Download Child and Adolescent Psychopathology

Impulsivity and
Vulnerability to
Psychopathology
Chapter 6
Emily Neuhaus and Theodore P. Beauchaine
HISTORICAL CONTEXT
 Early neurobiological theories of behavioral
control focused on frontal regions of the brain.
 Observations of altered behavior among those who
suffered from traumatic brain injuries (i.e., Phineas Gage
in 1814).
 Vagotonia hypothesis
 Eppinger and Hess (1915) describe vagotonia as an
abnormal irritability of all or only a few autonomic nerves.
HISTORICAL CONTEXT
 Minimal brain dysfunction (MBD)
 Children with an underlying neurological
disturbance, as well as learning disabilities and
other problems who may or may not have been
exposed to the 1918 encephalitic infection.
 DSM-III (1980)
 That the category of MBD was dropped, and
children with learning difficulties were
distinguished officially from those with behavioral
difficulties
TERMINOLOGICAL AND
CONCEPTUAL ISSUES
 Lacks a consistent operational definition and a
standard method of measurement
 Operationalizing impulsivity
 Definitions based on results from neuropsychological
tests (i.e., Wisconsin Card Sorting Test)
 Do not speak to the neural mechanisms underlying the
construct
 Models of disinhibition
 Integrate multiple components of the trait, suggesting
several alternative brain mechanisms that may be
responsible for impulsive behavior.
TERMINOLOGICAL AND
CONCEPTUAL ISSUES
 Behavioral Definitions
• “Behavior that is socially inappropriate or maladaptive and is quickly
emitted without forethought” (Oas, 1984, 1985).
• Strengths include not ruling out cognitively mediated mechanisms,
emphasizes disinhibition as a maladaptive trait, does not include
causal assumptions regarding the etiology of disinhibition, allowing
for both psychological and biological contributions.
 DSM-IV (2000)
• Attention-deficit/hyperactivity disorder (ADHD)
• Taking action without forethought, failing to plan ahead, risk taking,
novelty-seeking, sensation-seeking, over-rapid responding, and
susceptibility to the pull of immediate rewards (Hirshfeld-Becker et al.,
2002).
ETIOLOGICAL FORMULATIONS
 Heterogeneity in the Impulsivity Phenotype
 Behavioral (phenotypic) expression of impulsivity may derive
from several sources
• Brain injuries, exposure to teratogens such as alcohol, early traumatic
experiences including social deprivation, child abuse, and neglect, or
genetic vulnerabilities that give rise to deficient executive control over
behavior.
 Neurobiological substrates of disinhibition
• Give rise to individual differences in impulsivity that are temperamental,
present very early in life, and emerge before ADHD can be diagnosed.
• Are supported by voluminous literatures derived from both animal models
and humans.
• Confer vulnerability to externalizing disorders across the life span,
particularly in the context of high-risk environments characterized by
violence, trauma, and emotional lability.
ETIOLOGICAL FORMULATIONS
 Temperamental Impulsivity and Central
Dopamine Functioning
 Early theories (mostly animal studies on reinforcement
motivation and substance dependence)
• Electrical and pharmacological stimulation of dopaminergically
mediated mesolimbic structures is reinforcing, such that trained
animals will engage in prolonged periods of operant behaviors.
• Neural activity increases within mesolimbic structures during both
reward anticipation and reward-seeking behaviors, and following
administration of DA agonists.
• DA antagonists attenuate—and in extreme cases block—the
rewarding properties of food, water, and stimulant drugs of abuse.
ETIOLOGICAL FORMULATIONS
 Evidence for reduced DA functioning as a neural
substrate of impulsivity have led to a reformulation of firstgeneration models indicating:
• Associations between low basal DA activity/blunted DA reactivity
and a propensity to use DA agonist drugs of abuse.
• Significant correlations between blunted DA responses to
amphetamine administration and the personality trait of novelty
seeking.
• Recent neuroimaging studies indicating reduced striatal activity
during reward tasks among children and adolescents with ADHD
and CD.
GENETICS AND HERITABILITY
 Behavioral Genetics of Impulsivity
 Impulsivity is among the most highly heritable of all behavioral
traits.
 However, a common genetic vulnerability can result in
divergent multifinal outcomes depending on environmental
experience.
 Molecular Genetics of Impulsivity
 A significant linkage for ADHD on Chromosome 16, however,
no specific gene has yet been identified through linkage
analysis.
 A small but significant role for the DRD4 gene, which codes for
DA receptors located throughout the central and peripheral
nervous systems linked to impulsivity.
IMPULSIVITY AND VULNERABILITY
TO PSYCHOPATHOLOGY
 Behavioral Inhibition
 This term refers to a general tendency to be wary in novel
situations, to be slow to warm up, and to avoid overly
stimulating environments.
 A person who is temperamentally impulsive due to a heritable
DA deficiency may be protected from severe psychopathology
if he or she is also high on behavioral inhibition.
 Environmental Risk
 Parenting
• Parents of impulsive and aggressive children are more negative, lax,
verbose, and overreactive in their discipline practices than the parents
of control children (Arnold, O’Leary, Wolff, & Acker, 1993; Barkley, Karlsson, &
Pollard, 1985).
IMPULSIVITY AND VULNERABILITY
TO PSYCHOPATHOLOGY
 Child abuse and neglect
• Although the direction of effects is unclear, maltreated children are
more impulsive than nonmaltreated children and histories of abuse
are associated with higher levels of externalizing symptoms among
children with ADHD (Briscoe-Smith & Hinshaw, 2006; Famularo, Kinscherff, &
Fenton, 1992).
 Neighborhood effects
• Impulsive children who are reared in high-risk neighborhoods
(typically defined by such factors as low socioeconomic status, high
rates of violence and criminality, and low community involvement)
are more prone to engage in antisocial behavior than impulsive
children reared in low-risk neighborhoods (Meier, Slutske, Arndt, &
Cadoret, 2008).
IMPULSIVITY AND VULNERABILITY
TO PSYCHOPATHOLOGY
 Epigenetic and Other Experience-Dependent
Effects
 Epigenetic effects
• Brain-derived neurotrophic factor (BDNF), which is involved in the
differentiation of DA neurons in developing mesolimbic structures and
has been implicated in the pathogenesis of impulsivity, may be
susceptible to paternally mediated epigenetic effects (Kent et al., 2005).
• Animal studies suggest that prenatal exposure to synthetic
glucocorticoids leads to overactivity and ADHD-like behaviors,
suggesting that such exposure may influence the “programming” of
nascent DA systems (Kapoor, Petropoulos, & Matthews, 2007).
• Brain tissue from spontaneously hypertensive rats exposed to
polychlorinated biphenyls (PCBs) evidenced differences in mRNA,
suggesting an epigenetic effect of PCB on gene expression
(DasBanerjee et al., 2008).
IMPULSIVITY AND VULNERABILITY
TO PSYCHOPATHOLOGY
 Neural plasticity
• Examples of experience-dependent changes occur in several neural
systems including mesolimbic DA structures:
• Male rats that were exposed repeatedly to more dominant males in a stressinducing paradigm.
• Repeated episodes of maternal separation early in the lives of rat pups.
• Stimulant use.
 Implications for Learning
 Alterations in DA responding that arise from genetic, epigenetic,
and experience-dependent effects are likely to influence the
efficiency of knowledge acquisition by:
• Sensation-seeking tendencies that reduce motivation for learning
mundane information.
• Reduced efficacy of associative learning due to dampened activation of
mesolimbic structures.
• Compromised executive functioning.
SYNTHESIS AND FUTURE
DIRECTIONS
 In the worst cases, impulsive children are reared by
impulsive parents who, in addition to conferring genetic
liability, transmit risk through inconsistent and stressful
caretaking during infancy, child maltreatment, and coercive,
labile parenting (Beauchaine et al., 2011).
 Further accumulation of risk may occur via exposure to
violence in high-risk neighborhoods, early escalation of
substance use, low motivation, and learning difficulties.
 In contrast, an impulsive child who is reared in a maximally
protective environment faces few or none of these additional
risk factors, and may develop both psychological and
biological resilience given enriched educational experiences
and competent parenting that teaches strong emotion
regulation skills.