of boredom and potentially break the identified feedback loop.

Activation of the mPFC-NAc Pathway Reduces Motor Impulsivity but Does Not Affect Risk-Related Decision-Making in Innately High-Impulsive Male Rats

Attention-deficit/hyperactivity disorder (ADHD) and substance use disorders (SUD) are characterized by exacerbated motor and risk-related impulsivities, which are associated with decreased cortical activity. In rodents, the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) have been separately implicated in impulsive behaviors, but studies on the specific role of the mPFC-NAc pathway in these behaviors are limited. Here, we investigated whether heightened impulsive behaviors are associated with reduced mPFC activity in rodents and determined the involvement of the mPFC-NAc pathway in motor and risk-related impulsivities. We used the Roman High- (RHA) and Low-Avoidance (RLA) rat lines, which display divergent phenotypes in impulsivity. To investigate alterations in cortical activity in relation to impulsivity, regional brain glucose metabolism was measured using positron emission tomography and [18F]-fluorodeoxyglucose ([18F]FDG). Using chemogenetics, the activity of the mPFC-NAc pathway was either selectively activated in high-impulsive RHA rats or inhibited in low-impulsive RLA rats, and the effects of these manipulations on motor and risk-related impulsivity were concurrently assessed using the rat gambling task. We showed that basal [18F]FDG uptake was lower in the mPFC and NAc of RHA compared to RLA rats. Activation of the mPFC-NAc pathway in RHA rats reduced motor impulsivity, without affecting risk-related decision-making. Conversely, inhibition of the mPFC-NAc pathway had no effect in RLA rats. Our results suggest that the mPFC-NAc pathway controls motor impulsivity, but has limited involvement in risk-related decision-making in our current model. Our findings suggest that reducing fronto-striatal activity may help attenuate motor impulsivity in patients with impulse control dysregulation.

Differential phase-amplitude coupling in nucleus accumbens and orbitofrontal cortex reflects decision-making during a delay discounting task

BACKGROUND

The impulsive choice is characterized by the preference for a small immediate reward over a bigger delayed one. The mechanisms underlying impulsive choices are linked to the activity in the Nucleus Accumbens (NAc), the orbitofrontal cortex (OFC), and the dorsolateral striatum (DLS). While the study of functional connectivity between brain areas has been key to understanding a variety of cognitive processes, it remains unclear whether functional connectivity differentiates impulsive-control decisions.

METHODS

To study the functional connectivity both between and within NAc, OFC, and DLS during a delay discounting task, we concurrently recorded local field potential in NAc, OFC, and DLS in rats. We then quantified the degree of phase-amplitude coupling (PAC), coherence, and Granger Causality between oscillatory activities in animals exhibiting either a high (HI) or low (LI) tendency for impulsive choices.

RESULTS

Our results showed a differential pattern of PAC during decision-making in OFC and NAc, but not in DLS. While theta-gamma PAC in OFC was associated with self-control decisions, a higher delta-gamma PAC in both OFC and NAc biased decisions toward impulsive choices in both HI and LI groups. Furthermore, during the reward event, Granger Causality analysis indicated a stronger NAc➔OFC gamma contribution in the HI group, while the LI group showed a higher OFC➔NAc gamma contribution.

CONCLUSIONS

The overactivity in NAc during reward in the HI group suggests that exacerbated contribution of NAcCore can lead to an overvaluation of reward that biases the behavior toward the impulsive choice.

Incremental Validity of Trait Impulsivity, Dysfunctional Emotional Regulation, and Affect Lability in the Predictions of Attention Deficit Hyperactivity Disorder and Oppositional Defiant Disorder Symptoms in Adults

Difficulties in emotion regulation (DER) is a defining feature of attention deficit hyperactivity disorder (ADHD), and arguments are being made for it to be considered as a defining feature of oppositional defiant disorder (ODD). However, the consensus is that it is better viewed as an important correlate distinct from ADHD. This study examined the incremental validity of DER over and above trait impulsivity (TI) in the predictions of ADHD and ODD symptoms. It also examined the incremental validity of affect lability (AL) over and above TI and (DER) in these predictions. Five hundred and twenty-five adults from the general community completed a series of questionnaires. A model-based SEM approach for evaluating incremental validity indicated that TI predicted ADHD and ODD symptoms over age; DER predicted ADHD and ODD symptoms over age and TI; and AL did not predict ADHD and ODD symptoms over and above age, IT, or DER. In addition, AL predicted ADHD and ODD symptoms over age and TI, and DER also predicted ADHD and ODD symptoms over and above age, TI, and AL. In conclusion, TI is core to ADHD, and although DER is important, it is unlikely to be relevant as a diagnostic indicator for ADHD or ODD. These findings notwithstanding, there is need for caution when interpreting our findings, as the study did not control for potentially influencing factors on emotional regulation such as age, gender, culture, and existing psychopathologies.

BK channel dysfunction disrupts attention-controlled behaviors and altered perseverative responses in murine instrumental learning

This study examined the effect of knockout of KCNMA1 gene, coding for the BK channel, on cognitive and attentional functions in mice, with an aim to better understand its implications for human neurodevelopmental disorders. The study used the 3-choice serial reaction time task (3-CSRTT) to assess the learning performance, attentional abilities, and repetitive behaviors in mice lacking the KCNMA1 gene (KCNMA1-/-) compared to wild-type (WT) controls. Results showed no significant differences in learning accuracy between the two groups. However, KCNMA1-/- mice were more prone to omitting responses to stimuli. In addition, when the timing of cue presentation was randomized, the KCNMA1-/- showed premature responses. Notably, these mice also demonstrated a marked reduction in perseverative responses, which include repeated nose-poke behaviors following decisions. These findings highlight the involvement of the KCNMA1 gene in managing attention, impulsivity, and potentially moderating repetitive actions.

Methylphenidate, but not citalopram, decreases impulsive choice in rats performing a temporal discounting task

Introduction

Drugs targeting monoamine systems remain the most common treatment for disorders with impulse control impairments. There is a body of literature suggesting that drugs affecting serotonin reuptake and dopamine reuptake can modulate distinct aspects of impulsivity - though such tests are often performed using distinct behavioral tasks prohibiting easy comparisons.

Methods

Here, we directly compare pharmacologic agents that affect dopamine (methylphenidate) vs serotonin (citalopram) manipulations on choice impulsivity in a temporal discounting task where rats could choose between a small, immediate reward or a large reward delayed at either 2 or 10s. In control conditions, rats preferred the large reward at a small (2s) delay and discounted the large reward at a long (10s) delay.

Results

Methylphenidate, a dopamine transport inhibitor that blocks reuptake of dopamine, dose-dependently increased large reward preference in the long delay (10s) block. Citalopram, a selective serotonin reuptake inhibitor, had no effect on temporal discounting behavior. Impulsive behavior on the temporal discounting task was at least partially mediated by the nucleus accumbens shell. Bilateral lesions to the nucleus accumbens shell reduced choice impulsivity during the long delay (10s) block. Following lesions, methylphenidate did not impact impulsivity.

Discussion

Our results suggest that striatal dopaminergic systems modulate choice impulsivity via actions within the nucleus accumbens shell, whereas serotonin systems may regulate different aspects of behavioral inhibition/impulsivity.

Lateral Orbitofrontal Cortex Encodes Presence of Risk and Subjective Risk Preference During Decision-Making

Adaptive decision-making requires consideration of objective risks and rewards associated with each option, as well as subjective preference for risky/safe alternatives. Inaccurate risk/reward estimations can engender excessive risk-taking, a central trait in many psychiatric disorders. The lateral orbitofrontal cortex (lOFC) has been linked to many disorders associated with excessively risky behavior and is ideally situated to mediate risky decision-making. Here, we used single-unit electrophysiology to measure neuronal activity from lOFC of freely moving rats performing in a punishment-based risky decision-making task. Subjects chose between a small, safe reward and a large reward associated with either 0% or 50% risk of concurrent punishment. lOFC activity repeatedly encoded current risk in the environment throughout the decision-making sequence, signaling risk before, during, and after a choice. In addition, lOFC encoded reward magnitude, although this information was only evident during action selection. A Random Forest classifier successfully used neural data accurately to predict the risk of punishment in any given trial, and the ability to predict choice via lOFC activity differentiated between and risk-preferring and risk-averse rats. Finally, risk preferring subjects demonstrated reduced lOFC encoding of risk and increased encoding of reward magnitude. These findings suggest lOFC may serve as a central decision-making hub in which external, environmental information converges with internal, subjective information to guide decision-making in the face of punishment risk.

Moderating effects of impulsivity and morning cortisol on the genotype-phenotype relationship of attention deficit hyperactivity disorder in young adults

Dysregulation of the morning cortisol response in young adults with attention deficit hyperactivity disorder (ADHD) has been shown to underlie several of the alterations present in their lives. Thus, the interaction of this mechanism with genetic and behavioural characteristics could explain a large proportion of the aetiology of ADHD in this population. For these reasons, the present study explores the associations of 30 single nucleotide polymorphisms (SNPs) previously identified as significant (after correction for multiple comparisons) in the aetiology of ADHD with an assessment of morning cortisol and impulsivity traits in a group of 120 adults aged 18-24 years. Participants were recruited through private centres of neuropsychology and psychiatry, as well as through events in local universities. Morning cortisol within 30 min of awakening and motor impulsivity traits were shown to moderate the effect of SNP rs10129500 on the severity of the symptoms of ADHD measured by the Adult Self-Report Scale. This variant associated with cortisol-binding globulin would explain the low concentrations of this hormone found in young adults with high symptoms of ADHD, which is accentuated when there are high levels of impulsivity. The proposed model allows for transferring the theoretical relationships between the dimensions that explain the aetiology of ADHD to an applied exploratory model with good performance.

The novel peptide LCGM-10 attenuates metabotropic glutamate receptor 5 activity and demonstrates behavioral effects in animal models

We employed a structural bioinformatics approach to develop novel peptides with predicted affinity to the binding site for negative allosteric modulators (NAMs) of metabotropic glutamate receptor 5 (mGluR5). Primary screening in zebrafish (Danio rerio) revealed a stimulatory effect of two peptides, LCGM-10 and LCGM-15. Target validation studies using calcium ion flux imaging and a luciferase reporter assay confirmed mGluR5 as the target. LCGM-10 showed greater potency than LCGM-15; it was comparable to that of the mGluR5 NAM 2-methyl-6-(phenylethynyl) pyridine (MPEP). Rodent behavioral screening in the open field and elevated plus maze revealed increased locomotor activity in both tests after acute LCGM-10 treatment, supported by further analysis of home cage spontaneous locomotor activity (SLA). The stimulating effect of a single LCGM-10 administration on SLA was evident up to 60 min after administration and was not accompanied by hypokinetic rebound observed for caffeine. According to our results, LCGM-10 has therapeutic potential to treat hypo- and dyskinesias of various etiologies. Further investigation of LCGM-10 effects in the delay discounting model of impulsive choice in rats revealed reduced trait impulsivity after single and chronic administrations, suggesting potential implication for attention deficit hyperactivity disorder, obsessive compulsive disorder, and addictions.

Delay discounting demonstrates lower impulsivity linked to a higher likelihood of succeeding at smoking cessation

Sixty-eight percent of smokers want to quit, but only one in 10 are successful at smoking cessation. Recently, impulsivity has been studied in relation to smoking cessation with measures like the delay discounting task (DDT). We aimed to build on the robust literature that has already revealed the association between impulsivity and smoking cessation, as well as look at the differences between sexes for which there is conflicting evidence. We hypothesized that lower impulsivity would be positively associated with cessation success. In the parent cessation trial, participants were randomized to 12 weeks of progesterone or placebo. Participants were asked to quit smoking, and their smoking status was monitored via expired carbon monoxide throughout the study. Participants completed a DDT at screening, week 4, and week 8 using the 27-item Monetary Choice Questionnaire, where participants decided between a small immediate reward or a larger delayed reward (LDR). The effective delay 50 (ED50), which is the delay at which the LDR loses half its value, was analyzed. To estimate the association between ED50 and cessation, a logistic mixed model with a participant random intercept was fit, controlling for study week, randomization, sex, and age. For the 181 participants, a doubling of the ED50 was associated with an 18% increase in the odds of tobacco cessation (95% confidence interval: 0.2-38% increase; p=0.05). In agreement with our hypothesis, lower impulsivity correlated to greater tobacco cessation success. Our study also showed no evidence of sex differences in the association between ED50 and smoking cessation.

Understanding the Impact of Deviant Peer Association on Dual Systems Model Development: Testing the Moderating Role of ADHD

ABSTRACT

Recent research has indicated that deviant peers may play a role in cognitive development. This is particularly the case for the dual systems model, a key framework for understanding engagement in antisocial behavior during adolescence and emerging adulthood. However, limited research has examined how preexisting mental health concerns may moderate these relationships. This study used the Pathways to Desistance data to examine attention deficit hyperactivity disorder (ADHD) as a moderator of the relationships between deviant peer association and dual systems model constructs. Generalized estimating equations were used to test these relationships. Results indicated that deviant peer association and the presence of ADHD both predicted increased sensation-seeking and lower impulse control. ADHD significantly moderated the relationship between deviant peer association and impulse control, indicating a weaker impact of deviant peer association on impulse control among participants with ADHD. No significant interaction was observed for the relationship between deviant peer association and sensation-seeking.

Development of a human-analogue, 3-symptom domain Dog ADHD and Functionality Rating Scale (DAFRS)

The family dog, in its natural environment, exhibits neuropsychological deficits redolent of human psychiatric disorders, including behaviours that are similar to human attention-deficit/hyperactivity disorder (ADHD) symptoms. Based on standard questionnaire methods in humans, we aimed to develop and validate a detailed, psychometrically improved tool to assess owner views on relevant dog behaviours. We modified available questionnaires by adding items that allow for separate analysis of impulsivity, and items on functional impairment. We collected data from 1168 owners for different validation steps of the new questionnaire and, similarly to assessment of humans where teachers also evaluate as an expert control, we collected data from dog trainers. Exploratory and confirmatory factor analysis revealed 3 factors: inattention (IA), hyperactivity (H) and impulsivity (I), corresponding to all three human symptom dimensions in dogs. Test-retest analyses showed excellent agreement between measurements for all factors. Similarly to findings with humans, trainer-owner rating comparisons showed fair (IA) to moderate (H, I) agreement. As in humans, greater ADHD scores were associated with greater functional impairment scores. We suggest that in dogs, similarly to humans, parallel examination of (extreme) ADHD and functional impairment scores could help distinguish diagnosable individuals, after further validation of the questionnaire using a relevant behaviour test.

Exploring the steps of learning: computational modeling of initiatory-actions among individuals with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is characterized by difficulty in acting in a goal-directed manner. While most environments require a sequence of actions for goal attainment, ADHD was never studied in the context of value-based sequence learning. Here, we made use of current advancements in hierarchical reinforcement-learning algorithms to track the internal value and choice policy of individuals with ADHD performing a three-stage sequence learning task. Specifically, 54 participants (28 ADHD, 26 controls) completed a value-based reinforcement-learning task that allowed us to estimate internal action values for each trial and stage using computational modeling. We found attenuated sensitivity to action values in ADHD compared to controls, both in choice and reaction-time variability estimates. Remarkably, this was found only for first-stage actions (i.e., initiatory actions), while for actions performed just before outcome delivery the two groups were strikingly indistinguishable. These results suggest a difficulty in following value estimation for initiatory actions in ADHD.

A thalamocortical pathway controlling impulsive behavior

Planning and anticipating motor actions enables movements to be quickly and accurately executed. However, if anticipation is not properly controlled, it can lead to premature impulsive actions. Impulsive behavior is defined as actions that are poorly conceived and are often risky and inappropriate. Historically, impulsive behavior was thought to be primarily controlled by the frontal cortex and basal ganglia. More recently, two additional brain regions, the ventromedial (VM) thalamus and the anterior lateral motor cortex (ALM), have been shown to have an important role in mice. Here, we explore this newly discovered role of the thalamocortical pathway and suggest cellular mechanisms that may be involved in driving the cortical activity that contributes to impulsive behavior.

Mechanisms of impulsive choice: Experiments to explore and models to map the empirical terrain

Impulsive choice is preference for a smaller-sooner (SS) outcome over a larger-later (LL) outcome when LL choices result in greater reinforcement maximization. Delay discounting is a model of impulsive choice that describes the decaying value of a reinforcer over time, with impulsive choice evident when the empirical choice-delay function is steep. Steep discounting is correlated with multiple diseases and disorders. Thus, understanding the processes underlying impulsive choice is a popular topic for investigation. Experimental research has explored the conditions that moderate impulsive choice, and quantitative models of impulsive choice have been developed that elegantly represent the underlying processes. This review spotlights experimental research in impulsive choice covering human and nonhuman animals across the domains of learning, motivation, and cognition. Contemporary models of delay discounting designed to explain the underlying mechanisms of impulsive choice are discussed. These models focus on potential candidate mechanisms, which include perception, delay and/or reinforcer sensitivity, reinforcement maximization, motivation, and cognitive systems. Although the models collectively explain multiple mechanistic phenomena, there are several cognitive processes, such as attention and working memory, that are overlooked. Future research and model development should focus on bridging the gap between quantitative models and empirical phenomena.

The Paradoxical Clinical Course of Persons with Gambling Disorder and Comorbid Attention-Deficit/Hyperactivity Disorder (ADHD)

The co-occurrence of gambling disorder (GD) and attention-deficit/hyperactivity disorder (ADHD) has been widely reported. In this study, we aimed to investigate the social background, clinical characteristics, and clinical course of initial-visit GD patients with and without ADHD in a Japanese psychiatric hospital. We recruited 40 initial-visit GD patients and collected comprehensive information by self-report questionnaires, direct interviews, and medical records. 27.5% of the GD patients had comorbid ADHD. Compared to the GD patients without ADHD, those with ADHD had significantly higher comorbidity rates of autism spectrum disorder (ASD), lower rates of marriage, slightly less years of education and marginally lower employment rates. On the other hand, the GD patients with ADHD showed higher treatment retention rates and participation rates in the mutual support group. Despite presenting with disadvantageous characteristics, GD patients with ADHD exhibited a more favourable clinical course. Therefore, clinicians should be mindful of the possibility of ADHD comorbidity and the potential for better clinical outcomes among GD patients with ADHD.

Do Differences Exist in Impact Test Domains between Youth Athletes with and without an Anterior Cruciate Ligament Injury?

Poor baseline reaction time, as measured via the Immediate Post-Concussion Assessment and Cognitive Test (ImPACT), has been associated with anterior cruciate ligament (ACL) injury risk in adult athletes. Our study sought to determine whether the reaction time and impulse control ImPACT test domains differed between ACL injured and uninjured pediatric athletes. A total of 140 high-school aged athletes comprising 70 athletes who went on to sustain an ACL injury between 2012 and 2018 and 70 age- and sex-matched uninjured controls were included in the study. Mean reaction times were similar for the injured (0.67 s) and uninjured (0.66 s) athletes (p = 0.432), and the impulse control scores were also similar for those with (5.67) and without (6.07) an ACL injury (p = 0.611). Therefore, neurocognitive risk factors for sustaining an ACL injury in adults cannot necessarily be extrapolated to adolescent athletes. Further research is needed to understand why differences exist between injury risk in youth and adult athletes.

adgrl3.1-deficient zebrafish show noradrenaline-mediated externalizing behaviors, and altered expression of externalizing disorder-candidate genes, suggesting functional targets for treatment

Externalizing disorders (ED) are a cause of concern for public health, and their high heritability makes genetic risk factors a priority for research. Adhesion G-Protein-Coupled Receptor L3 (ADGRL3) is strongly linked to several EDs, and loss-of-function models have shown the impacts of this gene on several core ED-related behaviors. For example, adgrl3.1-/- zebrafish show high levels of hyperactivity. However, our understanding of the mechanisms by which this gene influences behavior is incomplete. Here we characterized, for the first time, externalizing behavioral phenotypes of adgrl3.1-/- zebrafish and found them to be highly impulsive, show risk-taking in a novel environment, have attentional deficits, and show high levels of hyperactivity. All of these phenotypes were rescued by atomoxetine, demonstrating noradrenergic mediation of the externalizing effects of adgrl3.1. Transcriptomic analyses of the brains of adgrl3.1-/- vs. wild-type fish revealed several differentially expressed genes and enriched gene clusters that were independent of noradrenergic manipulation. This suggests new putative functional pathways underlying ED-related behaviors, and potential targets for the treatment of ED.

Trans-ancestry meta-analysis of genome wide association studies of inhibitory control

Deficits in effective executive function, including inhibitory control are associated with risk for a number of psychiatric disorders and significantly impact everyday functioning. These complex traits have been proposed to serve as endophenotypes, however, their genetic architecture is not yet well understood. To identify the common genetic variation associated with inhibitory control in the general population we performed the first trans-ancestry genome wide association study (GWAS) combining data across 8 sites and four ancestries (N = 14,877) using cognitive traits derived from the stop-signal task, namely - go reaction time (GoRT), go reaction time variability (GoRT SD) and stop signal reaction time (SSRT). Although we did not identify genome wide significant associations for any of the three traits, GoRT SD and SSRT demonstrated significant and similar SNP heritability of 8.2%, indicative of an influence of genetic factors. Power analyses demonstrated that the number of common causal variants contributing to the heritability of these phenotypes is relatively high and larger sample sizes are necessary to robustly identify associations. In Europeans, the polygenic risk for ADHD was significantly associated with GoRT SD and the polygenic risk for schizophrenia was associated with GoRT, while in East Asians polygenic risk for schizophrenia was associated with SSRT. These results support the potential of executive function measures as endophenotypes of neuropsychiatric disorders. Together these findings provide the first evidence indicating the influence of common genetic variation in the genetic architecture of inhibitory control quantified using objective behavioural traits derived from the stop-signal task.

Divergent risky decision-making and impulsivity behaviors in Lewis rat substrains with low genetic difference

Substance use disorder (SUD) is associated with a cluster of cognitive disturbances that engender vulnerability to ongoing drug seeking and relapse. Two of these endophenotypes-risky decision-making and impulsivity-are amplified in individuals with SUD and are augmented by repeated exposure to illicit drugs. Identifying genetic factors underlying variability in these behavioral patterns is critical for early identification, prevention, and treatment of SUD-vulnerable individuals. Here, we compared risky decision-making and different facets of impulsivity between two fully inbred substrains of Lewis rats-LEW/NCrl and LEW/NHsd. We performed whole genome sequencing of both substrains to identify almost all relevant variants. We observed substantial differences in risky decision-making and impulsive behaviors. Relative to LEW/NHsd, the LEW/NCrl substrain accepts higher risk options in a decision-making task and higher rates of premature responses in the differential reinforcement of low rates of responding task. These phenotypic differences were more pronounced in females than males. We defined a total of ∼9,000 polymorphisms between these substrains at 40× whole genome short-read coverage. Roughly half of variants are located within a single 1.5 Mb region of Chromosome 8, but none impact protein-coding regions. In contrast, other variants are widely distributed, and of these, 38 are predicted to cause protein-coding variants. In conclusion, Lewis rat substrains differ significantly in risk-taking and impulsivity and only a small number of easily mapped variants are likely to be causal. Sequencing combined with a reduced complexity cross should enable identification of one or more variants underlying multiple complex addiction-relevant behaviors. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Assessment of goal-directed behavior and prospective memory in adult ADHD with an online 3D videogame simulating everyday tasks

The diagnosis of ADHD is based on real-life attentional-executive deficits, but they are harder to detect in adults than in children and objective quantitative measures reflecting these everyday problems are lacking. We developed an online version of EPELI 3D videogame for naturalistic and scalable assessment of goal-directed action and prospective memory in adult ADHD. In EPELI, participants perform instructed everyday chores in a virtual apartment from memory. Our pre-registered hypothesis predicted weaker EPELI performances in adult ADHD compared to controls. The sample comprised 112 adults with ADHD and 255 neurotypical controls comparable in age (mean 31, SD = 8 years), gender distribution (71% females) and educational level. Using web-browser, the participants performed EPELI and other cognitive tasks, including Conner's Continuous Performance Test (CPT). They also filled out questionnaires probing everyday executive performance and kept a 5-day diary of everyday prospective memory errors. Self-reported strategy use in the EPELI game was also examined. The ADHD participants' self-ratings indicated clearly more everyday executive problems than in the controls. Differences in the EPELI game were mostly seen in the ADHD participants' higher rates of task-irrelevant actions. Gender differences and a group × gender interaction was found in the number of correctly performed tasks, indicating poorer performance particularly in ADHD males. Discriminant validity of EPELI was similar to CPT. Strategy use strongly predicted EPELI performance in both groups. The results demonstrate the feasibility of EPELI for online assessment and highlight the role of impulsivity as a distinctive everyday life problem in adult ADHD.

Motor impulsivity but not risk-related impulsive choice is associated to drug intake and drug-primed relapse

Introduction

Motor impulsivity and risk-related impulsive choice have been proposed as vulnerability factors for drug abuse, due to their high prevalence in drug abusers. However, how these two facets of impulsivity are associated to drug abuse remains unclear. Here, we investigated the predictive value of both motor impulsivity and risk-related impulsive choice on characteristics of drug abuse including initiation and maintenance of drug use, motivation for the drug, extinction of drug-seeking behavior following drug discontinuation and, finally, propensity to relapse.

Methods

We used the Roman High- (RHA) and Low- Avoidance (RLA) rat lines, which display innate phenotypical differences in motor impulsivity, risk-related impulsive choice, and propensity to self-administer drugs. Individual levels of motor impulsivity and risk-related impulsive choice were measured using the rat Gambling task. Then, rats were allowed to self-administer cocaine (0.3 mg/kg/infusion; 14 days) to evaluate acquisition and maintenance of cocaine self-administration, after which motivation for cocaine was assessed using a progressive ratio schedule of reinforcement. Subsequently, rats were tested for their resistance to extinction, followed by cue-induced and drug-primed reinstatement sessions to evaluate relapse. Finally, we evaluated the effect of the dopamine stabilizer aripiprazole on reinstatement of drug-seeking behaviors.

Results

We found that motor impulsivity and risk-related impulsive choice were positively correlated at baseline. Furthermore, innate high levels of motor impulsivity were associated with higher drug use and increased vulnerability to cocaine-primed reinstatement of drug-seeking. However, no relationships were observed between motor impulsivity and the motivation for the drug, extinction or cue-induced reinstatement of drug-seeking. High levels of risk-related impulsive choice were not associated to any aspects of drug abuse measured in our study. Additionally, aripiprazole similarly blocked cocaine-primed reinstatement of drug-seeking in both high- and low-impulsive animals, suggesting that aripiprazole acts as a D_2/3R antagonist to prevent relapse independently of the levels of impulsivity and propensity to self-administer drugs.

Discussion

Altogether, our study highlights motor impulsivity as an important predictive factor for drug abuse and drug-primed relapse. On the other hand, the involvement of risk-related impulsive choice as a risk factor for drug abuse appears to be limited.

Electrophysiological underpinnings of dysfunctional inhibitory control in adults with attention-deficit/hyperactivity disorder: evidence for reduced NoGo anteriorization

Our aim was to delineate the electrophysiological basis of dysfunctional inhibitory control of adult ADHD via investigating the anteriorization of the P3 component of the event-related brain response associated with the NoGo task condition (i.e., NoGo anteriorization, NGA). NGA is a neurophysiological measure of brain topography for cognitive response control, which indexes an overall shift of the brain's electrical activity in anterior direction towards the prefrontal areas. While the NoGo P3 received considerable attention in the adult ADHD literature, the brain topography of this component, which reflects the inhibitory process, remains largely unaddressed. EEG recordings were obtained during a Go/NoGo task from 51 subjects (n = 26 adult patients with ADHD, n = 25 healthy controls) using a high-density, 128-channel BioSemi ActiveTwo recording system. ADHD patients had significantly lower P3 NGA response compared to controls. The decrease in NGA was related to impulsivity scores as measured by the Conners' Adult ADHD Rating Scale: patients with higher impulsivity scores had significantly lower NGA. Treatment with stimulant medication, as compared to the lack of such treatment, was associated with a correction of the lower NGA response in ADHD patients. The current study revealed a lower NGA in adult ADHD, a finding which is consistent with the inhibitory control and frontal lobe dysfunctions described in the disorder. Our finding of the inverse relationship between NGA and impulsivity suggests that clinically more severe impulsivity is linked to a more pronounced frontal dysfunction in adult ADHD subjects.

Longitudinal Changes of Resting-State Networks in Children With Attention-Deficit/Hyperactivity Disorder and Typically Developing Children

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent childhood neurodevelopmental disorder. Given the profound brain changes that occur across childhood and adolescence, it is important to identify functional networks that exhibit differential developmental patterns in children with ADHD. This study sought to examine whether children with ADHD exhibit differential developmental trajectories in functional connectivity compared with typically developing children using a network-based approach.

METHODS

This longitudinal neuroimaging study included 175 participants (91 children with ADHD and 84 control children without ADHD) between ages 9 and 14 and up to 3 waves (173 total resting-state scans in children with ADHD and 197 scans in control children). We adopted network-based statistics to identify connected components with trajectories of development that differed between groups.

RESULTS

Children with ADHD exhibited differential developmental trajectories compared with typically developing control children in networks connecting cortical and limbic regions as well as between visual and higher-order cognitive regions. A pattern of reduction in functional connectivity between corticolimbic networks was seen across development in the control group that was not present in the ADHD group. Conversely, the ADHD group showed a significant decrease in connectivity between predominantly visual and higher-order cognitive networks that was not displayed in the control group.

CONCLUSIONS

Our findings show that the developmental trajectories in children with ADHD are characterized by a subnetwork involving different trajectories predominantly between corticolimbic regions and between visual and higher-order cognitive network connections. These findings highlight the importance of examining the longitudinal maturational course to understand the development of functional connectivity networks in children with ADHD.

Pharmacological Mechanism of Ketamine in Suicidal Behavior Based on Animal Models of Aggressiveness and Impulsivity: A Narrative Review

Around 700,000 people die from suicide each year in the world. Approximately 90% of suicides have a history of mental illness, and more than two-thirds occur during a major depressive episode. Specific therapeutic options to manage the suicidal crisis are limited and measures to prevent acting out also remain limited. Drugs shown to reduce the risk of suicide (antidepressants, lithium, or clozapine) necessitate a long delay of onset. To date, no treatment is indicated for the treatment of suicidality. Ketamine, a glutamate NMDA receptor antagonist, is a fast-acting antidepressant with significant effects on suicidal ideation in the short term, while its effects on suicidal acts still need to be demonstrated. In the present article, we reviewed the literature on preclinical studies in order to identify the potential anti-suicidal pharmacological targets of ketamine. Impulsive-aggressive traits are one of the vulnerability factors common to suicide in patients with unipolar and bipolar depression. Preclinical studies in rodent models with impulsivity, aggressiveness, and anhedonia may help to analyze, at least in part, suicide neurobiology, as well as the beneficial effects of ketamine/esketamine on reducing suicidal ideations and preventing suicidal acts. The present review focuses on disruptions in the serotonergic system (5-HT_B receptor, MAO-A enzyme), neuroinflammation, and/or the HPA axis in rodent models with an impulsive/aggressive phenotype, because these traits are critical risk factors for suicide in humans. Ketamine can modulate these endophenotypes of suicide in human as well as in animal models. The main pharmacological properties of ketamine are then summarized. Finally, numerous questions arose regarding the mechanisms by which ketamine may prevent an impulsive-aggressive phenotype in rodents and suicidal ideations in humans. Animal models of anxiety/depression are important tools to better understand the pathophysiology of depressed patients, and in helping develop novel and fast antidepressant drugs with anti-suicidal properties and clinical utility.

Leveraging related health phenotypes for polygenic prediction of impulsive choice, impulsive action, and impulsive personality traits in 1534 European ancestry community adults

Impulsivity refers to a number of conceptually related phenotypes reflecting self-regulatory capacity that are considered promising endophenotypes for mental and physical health. Measures of impulsivity can be broadly grouped into three domains, namely, impulsive choice, impulsive action, and impulsive personality traits. In a community-based sample of ancestral Europeans (n = 1534), we conducted genome-wide association studies (GWASs) of impulsive choice (delay discounting), impulsive action (behavioral inhibition), and impulsive personality traits (UPPS-P), and evaluated 11 polygenic risk scores (PRSs) of phenotypes previously linked to self-regulation. Although there were no individual genome-wide significant hits, the neuroticism PRS was positively associated with negative urgency (adjusted R²  = 1.61%, p = 3.6 × 10^-7 ) and the educational attainment PRS was inversely associated with delay discounting (adjusted R²  = 1.68%, p = 2.2 × 10^-7 ). There was also evidence implicating PRSs of attention-deficit/hyperactivity disorder, externalizing, risk-taking, smoking cessation, smoking initiation, and body mass index with one or more impulsivity phenotypes (adjusted R² s: 0.35%-1.07%; FDR adjusted ps = 0.05-0.0006). These significant associations between PRSs and impulsivity phenotypes are consistent with established genetic correlations. The combined PRS explained 0.91%-2.46% of the phenotypic variance for individual impulsivity measures, corresponding to 8.7%-32.5% of their reported single-nucleotide polymorphism (SNP)-based heritability, suggesting a non-negligible portion of the SNP-based heritability can be recovered by PRSs. These results support the predictive validity and utility of PRSs, even derived from related phenotypes, to inform the genetics of impulsivity phenotypes.

Age-dependent effects of tobacco smoke and nicotine on cognition and the brain: A systematic review of the human and animal literature comparing adolescents and adults

Cigarette smoking is often initiated during adolescence and an earlier age of onset is associated with worse health outcomes later in life. Paradoxically, the transition towards adulthood also marks the potential for recovery, as the majority of adolescents are able to quit smoking when adulthood emerges. This systematic review aimed to evaluate the evidence from both human and animal studies for the differential impact of adolescent versus adult repeated and long-term tobacco and nicotine exposure on cognitive and brain outcomes. The limited human studies and more extensive yet heterogeneous animal studies, provide preliminary evidence of heightened fear learning, anxiety-related behaviour, reward processing, nicotinic acetylcholinergic receptors expression, dopamine expression and serotonin functioning after adolescent compared to adult exposure. Effects of nicotine or tobacco use on impulsivity were comparable across age groups. These findings provide novel insights into the mechanisms underlying adolescents' vulnerability to tobacco and nicotine. Future research is needed to translate animal to human findings, with a focus on directly linking a broader spectrum of brain and behavioural outcomes.

Blockade of the orexin 1-receptors and 'cocaine- and amphetamine-regulated transcript' in the nucleus accumbens shell alters impulse control in rats

Impulsivity is a multifaceted construct and alterations in impulsiveness are often associated with psychiatric diseases, including drug addiction and binge eating disorder. Impulse control involves several brain regions. The present study assessed the role of the orexigenic, appetite stimulating neuropeptide orexin (OX) and the anorexigenic, appetite reducing neuropeptide cocaine- and amphetamine-regulated transcript (CART) within the nucleus accumbens shell (NAcSh) in impulse control in rats. The animals were ranked for their trait impulsivity based on a screening in the 5-choice serial reaction time task (5-CSRTT). The rats' performances were analysed after bilateral infusions of the OX 1-receptor antagonist SB-334867 (SB) and CART-antibodies (CART-ABs) into the NAcSh. After SB infusions, there was no change in premature responses observed on average. Further analysis revealed a negative linear correlation between the effect of intra-NAcSh SB infusions on premature responses and trait impulsivity. The effect of SB ranged from an increase, no change to a decrease in premature responses in the individual animals with increasing trait impulsivity. Infusions of CART-ABs led to consistently enhanced impulse control with fewer irrelevant actions, independent of trait impulsivity. These data suggest that both OX, especially OX A, and CART in the NAcSh, can be considered endogenous regulators of impulsive action, dependent on underlying impulsivity in the case of OX and independent from trait impulsivity in the case of CART.

A behavioral timing intervention upregulates striatal serotonergic markers and reduces impulsive action in adult male mice

Many studies support the hypothesis that time-based interventions reduce impulsive behavior in rodents. However, few studies have directly assessed 1) how such interventions affect impulsive action rather than impulsive choice, 2) if intervention effects differ by sex, and 3) how time-based interventions affect neurochemistry in regions mediating decision-making and reward. Thus, we assessed how a fixed-interval (FI) intervention initiated during late adolescence and extending into adulthood affected dopaminergic and serotonergic analytes in the frontal cortex and striatum and subsequent impulsive action in adult male and female mice. Beginning on postnatal day (PND) 45, mice were either trained on a progressive series of FI schedules (FI 20, 40, & 60 s) or remained in the home cage. Following the intervention, increases in striatal serotonergic analytes were found in FI-exposed males and females (n = 8/sex/group) with few changes found in the frontal cortex. Impulsive action was assessed in the remaining mice (n = 10/sex/group) using a fixed-ratio waiting-for-reward (FR-wait) task in which completion of an FR-25 component initiated a "free" pellet component in which pellets were delivered at increasing intervals according to a fixed delay increment that varied across sessions. Responses reset the additive delay and initiated a new FR-25 component. FI-exposed males, but not females, showed fewer delay resets and no-wait resets relative to control mice. Importantly, FI-exposure did not affect discrimination reversal performance in either sex. These data suggest that time-based interventions may reduce impulsive action in addition to impulsive choice perhaps with increased male sensitivity. Additionally, time-based interventions appear to operate through striatal serotonergic augmentation.

Previous experience with delays affects delay discounting in animal model of ADHD

BACKGROUND

ADHD is a disorder where a common symptom is impulsive behaviour, a broad term associated with making sub-optimal choices. One frequently used method to investigate impulsive behaviour is delay discounting, which involves choosing between a small, immediate reinforcer and a delayed, larger one. Choosing the small immediate reinforcer is by itself, however, not sufficient for terming the choice impulsive, as all organisms eventually switch to choosing the small, immediate reinforcer when the delay to the larger reinforcer becomes long. This switch can be termed impulsive only when it occurs more frequently, or at shorter LL delays, than typically observed in normal controls. A poorly understood aspect is how choice is influenced by previous experience with delays. Using an animal model of Attention-Deficit/Hyperactivity Disorder, the Spontaneously Hypertensive Rat, we manipulated the order of exposure to delays in a delay discounting task. Following a preference test, the Ascending group experienced gradually increasing delays between choice and reinforcer while the Descending group were exposed to these delays in reverse order.

RESULTS

The results showed that the Descending group chose the small, immediate reinforcer over the larger delayed to a much larger extent than the Ascending group, and continued to do so even when the delay component was ultimately removed. Strain effects were found in the Ascending group, with SHRs switching to the small, immediate reinforcer earlier than controls as the delay to the larger reinforcer increased.

CONCLUSION

The data suggests that delay discounting is affected by history of exposure to delayed consequences. When reinforcement contingencies are incrementally changed from having no response-reinforcer delay to a long delay, discounting of delayed consequences is gradual. However, a sudden change from no delay to a long delay, without intermediate training, results in a rapid switch to the small, immediate reinforcer option, and this behaviour is somewhat resilient to the shortening and eventual removal of the large reinforcer delay. The implication is that attempting to reduce already existing impulsive behaviour in children with ADHD will require gradual habituation and not sudden changes in reinforcement contingencies.