Part III: Externalizing Behavior Disorders

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Part III Externalizing Behavior Disorders
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Attention-Deficit/Hyperactivity Disorder

• Chapter 12
• Joel Nigg

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HISTORICAL CONTEXT

• In the 1930s, it was discovered that Benzedrine
  (an amphetamine-like stimulant) seemed to calm
  hyperkinetic children.
• FDA approval was granted for Ritalin in the early
  1960s.
• By the 1970s, treating inattentive and
  hyperactive children with stimulants began to
  spark controversy.
• Treatment rates rose markedly from 1990 to the
  present, attributable in part to changes in
  educational policy that facilitated
  identification of children with ADHD in the
  United States.
• Traditionally considered a disorder of childhood,
  by the end of the 20th century it became clear
  that ADHD often persists into adolescence and
  adulthood.

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TERMINOLOGICAL AND CONCEPTUAL ISSUES

• It is important to note that symptom domains are
  divided into distinct dimensionsin the DSM-IV
• Inattentive-disorganized
• Strongly associated with academic problems and a
  range of other impairments
• Hyperactive-impulsive
• Associated with peer rejection and disruptive
  tendencies in school and at home

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PREVALENCE

• In one national survey, a 1-year prevalence rate
  for children and adolescents of 8.5 is reported
  (Merikangas et al., 2010).
• Among U.S. adults, the prevalence of ADHD is 4.4
  (Kessler et al., 2006).

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RISK FACTORS AND ETIOLOGICAL FORMULATIONS

• Within-child correlates may elucidate etiology
  and help explain the behavioral problems
  observed.
• Risk factors may contribute to the disorder,
  perhaps via these internal mechanisms.
• Genetic Influences on Liability to ADHD
• Hereditability of ADHD is likely to be around .7.
  
• Nonshared environmental effects account for the
  remainder of variance in ADHD liability.

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  Gene Environment Effects

• Environmental Risks and Triggers
• Specific environments
• Inadequate schooling, rapid societal tempo, and
  family stress are contributing to an alleged
  increase in ADHD incidence.
• Many of these sociological ideas are interesting
  but untested (or untestable) and some (like
  schooling) occur too late in development to
  account for ADHD onset.
• Regarding other potential environmental
  potentiators of genetic liability, biological
  context, both pre- and postnatally, may be
  especially important

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  Gene Environment Effects

• Mechanisms I Neuroimaging Findings
• Structural findings demonstrate that on average,
  children with ADHD evidence a 5 reduction in
  overall brain volume and a 12 reduction in
  volume of key frontal and subcortical structures,
  particularly the prefrontal cortex (PFC), which
  is crucial to complex, planned behavior, keeping
  goals in mind, and overriding inappropriate
  responses.
• The most compelling evidence points to a neural
  circuit that links the prefrontal cortex and a
  subcortical region known as the striatum, a
  circuit thought to be important in response
  output control.

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Gene Environment Effects

• Mechansism II Performance Studies of
  Neuropsychological and Cognitive Abilities
• Four key functional systems in the brain are
  implicated in ADHD
• Nonexecutive attention and arousal
• Executive functioning and cognitive control
• Motivation and reinforcement
• Temporal information processing

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Gene Environment Effects

• Motivation, Approach, and Reinforcement Response
• A comprehensive review by Luman et al. (2005)
  concluded that ADHD is associated with
• Increased weighting of near-term over long-term
  (but larger) reward.
• Possible positive response to high-intensity
  reinforcement.
• Lack of physiological response (e.g., heart rate
  acceleration) to potential rewards.
• Temporal Information Processing and Motor Control
• Problems in cerebellar functioning and temporal
  information processing could contribute to poor
  reinforcement learning, poor executive
  functioning, and even poor motor coordination.

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DEVELOPMENTAL PROGRESSION

• Motoric hyperactivity is more pronounced in
  preschool, and tends to decline with time.
• Problems with inattention can become more
  pronounced with age as peers undergo rapid
  maturation of prefrontal cortical structures and
  accompanying cognitive abilities at the same time
  that school demands intensify.

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COMORBIDITY

• ADHD is highly likely to exist in concert with
  one or more disruptive behavior disorders, this
  rate is about 50 for ODD and about 22 for CD
  (Willcutt et al., in press).
• Anxiety co-occurs with ADHD, but any one anxiety
  disorder is seen only in a minority of cases
  (e.g., 10 to 15 of children with ADHD will have
  a generalized anxiety disorder (Willcutt et al.,
  in press).
• About one quarter of children with ADHD meet
  criteria for a learning disorder.

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SEX DIFFERENCES and CULTURAL CONSIDERATIONS

• ADHD shows a male preponderance, on the order of
  21 or higher but seems to drop in adolescence
  and adulthood (Polanczyl et al., 2007).
• ADHD-related behaviors may not have the same
  meaning in the eyes of teachers and parents
  across cultural groups.
• It is unclear to what extent the ADHD syndrome
  has similar internal validity across ethnic or
  cultural groups.
• Treatment rates vary radically across nations and
  approaches to treatment may be different across
  cultural groups even within the United States
  (Visser, Bitsko, Danielson, Perou, 2010).

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PROTECTIVE FACTORS

• Tully et al. (2004) found that parental warmth
  moderated the effect of low birth weight on ADHD
  outcomes.
• Children exposed to multiple indicators of
  adversity, but who are below clinical cutoffs for
  ADHD symptoms, are more effective in
  neuropsychological response inhibition and have
  fewer risk catecholamine genotypes (Nigg,
  Nikolas, Friderici, Park, Zucker, 2007).
• Secondary protective factors include
• Stronger reading ability
• Absence of aggressive behavior
• Positive peer relations
• Effective parenting

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FUTURE DIRECTIONS

• How will the phenotype best be defined, and in
  how will heterogeneity and specificity issues be
  resolved?
• What are the specific etiologies of the expected
  subgroups currently defined as having ADHD?
• What are key moderators of the meaning and
  outcome of these behaviors?