|Attention deficit hyperactivity disorder|
Children with ADHD find it more difficult to focus and to complete their schoolwork.
|Classification and external resources|
|Patient UK||Attention deficit hyperactivity disorder|
Attention deficit hyperactivity disorder (ADHD, similar to hyperkinetic disorder in the ICD-10) is a neurodevelopmental psychiatric disorder in which there are significant problems with executive functions (e.g., attentional control and inhibitory control) that cause attention deficits, hyperactivity, or impulsiveness which is not appropriate for a person's age. These symptoms must begin by age six to twelve and persist for more than six months for a diagnosis to be made. In school-aged individuals inattention symptoms often result in poor school performance. Although it causes impairment, particularly in modern society, many children with ADHD have a good attention span for tasks they find interesting.
Despite being the most commonly studied and diagnosed psychiatric disorder in children and adolescents, the cause in the majority of cases is unknown. It affects about 6–7% of children when diagnosed via the DSM-IV criteria and 1–2% when diagnosed via the ICD-10 criteria. Rates are similar between countries and depend mostly on how it is diagnosed. ADHD is diagnosed approximately three times more in boys than in girls. About 30–50% of people diagnosed in childhood continue to have symptoms into adulthood and between 2–5% of adults have the condition. The condition can be difficult to tell apart from other disorders as well as that of high normal activity.
ADHD management usually involves some combination of counseling, lifestyle changes, and medications. Medications are only recommended as a first-line treatment in children who have severe symptoms and may be considered for those with moderate symptoms who either refuse or fail to improve with counseling. Stimulant therapy is not recommended in preschool-aged children. Treatment with stimulants is effective for up to 14 months; however, its long term effectiveness is unclear. Adolescents and adults tend to develop coping skills which make up for some or all of their impairments.
ADHD, its diagnosis, and its treatment have been considered controversial since the 1970s. The controversies have involved clinicians, teachers, policymakers, parents, and the media. Topics include ADHD's causes and the use of stimulant medications in its treatment. Most healthcare providers accept ADHD as a genuine disorder, and the debate in the scientific community mainly centers on how it is diagnosed and treated.
Inattention, hyperactivity (restlessness in adults), disruptive behavior, and impulsivity are common in ADHD. Academic difficulties are frequent as are problems with relationships. The symptoms can be difficult to define as it is hard to draw a line at where normal levels of inattention, hyperactivity, and impulsivity end and significant levels requiring interventions begin.
To be diagnosed per DSM-5, symptoms must be observed in multiple settings for six months or more and to a degree that is much greater than others of the same age. They must also cause problems in the person's social, academic, or work life.
Based on the presenting symptom ADHD can be divided into three subtypes: predominantly inattentive, predominantly hyperactive-impulsive, and combined type.
An individual with inattention may have some or all of the following symptoms:
An individual with hyperactivity may have some or all of the following symptoms:
These hyperactivity symptoms tend to go away with age and turn into "inner restlessness" in teens and adults with ADHD.
An individual with impulsivity may have some or all of the following symptoms:
People with ADHD more often have difficulties with social skills, such as social interaction and forming and maintaining friendships. This is true for all subtypes. About half of children and adolescents with ADHD experience social rejection by their peers compared to 10–15% of non-ADHD children and adolescents. People with ADHD have attention deficits which cause difficulty processing verbal and nonverbal language which can negatively affect social interaction. They also may drift off during conversations, and miss social cues.
Difficulties managing anger are more common in children with ADHD as are poor handwriting and delays in speech, language and motor development. Although it causes significant impairment, particularly in modern society, many children with ADHD have a good attention span for tasks they find interesting.
In children ADHD occurs with other disorders about ⅔ of the time. Some commonly associated conditions include:
There is an association with persistent bed wetting, language delay, and developmental coordination disorder (DCD), with about half of people with DCD having ADHD. The language delay in people with ADHD can include problems with auditory processing disorders such as short-term auditory memory weakness, difficulty following instructions, slow speed of processing written and spoken language, difficulties listening in distracting environments e.g. the classroom, and weakness in reading comprehension.
The cause of most cases of ADHD is unknown; however, it is believed to involve interactions between genetic and environmental factors. Certain cases are related to previous infection of or trauma to the brain.
Twin studies indicate that the disorder is often inherited from one's parents with genetics determining about 75% of cases. Siblings of children with ADHD are three to four times more likely to develop the disorder than siblings of children without the disorder. Genetic factors are also believed to be involved in determining whether ADHD persists into adulthood.
Typically, a number of genes are involved, many of which directly affect dopamine neurotransmission. Those involved with dopamine include DAT, DRD4, DRD5, TAAR1, MAOA, COMT, and DBH. Other genes associated with ADHD include SERT, HTR1B, SNAP25, GRIN2A, ADRA2A, TPH2, and BDNF. A common variant of a gene called LPHN3 is estimated to be responsible for about 9% of cases and when this gene is present, people are particularly responsive to stimulant medication.
As ADHD is common, natural selection likely favored the traits, at least individually, and they may have provided a survival advantage. For example, some women may be more attracted to males who are risk takers, increasing the frequency of genes that predispose to ADHD in the gene pool. As it is more common in children of anxious or stressed mothers, some argue that ADHD is an adaptation that helps children face a stressful or dangerous environment with, for example, increased impulsivity and exploratory behavior.
Hyperactivity might have been beneficial, from an evolutionary perspective, in situations involving risk, competition, or unpredictable behavior (i.e. exploring new areas or finding new food sources). In these situations, ADHD could have been beneficial to society as a whole even while being harmful to the individual. Additionally, in certain environments it may have offered advantages to the individuals themselves, such as quicker response to predators or superior hunting skills.
Environmental factors are believed to play a lesser role. Alcohol intake during pregnancy can cause fetal alcohol spectrum disorder which can include symptoms similar to ADHD. Exposure to tobacco smoke during pregnancy can cause problems with central nervous system development and can increase the risk of ADHD. Many children exposed to tobacco do not develop ADHD or only have mild symptoms which do not reach the threshold for a diagnosis. A combination of a genetic predisposition with tobacco exposure may explain why some children exposed during pregnancy may develop ADHD and others do not. Children exposed to lead, even low levels, or polychlorinated biphenyls may develop problems which resemble ADHD and fulfill the diagnosis. Exposure to the organophosphate insecticides chlorpyrifos and dialkyl phosphate is associated with an increased risk; however, the evidence is not conclusive.
Very low birth weight, premature birth and early adversity also increase the risk as do infections during pregnancy, at birth, and in early childhood. These infections include, among others, various viruses (measles, varicella, rubella, enterovirus 71) and streptococcal bacterial infection. At least 30% of children with a traumatic brain injury later develop ADHD and about 5% of cases are due to brain damage.
Some children may react negatively to food dyes or preservatives. It is possible that certain food coloring may act as a trigger in those who are genetically predisposed but the evidence is weak.:452 The United Kingdom and European Union have put in place regulatory measures based on these concerns; the FDA has not.
The diagnosis of ADHD can represent family dysfunction or a poor educational system rather than an individual problem. Some cases may be explained by increasing academic expectations, with a diagnosis being a method for parents in some countries to get extra financial and educational support for their child. The youngest children in a class have been found to be more likely to be diagnosed as having ADHD possibly due to their being developmentally behind their older classmates. Behavior typical of ADHD occurs more commonly in children who have experienced violence and emotional abuse.
Per social construction theory it is societies that determine the boundary between normal and abnormal behavior. Members of society, including physicians, parents, and teachers, determine which diagnostic criteria are used and, thus, the number of people affected. This leads to the current situation where the DSM-IV arrives at levels of ADHD three to four times higher than those obtained with the ICD-10. Thomas Szasz, a supporter of this theory, has argued that ADHD was "invented and not discovered."
Current models of ADHD suggest that it is associated with functional impairments in some of the brain's neurotransmitter systems, particularly those involving dopamine and norepinephrine. The dopamine and norepinephrine pathways that originate in the ventral tegmental area and locus coeruleus project to diverse regions of the brain and govern a variety of cognitive processes. The dopamine pathways and norepinephrine pathways which project to the prefrontal cortex and striatum (particularly, the nucleus accumbens) are directly responsible for modulating executive function (cognitive control of behavior), motivation, and reward perception; these pathways are known to play a central role in the pathophysiology of ADHD. Larger models of ADHD with additional pathways have been proposed.
In children with ADHD, there is a general reduction of volume in certain brain structures, with a proportionally greater decrease in the volume in the left-sided prefrontal cortex. The posterior parietal cortex also shows thinning in ADHD individuals compared to controls. Other brain structures in the prefrontal-striatal-cerebellar and prefrontal-striatal-thalamic circuits have also been found to differ between people with and without ADHD.
Previously it was thought that the elevated number of dopamine transporters in people with ADHD was part of the pathophysiology but it appears that the elevated numbers are due to adaptation to exposure to stimulants. Current models involve the mesocorticolimbic dopamine pathway and the locus coeruleus-noradrenergic system. ADHD psychostimulants possess treatment efficacy because they increase neurotransmitter activity in these systems. There may additionally be abnormalities in serotoninergic and cholinergic pathways. Neurotransmission of glutamate, a cotransmitter with dopamine in the mesolimbic pathway, seems to be also involved.
ADHD symptoms involve a difficulty with executive functions. Executive function refers to a number of mental processes that are required to regulate, control, and manage daily life tasks. Some of these impairments include problems with organization, time keeping, excessive procrastination, concentration, processing speed, regulating emotions, and utilizing working memory. People usually have decent long-term memory. The criteria for an executive function deficit are met in 30–50% of children and adolescents with ADHD. One study found that 80% of individuals with ADHD were impaired in at least one executive function task, compared to 50% for individuals without ADHD. Due to the rates of brain maturation and the increasing demands for executive control as a person gets older, ADHD impairments may not fully manifest themselves until adolescence or even early adulthood.
ADHD has also been associated with motivational deficits in children. Children with ADHD find it difficult to focus on long-term over short-term rewards, and exhibit impulsive behavior for short-term rewards. In these individuals, a large amount of positive reinforcement effectively improves task performance. ADHD stimulants may improve persistence in ADHD children as well.
ADHD is diagnosed by an assessment of a person's childhood behavioral and mental development, including ruling out the effects of drugs, medications and other medical or psychiatric problems as explanations for the symptoms. It often takes into account feedback from parents and teachers with most diagnoses begun after a teacher raises concerns. It may be viewed as the extreme end of one or more continuous human traits found in all people. Whether someone responds to medications does not confirm or rule out the diagnosis. As imaging studies of the brain do not give consistent results between individuals, they are only used for research purposes and not diagnosis.
In North America, the DSM-IV or DSM-5 criteria are often used for diagnosis, while European countries usually use the ICD-10. With the DSM-IV criteria a diagnosis of ADHD is 3–4 times more likely than with the ICD-10 criteria. It is classified as neurodevelopmental psychiatric disorder. Additionally, it is classified as a disruptive behavior disorder along with oppositional defiant disorder, conduct disorder, and antisocial personality disorder. A diagnosis does not imply a neurological disorder.
Associated conditions that should be screened for include anxiety, depression, oppositional defiant disorder, conduct disorder, and learning and language disorders. Other conditions that should be considered are other neurodevelopmental disorders, tics, and sleep apnea.
Diagnosis of ADHD using quantitative electroencephalography (QEEG) is an ongoing area of investigation, although the value of QEEG in ADHD is currently unclear. In the United States, the Food and Drug Administration has approved the use of QEEG to evaluate the morbidity of ADHD.
As with many other psychiatric disorders, formal diagnosis is made by a qualified professional based on a set number of criteria. In the United States, these criteria are defined by the American Psychiatric Association in the DSM. Based on the DSM criteria, there are three sub-types of ADHD:
This subdivision is based on presence of at least six out of nine long-term (lasting at least six months) symptoms of inattention, hyperactivity–impulsivity, or both. To be considered, the symptoms must have appeared by the age of six to twelve and occur in more than one environment (e.g. at home and at school or work). The symptoms must be not appropriate for a child of that age and there must be evidence that it is causing social, school or work related problems.
Most children with ADHD have the combined type. Children with the inattention subtype are less likely to act out or have difficulties getting along with other children. They may sit quietly, but without paying attention resulting in the child difficulties being overlooked.[medical citation needed]
In the ICD-10, the symptoms of "hyperkinetic disorder" are analogous to ADHD in the DSM-5. When a conduct disorder (as defined by ICD-10) is present, the condition is referred to as hyperkinetic conduct disorder. Otherwise, the disorder is classified as disturbance of activity and attention, other hyperkinetic disorders or hyperkinetic disorders, unspecified. The latter is sometimes referred to as, hyperkinetic syndrome.
Adults with ADHD are diagnosed under the same criteria, including that their signs must have been present by the age of six to twelve. Questioning parents or guardians as to how the person behaved and developed as a child may form part of the assessment; a family history of ADHD also adds weight to a diagnosis. While the core symptoms of ADHD are similar in children and adults they often present differently in adults than in children, for example excessive physical activity seen in children may present as feelings of restlessness and constant mental activity in adults.
|ADHD symptoms which may be related to other disorders|
Symptoms of ADHD such as low mood and poor self-image, mood swings, and irritability can be confused with dysthymia, cyclothymia or bipolar disorder as well as with borderline personality disorder. Some symptoms that are due to anxiety disorders, antisocial personality disorder, developmental disabilities or mental retardation or the effects of substance abuse such as intoxication and withdrawal can overlap with some ADHD. These disorders can also sometimes occur along with ADHD. Medical conditions which can cause ADHD type symptoms include: hyperthyroidism, seizure disorder, lead toxicity, hearing deficits, hepatic disease, sleep apnea, drug interactions, and head injury.
Primary sleep disorders may affect attention and behavior and the symptoms of ADHD may affect sleep. It is thus recommended that children with ADHD be regularly assessed for sleep problems. Sleepiness in children may result in symptoms ranging from the classic ones of yawning and rubbing the eyes, to hyperactivity and inattentiveness. Obstructive sleep apnea, can also cause ADHD type symptoms.
The management of ADHD typically involves counseling or medications either alone or in combination. While treatment may improve long-term outcomes, it does not get rid of negative outcomes entirely.
Medications used include stimulants, atomoxetine, alpha-2 adrenergic receptor agonists, and sometimes antidepressants. Dietary modifications may also be of benefit with evidence supporting free fatty acids and reduced exposure to food coloring. Removing other foods from the diet is not currently supported by the evidence.
There is good evidence for the use of behavioral therapies in ADHD and they are the recommended first line treatment in those who have mild symptoms or are preschool-aged. Psychological therapies used include: psychoeducational input, behavior therapy, cognitive behavioral therapy (CBT), interpersonal psychotherapy, family therapy, school-based interventions, social skills training, parent management training, and neurofeedback. Parent training and education have been found to have short-term benefits. There is little high quality research on the effectiveness of family therapy for ADHD, but the evidence that exists shows that it is similar to community care and better than a placebo. Several ADHD specific support groups exist as informational sources and may help families cope with ADHD.
Training in social skills, behavioral modification and medication may have some limited beneficial effects. The most important factor in reducing later psychological problems, such as major depression, criminality, school failure, and substance use disorders is formation of friendships with people who are not involved in delinquent activities.
Regular physical exercise, particularly aerobic exercise, is an effective add on treatment for ADHD, although the best type and intensity is not currently known. In particular, physical exercise has been shown to result in better behavior and motor abilities without causing any side effects.
Stimulant medications are the pharmaceutical treatment of choice. They have at least some effect in the short term in about 80% of people. There are a number of non-stimulant medications, such as atomoxetine, bupropion, guanfacine, and clonidine that may be used as alternatives. There are no good studies comparing the various medications; however, they appear more or less equal with respect to side effects. Stimulants appear to improve academic performance while atomoxetine does not. There is little evidence on their effects on social behaviors. Medications are not recommended for preschool children, as the long-term effects in this age group are not known. The long-term effects of stimulants generally are unclear with one study finding benefit, another finding no benefit and a third finding evidence of harm. Magnetic resonance imaging studies suggest that long-term treatment with amphetamine or methylphenidate decreases abnormalities in brain structure and function found in subjects with ADHD. Atomoxetine, due to its lack of abuse potential, may be preferred in those who are at risk of abusing stimulant medication. Guidelines on when to use medications vary by country, with the United Kingdom's National Institute for Health and Care Excellence recommending use only in severe cases, while most United States guidelines recommend medications in nearly all cases.
While stimulants and atomoxetine are usually safe, there are side-effects and contraindications to their use. Stimulants may result in psychosis or mania; however, this is relatively uncommon. Regular monitoring has been recommended in those on long-term treatment. Stimulant therapy should be stopped from time to assess for continuing need for medication. Stimulant medications have the potential for abuse and dependence; several studies indicate that untreated ADHD is associated with elevated risk of substance abuse and conduct disorders. The use of stimulants appears to either reduce this risk or have no effect on it. The safety of these medications in pregnancy is unclear.
Zinc deficiency has been associated with inattentive symptoms and there is evidence that zinc supplementation can benefit children with ADHD who have low zinc levels. Iron, magnesium and iodine may also have an effect on ADHD symptoms. There is evidence of a modest benefit of omega 3 fatty acid supplementation, but it is not recommended in place of traditional medication.
An 8-year follow up of children diagnosed with ADHD (combined type) found that they often have difficulties in adolescence, regardless of treatment or lack thereof. In the US, less than 5% of individuals with ADHD get a college degree, compared to 28% of the general population aged 25 years and older. The proportion of children meeting criteria for ADHD drops by about half in the three years following the diagnosis and this occurs regardless of treatments used. ADHD persists into adulthood in about 30–50% of cases. Those affected are likely to develop coping mechanisms as they mature, thus compensating for their previous symptoms.
ADHD is estimated to affect about 6–7% of people aged 18 and under when diagnosed via the DSM-IV criteria. When diagnosed via the ICD-10 criteria rates in this age group are estimated at 1–2%. Children in North America appear to have a higher rate of ADHD than children in Africa and the Middle East; this is believed to be due to differing methods of diagnosis rather than a difference in underlying frequency. If the same diagnostic methods are used, the rates are more or less the same between countries. It is diagnosed approximately three times more often in boys than in girls. This difference between sexes may reflect either a difference in susceptibility or that females with ADHD are less likely to be diagnosed than males.
Rates of diagnosis and treatment have increased in both the United Kingdom and the United States since the 1970s. This is believed to be primarily due to changes in how the condition is diagnosed and how readily people are willing to treat it with medications rather than a true change in how common the condition is. It is believed that changes to the diagnostic criteria in 2013 with the release of the DSM-5 will increase the percentage of people diagnosed with ADHD, especially among adults.
Hyperactivity has long been part of the human condition. Sir Alexander Crichton describes "mental restlessness" in his book An inquiry into the nature and origin of mental derangement written in 1798. ADHD was first clearly described by George Still in 1902. The terminology used to describe the condition has changed over time and has included: in the DSM-I (1952) "minimal brain dysfunction", in the DSM-II (1968) "hyperkinetic reaction of childhood", in the DSM-III (1980) "attention-deficit disorder (ADD) with or without hyperactivity". In 1987 this was changed to ADHD in the DSM-III-R and the DSM-IV in 1994 split the diagnosis into three subtypes, ADHD inattentive type, ADHD hyperactive-impulsive type and ADHD combined type. These terms were kept in the DSM-5 in 2013. Other terms have included "minimal brain damage" used in the 1930s.
The use of stimulants to treat ADHD was first described in 1937. In 1934, Benzedrine became the first amphetamine medication approved for use in the United States. Methylphenidate was introduced in the 1950s, and enantiopure dextroamphetamine in the 1970s.
ADHD, its diagnosis, and its treatment have been controversial since the 1970s. The controversies involve clinicians, teachers, policymakers, parents, and the media. Positions range from the view that ADHD is within the normal range of behavior to the hypothesis that ADHD is a genetic condition. Other areas of controversy include the use of stimulant medications in children, the method of diagnosis, and the possibility of overdiagnosis. In 2012, the National Institute for Health and Care Excellence, while acknowledging the controversy, states that the current treatments and methods of diagnosis are based on the dominant view of the academic literature. In 2014, Keith Conners, one of the early advocates for recognition of the disorder, spoke out against overdiagnosis in a NY Times article. In contrast, a 2014 peer-reviewed medical literature review indicated that ADHD is underdiagnosed in adults.
With widely differing rates of diagnosis across countries, states within countries, races, and ethnicities, some suspect factors other than the presence of the symptoms of ADHD are playing a role in diagnosis. Some sociologists consider ADHD to be an example of the medicalization of deviant behavior, that is, the turning of the previously non-medical issue of school performance into a medical one. Most healthcare providers accept ADHD as a genuine disorder, at least in the small number of people with severe symptoms. Among healthcare providers the debate mainly centers on diagnosis and treatment in the much larger number of people with less severe symptoms.
As of 2009[update], 8% of all United States Major League Baseball players had been diagnosed with ADHD, making the disorder common among this population. The increase coincided with the League's 2006 ban on stimulants, which has raised concern that some players are mimicking or falsifying the symptoms or history of ADHD to get around the ban on the use of stimulants in sport.
A number of notable individuals have given controversial statements regarding ADHD. Tom Cruise has referred to the medications Ritalin and Adderall as "street drugs". Ushma S. Neill criticized this view, stating that the doses of stimulants used in the treatment of ADHD do not cause addiction and that there is some evidence of a reduced risk of later substance addiction in children treated with stimulants. In England, Susan Greenfield spoke out publicly in 2007 in the House of Lords about the need for a wide-ranging inquiry into the dramatic increase in the diagnosis of ADHD in the UK and possible causes. Her comments followed a BBC Panorama program that highlighted research that suggested medications are no better than other forms of therapy in the long term. In 2010, the BBC Trust criticized the 2007 BBC Panorama program for summarizing the research as showing "no demonstrable improvement in children's behavior after staying on ADHD medication for three years" when in actuality "the study found that medication did offer a significant improvement over time" although the long-term benefits of medication were found to be "no better than children who were treated with behavior therapy."
It is estimated that between 2–5% of adults have ADHD. Around half of children with ADHD continue to have ADHD as adults. Approximately 25% of children continue to experience ADHD symptoms into adulthood, while the remaining 75% experience fewer or no symptoms. Most adults remain untreated. Many have a disorganized life and use non-prescribed drugs or alcohol as a coping mechanism. Other problems may include relationship and job difficulties, and an increased risk of criminal activities. Associated mental health problems include: depression, anxiety disorder, and learning disabilities.
Some ADHD symptoms in adults differ from those seen in children. While children with ADHD may climb and run about excessively, adults may experience an inability to relax or talk excessively in social situations. Adults with ADHD may start relationships impulsively, display sensation-seeking behavior, and be short-tempered. Addictive behavior such as substance abuse and gambling are common. The DSM-IV criteria have been criticized for not being appropriate for adults; those who present differently may lead to the claim that they outgrew the diagnosis.
The diagnosis of ADHD and the significance of its impact on children with a high intelligence quotient (IQ) is controversial. Most studies have found similar impairments regardless of IQ, with higher rates of repeating grades and having social difficulties. Additionally, more than half of people with high IQ and ADHD experience major depressive disorder or oppositional defiant disorder at some point in their lives. Generalised anxiety disorder, separation anxiety disorder and social phobia are also more common. There is some evidence that individuals with high IQ and ADHD have a lowered risk of substance abuse and anti-social behavior compared to children with low and average IQ and ADHD. Children and adolescents with high IQ can have their level of intelligence mismeasured during a standard evaluation and may require more comprehensive testing.
Reports indicate that ADHD affects 2.5%–5% of adults in the general population,5–8 compared with 5%–7% of children.9,10 ... However, fewer than 20% of adults with ADHD are currently diagnosed and/or treated by psychiatrists.7,15,16
Results suggest there is moderate-to-high-level evidence that combined pharmacological and behavioral interventions, and pharmacological interventions alone can be effective in managing the core ADHD symptoms and academic performance at 14 months. However, the effect size may decrease beyond this period. ... Only one paper53 examining outcomes beyond 36 months met the review criteria. ... There is high level evidence suggesting that pharmacological treatment can have a major beneficial effect on the core symptoms of ADHD (hyperactivity, inattention, and impulsivity) in approximately 80% of cases compared with placebo controls, in the short term.22
New, palatable foods cause dopamine release from VTA neurons of the midbrain that project to the nucleus accumbens, prefrontal cortex, and other limbic structures that regulate emotion. Dopamine acts in the nucleus accumbens to attach motivational significance to stimuli associated with reward. ... It acts in the orbital prefrontal cortex to set a value on rewards ...
Therapeutic (relatively low) doses of psychostimulants, such as methylphenidate and amphetamine, improve performance on working memory tasks both in normal subjects and those with ADHD. Positron emission tomography (PET) demonstrates that methylphenidate decreases regional cerebral blood flow in the dorsolateral prefrontal cortex and posterior parietal cortex while improving performance of a spacial working memory task. This suggests that cortical networks that normally process spatial working memory become more efficient in response to the drug. ... [It] is now believed that dopamine and norepinephrine, but not serotonin, produce the beneficial effects of stimulants on working memory. At abused (relatively high) doses, stimulants can interfere with working memory and cognitive control ... stimulants act not only on working memory function, but also on general levels of arousal and, within the nucleus accumbens, improve the saliency of tasks. Thus, stimulants improve performance on effortful but tedious tasks ... through indirect stimulation of dopamine and norepinephrine receptors.
DA has multiple actions in the prefrontal cortex. It promotes the "cognitive control" of behavior: the selection and successful monitoring of behavior to facilitate attainment of chosen goals. Aspects of cognitive control in which DA plays a role include working memory, the ability to hold information "on line" in order to guide actions, suppression of prepotent behaviors that compete with goal-directed actions, and control of attention and thus the ability to overcome distractions. Cognitive control is impaired in several disorders, including attention deficit hyperactivity disorder. ... Noradrenergic projections from the LC thus interact with dopaminergic projections from the VTA to regulate cognitive control. ... it has not been shown that 5HT makes a therapeutic contribution to treatment of ADHD.
Recent conceptualizations of ADHD have taken seriously the distributed nature of neuronal processing [10,11,35,36]. Most of the candidate networks have focused on prefrontal-striatal-cerebellar circuits, although other posterior regions are also being proposed .
Behavioral studies show altered processing of reinforcement and incentives in children with ADHD. These children respond more impulsively to rewards and choose small, immediate rewards over larger, delayed incentives. Interestingly, a high intensity of reinforcement is effective in improving task performance in children with ADHD. Pharmacotherapy may also improve task persistence in these children. ... Previous studies suggest that a clinical approach using interventions to improve motivational processes in patients with ADHD may improve outcomes as children with ADHD transition into adolescence and adulthood.
The present review summarises the impact of exercise interventions (1–10 weeks in duration with at least two sessions each week) on parameters related to ADHD in 7-to 13-year-old children. We may conclude that all different types of exercise (here yoga, active games with and without the involvement of balls, walking and athletic training) attenuate the characteristic symptoms of ADHD and improve social behaviour, motor skills, strength and neuropsychological parameters without any undesirable side effects. Available reports do not reveal which type, intensity, duration and frequency of exercise is most effective in this respect and future research focusing on this question with randomised and controlled long-term interventions is warranted.
As exercise has been found to enhance neural growth and development, and improve cognitive and behavioural functioning in [healthy] individuals and animal studies, we reviewed the literature on the effects of exercise in children and adolescents with ADHD and animal models of ADHD behaviours.
A limited number of undersized non-randomized, retrospective and cross-sectional studies have investigated the impact of exercise on ADHD and the emotional, behavioural and neuropsychological problems associated with the disorder. The findings from these studies provide some support for the notion that exercise has the potential to act as a protective factor for ADHD. ... Although it remains unclear which role, if any, BDNF plays in the pathophysiology of ADHD, enhanced neural functioning has been suggested to be associated with the reduction of remission of ADHD symptoms.49,50,72 As exercise can elicit gene expression changes mediated by alterations in DNA methylation38, the possibility emerges that some of the positive effects of exercise could be caused by epigenetic mechanisms, which may set off a cascade of processes instigated by altered gene expression that could ultimately link to a change in brain function.
Basal ganglia regions like the right globus pallidus, the right putamen, and the nucleus caudatus are structurally affected in children with ADHD. These changes and alterations in limbic regions like ACC and amygdala are more pronounced in non-treated populations and seem to diminish over time from child to adulthood. Treatment seems to have positive effects on brain structure.
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