Attention-deficit hyperactivity disorder and cardiac vagal control: a systematic review

Methylphenidate Improves Autonomic Functioning among Youth with Attention-Deficit/Hyperactivity Disorder

Psychostimulants are commonly prescribed medications for youth with attention-deficit/hyperactivity disorder (ADHD). Limited studies have evaluated how psychostimulants (e.g., methylphenidate [MPH]) impact autonomic nervous system (ANS) indexes among youth with ADHD. Understanding the effects of MPH on autonomic functioning is essential, given that youth with ADHD have been shown to experience atypical autonomic functioning (i.e., reduced activity across both sympathetic and parasympathetic branches) compared to typically developing youth. The current study investigated how a specific psychostimulant, Osmotic Release Oral System [OROS] MPH, impacts parasympathetic (indexed by respiratory sinus arrhythmia [RSA]) and sympathetic (indexed by electrodermal activity [EDA]) functioning among youth with ADHD via a within-subjects, double-masked, cross-over design. Two hundred fifty-six participants (157 youth with ADHD), ages 5 to 13 years, completed a two-minute resting baseline task while electrocardiograph and electrodermal data were obtained. Youth with ADHD completed the resting baseline task twice, 3 weeks apart, once during active medication and once during placebo conditions (counterbalanced). Typically developing youth were assessed without medication or placebo. Youth with ADHD during the placebo condition exhibited reduced RSA and EDA compared to typically developing youth. In contrast, youth with ADHD during the medication condition did not differ significantly from typically developing youth with respect to either RSA nor EDA. As such, OROS MPH appears to normalize RSA and EDA levels among youth with ADHD to levels comparable to typically developing youth. Future studies including indexes of the ANS among youth with ADHD are urged to consider the impact of MPH.

The Physiologic and Emotional Effects of 360-Degree Video Simulation on Head-Mounted Display Versus In-Person Simulation: A Noninferiority, Randomized Controlled Trial

INTRODUCTION

A key simulation component is its capability to elicit physiological changes, improving recall. The primary aim was to determine whether parasympathetic responses to head-mounted display simulations (HMDs) were noninferior to in-person simulations. The secondary aims explored sympathetic and affective responses and learning effectiveness.

METHODS

The authors conducted a noninferiority trial. Hospital providers who did not use chronotropic medications, have motion sickness, or have seizures were included. The authors randomized participants to in-person or HMD simulation. Biometric sensors collected respiratory sinus arrhythmia and skin conductance levels to measure parasympathetic and sympathetic states at baseline, during, and after the simulation. Affect was measured using a schedule. The authors measured 3-month recall of learning points and used split-plot analysis of variance and Mann-Whitney U tests to analyze.

RESULTS

One hundred fifteen participants qualified, and the authors analyzed 56 in each group. Both groups experienced a significant change in mean respiratory sinus arrhythmia from baseline to during and from during to afterward. The difference of change between the groups from baseline to during was 0.134 (95% confidence interval = 0.142 to 0.410, P = 0.339). The difference of change from during the simulation to after was -0.060 (95% confidence interval = -0.337 to 0.217, P = 0.670). Noninferiority was not established for either period. Sympathetic arousal did not occur in either group. Noninferiority was not established for the changes in affect that were demonstrated. The mean scores of teaching effectiveness and achievement scores were not different.

CONCLUSIONS

Although a parasympathetic and affective response to the video simulation on an HMD did occur, it was not discernibly noninferior to in-person in this study.

Childhood ADHD, Going Beyond the Brain: A Meta-Analysis on Peripheral Physiological Markers of the Heart and the Gut

Attention-Deficit/Hyperactivity Disorder (ADHD) is the most common neurodevelopmental disorder diagnosed in children. Questions regarding its increased diagnostic rates and pharmacological treatments in developing children have led to a more holistic review of the multi-system pathophysiology observed in ADHD. The dopaminergic neurotransmitter system, known for its influence on reward-motivated behaviors and motor control, and the frontostriatal systems, that mediate motor, cognition, and behavior, are associated with ADHD's development. However, studies have shown that these neural systems do not wholly account for ADHD's multilayered and heterogeneous symptom presentation. For instance, the literature suggests that emotional dysregulation, the inability to regulate one's emotional responses to provoking stimuli, is associated with increased risk for social impairment in ADHD. A broader examination of physiological systems in children with ADHD has found potential markers in the heart-brain and gut-brain axes that correspond with certain behaviors associated with emotional dysregulation in recent studies. Hence, the purpose of this meta-analysis is to aggregate ten applicable published case studies and analyze task-related heart rate reactivity (HRR; n = 5 studies) and gut microbiota (n = 5 studies) data in children with and without ADHD. Data from a total of 531 youth with ADHD and 603 youth without ADHD revealed significant small and medium effect sizes for higher Chao1 levels and Actinobacteria levels in the ADHD group, respectively, but no evidence of altered task-related HRR. Thus, further research into multi-system psychophysiological measures of emotional dysregulation and ADHD is warranted. The clinical, empirical, and educational implications of these findings are discussed.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier PROSPERO (CRD42021236819).

Cardiovascular reactivity as a measure of irritability in a transdiagnostic sample of youth: Preliminary associations

OBJECTIVES

Irritability is a transdiagnostic symptom in developmental psychopathology, conceptualized as a low threshold for frustration and increased proneness to anger. While central to emotion regulation, there is a vital need for empirical studies to explore the relationship between irritability and underlying physiological mechanisms of cardiovascular arousal.

METHODS

We examined the relationship between irritability and cardiovascular arousal (i.e., heart rate [HR] and heart rate variability [HRV]) in a transdiagnostic sample of 51 youth (M = 12.63 years, SD = 2.25; 62.7% male). Data was collected using the Empatica E4 during a laboratory stop-signal task. In addition, the impact of motion activity, age, medication, and sleep on cardiovascular responses was explored.

RESULTS

Main findings showed that irritability was associated with increased HR and decreased HRV during task performance.

CONCLUSIONS

Findings support the role of peripheral physiological dysregulation in youth with emotion regulation problems and suggest the potential use of available wearable consumer electronics as an objective measure of irritability and physiological arousal in a transdiagnostic sample of youth.

Characterizing change in vagal tone during the first three years of life: A systematic review and empirical examination across two longitudinal samples

Functioning of the parasympathetic nervous system (PNS), most often indexed by respiratory sinus arrhythmia (RSA), influences the volitional, cognitively-mediated forms of self-regulation across development. However, despite its clear relevance to children's self-regulation, and its utility as a transdiagnostic biomarker of emotion dysregulation and psychopathology, the ontogeny of vagal tone under conditions of homeostasis across infancy and early childhood is not well understood. The current research is comprised of two complementary studies. The first aims to address this gap by conducting a systematic review of the literature which has assessed resting RSA in the first three years of life. The second study uses data from two diverse, longitudinal datasets (n = 203 and n = 370) to model change in RSA from infancy to toddlerhood. Results from a systematic review of 62 studies meeting inclusion criteria suggest that measures of resting RSA increase over time and demonstrate moderate stability across infancy, toddlerhood, and preschool ages. Results from a series of models fit to longitudinal data in study two suggest that baseline RSA is characterized by stable increases across infancy and early childhood. Moreover, although there was equivocal evidence for individual variability in trajectories of RSA, the findings suggest that the individual differences in resting RSA may become entrenched in early life based on observed significant variance in growth model intercepts. In all, the current study contributes to our understanding of the developmental trajectories of baseline RSA across infancy and early childhood and should support future research examining links between children's parasympathetic regulation and their adjustment in early life.

Impact of stress and parenting on respiratory sinus arrythmia trajectories in early adolescence

The effects of stress and parenting on 1-year trajectories of physiological emotion regulation capacity among adolescents were examined. Consistent with the vulnerability-stress and allostatic load models, stress (chronic family and marital) was hypothesized to be associated with less favorable trajectories of basal respiratory sinus arrhythmia (RSA) over 1 year. This relationship was further hypothesized to be moderated by parenting practices (warmth, neglect, and rejection) and adolescent sex. Participants included 150 adolescents (51.3% female), 11-15 years of age (M = 13.04, SD = 0.89). Basal RSA and stress were assessed four times across 1 year. Results indicated a significant decrease in RSA over the course of 1 year (β = -0.15, p = .010). Warm parenting style was associated with lower RSA in environments of low marital stress and was also related with higher RSA in environments of high marital stress (β = 0.86, p = .021). Rejecting parenting styles were associated with higher RSA in environments of low family stress and lower RSA in environments of high family stress (β = -0.60, p = .014). These findings may be explained by the Yerkes-Dodson law of optimal stress, suggesting that sufficient environmental challenge is needed to catalyze regulatory development.

Brain structure and parasympathetic function during rest and stress in young adult women

Heart rate variability (HRV) is an important biomarker for parasympathetic function and future health outcomes. The present study examined how the structure of regions in a neural network thought to maintain top-down control of parasympathetic function is associated with HRV during both rest and social stress. Participants were 127 young women (90 Black American), who completed a structural MRI scan and the Trier Social Stress Test (TSST), during which heart rate was recorded. Regression analyses were used to evaluate associations between cortical thickness in five regions of the Central Autonomic Network (CAN; anterior midcingulate cortex [aMCC], pregenual and subgenual anterior cingulate cortex [pgACC, sgACC], orbitofrontal cortex [OFC], and anterior insula) and high-frequency HRV during rest and stress. Results indicated that cortical thickness in CAN regions did not predict average HRV during rest or stress. Greater cortical thickness in the right pgACC was associated with greater peak HRV reactivity during the TSST, and survived correction for multiple comparisons, but not sensitivity analyses with outliers removed. The positive association between cortical thickness in the pgACC and peak HRV reactivity is consistent with the direction of previous findings from studies that examined tonic HRV in adolescents, but inconsistent with findings in adults, which suggests a possible neurodevelopmental shift in the relation between brain structure and autonomic function with age. Future research on age-related changes in brain structure and autonomic function would allow a more thorough understanding of how brain structure may contribute to parasympathetic function across neurodevelopment.

Possible links between gut-microbiota and attention-deficit/hyperactivity disorders in children and adolescents

An association between gut-microbiota and several neuropsychiatric conditions including autism, depression, anxiety, schizophrenia, and attention-deficit/hyperactivity disorder (ADHD) has been observed. Despite being the most prevalent neurodevelopmental disorders in children and adolescents worldwide, the etiology and curative approaches to treatment of ADHD remain unclear. There is a probability that gut-microbiota may contribute to ADHD via bidirectional communication between the gut and brain, a system known as the "gut-brain axis". Although a mechanistic link in the gut-brain axis in ADHD has been proposed, there is still a lack of information about the correlation of the microbiome profile with the mechanisms involved. The objective of this review was to summarize the diversity of the gut-microbiota and taxonomic profiles in children and adolescents with ADHD. In this review, we have provided an overview of the association between ADHD and gut-microbiota. The evidence pertinent to potentially distinctive gut-microbiota in children and adolescents with ADHD is also discussed and compared to that of their non-ADHD peers. Finally, the implications and future directions for investigation into the gut microbiome in ADHD patients are proposed.

Response Inhibition, Response Execution, and Emotion Regulation among Children with Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) is associated with deficits in response inhibition, response execution, and emotion regulation. However, the nature of the associations among these deficits remains unclear. Thus, this study examines these associations using a multi-method design. One hundred sixty-six children (aged 5-13 years; 66.3% male; 75 with ADHD) completed two conditions (i.e., neutral and fear) of an emotional go/no-go task. Parasympathetic-based regulation was indexed via respiratory sinus arrhythmia (RSA), and sympathetic-based reactivity was indexed via cardiac pre-ejection period (PEP). Overall, children exhibited more difficulty with response execution (i.e., more omission errors, fewer correct go responses) and less difficulty with response inhibition (i.e., fewer commission errors, more correct no-go responses) during the fear condition than the neutral condition. Children with ADHD displayed more difficulty with response execution during the fear condition compared to typically developing youth. Additionally, children with ADHD displayed parasympathetic-based dysregulation (i.e., RSA increase from baseline) and reduced sympathetic-based reactivity (i.e., PEP lengthening) compared to typically developing youth across task conditions. In sum, children with ADHD demonstrate greater difficulty with response execution during emotionally salient contexts, as well as parasympathetic-based emotion dysregulation. Future work should examine these associations longitudinally with the aim of predicting impairment and treatment response in youth with ADHD.

Z-Score Neurofeedback and Heart Rate Variability Training for Adults and Children with Symptoms of Attention-Deficit/Hyperactivity Disorder: A Retrospective Study

ADHD is a common condition that causes suffering for those affected and economic loss for society at large. The current standard treatment for ADHD includes stimulant medications, which are not effective for all patients, may include side effects, and can be non-medically misused. Z-score neurofeedback (NFB) and heart rate variability (HRV) biofeedback are alternative treatment strategies that have been associated with Attention-Deficit/Hyperactivity Disorder (ADHD) symptom improvement. We utilized a retrospective pre-post study design to quantify the change in clients' ADHD symptoms after combined NFB + HRV treatment (which included simultaneous z-score training at four sites). We also assessed whether relevant physiological measures changed in accordance with the protocol, which would be consistent with effective NFB + HRV training. Adults (n = 39) and children (n = 100) with Borderline or Clinical ADHD classifications by the Achenbach System of Empirically Based Assessment (ASEBA) received 30 sessions of NFB + HRV training. Measures were compared before and after treatment for the ASEBA, the Integrated Visual and Auditory Continuous Performance Test (IVA), ADHD medication use, HRV and breathing parameters, and quantitative electroencephalogram (QEEG) parameters. Average ASEBA Attention-Deficit/Hyperactive Problems score improved after treatment for adults and children (p < 0.0001), with Cohen effect sizes (dz) of -1.21 and -1.17, respectively. 87.2% of adults and 80.0% of children experienced improvements of a magnitude greater than or equal to the Minimal Clinically Important Difference. After treatment, 70.8% of adults and 52.8% of children who began in the ASEBA Clinical range, and 80.0% of adults and 63.8% of children who began in the ASEBA Borderline range, were classified in the Normal range. IVA scores also improved after treatment. Changes in HRV and breathing pattern after treatment were consistent with the protocol. QEEG parameters after treatment were closer to the age-based normative mean, which is consistent with effective z-score NFB training.

The Role of the Gut-Brain Axis in Attention-Deficit/Hyperactivity Disorder

Genetic and environmental factors play a role in the cause and development of attention-deficit/hyperactivity disorder (ADHD). Recent studies have suggested an important role of the gut-brain axis (GBA) and intestinal microbiota in modulating the risk of ADHD. Here, the authors provide a brief overview of the clinical and biological picture of ADHD and how the GBA could be involved in its cause. They discuss key biological mechanisms involved in the GBA and how these may increase the risk of developing ADHD. Understanding these mechanisms may help to characterize novel treatment options via identification of disease biomarkers.

Effects of manual cranial therapy on heart rate variability in children without associated disorders: Translation to clinical practice

BACKGROUND

and purpose: Heart rate variability (HRV) represents a marker of autonomic activity, self-regulation and psychiatric illness. Few studies of manual therapy have investigated the neurophysiological effects of manual cranial therapy (MC-t). This study assessed the neurophysiological short/medium-term effects of two manual therapy interventions: massage therapy (Mss-t) and MC-t.

MATERIALS AND METHODS

A double-blind clinical trial was conducted with 50 healthy children, randomized into two groups who received a Mss-t intervention or MC-t. The variables analysed included vital signs (temperature, respiratory rate, heart rate, blood pressure) and HRV components, including the root mean square of successive differences (RMSSD), high frequency (HF), low frequency (LF) and LF/HF ratio.

RESULTS

Both interventions produced short-term parasympathetic effects, although the effects of MC-t were more persistent.

CONCLUSION

The persistence of the MC-t intervention suggested a prominent vagal control and better self-regulation. Autonomic imbalances in mental pathologies may benefit from the neurophysiological effects of MC-t.

Stress and parenting predict changes in adolescent respiratory sinus arrhythmia

Adolescence is a critical period for the development of physiological emotion regulatory systems. While stressful life experiences are known to inhibit adaptive regulation, less is known about how parental socialization of emotion regulation may affect this relation. We examined the effect of stressful life experiences on changes in the resting respiratory sinus arrhythmia (RSA) levels of 107 (M_age  = 12.84, SD = 0.85) young adolescents over a year, moderated by supportive parental responses to negative emotions. The significant interaction (B = 0.02, p = 0.04) indicated that young adolescents who experienced low levels of supportive parenting in the context of high levels of stressful life experiences showed significant decreases in resting RSA over the year, while adolescents who experienced high levels of supportive parenting showed minimal decreases in RSA. Thus, more supportive parenting significantly compensated for the effect of greater stressful life experiences on changes in resting RSA over time.

Complex cardiac vagal regulation to mental and physiological stress in adolescent major depression

BACKGROUND

Cardiovagal control is known to be reduced in major depressive disorder (MDD), however, the neurocardiac reflex control to distinct types of stressors is still unclear. We aimed to study parasympathetically mediated cardiac reflex functioning in response to mental and physiological stressors using heart rate variability (HRV) linear and nonlinear analysis in adolescent MDD.

METHODS

We examined 60 adolescents (40 girls) with MDD (age 14.9 ± 0.3 years) and 60 age and gender-matched controls. ECG was continuously recorded during stress protocol: baseline, Go/NoGo test, recovery, supine position, and orthostasis. Evaluated HRV linear and nonlinear indices: RR interval, pNN50, rMSSD, HF-HRV, Poincaré plot (SD1), symbolic dynamics 2UV%. Cardiovagal reactivity expressed as percentual change (%) was calculated in response to both stressors.

RESULTS

In each phase of stress protocol, the MDD group had significantly reduced HRV parameters compared to controls, except for symbolic dynamics index 2UV% in supine position. The reactivity of HRV indices was significantly greater in response to orthostasis in MDD compared to controls. No significant differences were found in response to Go/NoGo test.

LIMITATIONS

The smoking status and the menstrual cycle phase potentially affecting the HRV parameters were not monitored. Future research is needed to expand a sample size with respect to sex and to study neurocardiac response to other different stressors in MDD.

CONCLUSIONS

This study revealed reduced resting cardiovagal regulation and greater vagal withdrawal indicating abnormal neurocardiac reflex functioning to physiological stressor (orthostasis) in adolescent MDD patients. Nonlinear HRV analysis was sensitive to detect cardiac-linked regulatory differences in adolescent depression.

Mean Heart Rate and Parameters of Heart Rate Variability in Depressive Children and the Effects of Antidepressant Medication

Introduction: Researchers have repeatedly discovered an association between depression and autonomic cardiac dysregulation in adults. However, corresponding data concerning minors are still rare. Method: For this exploratory, cross-sectional study, we included N = 43 minors (age range 9-17 years). The subjects were depressive subjects with or without antidepressant medication (N = 23) or healthy control children (HC) (N = 20). We assessed several indices of cardiac functioning using long-term electrocardiogram data (mean heart rate, HR, and several parameters of heart rate variability, HRV). We hypothesized that increased HR and reduced HRV are associated with depressive disorders. Furthermore, we assessed the impact of age, sex, and antidepressant medication on HR and HRV. Results: When sex and age were controlled for, HR was significantly increased in depressive minors compared to HC. However, our preliminary data suggest that this might not be the case in medicated patients, and there were no differences between groups regarding HRV parameters. There was no significant correlation in the whole sample between severity of depression and both HR and HRV. In the subsample of patients with depression, antidepressant medication was associated with lower HR and higher indices of HRV. Conclusion: The data indicate an association between depression and altered autonomic cardiac regulation, which can already manifests in minors.

Reduced heart rate variability in adults with autism spectrum disorder

A growing body of research has suggested heart rate variability (HRV) may be reduced in autism spectrum disorder (ASD) in comparison to neurotypical cohorts. While there have been several studies investigating HRV in children diagnosed with ASD, few studies have been conducted in adults. The objective of the current study was to investigate autonomic nervous system activity as assessed by HRV in adults diagnosed with ASD. We hypothesized that adults with ASD would show a reduction in HRV compared to neurotypical participants. Participants diagnosed with ASD (n = 55) were recruited from the Autism Clinic for Translational Research at the Brain and Mind Centre (University of Sydney) between 2013 and 2017. Neurotypical participants were recruited from advertisements and online media. Resting state heart rate was measured for 5 min while participants sat in an upright position. Results showed there was an overall significant difference in resting-state HRV between adults diagnosed with ASD compared to the neurotypical control group. Logarithmically transformed high frequency (HF) and root mean square of successive differences were particularly decreased in the ASD group, suggesting lower parasympathetic activity. The use of psychotropic medications and comorbidities were associated with reductions in low frequency of HRV. Our data suggest an overall dysregulation in resting autonomic activity in adults with ASD. This may represent an important physiological mechanism leading to potential cardiovascular risk in ASD, which warrants further investigation. Autism Res 2019, 12: 922-930. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: ASD is commonly associated with a range of physical and mental health comorbidities. Autonomic disruptions underlying reductions in heart rate variability (HRV) have been linked to a range of mental and physical health conditions. We assessed resting-state HRV in adults diagnosed with ASD in comparison to healthy individuals. Our results showed reduced heart rate variability in people diagnosed with ASD compared to adults without ASD. These findings implicate a role for autonomic activity as a potentially modifiable risk factor for ASD.

Parent Emotion Expression and Autonomic-Linked Emotion Dysregulation in Childhood ADHD

Despite evidence that ADHD is associated with disruptions in emotion regulation, few studies have examined the biological correlates of emotion dysregulation among children with this disorder. Prior work has pointed to roles of the parasympathetic and sympathetic nervous system, as indexed via respiratory sinus arrhythmia (RSA) and cardiac pre-ejection period (PEP), respectively. Work in typically developing populations suggests that parenting behavior and parental emotion expression may shape the development of these systems. To date, a single study has examined the independent and interactive roles of autonomic nervous system functioning and parent emotion expression in youth with ADHD. This study seeks to extend that work. 86 children (42 with ADHD), aged 8-12 years, and a parent completed a parent-child interaction task, while electrocardiography and impedance cardiography data were recorded to derive RSA and PEP. Parent and child emotion word use (positive and negative valence) were coded from recordings of the task. Parents of youth with ADHD used fewer positive emotion words throughout the task. Additionally, throughout the task, children with ADHD engaged in excessive RSA withdrawal from baseline. Further, the association between RSA reactivity and ADHD diagnosis was moderated by parent positive emotion word use. Specifically, those with RSA augmentation and parents displaying high positive affect across the task conditions were least likely to have an ADHD diagnosis. If replicated and extended, these results support the use of interventions specifically designed to increase parental modeling of positive emotions, while simultaneously focusing on building emotion regulation skills in youth with ADHD.

Specificity of Reward Sensitivity and Parasympathetic-Based Regulation among Children with Attention-Deficit/Hyperactivity and Disruptive Behavior Disorders

Attention-deficit/hyperactivity disorder (ADHD) is associated with disruptionsin reward sensitivity and regulatory processes. However, it is unclear whether thesedisruptions are better explained by comorbid disruptive behavior disorder (DBD)symptomology. This study sought to examine this question using multiple levels ofanalysis (i.e., behavior, autonomic reactivity). One hundred seventeen children (aged 6 to 12 years; 72.6% male; 69 with ADHD) completed theBalloon-Analogue Risk Task (BART) to assess external reward sensitivity behaviorally.Sympathetic-based internal reward sensitivity and parasympathetic-based regulationwere indexed via cardiac pre-ejection period (PEP) and respiratory sinus arrhythmia(RSA), respectively. Children with ADHD exhibited reduced internal reward sensitivity (i.e.,lengthened PEP; F(1,112)=4.01, p=0.047) compared to healthy controls and werecharacterized by greater parasympathetic-based dysregulation (i.e., reduced RSAaugmentation F(1,112)=10.12, p=0.002). However, follow-up analyses indicated theADHD effect was better accounted for by comorbid DBD diagnoses; that is, childrenwith ADHD and comorbid ODD were characterized by reduced internal rewardsensitivity (i.e., lengthened PEP; t=2.47, p=0.046) and by parasympathetic-baseddysregulation (i.e., reduced RSA augmentation; t=3.51, p=0.002) in response to rewardwhen compared to typically developing youth. Furthermore, children with ADHD and comorbid CD exhibited greater behaviorally-based external reward sensitivity (i.e.,more total pops; F(3,110)= 5.96, p=0.001) compared to children with ADHD only (t=3.87, p=0.001) and children with ADHD and ODD (t=3.56, p=0.003). Results suggest that disruptions in sensitivity to reward may be betteraccounted for, in part, by comorbid DBD.Key Words: attention-deficit/hyperactivity disorder, autonomic nervous system,disruptive behavior disorders, reward sensitivityPowered.

Respiratory sinus arrhythmia as a non-invasive index of 'brain-heart' interaction in stress

Respiratory sinus arrhythmia (RSA) is accepted as a peripheral marker of cardiac-linked parasympathetic regulation. According to polyvagal theory, the RSA is also considered as the index of emotion regulation. The neurovisceral integration model posits that parasympathetic modulation of the heart marked by RSA is related to complex nervous regulation associated with emotional and cognitive processing. From this perspective, high resting RSA amplitude associated with a greater withdrawal during stressors and subsequent recovery could represent a flexible and adaptive physiological response system to a challenge. Conversely, low resting RSA accompanied by an inadequate reactivity to stress might reflect maladaptive regulatory mechanisms. The RSA reactivity is different with various types of stressors: while the RSA decreases to cognitive tasks indicating a vagal withdrawal, the RSA magnitude increases to emotional challenge indicating an effective cognitive processing of emotional stimuli. The RSA reactivity to stress could have important implications for several mental disorders, e.g. depressive or anxiety disorder. It seems that the study of the RSA, as a non-invasive index of ‘brain-heart’ communication, could provide important information on the pathway linked to mental and physical health.

Clinical features and subjective/physiological responses to emotional stimuli in the presence of emotion dysregulation in attention-deficit hyperactivity disorder

INTRODUCTION

Emotion dysregulation (ED) has long been recognized in clinical descriptions of attention-deficit hyperactivity disorder (ADHD), but a renewed interest in ED has advanced research on the overlap between the two entities. Autonomic reactivity (AR) is a neurobiological correlate of emotion regulation; however, the association between ADHD and AR remains unclear. Our aim was to explore the clinical differences, AR, and subjective emotional responses to visual emotional stimuli in ADHD children with and without ED.

METHOD

School-aged ADHD children with (n = 28) and without (n = 20) ED, according to the definition of deficiency in emotional self-regulation (DESR), and healthy controls (n = 22) were interviewed by using the Schedule for Affective Disorders and Schizophrenia for School Aged Children-Present and Lifetime version (K-SADS-PL) to screen frequent psychopathologies for these ages. All subjects were evaluated with Child Behavior Checklist 6-18 (CBCL), the Strengths and Difficulties Questionnaire (SDQ), the McMaster Family Assessment Device (FAD), the School-Age Temperament Inventory (SATI), and Conners' Parent Rating Scale (CPRS-48), which were completed by parents. To evaluate emotional responses, the International Affective Picture System (IAPS) and the subjective and physiological responses (electrodermal activity and heart rate reactivity) to selected pictures were examined.

RESULTS

Regarding clinically distinctive features, the ADHD+ED group differed from the ADHD-ED and the control groups in terms of having higher temperamental negative reactivity, more oppositional/conduct problems, and lower prosocial behaviors. In the AR measures, children in the ADHD+ED group rated unpleasant stimuli as more negative, but they still had lower heart rate reactivity (HRR) than the ADHD-ED and control groups; moreover, unlike the two other groups, the ADHD+ED group showed no differences in HRR between different emotional stimuli.

CONCLUSION

The presented findings are unique in terms of their ability to clinically and physiologically differentiate between ADHD children with and without ED.

Resting state vagal tone in attention deficit (hyperactivity) disorder: A meta-analysis

OBJECTIVES

To quantify evidence on resting-state vagal activity in patients with attention deficit hyperactivity disorder (ADHD) relative to controls using meta-analysis.

METHODS

Three electronic databases (PubMed, PsycINFO, CINAHL Plus) were reviewed to identify studies. Studies reporting on any measure of short-term, vagally mediated heart rate variability during resting state in clinically diagnosed ADHD patients as well as non-ADHD healthy controls were eligible for inclusion.

RESULTS

Eight studies reporting on 587 participants met inclusion criteria. Random-effect meta-analysis revealed no significant main effect comparing individuals with ADHD (n = 317) and healthy controls (n = 270) (Hedges' g = 0.06, 95% CI: 0.18-0.29, Z = 0.48, P = 0.63; k = 8). Sub-group analysis showed consistent results among studies in adults (k = 2) and children (k = 6) with ADHD.

CONCLUSIONS

Unlike a variety of internalising psychiatric disorders, ADHD is not associated with altered short-term measures of resting-state vagal tone.

Quantifying respiratory sinus arrhythmia: Effects of misspecifying breathing frequencies across development

Low resting respiratory sinus arrhythmia (RSA), and to a lesser extent excessive RSA reactivity to emotion evocation, are observed in many psychiatric disorders characterized by emotion dysregulation, including syndromes spanning the internalizing and externalizing spectra, and other conditions such as nonsuicidal self-injury. Nevertheless, some inconsistencies exist. For example, null outcomes in studies of RSA–emotion dysregulation relations are sometimes observed among younger participants. Such findings may derive from use of age inappropriate frequency bands in calculating RSA. We combine data from five published samples (N = 559) spanning ages 4 to 17 years, and reanalyze RSA data using age-appropriate respiratory frequencies. Misspecifying respiratory frequencies results in overestimates of resting RSA and underestimates of RSA reactivity, particularly among young children. Underestimates of developmental shifts in RSA and RSA reactivity from preschool to adolescence were also observed. Although correlational analyses revealed weak negative associations between resting RSA and aggression, those with clinical levels of externalizing exhibited lower resting RSA than their peers. No associations between RSA reactivity and externalizing were observed. Results confirm that age-corrected frequency bands should be used when estimating RSA, and that literature-wide overestimates of resting RSA, underestimates of RSA reactivity, and underestimates of developmental shifts in RSA and RSA reactivity may exist.

Attention-deficit/hyperactivity disorder symptoms and stress-related biomarkers

OBJECTIVE

The current study examined whether (a) Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms were associated with dysregulation of stress-related mechanisms, and (b) whether ADHD symptoms interact with affective disorders in their association with dysregulated stress-related mechanisms.

METHODS

Data were obtained from 2307 subjects participating in the Netherlands Study of Depression and Anxiety. Stress-related mechanisms were reflected by the following biomarkers: (1) hypothalamic-pituitary-adrenal axis indicators (salivary cortisol awakening curve, evening cortisol, cortisol suppression after a 0.5mg dexamethasone suppression test (DST)); (2) autonomic nervous system measures (heart rate, pre-ejection period, respiratory sinus arrhythmia); (3) inflammatory markers (C-reactive protein, interleukin-6, tumor necrosis factor-alpha); (4) brain-derived neurotrophic factor. ADHD symptoms were measured using Conners' Adult ADHD Rating Scale and used both dichotomous (High ADHD symptoms (yes/no)) and continuous (Inattentive symptoms, Hyperactive/Impulsive symptoms, and the ADHD index).

RESULTS

Regression analyses showed associations between High ADHD symptoms, Inattentive symptoms, the ADHD index and a higher cortisol awakening curve, between Hyperactive/Impulsive symptoms and less cortisol suppression after DST, and between Inattentive symptoms and a longer pre-ejection period. However, the associations with the cortisol awakening curve disappeared after adjustment for depressive and anxiety disorders. No associations were observed between ADHD symptoms and inflammatory markers or BDNF. ADHD symptoms did not interact with affective disorders in dysregulation of stress-related mechanisms.

CONCLUSION

Some associations were observed between ADHD symptoms, the HPA-axis, and the pre-ejection period, but these were mostly driven by depressive and anxiety disorders. This study found no evidence that ADHD symptomatology was associated with dysregulations in inflammatory markers and BDNF. Consequently, ADHD symptoms did not confer an added risk to the disturbances of stress-related mechanisms in an - already at-risk - population with affective disorders.

Altered Pre-Ejection Period Response to Social Evaluative Threat in Adolescents with Autism Spectrum Disorder

INTRODUCTION

The autonomic nervous system (ANS) is involved in regulating social behavior; Autism Spectrum Disorder (ASD) is characterized by alterations in social behavior and reduced physiological response to threat. We hypothesized that adolescents with ASD would show reduced ANS response to social threat.

METHODS

Eighteen males with ASD and thirteen males with typical development (TD), ages 12 to 17, completed a social threat paradigm while wearing an impedance cardiography apparatus. We calculated pre-ejection period (PEP) and tested for between-group differences in PEP response to social threat. We also conducted correlation analyses between PEP change scores and clinical symptom scales.

RESULTS

There was an effect of diagnosis on change in PEP from baseline to the onset of social threat (F=7.60, p=0.01), with greater changes in PEP in TD compared to ASD. PEP change score and the Social Communication Questionnaire (r=0.634, p=0.005) and the ADHD Problems Subscale of the Child Behavior Checklist (r=0.568, p=0.014) were correlated.

CONCLUSIONS

These findings suggest reduced arousal in response to social threat in ASD, with preliminary evidence that reduced sympathetic activation is associated with increased social behavior symptoms.

Blood pressure and anthropometry in children treated with stimulants: a longitudinal cohort study with an individual approach

BACKGROUND

Knowledge about the long-term effects on blood pressure (BP) and body mass index (BMI) when treating young patients for attention-deficit/hyperactivity disorder (AD/HD) with stimulants is limited. Most of the studies have reported mean and not individual values for anthropometrics and BP in treatment with stimulants. This seems to be the first study of changes based on the analyses of individual data measured over time.

PATIENTS AND METHODS

Seventy young patients (aged 8-18 years) diagnosed with AD/HD and responding well to treatment with stimulants were followed for a mean period of 3 years and 3 months. BP, heart rate, height, weight, and BMI were transformed to standard deviations or z-scores from before treatment to the last registered visit.

RESULTS

The mean dose of methylphenidate was 0.95 mg/kg. The mean increase of systolic and diastolic BP was 0.4 z-score and 0.1 z-score, respectively. The systolic BP was associated with BMI; a higher BMI at baseline increased the risk for an increase in systolic BP. Ten percent of the total group had a weight at follow-up of <-1.5 standard deviation (SD) and 12% had a height of <-1.5 SD. Mean height at follow-up was -0.2 SD, but 40% had a reduced height of at least 0.5 SD during the treatment period. BMI on a group level was reduced from +0.8 SD to +0.3 SD. Of the 19 patients with a BMI >+1.5 SD at baseline, 50% had a significantly reduced BMI.

CONCLUSION

Consequences of stimulant treatment must be evaluated individually. Besides significant effects on core AD/HD symptoms, some patients have lower BMI and BP and some increase/maintain their BMI and/or increase their systolic BP. The risk of reduced height trajectory needs further research.

Heart Rate Variability in Children with Attention-Deficit/Hyperactivity Disorder: A Pilot Study

BACKGROUND

Attention deficit/hyperactivity disorder (ADHD) is a common childhood neuropsychiatric disorder. Autonomic nervous system plays a vital role in attention, self-regulation, emotional stability and social affiliation, which are affected in ADHD. The prefrontal cortex, which is vital for attention, motor control, emotional regulation and higher order autonomic control, is hypofunctional in ADHD. In addition, catecholamine dysregulation is there.

PURPOSE

We hypothesized that there is autonomic dysfunction: reduction in overall heart rate variability (HRV) and sympathovagal imbalance in children with ADHD.

METHODS

Study criteria were drug-naïve ADHD children who were 7-12 years of age of either gender who fulfilled DSM-IV criteria for ADHD and did not have any associated comorbid psychiatric/neurological/medical disorders. Two hundred and seventy ADHD children were screened out of which only 12 were found eligible and 10 participated. Sample size was 20 (cases = 10, age- and gender-matched healthy controls = 10). Short-term HRV of both time and frequency domains were assessed by recording lead II electrocardiogram after using Tell-Show-Do, a behavior shaping technique. Comparison between groups was done using Mann-Whitney and Wilcoxon test. Demographic variables like age, height, weight and body mass index were similar between groups.

RESULTS

Among time domain parameters, SD of all NN intervals, square root of the mean of the sum of squares of differences between adjacent NN intervals and percentage of count of number of pairs of adjacent NN intervals differing by more than 50 ms were reduced in ADHD group with p < 0.05. Among frequency domain parameters, total power was reduced in ADHD group with p < 0.05, high frequency power (HF) was reduced in ADHD group with p < 0.01 and low frequency power to HF ratio was higher in ADHD group with p < 0.01.

CONCLUSION

There is autonomic dysfunction in children with ADHD - reduction in overall HRV with sympathovagal imbalance with sympathetic dominance.

Symbolic dynamics of heart rate variability — a promising tool to investigate cardiac sympathovagal control in attention deficit/hyperactivity disorder (ADHD)?

We aimed to evaluate complex cardiac sympathovagal control in attention deficit/hyperactivity disorder (ADHD) by using heart rate variability (HRV) nonlinear analysis — symbolic dynamics. We examined 29 boys with untreated ADHD and 25 healthy boys (age 8–13 years). ADHD symptoms were evaluated by ADHD-RS-IV scale. ECG was recorded in 3 positions: baseline supine position, orthostasis, and clinostasis. Symbolic dynamics indices were used for the assessment of complex cardiac sympathovagal regulation: normalised complexity index (NCI), normalised unpredictability index (NUPI), and pattern classification measures (0V%, 1V%, 2LV%, 2UV%). The results showed that HRV complexity was significantly reduced at rest (NUPI) and during standing position (NCI, NUPI) in ADHD group compared to controls. Cardiac-linked sympathetic index 0V% was significantly higher during all posture positions and cardiovagal index 2LV% was significantly lower to standing in boys suffering from ADHD. Importantly, ADHD symptom inattention positively correlated with 0V%, and negatively correlated with NCI, NUPI. Concluding, symbolic dynamics revealed impaired complex neurocardiac control characterised by potential cardiac beta-adrenergic overactivity and vagal deficiency at rest and to posture changes in boys suffering from ADHD that is correlated with inattention. We suggest that symbolic dynamics indices could represent promising cardiac biomarkers in ADHD.

Variation in Parasympathetic Dysregulation Moderates Short-term Memory Problems in Childhood Attention-Deficit/Hyperactivity Disorder

Although attention deficit/hyperactivity disorder (ADHD) is associated with impairment in working memory and short-term memory, up to half of individual children with ADHD perform within a normative range. Heterogeneity in other ADHD-related mechanisms, which may compensate for or combine with cognitive weaknesses, is a likely explanation. One candidate is the robustness of parasympathetic regulation (as indexed by respiratory sinus arrhythmia; RSA). Theory and data suggest that a common neural network is likely tied to both heart-rate regulation and certain cognitive functions (including aspects of working and short-term memory). Cardiac-derived indices of parasympathetic reactivity were collected during short-term memory (STM) storage and rehearsal tasks from 243 children (116 ADHD, 127 controls). ADHD was associated with lower STM performance, replicating previous work. In addition, RSA reactivity moderated the association between STM and ADHD - both as a category and a dimension - independent of comorbidity. Specifically, conditional effects revealed that high levels of withdrawal interacted with weakened STM but high levels of augmentation moderated a positive association predicting ADHD. Thus, variations in parasympathetic reactivity may help explain neuropsychological heterogeneity in ADHD.

Heart rate variability as a transdiagnostic biomarker of psychopathology

The Research Domain Criteria (RDoC), developed by the National Institute of Mental Health as a neuroscience-informed alternative to traditional psychiatric nosology, is an explicitly dimensional system in which classification of psychopathology is derived inductively (i.e., from basic science), across multiple levels of analysis (e.g., genetic, neural, psychophysiological, and behavioral). Although RDoC is often presented as paradigmatically revolutionary, a review of the history of psychophysiology suggests that roots of RDoC thinking extend at least as far back as the mid-20th Century. In this paper, we briefly and selectively review the historical emergence of neurobiologically-informed dimensional trait models of psychopathology, and we summarize our thinking regarding high frequency heart rate variability (HF-HRV) as a transdiagnostic biomarker of self-regulation and cognitive control. When functional interactions between HF-HRV and systems of behavioral approach and avoidance are considered, diverse patterns of behavioral maladjustment can be subsumed into a single model. This model accommodates the general bifactor structure of psychopathology, and suggests that HF-HRV can be viewed as an autonomic, transdiagnostic biomarker of mental illness.

Respiratory Sinus Arrhythmia: A Transdiagnostic Biomarker of Emotion Dysregulation and Psychopathology

In the past two decades, respiratory sinus arrhythmia (RSA)-an index of parasympathetic nervous system (PNS)-mediated cardiac control-has emerged as a reliable peripheral biomarker of emotion regulation (ER). Reduced RSA and excessive RSA reactivity (i.e., withdrawal) to emotional challenge are observed consistently among individuals with poor ER capabilities, including those with various forms of internalizing and externalizing psychopathology, and those with specific psychopathological syndromes, including anxiety, phobias, attention problems, autism, callousness, conduct disorder, depression, non-suicidal self-injury, panic disorder, and trait hostility. Emerging evidence suggests that low RSA and excessive RSA reactivity index poor ER because they are downstream peripheral markers of prefrontal cortex (PFC) dysfunction. Poorly modulated inhibitory efferent pathways from the medial PFC to the PNS result in reduced RSA and excessive RSA reactivity. According to this perspective, RSA is a non-invasive proxy for poor executive control over behavior, which characterizes most forms of psychopathology.

Assessment of potential cardiovascular risks of methylphenidate in comparison with sibutramine: do we need a SCOUT (trial)?

With the recent approval of methylphenidate (MPH) for treating attention-deficit/hyperactivity disorder (ADHD) in adults, the number of patients exposed will increase tremendously. The ongoing debate on the cardiovascular safety of MPH has triggered two large retrospective cohort studies in children and adolescents as well as in young to middle-aged adults. These studies looked into serious cardiovascular events (sudden cardiac death, acute myocardial infarction and stroke) as primary endpoints and concluded that MPH was safe after a mean duration of 2.1 years of follow-up in children and adolescents and mean duration of 0.33 years of current use in adults. The results are encouraging with respect to the short- and medium-term use of MPH. Without the inherent limitations of retrospective cohort studies, a prospective randomized, double-blind, placebo-controlled, multicenter trial in individuals stratified for cardiovascular risk factors would allow for an optimized risk assessment. With many millions of patients treated per year and drawing parallels to the lately discovered risks of sibutramine, another sympathomimetic with an overlapping mode of action and similar side effects on heart rate and blood pressure, we hypothesize that such a trial might be a dedicated risk mitigation strategy for public health. A critical assessment of cardiovascular side effects of MPH appears particularly warranted, because ADHD is associated with obesity, smoking and poor health in general. We summarize recent findings with the focus on cardiovascular risks of MPH in humans; we additionally analyze the limited number of rodent studies that have addressed cardiovascular risks of MPH.

Cardiac autonomic regulation in autism and Fragile X syndrome: a review

Despite the significance of efforts to understand the biological basis of autism, progress in this area has been hindered, in part, by the considerable heterogeneity in the disorder. Fragile X syndrome (FXS), a monogenic condition associated with high risk for autism, may pave the way for the dissection of biological heterogeneity within idiopathic autism. This article adopts a cross-syndrome biomarker approach to evaluate potentially overlapping profiles of cardiac arousal dysregulation (and broader autonomic dysfunction) in autism and FXS. Approaches such as this, aimed at delineating shared mechanisms across genetic syndromes, hold great potential for improving diagnostic precision, promoting earlier identification, and uncovering key systems that can be targeted in pharmaceutical/behavioral interventions. Biomarker approaches may be vital to deconstructing complex psychiatric disorders and are currently promoted as such by major research initiatives such as the NIMH Research Domain Criteria (RDoC). Evidence reviewed here supports physiological dysregulation in a subset of individuals with autism, as evidenced by patterns of hyperarousal and dampened parasympathetic vagal tone that overlap with the well-documented physiological profile of FXS. Moreover, there is growing support for a link between aberrant cardiac activity and core deficits associated with autism, such as communication and social impairment. The delineation of physiological mechanisms common to autism and FXS could lend insight into relationships between genetic etiology and behavioral endstates, highlighting FMR1 as a potential candidate gene. Research gaps and potential pitfalls are discussed to inform timely, well-controlled biomarker research that will ultimately promote better diagnosis and treatment of autism and associated conditions.

Guanfacine enhances cardiac acetylcholine release with little effect on norepinephrine release in anesthetized rabbits

An α2A-adrenergic agonist guanfacine improves autonomic imbalance in attention-deficit hyperactivity disorder, suggesting that it may be useful to correct autonomic imbalance in chronic heart failure (CHF) patients. To investigate the effects of guanfacine on cardiac autonomic nerve activities, a microdialysis technique was applied to anesthetized rabbit heart. Acetylcholine (ACh) and norepinephrine (NE) concentrations in atrial dialysates were measured as indices of cardiac autonomic nerve activities. Guanfacine at a dose of 100 μg/kg significantly decreased heart rate and increased dialysate ACh concentration without decreasing sympathetic NE release. Guanfacine may be useful for vagal activation therapy in CHF patients.

Attention Deficit/Hyperactivity Disorder (ADHD) Is Associated With Altered Heart Rate Asymmetry

Attention deficit/hyperactivity disorder (ADHD) is associated with complex neurocardiac integrity. We aimed to study heart rate time asymmetry as a nonlinear qualitative feature of heart rate variability indicating complexity of cardiac autonomic control at rest and in response to physiological stress (orthostasis) in children suffering from ADHD. Twenty boys with ADHD and 20 healthy age-matched boys at the age of 8 to 12 years were examined. The continuous ECG was recorded in a supine position and during postural change from lying to standing (orthostasis). Time irreversibility indices – Porta’s (P%), Guzik’s (G%) and Ehlers’ (E) – were evaluated. Our analysis showed significantly reduced heart rate asymmetry indices at rest (P%: 49.8 % vs. 52.2 %; G%: 50.2 % vs. 53.2 %; p<0.02), and in response to orthostatic load (P%: 52.4 % vs. 54.5 %, G%: 52.3 % vs. 54.5 %; p<0.05) associated with tachycardia in ADHD children compared to controls. Concluding, our study firstly revealed the altered heart rate asymmetry pattern in children suffering from ADHD at rest as well as in response to posture change from lying to standing (orthostasis). These findings might reflect an abnormal complex cardiac regulatory system as a potential mechanism leading to later cardiac adverse outcomes in ADHD.

Regulation of sadness via acceptance or suppression in adult Attention Deficit Hyperactivity Disorder (ADHD)

Emotion dysregulation is a recognized symptom of adult Attention Deficit Hyperactivity Disorder (ADHD). The aim of this study is to induce sadness in adults suffering from ADHD and to investigate the impact of emotion regulation strategies on sadness intensity, and psychophysiological measures. Thirty-six adults diagnosed with ADHD were randomly assigned to either expressive suppression (SUPP) or acceptance (ACC) of emotion. Sadness was induced using a film clip. Participants estimated the intensity of sadness and the perception of being overwhelmed with emotion before (T1), immediately after (T2) and 2 min after the film (T3). Physiological measures were obtained. Sadness induction was effective in both conditions. The perception of being overwhelmed with emotion increased between T1 and T2 in both conditions, but persisted until T3 only in the expressive suppression condition whereas a decrease was observed in the acceptance condition. In ADHD expressive suppression of sadness seems to be associated to a prolonged recovery from the perception of being overwhelmed with emotion. Emotion-regulation via acceptance in contrast appears to allow faster recovery from the perception of being overwhelmed with emotion. To our knowledge, this is the first study to identify suppression as a critical mediator between an induced emotion and delayed recovery from emotional reactions in adult ADHD.

Common ground in Attention Deficit Hyperactivity Disorder (ADHD) and Borderline Personality Disorder (BPD)-review of recent findings

Considerable overlap in diagnostic criteria and shared psychopathologic symptoms in attention deficit hyperactivity disorder (ADHD) and borderline personality disorder (BPD) have stimulated research activities in this field. Longitudinal studies have shown that BPD is frequently diagnosed in adult patients who had been diagnosed with ADHD in childhood. The question of whether ADHD and BPD randomly co-occur as comorbidities, have similar origins or share common pathological mechanisms remains unresolved. Some authors suggest that ADHD contributes to the development of BPD via various mechanisms, and therefore consider it a risk factor for later BPD development. In this article the evidence for the co-occurrence of these disorders will be reviewed as well as studies on their common genetic and environmental influences. Temperamental and developmental issues will be reviewed, and shared features such as impulsivity and emotion dysregulation discussed. From a therapeutic perspective, few studies have investigated psychotherapeutic treatment of the comorbid condition, though the issue is highly important to the management of patients suffering from both disorders. Some thought is given to how therapeutic methods and approaches can be modified to benefit patients, and to their possible succession.

Is the treatment with psychostimulants in children and adolescents with attention deficit hyperactivity disorder harmful for the dopaminergic system?

A major concern regarding psychostimulant medication (amphetamine and methylphenidate) in the treatment of children and adolescents with attention deficit/hyperactivity disorder (ADHD) are the potential adverse effects to the developing brain, particularly in regard to dopaminergic brain function. The present review focuses on the pharmacology of these psychostimulants, their mode of action in the human brain and their potential neurotoxic effects to the developing brain in animals, particularly concerning DA brain function. The potential clinical significance of these findings for the treatment of ADHD in children and adolescents is discussed. Studies on sensitization to psychostimulants' rewarding effects, which is a process expected to increase the risk of substance abuse in humans, are not included. The available findings in non-human primates support the notion that the administration of amphetamine and methylphenidate with procedures simulating clinical treatment conditions does not lead to long-term adverse effects in regard to development, neurobiology or behaviour as related to the central dopaminergic system.