Inattentive and hyperactive preschool-age boys have lower sympathetic and higher parasympathetic activity

Arousal dysregulation and executive dysfunction in attention deficit hyperactivity disorder (ADHD)

Attention deficit/hyperactivity disorder (ADHD) is a heterogeneous neurodevelopmental condition, that continues to have an elusive etiological background. A number of extant models and theories have historically intended to explain the many factors contributing to ADHD behaviors. One of the most accepted hypotheses has been the executive dysfunction theory associating reduction in executive control to abnormalities in structure and operational dysfunction of dopaminergic signaling networks. Nevertheless, executive functions are not always impaired in ADHD, and the literature describes other symptoms commonly reported suggesting individuals with ADHD would appear to suffer from a more general deficit. Another existing line of research, that has gained much attention recently, establishes that ADHD would have dysregulated states of brain arousal that would account for its commonly observed cognitive deficits and behavioral symptoms, described as the state regulation theory, which has now included measures of autonomic function. This article describes some important aspects that compose and challenge these two most influential theoretical constructs, executive dysfunction and state-regulation, based on their empirical evidence, implying the need to reevaluate the norms used to classify individuals and establish ADHD diagnosis. Large number of controversial results continue to exist within the study of ADHD biological and/or performance markers, possibly due to such heterogeneity and variability within the same diagnosis. The need to resolve these issues and establish newly revised diagnostic criteria for ADHD is critical, as therapeutic success depends on having accurately identified underlying neurophysiological factors in order to appropriately address them in treatment.

Subjective and Autonomic Arousal toward Emotional Stimuli in Preadolescents with Externalizing Problems and the Role of Explicit and Implicit Emotion Regulation

Children and adolescents with externalizing problems show physiological hypo-reactivity toward affective stimuli, which may relate to their disruptive, antisocial, and thrill-seeking behaviors. This study examines differences in explicit and implicit emotion regulation between preadolescents with and without externalizing problems as well as the role of emotion regulation in subjective and autonomic responses to emotional stimuli. Preadolescents showing self- and other-reported externalizing psychopathology, and a control sample, without such difficulties, participated in a passive affective picture-viewing task with neutral, fearful, joyful, and sad images, while their heart rate and heart rate variability were measured. Participants also reported on their emotion regulation difficulties using the Difficulties in Emotion Regulation Scale. Compared to controls, youths scoring high on externalizing problems (1) reported greater emotion regulation difficulties, especially a lack of emotional clarity and difficulty in controlling impulsive actions, (2) showed higher resting heart rate variability and a lower resting heart rate, suggestive of higher emotion/autonomic regulation ability, and (3) showed both subjective and physiological hypo-arousal to emotional pictures. Heart rate variability and, to a lesser degree difficulties in emotional clarity, modulated the effects of emotional pictures on subjective and physiological arousal. Findings suggest that interventions to improve emotion regulation and awareness may help to prevent externalizing problems.

Association between Stroop tasks and heart rate variability features in patients with somatic symptom disorder

OBJECTIVE

Patients with somatic symptom disorder (SSD) may have declined parasympathetic activity and selective attention to negative information. We combined Stroop tasks and heart rate variability (HRV) measurements to explore the brain mechanism of SSD.

METHODS

104 SSD patients (64 women) and 100 healthy adults (76 women) received three Stroop tasks (the "cognitive" color-word Stroop, "emotional" emotion Stroop, and "cognitive and emotional" face-word Stroop) with low and high interference conditions. The key HRV indexes included high-frequency power (HF) and standard deviation of normal to normal RR intervals (SDNN). The generalized estimating equation model was used to examine the effects of SSD on three Stroop tasks performance (accuracy and reaction time) and HRV (HF and SDNN) controlling for sex, age, body mass index, and the levels of anxiety and depression.

RESULTS

For Stroop tasks, the significant group difference in emotion Stroop task with the high level of interference (SSD patients had lower accuracy than healthy ones) was only found in women. As for HRV, only men during color-word Stroop, women during emotion Stroop revealed significant between-group differences; SDNN in SSD men was higher than healthy men, and HF in SSD women was lower than healthy women controlling for the confounding factors. The significantly longer reaction time in SSD women than in healthy women diminished in the adjusted analysis.

CONCLUSION

Emotion Stroop task and HRV helps distinguish SSD patients from healthy adults, particularly in women. Sex-specific measures for early detection and intervention for SSD are suggested.

Attention Deficit Hyperactivity Disorder in Preschool-Age Children

Attention deficit hyperactivity disorder is a neurodevelopmental disorder marked by age-inappropriate deficits in attention or hyperactivity/impulsivity that interfere with functioning or development. It is highly correlated with other disorders, such as oppositional defiant disorder, conduct disorder, and mood symptoms. The etiology is multifactorial, and neuroimaging findings are nonspecific. Although assessment tools exist, there is variability among them, and historically, parent-teacher agreement has not been consistent. Treatment algorithm for attention deficit hyperactivity disorder in preschoolers includes behavioral interventions first followed by psychopharmacologic treatment when behavioral therapies fail. Other nonpharmacologic and nonbehavioral interventions are discussed including the role of exercise and nutrition.

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.

Differential effects of cannabinoid CB1 inverse agonists and antagonists on impulsivity in male Sprague Dawley rats: identification of a possibly clinically relevant vulnerability involving the serotonin 5HT1A receptor

RATIONALE

Cannabinoid CB1 inverse agonists hold therapeutic promise as appetite suppressants but have produced suicidal behaviors among a small subpopulation in clinical trials. Anatomical and pharmacological evidence implicate the 5HT_1A serotonin receptor in suicide in humans and impulsivity in humans and animals.

OBJECTIVE

The objective of the study is to assess whether 5HT_1A blockade is necessary for CB1 ligands to produce impulsivity.

METHODS

Sprague Dawley rats were administered the CB1 inverse agonist AM 251, the CB1 antagonist AM 6527, or the peripherally restricted antagonist AM 6545, with or without pretreatment with the 5HT_1A antagonist WAY 100,635 (WAY) on the paced fixed consecutive number (FCN) task, which measures choice to terminate a chain of responses prematurely. As FCN is sensitive to changes in time perception, which have been demonstrated with CB1 blockade, a novel variable consecutive number task with discriminative stimulus (VCN-S _D ) was also performed and proposed to be less sensitive to changes in timing.

RESULTS

Pretreatment with WAY enabled mild but significant reductions in FCN accuracy for AM 251 and AM 6527. No effects were found for AM 6545. On the VCN-S _D task, substantial impairments were found for the combination of WAY and AM 251.

CONCLUSIONS

AM 251, but not the antagonists AM 6527 or AM 6545, produced impulsivity only following systemic 5HT_1A blockade. Although preliminary, the results may indicate that disrupted serotonin signaling produces a vulnerability to undesirable effects of CB1 inverse agonists, which is not evident in the general population. Furthermore, neutral CB1 antagonists do not produce this effect and therefore may have greater safety.

Measures of Heart Rate Variability in Individuals With Somatic Symptom Disorder

OBJECTIVE

Little is known about autonomic nervous system activity in individuals with somatic symptom disorder (SSD) as defined by DSM-V criteria. The aims of this study were to investigate whether individuals with SSD differ from healthy controls in heart rate variability (HRV) measures of autonomic nervous system activity and whether sex has a moderating effect on this association.

METHODS

We recruited 168 individuals with SSD (35.1% men) and 106 healthy controls (27.4% men). Demographics, HRV, and psychological factors were measured using the Patient Health Questionnaire-15, Health Anxiety Questionnaire, Beck Depression Inventory-II (BDI-II), and Beck Anxiety Inventory. Multiple regression analysis was used to examine the association of SSD with HRV, adjusting for demographic and psychological measures.

RESULTS

Individuals with SSD had lower levels of total-power HRV and low-frequency HRV, but no differences in high-frequency (HF)-HRV were found. HRV differences between SSD and controls varied by sex and age (triple interaction TP-HRV β = -0.222, p < .001; low-frequency HRV β = -0.332, p < .001; and HF-HRV β = -0.167, p = .006). Whole-sample multiple regression analyses revealed significant sex differences in the magnitudes of the association between BDI-II with HF-HRV (β of sex*BDI-II: 0.761, p = .005) and analyses stratified by sex indicated that HF-HRV was significantly correlated with depression in men with SSD (r = -0.491, p < .001) but not in women with SSD (r = 0.057, p = .558).

CONCLUSIONS

These results suggest that patients with SSD demonstrate different patterns of HRV and the patterns of association between HRV indices and psychological factors vary between men and women.

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.

Sex differences in healthy human heart rate variability: A meta-analysis

The present meta-analysis aimed to quantify current evidence on sex differences in the autonomic control of the heart, indexed by measures of heart rate variability (HRV) in healthy human subjects. An extensive search of the literature yielded 2020 titles and abstracts, of which 172 provided sufficient reporting of sex difference in HRV. Data from 63,612 participants (31,970 females) were available for analysis. Meta-analysis yielded a total of 1154 effect size estimates (k) across 50 different measures of HRV in a cumulated total of 296,247 participants. Females showed a significantly lower mean RR interval and standard deviation of RR intervals (SDNN). The power spectral density of HRV in females is characterized by significantly less total power that contains significantly greater high- (HF) and less low-frequency (LF) power. This is further reflected by a lower LF/HF ratio. Meta-regression revealed significant effects of age, respiration control and the length of recording available for analysis. Although women showed greater mean heart rate, they showed greater vagal activity indexed by HF power of HRV. Underlying mechanisms of these findings are discussed.

Is Heart Rate Variability Related to Season of Birth?

BACKGROUND

Season of birth (SOB) has been found to be related to cardiovascular mortality, but the mechanisms are unclear. It is suggested that birth in winter is a protective factor for the circulatory system, and this should be able to be observed using heart rate variability (HRV) measurements. The phenomenon may have a sex difference and is likely to be modulated by climatic factors. This study focused on this problem and investigates healthy school-age children to minimize confounding factors.

HYPOTHESIS

Birth in winter is protective to cardiovascular system via autonomic modulation. There is a gender difference in the relationship between SOB and autonomic activity. Climatic factors are the cause of SOB effects on autonomic system.

METHODS

A total of 381 healthy school-age children were recruited for this study. Their HRV profiles were measured once and climatic information related to their month of birth was gathered. The HRV profiles of the 2 sexes and 4 seasons of birth were compared. Correlation and regression analysis were performed to clarify the relationship between climatic factors and the HRV results.

RESULTS

Boys born in winter have higher high-frequency power (HF) but a lower ratio of low-frequency power to high-frequency power (LF/HF) than do males born in other seasons. This result is not found for girls. Age and the temperature of the SOB are predictive factors for HF among boys. The humidity of SOB is a predictive factor for normalized low-frequency power (LF%) and LF/HF among girls.

CONCLUSIONS

Season of birth is related to both parasympathetic and sympathetic activity among school-age children, especially boys. Temperature and humidity are potential causes of this SOB phenomenon.

Barratt Impulsivity and Neural Regulation of Physiological Arousal

Background

Theories of personality have posited an increased arousal response to external stimulation in impulsive individuals. However, there is a dearth of studies addressing the neural basis of this association.

Methods

We recorded skin conductance in 26 individuals who were assessed with Barratt Impulsivity Scale (BIS-11) and performed a stop signal task during functional magnetic resonance imaging. Imaging data were processed and modeled with Statistical Parametric Mapping. We used linear regressions to examine correlations between impulsivity and skin conductance response (SCR) to salient events, identify the neural substrates of arousal regulation, and examine the relationship between the regulatory mechanism and impulsivity.

Results

Across subjects, higher impulsivity is associated with greater SCR to stop trials. Activity of the ventromedial prefrontal cortex (vmPFC) negatively correlated to and Granger caused skin conductance time course. Furthermore, higher impulsivity is associated with a lesser strength of Granger causality of vmPFC activity on skin conductance, consistent with diminished control of physiological arousal to external stimulation. When men (n = 14) and women (n = 12) were examined separately, however, there was evidence suggesting association between impulsivity and vmPFC regulation of arousal only in women.

Conclusions

Together, these findings confirmed the link between Barratt impulsivity and heightened arousal to salient stimuli in both genders and suggested the neural bases of altered regulation of arousal in impulsive women. More research is needed to explore the neural processes of arousal regulation in impulsive individuals and in clinical conditions that implicate poor impulse control.