The evolution of hyperactivity, impulsivity and cognitive diversity

Dynamics of spontaneous thoughts: Exploration, attentional profile and the segmentation of the stream of thoughts

For a long time, clinical knowledge and first-person reports have pointed to individual differences in the dynamics of spontaneous thoughts, in particular in the extreme case of psychiatric conditions (e.g. racing thoughts in Attention Deficit / Hyperactivity Disorder, ADHD; rumination in depression). We used a novel procedure to investigate this individual variability by combining verbal fluency tasks and introspective reports of thought content. Our goal was twofold. First, we tested the hypothesis that a greater segmentation of the stream of thoughts would be associated with trait inattention, in line with subjective reports of ADHD patients. Second, we tested whether the segmentation of the stream of thoughts increased with an increased tendency for exploratory behavior, following recent theoretical claims on the mechanisms underpinning the generation of spontaneous thoughts. Our results support both hypotheses, shedding light on the factors contributing to the individual variability in the dynamics of the stream of thought.

Impulsiveness among Undergraduates from the United Arab Emirates and Jordan: Role of Socio-demographic Variables

BACKGROUND

Some undergraduate students may appear impulsive in their behavior without taking enough time to think, and impulsiveness may vary according to gender, academic specialization, and academic level.

OBJECTIVE

This study investigated the differences in impulsiveness between undergraduates of different gender, academic specializations, and academic years at three private universities in the United Arab Emirates and Jordan.

METHOD

The research design of the study was a survey in nature. The researchers collected data online using a translated Arabic version of the Barratt Impulsiveness Scale (BIS-11) as described in Patton et al..1 A sample of 334 undergraduates was selected using the convenient non-probability sample technique.

RESULTS

To analyze data, the researchers deployed descriptive and inferential statistics and found no significant differences between the students in the subscales of motor impulsiveness, non-planning, attentional impulsiveness, and the total scale score according to gender, academic specializations, and academic years variables.

CONCLUSION

The researchers concluded that undergraduates have a moderate level of impulsiveness; except for attentional impulsiveness, the results indicated that the average student's score on the subscale was low. Motor impulsiveness, non-planning impulsiveness, and attentional impulsiveness were not significantly different between males and females, academic specialization, academic year variables, and their interaction. The limitations and implications of these findings are discussed.

Prenatal Exposure to Air Pollutants and Attentional Deficit Hyperactivity Disorder Development in Children: A Systematic Review

Up to 9.5% of the world's population is diagnosed with attention deficit/hyperactivity disorder (ADHD), making it one of the most common childhood disorders. Air pollutants could be considered an environmental risk condition for ADHD, but few studies have specifically investigated the effect of prenatal exposure. The current paper reviews the studies conducted on the association between prenatal air pollutants (PM, NO_x, SO₂, O₃, CO and PAH) and ADHD development in children. From the 890 studies searched through PubMed, Google Scholar, Scopus, and Web of Science, 15 cohort studies met the inclusion criteria. NOS and WHO guidelines were used for quality and risk of bias assessment. The accumulative sample was 589,400 of children aged 3-15 years. Most studies reported an association between ADHD symptoms and prenatal PAH and PM exposure. Data available on NO₂ and SO₂ were inconsistent, whereas the effect of CO/O₃ is barely investigated. We observed heterogeneity through an odd ratio forest plot, and discrepancies in methodologies across the studies. Eight of the fifteen studies were judged to be of moderate risk of bias in the outcome measurement. In a nutshell, future studies should aim to minimize heterogeneity and reduce bias by ensuring a more representative sample, standardizing exposure and outcome assessments.

The evolution of personality disorders: A review of proposals

Personality disorders (PDs) are currently considered dysfunctions. However, personality differences are older than humanity and are ubiquitous in nature, from insects to higher primates. This suggests that a number of evolutionary mechanisms-other than dysfunctions-may be able to maintain stable behavioral variation in the gene pool. First of all, apparently maladaptive traits may actually improve fitness by enabling better survival or successful mating or reproduction, as exemplified by neuroticism, psychopathy, and narcissism. Furthermore, some PDs may harm important biological goals while facilitating others, or may be globally beneficial or detrimental depending on environmental circumstances or body condition. Alternatively, certain traits may form part of life history strategies: Coordinated suites of morphological, physiological and behavioral characters that optimize fitness through alternative routes and respond to selection as a whole. Still others may be vestigial adaptations that are no longer beneficial in present times. Finally, variation may be adaptative in and by itself, as it reduces competition for finite resources. These and other evolutionary mechanisms are reviewed and illustrated through human and non-human examples. Evolutionary theory is the best-substantiated explanatory framework across the life sciences, and may shed light on the question of why harmful personalities exist at all.

Exploration heuristics decrease during youth

Deciding between exploring new avenues and exploiting known choices is central to learning, and this exploration-exploitation trade-off changes during development. Exploration is not a unitary concept, and humans deploy multiple distinct mechanisms, but little is known about their specific emergence during development. Using a previously validated task in adults, changes in exploration mechanisms were investigated between childhood (8-9 y/o, N = 26; 16 females), early (12-13 y/o, N = 38; 21 females), and late adolescence (16-17 y/o, N = 33; 19 females) in ethnically and socially diverse schools from disadvantaged areas. We find an increased usage of a computationally light exploration heuristic in younger groups, effectively accommodating their limited neurocognitive resources. Moreover, this heuristic was associated with self-reported, attention-deficit/hyperactivity disorder symptoms in this population-based sample. This study enriches our mechanistic understanding about how exploration strategies mature during development.

Value-free random exploration is linked to impulsivity

Deciding whether to forgo a good choice in favour of exploring a potentially more rewarding alternative is one of the most challenging arbitrations both in human reasoning and in artificial intelligence. Humans show substantial variability in their exploration, and theoretical (but only limited empirical) work has suggested that excessive exploration is a critical mechanism underlying the psychiatric dimension of impulsivity. In this registered report, we put these theories to test using large online samples, dimensional analyses, and computational modelling. Capitalising on recent advances in disentangling distinct human exploration strategies, we not only demonstrate that impulsivity is associated with a specific form of exploration—value-free random exploration—but also explore links between exploration and other psychiatric dimensions.

The Stage 1 protocol for this Registered Report was accepted in principle on 19/03/2021. The protocol, as accepted by the journal, can be found at 10.6084/m9.figshare.14346506.v1.

Deciding between known rewarding options and exploring novel avenues is central to decision making. Humans show variability in their exploration. Here, the authors show that impulsivity is associated to an increased usage of a cognitively cheap (and sometimes sub-optimal) exploration strategy.

Is There a Relationship Between ADHD and COVID-19 Prevalence and Mortality Indices? An Analysis of Data From 156 Countries

OBJECTIVE

To examine the relationship between nation-level prevalence of ADHD and COVID-19 prevalence and mortality indices.

METHOD

Associations between nation-wise estimated prevalence, crude mortality rates and case-fatality ratios for COVID-19 and estimated prevalence rates for ADHD were examined, controlling for medical conditions known to be associated with COVID-19 outcome, as well as demographic, climate-related, and economic variables.

RESULTS

Prevalence of ADHD was positively correlated with COVID-19 prevalence and crude mortality rates on bivariate analyses, though the strength of this association was low. On multivariate regression, prevalence of ADHD was negatively associated with COVID-19 prevalence and crude mortality rates, though only the former finding was statistically significant.

CONCLUSION

The association between ADHD and COVID-19 prevalence and mortality at a national level is inconsistent, modest, and may be largely due to confounding factors such as age, lifestyle factors, and medical comorbidities.

Specialised minds: extending adaptive explanations of personality to the evolution of psychopathology

Traditional evolutionary theory invoked natural and sexual selection to explain species- and sex-typical traits. However, some heritable inter-individual variability in behaviour and psychology - personality - is probably adaptive. Here we extend this insight to common psychopathological traits. Reviewing key findings from three background areas of importance - theoretical models, non-human personality and evolved human social dynamics - we propose that a combination of social niche specialisation, negative frequency-dependency, balancing selection and adaptive developmental plasticity should explain adaptation for individual differences in psychology - 'specialised minds' - explaining some variance in personality and psychopathology trait dimensions, which share various characteristics. We suggest that anthropological research of behavioural differences should be extended past broad demographic factors (age and sex) to include individual specialisations. As a first step towards grounding psychopathology in ancestral social structure, we propose a minimum plausible prevalence, given likely ancestral group sizes, for negatively frequency-dependent phenotypes to be maintained as specialised tails of adaptive distributions - below the calculated prevalence, specialisation is highly unlikely. For instance, chronic highly debilitating forms of autism or schizophrenia are too rare for such explanations, whereas attention-deficit-hyperactivity disorder and broad autism phenotypes are common enough to have existed in most hunter-gatherer bands, making adaptive explanations more plausible.

Testing the evolutionary advantage theory of attention-deficit/hyperactivity disorder traits

To reconcile the strong secular persistence of attention-deficit/hyperactivity disorder (ADHD) despite its impairing effects, ADHD traits have been postulated to offer an evolutionary advantage. It has been proposed that such advantages should in particular be observable under time-critical, novel, and resource-depleted conditions requiring response-readiness and high levels of scanning and exploration/foraging. Our objective was to provide the first behavioral test of this hypothesis. Schoolchildren from the general population with no/few (n = 56), mild (n = 50), moderate (n = 48), and severe (n = 48) ADHD traits, defined according to their ADHD-Rating Scale IV (ADHD-RS-IV) total score, participated in an exploratory foraging and response-readiness laboratory test. Here, children searched for coins hidden in locations of varying obscurity in an unfamiliar room for 1 min. Test-performance (number of coins found) adjusted for age, sex, and estimated IQ was analyzed categorically using multiple linear regression analyses and dimensionally by fitting a regression model including the ADHD-RS-IV score as a continuous measure. There were no differences in the mean number of coins between the No/Few (Mean = 7.82), Mild (Mean = 7.76), Moderate (Mean = 7.58), and Severe (Mean = 7.88) groups [F(3,195) = 0.24, p = 0.871]. Furthermore, excluding children with functional impairment, adjusting for verbal working memory and response inhibition, and stratifying for sex did not change these findings. Finally, continuous ADHD traits were not found to be related to test-performance [F(3,195) = 0.73, p = 0.536]. While our results do generally not support the evolutionary advantage theory (i.e., ADHD traits neither conferred an advantage nor a disadvantage), this does not disprove that ADHD traits may have offered advantages via other mechanisms.

A qualitative and quantitative study of self-reported positive characteristics of individuals with ADHD

Research in Attention-deficit/hyperactivity disorder (ADHD) has had a clear focus on treatment and the dysfunction in specific situation associated with the condition. However, self-report, observational and anecdotal evidence indicates that there are also positive aspects associated with ADHD. Research on the potential positive features in individuals with an ADHD diagnosis is still limited, especially studies with larger representative samples. Here we performed qualitative research to identify positive aspects and strengths associated with ADHD in a large convenience sample from the Dutch organization for people with ADHD, dyslexia and dyscalculia. We sent out open-ended questionnaires to the members of the organization, asking what they consider to be positive aspects of their ADHD. From the responses of individuals with ADHD (n = 206), we extracted 116 codes, which were assigned to thirteen subthemes, which in turn led to five themes. These themes were: Creativity, Being dynamic, Flexibility, Socio-affective skills, and Higher-order cognitive skills. Core symptoms of ADHD such as impulsivity and hyperactivity were also considered positive aspects of ADHD by a minority of participants. After showing our results to a group of additional individuals with ADHD (focus group) they confirmed the identified positive aspects of ADHD. They also helped us with the interpretation of our findings and mentioned certain positive aspects to be a consequence of living with ADHD (being open minded and being honest). In conclusion, experiencing positive aspects seems to be common in ADHD as almost all participants reported positive aspect of ADHD, these aspects cover many different domains. Awareness about ADHD's strengths might help individuals with ADHD and their environment to better cope with, accept or embrace their diagnosis and for example make educational or occupational choices that fit them well. To incorporate these positive aspects in the understanding of ADHD, future research should focus on quantifying strengths in ADHD, and on investigating the link between these aspects and clinical characteristics and how this new knowledge can be implemented in psychoeducation and find its way to education and occupational settings.

The role of impulsivity and delay discounting in student compliance with COVID-19 protective measures

During the 2020 COVID-19 pandemic, governments set recommendations and restrictions that have given rise to new situations that require residents to deliberate and respond nonautomatically. For highly impulsive individuals, dealing with these situations may be harder, as they tend to deliberate less about the consequences of their behaviors. In this study, we investigate the relationship between impulsivity and delay discounting on the one hand and compliance with COVID-19 restrictions on the other hand. We distinguish between compliance with social distancing measures and compliance with hygiene measures. Regression analyses of an international sample of 6759 students from seven European countries reveal that the self-reported personality construct of impulsivity is negatively related to both types of compliance behavior. However, and unexpectedly, we also find a weak positive association between the discount rate-as measured by a behavioral task-and compliance. Our study highlights the importance of individual differences in impulsivity in regard to compliance with public health measures during a pandemic.

Brain-Derived neurotrophic factor Val66Met induces female-specific changes in impulsive behaviour and alcohol self-administration in mice

Substance use disorders are a debilitating neuropsychiatric condition, however it remains unclear why some individuals are at greater risk of substance use disorders than others and what genetic factors determine such individual differences. Impulsivity appears a promising candidate endophenotype to bridge the gap between genetic risk and addiction. Brain-derived neurotrophic factor (BDNF), and in particular the BDNF^Val66Met polymorphism, has been suggested to be involved in both impulsivity and substance use disorders, however results so far have been inconsistent. To investigate the role of BDNF, and more specifically the BDNF^Val66Met polymorphism, in both impulsivity and operant alcohol self-administration using the same animal model. Separate cohorts of humanized Val66Met transgenic mice were assessed for either trait impulsivity in the 5-choice serial reaction time (5-CSRT) touchscreen task, or propensity towards obtaining ethanol in an operant paradigm. It was found that female hBDNF^Val/Val mice exhibited both greater impulsivity compared to hBDNF^Met/Met mice of the same sex as shown by a higher number of premature responses at one of three increased inter-trial intervals tested in the 5-CSRT task, and a greater propensity toward stable ethanol self-administration relative to male mice of the same genotype in the operant paradigm. By contrast, male mice showed no difference between genotypes in impulsivity or stable ethanol self-administration. The hBDNF^Met/Met genotype appears to sex-specifically alter aspects of both impulsive behaviour and addiction propensity. These results suggest that impulse behaviour may be a possible predictor of addiction risk.

Academic Outcomes Following a School-Based RCT for ADHD: 6-Year Follow-Up

Objective: For children with high levels of ADHD symptoms, to investigate the impact of early school-based interventions on academic outcomes in mid-childhood. Method: A 6-year follow-up of 4- to 5-year-olds (N = 52,075) whose schools participated in a cluster randomized controlled trial for children at risk of ADHD. School-level interventions involved the provision of a booklet with evidence-based information (book) and/or feedback of names (identification) of children with high levels of ADHD symptoms. At ages 10 to 11 years, outcome measures were scores in English and mathematics tests. Results: For children with high levels of ADHD symptoms, the interventions had no impact on academic outcomes. When all children were analyzed, the book intervention had a positive impact on mathematics. Baseline inattention was associated with poorer academic outcomes, whereas impulsiveness was associated with better academic outcomes. Conclusion: The provision of evidence-based information about helping children with ADHD at school may have wider academic benefits.

Cost of ADHD treatment using methylphenidate and atomoxetine in the South African private healthcare sector

Introduction: The prevalence of Attention-Deficit/Hyperactivity Disorder (ADHD) has risen over the last two decades, with a corresponding increase in the cost of its medication. Drug utilization studies in South Africa focusing on ADHD are limited.Areas covered: The primary aim was to determine the cost of methylphenidate and atomoxetine (used for ADHD). The Intercontinental Marketing Service (IMS) database which contains data of the private healthcare sector was interrogated from 2013 to 2016 (48-month period) focussing on methylphenidate and atomoxetine. Drug consumption was expressed in number of DDDs, DDDs/1000 inhabitants/day and cost in Rands.Expert opinion: Methylphenidate-containing products constituted a considerably higher percentage of the market share when compared to atomoxetine (90.30% versus 9.70%). The DDD/1000 inhabitants/day for methylphenidate was 6.010 with an annual cost for R266 691 778 in 2013, which increased to 7.827 DDDs/1000 inhabitants/day with an annual cost of R436 041 506 in 2016. Consumption of both methylphenidate and atomoxetine increased from 2013 to 2016. There was a preference for long-acting extended-release methylphenidate tablets even though the unit costs were higher when compared to the short-acting formulations. Despite increases in unit costs, the spend in South Africa showed an upward trend for methylphenidate and atomoxetine.

Lower Attentional Skills predict increased exploratory foraging patterns

When engaged in a search task, one needs to arbitrate between exploring and exploiting the environment to optimize the outcome. Many intrinsic, task and environmental factors are known to influence the exploration/exploitation balance. Here, in a non clinical population, we show that the level of inattention (assessed as a trait) is one such factor: children with higher scores on an ADHD (Attention Deficit/Hyperactivity Disorder) questionnaire exhibited longer transitions between consecutively retrieved items, in both a visual and a semantic search task. These more frequent exploration behaviours were associated with differential performance patterns: children with higher levels of ADHD traits performed better in semantic search, while their performance was unaffected in visual search. Our results contribute to the growing literature suggesting that ADHD should not be simply conceived as a pure deficit of attention, but also as a specific cognitive strategy that may prove beneficial in some contexts.

Consumption of methylphenidate and atomoxetine in the private healthcare sector in South Africa: a longitudinal study

Background Globally Attention-Deficit/Hyperactivity Disorder (ADHD) has been in the spotlight. Despite some controversies, treatment of ADHD remains the cornerstone of patient care. Objective To describe the consumption of methylphenidate and atomoxetine in the private healthcare sector in South Africa over a four-year period (2013-2016). Method Data were extracted from the Intercontinental Marketing Service (IMS) database for the drug utilisation study. Consumption patterns were expressed as number of Defined Daily Doses (DDDs)/1000 inhabitants/day and number of DDDs/1000 inhabitants/month. Results Methylphenidate (95.85%) was the medication of choice when compared to atomoxetine (4.15%) in 2013. The corresponding figures for 2016 were 96.40% and 3.60%. Consumption of ADHD medication showed slight changes over the 4-year period. If only the private healthcare sector population is considered, consumption of methylphenidate was 6.010 DDDs/1000 inhabitants/day in 2013, and 7.827 DDDs/1000 inhabitants/day in 2016. A previous study (1994-1996) reported 0.12 DDDs/1000 inhabitants/day for methylphenidate. Consumption of atomoxetine was 0.044 DDDs/1000 inhabitants/day in 2013 and 0.050 DDDs/1000 inhabitants/day in 2016. Conclusion Consumption showed an increase in use of methylphenidate in South Africa, with small changes observed over the study period. Further studies are required.

Early Visual Foraging in Relationship to Familial Risk for Autism and Hyperactivity/Inattention

OBJECTIVE

Information foraging is atypical in both autism spectrum disorders (ASDs) and ADHD; however, while ASD is associated with restricted exploration and preference for sameness, ADHD is characterized by hyperactivity and increased novelty seeking. Here, we ask whether similar biases are present in visual foraging in younger siblings of children with a diagnosis of ASD with or without additional high levels of hyperactivity and inattention.

METHOD

Fifty-four low-risk controls (LR) and 50 high-risk siblings (HR) took part in an eye-tracking study at 8 and 14 months and at 3 years of age.

RESULTS

At 8 months, siblings of children with ASD and low levels of hyperactivity/inattention (HR/ASD-HI) were more likely to return to previously visited areas in the visual scene than were LR and siblings of children with ASD and high levels of hyperactivity/inattention (HR/ASD+HI).

CONCLUSION

We show that visual foraging is atypical in infants at-risk for ASD. We also reveal a paradoxical effect, in that additional family risk for ADHD core symptoms mitigates the effect of ASD risk on visual information foraging.

A common copy-number variant within SIRPB1 correlates with human Out-of-Africa migration after genetic drift correction

Previous reports have proposed that personality may have played a role on human Out-Of-Africa migration, pinpointing some genetic variants that were positively selected in the migrating populations. In this work, we discuss the role of a common copy-number variant within the SIRPB1 gene, recently associated with impulsive behavior, in the human Out-Of-Africa migration. With the analysis of the variant distribution across forty-two different populations, we found that the SIRPB1 haplotype containing duplicated allele significantly correlated with human migratory distance, being one of the few examples of positively selected loci found across the human world colonization. Circular Chromosome Conformation Capture (4C-seq) experiments from the SIRPB1 promoter revealed important 3D modifications in the locus depending on the presence or absence of the duplication variant. In addition, a 3’ enhancer showed neural activity in transgenic models, suggesting that the presence of the CNV may compromise the expression of SIRPB1 in the central nervous system, paving the way to construct a molecular explanation of the SIRPB1 variants role in human migration.

Increased decision thresholds enhance information gathering performance in juvenile Obsessive-Compulsive Disorder (OCD)

Patients with obsessive-compulsive disorder (OCD) can be described as cautious and hesitant, manifesting an excessive indecisiveness that hinders efficient decision making. However, excess caution in decision making may also lead to better performance in specific situations where the cost of extended deliberation is small. We compared 16 juvenile OCD patients with 16 matched healthy controls whilst they performed a sequential information gathering task under different external cost conditions. We found that patients with OCD outperformed healthy controls, winning significantly more points. The groups also differed in the number of draws required prior to committing to a decision, but not in decision accuracy. A novel Bayesian computational model revealed that subjective sampling costs arose as a non-linear function of sampling, closely resembling an escalating urgency signal. Group difference in performance was best explained by a later emergence of these subjective costs in the OCD group, also evident in an increased decision threshold. Our findings present a novel computational model and suggest that enhanced information gathering in OCD can be accounted for by a higher decision threshold arising out of an altered perception of costs that, in some specific contexts, may be advantageous.

Paternal age and psychiatric disorders: A review

We review the hypotheses concerning the association between the paternal age at childbearing and childhood psychiatric disorders (autism spectrum- and attention deficit/hyperactive disorder) and adult disorders (schizophrenia, bipolar-, obsessive-compulsive-, and major depressive disorder) based on epidemiological studies. Several hypotheses have been proposed to explain the paternal age effect. We discuss the four main-not mutually exclusive-hypotheses. These are the de novo mutation hypothesis, the hypothesis concerning epigenetic alterations, the selection into late fatherhood hypothesis, and the environmental resource hypothesis. Advanced paternal age in relation to autism spectrum disorders and schizophrenia provided the most robust epidemiological evidence for an association, with some studies reporting a monotonic risk increase over age, and others reporting a marked increase at a given age threshold. Although there is evidence for the de novo mutation hypothesis and the selection into late fatherhood hypothesis, the mechanism(s) underlying the association between advanced paternal age and psychiatric illness in offspring remains to be further clarified. © 2016 The Authors. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics Published by Wiley Periodicals, Inc.

Hypothesizing Molecular Genetics of the Holocaust: Were Dopaminergic Genes Involved or Brain Wash?

Numerous studies indicated that the prevalence of certain alleles of the dopamine D2 receptor gene (DRD2) vary across different ethnic groups. Under adverse environmental conditions, these alleles can increase the risk of developing psychiatric symptoms. Thus, we hypothesized that the prevalence of the DRD2 gene Taq IA allele may serve to explain the horrific behaviours practiced by the Nazi regime. Hitler's 'Brain Washing' methods goaded his followers to carry out genocide at a time when carriers of the DRD2 TaqIA allele (the so called 'aggressive--genotype') were significantly higher among the Aryan Germans compared to resident German Jews. It would be of interest, to genotype the Jewish Holocaust survivors, to determine whether those with the Taq AI allele survived in greater numbers. The hypothesis being that, greater survival may result in enhanced frequency of not only the DRD2 AI allele but other reward gene polymorphisms among survivors. Understanding the molecular genetics of any population in terms of reward dependence and subsequent behaviours will be most beneficial in future human interaction whether negative (war) or positive (peace) in nature.

Empirical tests of natural selection-based evolutionary accounts of ADHD: a systematic review

OBJECTIVE

ADHD is a prevalent and highly heritable mental disorder associated with significant impairment, morbidity and increased rates of mortality. This combination of high prevalence and high morbidity/mortality seen in ADHD and other mental disorders presents a challenge to natural selection-based models of human evolution. Several hypotheses have been proposed in an attempt to resolve this apparent paradox. The aim of this study was to review the evidence for these hypotheses.

METHODS

We conducted a systematic review of the literature on empirical investigations of natural selection-based evolutionary accounts for ADHD in adherence with the PRISMA guideline. The PubMed, Embase, and PsycINFO databases were screened for relevant publications, by combining search terms covering evolution/selection with search terms covering ADHD.

RESULTS

The search identified 790 records. Of these, 15 full-text articles were assessed for eligibility, and three were included in the review. Two of these reported on the evolution of the seven-repeat allele of the ADHD-associated dopamine receptor D4 gene, and one reported on the results of a simulation study of the effect of suggested ADHD-traits on group survival. The authors of the three studies interpreted their findings as favouring the notion that ADHD-traits may have been associated with increased fitness during human evolution. However, we argue that none of the three studies really tap into the core symptoms of ADHD, and that their conclusions therefore lack validity for the disorder.

CONCLUSIONS

This review indicates that the natural selection-based accounts of ADHD have not been subjected to empirical test and therefore remain hypothetical.

The association between attention-deficit/hyperactivity (ADHD) symptoms and self-employment

Attention-deficit/hyperactivity (ADHD) symptoms have been associated with the decision to become self-employed. Although these symptoms are generally regarded as disadvantageous, there may also be a bright side. To our knowledge, however, there has been no systematic, epidemiological evidence to support this claim. This paper examines the association between ADHD symptoms and self-employment in a population-based sample from the STAGE cohort of the Swedish Twin Registry (N = 7208). For replication, we used a sample of Dutch students who participated in the Global University Entrepreneurial Spirit Students' Survey (N = 13,112). In the Swedish sample, we found a positive association with self-employment for both general ADHD symptoms [odds ratio (OR) 1.13; 95 % confidence intervals (CI) 1.04-1.23] and hyperactivity symptoms [OR 1.19; 95 % CI 1.08-1.32], whereas no association was found for attention-deficit symptoms [OR 0.99; 95 % CI 0.89-1.10]. The positive association between hyperactivity and self-employment was replicated in the Dutch student sample [OR 1.09; 95 % CI 1.03-1.15]. Our results show that certain aspects of ADHD, in particular hyperactivity, can have a bright side, as they are positively associated with self-employment.

Computational Psychiatry of ADHD: Neural Gain Impairments across Marrian Levels of Analysis

Attention-deficit hyperactivity disorder (ADHD), one of the most common psychiatric disorders, is characterised by unstable response patterns across multiple cognitive domains. However, the neural mechanisms that explain these characteristic features remain unclear. Using a computational multilevel approach, we propose that ADHD is caused by impaired gain modulation in systems that generate this phenotypic increased behavioural variability. Using Marr's three levels of analysis as a heuristic framework, we focus on this variable behaviour, detail how it can be explained algorithmically, and how it might be implemented at a neural level through catecholamine influences on corticostriatal loops. This computational, multilevel, approach to ADHD provides a framework for bridging gaps between descriptions of neuronal activity and behaviour, and provides testable predictions about impaired mechanisms.

Evaluation of children with ADHD on the Ball-Search Field Task

Searching, defined for the purpose of the present study as the displacement of an individual to locate resources, is a fundamental behavior of all mobile organisms. In humans this behavior underlies many aspects of everyday life, involving cognitive processes such as sustained attention, memory and inhibition. We explored the performance of 36 treatment-free children diagnosed with attention-deficit hyperactivity disorder (ADHD) and 132 children from a control school sample on the ecologically based ball-search field task (BSFT), which required them to locate and collect golf balls in a large outdoor area. Children of both groups enjoyed the task and were motivated to participate in it. However, performance showed that ADHD-diagnosed subjects were significantly less efficient in their searching. We suggest that the BSFT provides a promising basis for developing more complex ecologically-derived tests that might help to better identify particular cognitive processes and impairments associated with ADHD.

Relationships Between Impulsivity, Anxiety, and Risk-Taking and the Neural Correlates of Attention in Adolescents

Although impulsivity, anxiety, and risk-taking may relate to attentional processes, little research has directly investigated how each may be associated with specific facets of attentional processes and their underlying neural correlates. Nineteen adolescents performed a functional magnetic resonance imaging task involving simple, selective, and divided attention. Out-of-scanner-assessed impulsivity, anxiety, and risk-taking scores were not correlated with each other and showed task-phase-specific patterns of association. Results are discussed in light of research and theory suggesting a relationship between these domains and attention and may serve to focus future research aiming to understand these relationships.

The four causes of ADHD: a framework

In addition to the symptoms singled out by the diagnostic criteria for Attention-Deficit Hyperactivity Disorder (ADHD), a comprehensive definition should inform us of the events that trigger ADHD in both its acute and chronic manifestations; the neurobiology that underlies it; and the evolutionary forces that have kept it in the germ line of our species. These factors are organized in terms of Aristotle's four kinds of "causes," or explanations: formal, efficient, material, and final. This framework systematizes the nosology, biology, psychology, and evolutionary pressures that cause ADHD.

Dimensions of manic symptoms in youth: psychosocial impairment and cognitive performance in the IMAGEN sample

BACKGROUND

It has been reported that mania may be associated with superior cognitive performance. In this study, we test the hypothesis that manic symptoms in youth separate along two correlated dimensions and that a symptom constellation of high energy and cheerfulness is associated with superior cognitive performance.

METHOD

We studied 1755 participants of the IMAGEN study, of average age 14.4 years (SD = 0.43), 50.7% girls. Manic symptoms were assessed using the Development and Wellbeing Assessment by interviewing parents and young people. Cognition was assessed using the Wechsler Intelligence Scale For Children (WISC-IV) and a response inhibition task.

RESULTS

Manic symptoms in youth formed two correlated dimensions: one termed exuberance, characterized by high energy and cheerfulness and one of undercontrol with distractibility, irritability and risk-taking behavior. Only the undercontrol, but not the exuberant dimension, was independently associated with measures of psychosocial impairment. In multivariate regression models, the exuberant, but not the undercontrolled, dimension was positively and significantly associated with verbal IQ by both parent- and self-report; conversely, the undercontrolled, but not the exuberant, dimension was associated with poor performance in a response inhibition task.

CONCLUSIONS

Our findings suggest that manic symptoms in youth may form dimensions with distinct correlates. The results are in keeping with previous findings about superior performance associated with mania. Further research is required to study etiological differences between these symptom dimensions and their implications for clinical practice.

Advancing psychotherapy and evidence-based psychological interventions

Psychological models of mental disorders guide research into psychological and environmental factors that elicit and maintain mental disorders as well as interventions to reduce them. This paper addresses four areas. (1) Psychological models of mental disorders have become increasingly transdiagnostic, focusing on core cognitive endophenotypes of psychopathology from an integrative cognitive psychology perspective rather than offering explanations for unitary mental disorders. It is argued that psychological interventions for mental disorders will increasingly target specific cognitive dysfunctions rather than symptom-based mental disorders as a result. (2) Psychotherapy research still lacks a comprehensive conceptual framework that brings together the wide variety of findings, models and perspectives. Analysing the state-of-the-art in psychotherapy treatment research, "component analyses" aiming at an optimal identification of core ingredients and the mechanisms of change is highlighted as the core need towards improved efficacy and effectiveness of psychotherapy, and improved translation to routine care. (3) In order to provide more effective psychological interventions to children and adolescents, there is a need to develop new and/or improved psychotherapeutic interventions on the basis of developmental psychopathology research taking into account knowledge of mediators and moderators. Developmental neuroscience research might be instrumental to uncover associated aberrant brain processes in children and adolescents with mental health problems and to better examine mechanisms of their correction by means of psychotherapy and psychological interventions. (4) Psychotherapy research needs to broaden in terms of adoption of large-scale public health strategies and treatments that can be applied to more patients in a simpler and cost-effective way. Increased research on efficacy and moderators of Internet-based treatments and e-mental health tools (e.g. to support "real time" clinical decision-making to prevent treatment failure or relapse) might be one promising way forward.

Adults with attention-deficit hyperactivity disorder--diagnosis or normality?

Attention-deficit hyperactivity disorder in adults evokes extreme responses within British psychiatrists, because its diagnostic validity and pharmacological treatments are heavily contested. We propose a model that accommodates apparently divergent evidence, and provides a clinical framework for clinicians and patients, allowing safe, responsible and ethically balanced clinical practice.

A behavioral neuroenergetics theory of ADHD

Energetic insufficiency in neurons due to inadequate lactate supply is implicated in several neuropathologies, including attention-deficit/hyperactivity disorder (ADHD). By formalizing the mechanism and implications of such constraints on function, the behavioral Neuroenergetics Theory (NeT) predicts the results of many neuropsychological tasks involving individuals with ADHD and kindred dysfunctions, and entails many novel predictions. The associated diffusion model predicts that response times will follow a mixture of Wald distributions from the attentive state, and ex-Wald distributions after attentional lapses. It is inferred from the model that ADHD participants can bring only 75-85% of the neurocognitive energy to bear on tasks, and allocate only about 85% of the cognitive resources of comparison groups. Parameters derived from the model in specific tasks predict performance in other tasks, and in clinical conditions often associated with ADHD. The primary action of therapeutic stimulants is to increase norepinephrine in active regions of the brain. This activates glial adrenoceptors, increasing the release of lactate from astrocytes to fuel depleted neurons. The theory is aligned with other approaches and integrated with more general theories of ADHD. Therapeutic implications are explored.

Highly impulsive rats: modelling an endophenotype to determine the neurobiological, genetic and environmental mechanisms of addiction

Impulsivity describes the tendency of an individual to act prematurely without foresight and is associated with a number of neuropsychiatric co-morbidities, including drug addiction. As such, there is increasing interest in the neurobiological mechanisms of impulsivity, as well as the genetic and environmental influences that govern the expression of this behaviour. Tests used on rodent models of impulsivity share strong parallels with tasks used to assess this trait in humans, and studies in both suggest a crucial role of monoaminergic corticostriatal systems in the expression of this behavioural trait. Furthermore, rodent models have enabled investigation of the causal relationship between drug abuse and impulsivity. Here, we review the use of rodent models of impulsivity for investigating the mechanisms involved in this trait, and how these mechanisms could contribute to the pathogenesis of addiction.

The utility of chromosomal microarray analysis in developmental and behavioral pediatrics

Chromosomal microarray analysis (CMA) has emerged as a powerful new tool to identify genomic abnormalities associated with a wide range of developmental disabilities including congenital malformations, cognitive impairment, and behavioral abnormalities. CMA includes array comparative genomic hybridization (CGH) and single nucleotide polymorphism (SNP) arrays, both of which are useful for detection of genomic copy number variants (CNV) such as microdeletions and microduplications. The frequency of disease-causing CNVs is highest (20%-25%) in children with moderate to severe intellectual disability accompanied by malformations or dysmorphic features. Disease-causing CNVs are found in 5%-10% of cases of autism, being more frequent in severe phenotypes. CMA has replaced Giemsa-banded karyotype as the first-tier test for genetic evaluation of children with developmental and behavioral disabilities.

Enhancing ADHD medication adherence: challenges and opportunities

Safe and effective medication for attention deficit hyperactivity disorder (ADHD) is available and recommended as first-line treatment for the core symptoms of inattention, overactivity and impulsiveness. Despite impaired functioning during adolescence, many discontinue medication treatment. For children, healthcare decisions are usually made by the parent; older youth make their own decisions. Beliefs and attitudes may differ widely. Some families understand that ADHD is a neurobiological condition and accept that medication is indicated, for others, such treatment is unacceptable. Converging evidence describes negative perceptions of the burden associated with medication use as well as concerns about potential short and long term adverse effects. Indeed experiences of adverse effects are a frequent explanation for discontinuation among youth. Ways to improve shared decision making among practitioners, parents and youth, and to monitor effectiveness, safety and new onset of concurrent difficulties are likely to optimize outcomes.

Rate dependent effects of acute nicotine on risk taking in young adults are not related to ADHD diagnosis

Beneficial effects of nicotine on cognition and behavioral control are hypothesized to relate to the high rates of cigarette smoking in Attention-Deficit/Hyperactivity Disorder (ADHD). Given that ADHD is associated with both impulsivity and elevated risk taking, we hypothesized that nicotine modulates risk taking, as it does impulsivity. 26 non-smoking young adults (15 controls with normal impulsivity and 11 ADHD with high impulsivity) received 7 mg transdermal nicotine, 20mg oral mecamylamine, and placebo on separate days, followed by the Balloon Analog Risk Task (BART). Statistical analyses found no group differences in baseline risk taking. Reexamination of the data using a median split on baseline risk taking, to create high (HRT) and low (LRT) risk taking groups, revealed significant effects of nicotinic drugs that differed by group. Nicotine reduced risk taking in HRT and mecamylamine increased risk taking in LRT. This finding supports the hypothesis that nicotinic receptor function modulates risk taking broadly, beyond those with ADHD, and is consistent with rate dependent cholinergic modulation of other cognitive functions. Further, the results demonstrate that high impulsivity is separable from high risk taking in young adults with ADHD, supporting the utility of these differential behavioral phenotypes for neurobiological studies.

Dopamine receptor D4 exon 3 variable number of tandem repeat polymorphism: Distribution in eastern Indian population

BACKGROUND:

A 48bp variable number of tandem repeat (VNTR), in the dopamine receptor D4 (DRD4), has been extensively studied in association with a variety of traits and neuropsychiatric disorders in different ethnic groups; the VNTR has been found to affect receptor binding.

AIMS:

This investigation, for the first time, compared distribution of DRD4 VNTR in different Indian populations from the eastern part of the country, belonging to Indo-Caucasoid and Indo-Mongoloid ethnicity.

MATERIALS AND METHODS:

852 individuals were recruited and divided into six population groups; Brahmin, Kayastha, Scheduled Caste, Mahishya, Muslim and Manipuri (Meitei). Allele and genotype frequencies were compared among groups as well as with data available for south-western Indian population.

RESULTS:

A total of six alleles (2-7-repeats) were observed, of which the 4-repeat (4R) was most frequent. Gross genetic dissimilarities were noticed between the Indo-Caucasoid and Indo-Mongoloid ethnic groups. Muslim group lacked 5R and 7R, while Manipuri group exhibited a very high frequency of 2R. Populations from eastern India revealed lower 7R frequencies as compared to the south-western populations.

CONCLUSIONS:

The DRD4 VNTR has been reported to play important role in cognition and alleles with higher repeats have been found to be associated with novelty seeking and personality traits. The present comparative analysis of different eastern Indian population would be helpful in extending our knowledge on this particular DRD4 variant. It will also be useful in understanding the behavioural differences between populations in the light of their genetic make up.

Psychopathological aspects of dopaminergic gene polymorphisms in adolescence and young adulthood

Dopamine hypotheses of several psychiatric disorders are based upon the clinical benefits of drugs affecting dopamine transporter or receptors, and have prompted intensive candidate gene research within the dopaminergic system during the last two decades. The aim of this review is to survey the most important findings concerning dopaminergic gene polymorphisms in attention deficit hyperactivity disorder (ADHD), Tourette syndrome (TS), obsessive compulsive disorder, and substance abuse. Also, genetic findings of related phenotypes, such as inattention, impulsivity, aggressive behavior, and novelty seeking personality trait are presented, because recent studies have applied quantitative trait measures using questionnaires, symptom scales, or other objective endophenotypes. Unfortunately, genetic variants with minor effects are problematic to detect in these complex inheritance disorders, often leading to contradictory results. The most consistent association findings relate to ADHD and the dopamine transporter and the dopamine D4 receptor genes. Meta-analyses also support the association between substance abuse and the D2 receptor gene. The dopamine catabolizing enzyme genes, such as monoamine oxidase (MAO) A and catechol-O-methyltransferase (COMT) genes, have been linked to aggressive behaviors.

Annual Research Review: Prenatal stress and the origins of psychopathology: an evolutionary perspective

If a mother is stressed or anxious while pregnant her child is more likely to show a range of symptoms such as those of attention deficit hyperactivity disorder, conduct disorder, aggression or anxiety. While there remains some debate about what proportion of these effects are due to the prenatal or the postnatal environment, and the role of genetics, there is good evidence that prenatal stress exposure can increase the risk for later psychopathology. Why should this be? In our evolutionary history it is possible that some increase in these characteristics in some individuals was adaptive in a stressful environment, and that this type of fetal programming prepared the child or group for the environment in which they were going to find themselves. Anxiety may have been associated with increased vigilance, distractible attention with more perception of danger, impulsivity with more exploration, conduct disorder with a willingness to break rules, and aggression with the ability to fight intruders or predators. This adaptation for a future dangerous environment may explain why stress and anxiety, rather than depression, seem to have these programming effects; why there is a dose-response relationship with prenatal stress from moderate to severe and it is not only toxic stress that has consequences; why not all children are affected and why individual children are affected in different ways; and why the outcomes affected can depend on the sex of the offspring. An evolutionary perspective may give a different understanding of children in our society with these symptoms, and suggest new directions for research. For example, there is some evidence that the type of cognitive deficits observed after prenatal stress have specific characteristics; these may be those which were adaptive in a past environment.

Dopamine receptor D4 allele distribution in Amerindians: a reflection of past behavior differences?

The DRD4 variable number of tandem repeats (VNTR) allele distribution of 172 Guarani (Kaiowá and Ñandeva subgroups) and Kaingang Brazilian Amerindians is reported. These results are integrated with those previously obtained for this ethnic group. Allele frequencies for the three populations are within the interval observed for 15 other Native American populations and show intermediate values between those observed in Amazonia and Patagonia. Significant differences in allele distribution between recent past hunter-gatherer and agriculturalist populations are observed, with an increase of the 7R allele among hunter-gatherers (P < 0.001). Analysis of molecular variance (AMOVA) and pairwise F(ST) data suggest three distinct sectors for the genetic landscape of Native South America: Andes, Center/Southeast region, and Amazonia. Common traits among hunter-gatherers such as novelty-seeking temperament, hyperactivity, and impulsivity could have been important and advantageous in new environments during America's prehistoric colonization.

Wavelet-synchronization methodology: a new approach for EEG-based diagnosis of ADHD

A multi-paradigm methodology is presented for electroencephalogram (EEG) based diagnosis of Attention-Deficit/Hyperactivity Disorder (ADHD) through adroit integration of nonlinear science; wavelets, a signal processing technique; and neural networks, a pattern recognition technique. The selected nonlinear features are generalized synchronizations known as synchronization likelihoods (SL), both among all electrodes and among electrode pairs. The methodology consists of three parts: first detecting the more synchronized loci (group 1) and loci with more discriminative deficit connections (group 2). Using SLs among all electrodes, discriminative SLs in certain sub-bands are extracted. In part two, SLs are computed, not among all electrodes, but between loci of group 1 and loci of group 2 in all sub-bands and the band-limited EEG. This part leads to more accurate detection of deficit connections, and not just deficit areas, but more discriminative SLs in sub-bands with finer resolutions. In part three, a classification technique, radial basis function neural network, is used to distinguish ADHD from normal subjects. The methodology was applied to EEG data obtained from 47 ADHD and 7 control individuals with eyes closed. The Radial Basis Function (RBF) neural network classifier yielded a high accuracy of 95.6% for diagnosis of the ADHD in the feature space discovered in this research with a variance of 0.7%.