19. ADHD

12 01neurLecture 19; November 19, 2013ADHD

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In the Realm of the Hungry Ghosts Gabor Mat

Book recommendation


Die Geschichte vom Zappel-Philipp: An early tale of ADHD?!


Introduction to ADHD Attention-Deficit/Hyperactivity Disorder (ADHD) is

classified as a developmental disorder by the DSM5. Disorders that initially present in children tend to be labeled

as developmental disorders.

The essential feature of ADHD is a persistent pattern of inattention and/or hyperactivity-impulsivity. Importantly, these factors must be shown to impact development in a clinically significant manner.

Hyperactivity refers to excessive motor activity at inappropriate times. This could include running around, fidgeting, tapping, or

talkativeness.

Impulsivity refers to hasty actions that occur in the moment without any kind of forethought. Clinically relevant forms of impulsivity typically involve

possibly harmful behavior (i.e. running into traffic).

ADHD begins in childhood, and the DSM5 requires that symptoms be present before age 12.


Introduction to ADHD Children inevitably have occasional bouts of inattentiveness or

hyperactivity those are part of growing up. A key feature of the ADHD diagnostic is that manifestations of the disorder must appear in multiple settings. This means that ADHD symptoms are not just limited to one place (school, for

example), but appear no matter where the child is.

Context matters. Signs of the disorder may be minimal or absent when the individual is under close supervision, receiving frequent rewards for good behavior, in a novel setting, or doing something interesting. This can make the disorder challenging to diagnose, as the doctors office often

meets all of the above criteria.

The issues associated with ADHD tend to create other problems in the childs life. Academic performance tends to suffer. Social rejection is common as well.

ADHD is not considered an intellectual disorder per se. Nevertheless, mild delays in language, motor and social development are common in children with ADHD. This could be a consequence of simply not paying sufficient attention to things.


Prevalence of ADHD ADHD can be diagnosed in

approximately 2-5% of children in the US, 80% of which are boys.

Adult ADHD may have a prevalence as high as 2.5%. Longitudinal studies of ADHD show that symptoms gradually reduce across the lifespan. Impulsivity and hyperactivity tend to

drop off more than attention. Many adults continue to struggle with attention their entire lives.

ADHD prevalence appears to vary worldwide, though not by as much as is often claimed. North America, when considered as

a whole, has higher rates of ADHD than most other places (South America and Africa being exceptions).

Worldwide prevalence estimated by meta-analysis of 102 ADHD studies (Polanczyk 2007).


Prevalence of ADHD Several challenges exist in interpreting ADHD prevalence

data.

Diagnostic criteria can vary between studies. In the meta-analysis given in the last slide, this was controlled for statistically. Studies using the DSM-III or the ICD-10 (a manual of

disease classification published by the World Health Organization) found lower rates of ADHD than studies that used the DSM-IV.

DSM diagnostic criteria has changed over time. ADD was first defined in the DSM-III with three domains:

Inattention, Impulsivity, and Hyperactivity. Children required several symptoms in each domain to receive a diagnosis.

In the DSM-IV continued with this model, but allowed for diagnosis of either symptoms of inattention or hyperactive symptoms. These seem to be less strict diagnostic criteria.

The DSM5 retains similar criteria to the DSM-IV.

These issues can make it dicult to tell whether ADHD rates are actually increasing, or if its simply a matter of diagnostic criteria changing.


Prevalence of ADHD Even with the same ocial diagnostic criteria, the

diagnosis of ADHD is dicult to separate from the cultural context.

The current DSM5 diagnostic criteria still seem to be based largely on elementary school aged North American boys.

If ADHD occurs everywhere in the world, it would still only be diagnosable in certain cultural contexts. Hyperactivity and inattentiveness would not be as

much of a concern in times and places where children do not go to school.

On the other hand, in areas where academic achievement is prized above all else, even minor levels of inattentiveness and hyperactivity would seem pathological.

The rich interaction between cultural factors and ADHD is not unique. As we have seen, disorders such as anorexia nervosa

are also highly dependent on cultural context.

If ADHD prevalence is roughly the same worldwide, would it be noticed in hunter-gatherer children?

Or would it only be seen when children are subjected to extremely high academic standards from an early age?


Comorbidity of ADHD

Only about 1/3 of children are diagnosed with ADHD alone. The majority are diagnosed with at least one other DSM disorder.


Genetics of ADHD ADHD is elevated in first-degree biological

relatives of individuals with ADHD. First-degree biological relatives are relatives that

share 50% of their genetic material. Your siblings are your first-degree relatives, as are your parents.

The etiology of ADHD has been suggested to be up to 80% genetic. This makes it one of the most heritable disorders.

In spite of the strong evidence for a genetic link, research has not yet uncovered much in the way of specific genes that might be to blame. Weak associations have been found with genes for

the dopamine reuptake transporter and the D4 dopamine receptor.


Environmental/developmental risk factors There is evidence for gene-environment interactions in

ADHD.

Children with a specific mutation in the dopamine reuptake transporter (DAT1) are more likely to exhibit symptoms of ADHD if their mothers smoked during pregnancy.

Perinatal hypoxia a temporary shortage of oxygen around the time of birth has also been linked to the development of ADHD.

There is no convincing evidence that ADHD in the general population can be caused by exposure to food coloring or preservatives. Children who are known to be sensitive to these things do

show some hyperactivity when they are exposed, but they are not reflective of all ADHD cases.

There is also no evidence that ADHD is caused by, or

exacerbated by sugar.


The Stanford marshmallow experiment In the late 1960s, psychologist Walter Mischel

came up with an experiment to test childrens ability to delay gratification.

In this experiment, children (ages 4-6) were brought into the lab and oered a treat of some kind, usually a marshmallow.

They were told that they could eat the marshmallow right away, or they could wait 15 minutes and get two marshmallows instead.

The experimenter would then leave the room, and observe the child through a two-way mirror. Children would struggle to resist their urge to eat the

marshmallow. This level of self-control is quite difficult for a young child.


The Stanford marshmallow experiment When re-examined years later, it turned out that the childs

ability to delay gratification in this simple test was very predictive of their future success in life. Academic success, motivation, self-control, planning,

executive function, and SAT scores were all correlated with performance on the marshmallow test.

Grownup children from the study, 40 years after the fact, were subjected a to a go/no-go experiment that tests response inhibition, a form of impulse control while in an fMRI brain scanner. The authors of this study found that performance on this task

was still worse in those who had given in to marshmallow temptation as youngsters.

They also found that people who had been tempted showed increased ventral striatum activity and decreased prefrontal cortex activity relative to those who had resisted temptation.

The results of these studies seem to suggest that the ability to delay gratification is a skill that persists over the lifetime, and has a neurobiological basis.


Behavioral markers of ADHD Children with ADHD will usually opt for immediate

reward in psychological studies (such as the marshmallow study). This seems to happen regardless of previous

experience in the experiment.

Rewards apparently have less of an influence over the behavior of children with ADHD. Childrens performance in various cognitive tasks

(tests of reaction time, accuracy, etc.,) improves when a reward is offered. This is not the case in children with ADHD their performance remains low irrespective of reward.

Children with ADHD have impaired performance in go/no-go tasks. Interestingly, relatives of children with ADHD also

show impaired performance on these tasks, even if they dont have the disorder themselves. This suggests a possible endophenotype.


Behavioral markers of ADHD There is some evidence showing that

children with ADHD take more risks in gambling experiments.

So it seems that children with ADHD, despite their best intentions, make poor choices with respect to rewarding situations. These deficits point to issues with either

executive function (frontal lobe) or reward function (mesocorticolimbic dopamine system), or perhaps both at the same time.

The Dual Pathway Model is a theory about ADHD suggesting dysfunctions in both systems are to blame.


Neuroimaging findings in ADHD Numerous studies have shown evidence

for structural and functional brain abnormalities in children with ADHD.

Children with ADHD often have reduced volume of certain parts of the prefrontal cortex (PFC), striatum, cerebellum, and corpus callosum.

Problems with the PFC and striatum are perhaps not surprising, given the deficits in executive function and reward processing seen in ADHD. Findings in the cerebellum and corpus

callosum are somewhat more difficult to explain


Treatment of ADHD Despite the complexity of the ADHD diagnosis, the

ecacy of the available pharmacological treatment options is actually quite good. Psychostimulant drugs are effective in 70-90% of cases.

The most common pharmacological treatments for ADHD are drugs of the psychostimulant variety. These have been in regular use since at least the 1970s. Psychostimulants are drugs that stimulate the brain, and

generally increase the activity of the CNS. Caffeine is an example of a legal psychostimulant,

methamphetamine and cocaine are two examples of illegal psychostimulants.

Popular drugs include methylphenidate (Ritalin), amphetamine (Adderall), and d-amphetamine (Dexedrine). These drugs are given at low doses, in long-acting, slow-

release formats that limit the rush that characterizes their illegal counterparts.


Worldwide use of methylphenidate

Almost without exception, the rate of methylphenidate (Ritalin) use is increasing worldwide. Its not likely that the rate of ADHD has increased appreciably over these years.


Non-drug treatments for ADHD

Numerous non-drug treatments for ADHD have been proposed. Unfortunately, they do not seem to be very eective in controlled studies.


Ethics of ADHD treatment Because ADHD is mostly a disorder of childhood, its treatment requires special

consideration.

It is often suggested that children are overmedicated, or that medication is used as a substitute for eective parenting/schooling.

Children are not small adults, so studies of drug eects on adult brains cannot be safely generalized to children.

Emerging data from animal studies of chronic psychostimulant treatment suggest that long-term side eects may exist. Chronic methylphenidate treatment in young rats reduces the rewarding power of

cocaine in adulthood. Chronic amphetamine treatment reduces dopamine terminals in the striatum of

monkeys.

ADHD symptoms do tend to improve on their own as the child ages. Should we

just leave ADHD alone and let it resolve itself? Academic and social success during childhood strongly influences the rest of the

individuals life. The possible risks of medication may be a fair tradeoff for a lifetimes worth of positive outcomes?


Is ADHD real? The existence of ADHD is fairly uncontroversial among neuroscientists

and psychiatrists, but its existence is disputed by other academics and the popular press. Arguments used by those who deny the existence of ADHD are from a

common stock of arguments used by deniers of everything else.

Perhaps ADHD is simply the medicalization of youthful rambunctiousness. Maybe its an eort to sell more drugs to kids? It could even a childs way of communicating dissatisfaction with their current home/school environment

The fact that drugs are eective in treating ADHD does not necessarily point to a real underlying condition these drugs can help anybody pay attention.

The fact that modern diagnostic criteria for ADHD can produce reliable results, combined with the observation of neurobiological and behavioral correlates of the disorder suggest that it is real. Still, a nuanced view of mental illness is valuable


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A good way to think about mental illness

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Every human trait can be measured along a spectrum. The majority of people fall somewhere in the middle of the range. A minority of people may be on either the high or low extremes.

Based on their relative success in things that seem to matter, we establish cuto lines at the high and low ends of the spectrum. Those falling outside the cuto lines may be considered ill, or perhaps gifted, whatever the case may be.


A good way to think about mental illnessEvery aspect of our psychological function is related to the brain in some fashion. If you think about it, it has to be this way. What other part of the body could they possibly relate to?

This is why scientists speak of the neural correlates of behavior. Dierences in brain function correlate with dierences in behavioral and psychological function.

This approach tells us a great deal about how the brain works, and how psychological issues can be treated using neuroscience. But does it make mental illnesses any more real? Or does it simply move the problem inward?


So is ADHD real? If the previous two slides were eective, then you

should understand that any aspect of human variation, be it physical or psychological, could be classified as a disorder if it is suciently dierent from average.

But cuto points are fluid they change over time, across cultures, and between editions of the DSM. They also change as we understand more and more

about the brain.

So if we decide to question the ontological status of ADHD, we might justifiably ask the same questions about any other mental illness even one as severe as schizophrenia (and yes, people do occasionally argue that

schizophrenia doesnt exist)

19. ADHD

Documents

prevalence of adhd adhd

adhd children

adhd symptoms

adhd diagnostic

adult adhd

early tale of adhd

adhd studies polanczyk

longitudinal studies