Barkley’s Theory of ADHD

Barkley’s Theory of ADHD Laura M. Bimbo November 3, 2004

DSM-IV ADHD • Three core ADHD symptoms: • Hyperactivity • Impulsivity • Inattention • Three ADHD subtypes: • Predominately Inattentive • Predominately Hyperactive-Impulsive • Combined Type • Attention impairments have been thought to be the central ADHD deficit

Why a new theory on ADHD? • To date, most research is atheoretical • Descriptive • Exploratory • DSM-IV criteria is descriptive only • Observable behavior deficits only • Current criteria for ADHD assumes that subtypes represent similar deficits • Individuals with ADHD do not show inattention in all situations (Barkley, 1997)

Subtypes = Different Disorders? • Hyperactive-Impulsive type is a developmental precursor to Combined type • Preschool children vs. School aged children (Applegate et al., 1995) • Combined type = sustained attention and distractibility • High rates of ODD/CD comorbidity and other poor outcomes (school suspensions, substance use, etc.) (Barkley, 1997)

Subtypes = Different Disorders? • Purely Inattentive type usually appears at a later age • Inattentive type = deficit in speed of processing; focused & selective attention) • Symptoms = daydreaming, “spacing out”, “being in a fog”, hypoactive, “sluggish cognitive tempo” • Decreased rates of comorbidities (Barkley, 2001)

Barkley’s Theory of ADHD • Core impairment = Response Inhibition • Due to abnormalities in the prefrontal cortex and connections to other brain regions (striatum) • Response Inhibition affects four intermediate executive functions • So, poor response inhibition + deficits in executive functions = poor control • Barkley also asserts that individuals with ADHD don’t develop “future orientation and sense of self across time”

Barkley’s Theory of ADHD Response Inhibition Self-Regulation Of Affect/ Motivation/Arousal Internalization Of Speech Reconstitution Working Memory Motor Control/ Fluency/Syntax

Response Inhibition • Inhibiting the initial prepotent response to an event. • Interrupting an ongoing response, permitting a delay in the decision to respond or continue responding • Protecting this period of delay from disruption by competing events and responses (interference control) (Barkley, 1999)

Evidence for Poor Response Inhibition in ADHD • Behavioral Observations : • Greater activity level (Luk, 1985) • More talkative to others and self (Barkley, et al., 1983; Copeland, 1979) • More difficulty restricting behavior in laboratory settings than other children (Luk, 1985) • Less delay of gratification, less successful at resistance-to-temptation paradigms (Campbell, et al., 1994)

Response Inhibition • Inhibiting the initial prepotent response to an event. • Interrupting an ongoing response, permitting a delay in the decision to respond or continue responding • Protecting this period of delay from disruption by competing events and responses (interference control) (Barkley, 1999)

Measuring Prepotent Responses • Some studies have found no differences between kids with ADHD and those without ADHD on tasks measuring response inhibition • Methodological problems: • No immediate reinforcement within the task to encourage prepotent responding • If immediate rewards are provided, they are weak reinforcers for this individual • No history of reinforcement exists, so there is no prepotent response for this individual • (Barkley, 1999)

Evidence for Poor Inhibition of Prepotent Responses • Go-No-Go Paradigm (Barkley, 1997) • Continuous Performance Test • Errors of Commission • Stop-Signal Paradigm • Primary task of forced-choice letter discrimination • When presented with a signal (tone), response is inhibited • Kids with ADHD show: • Longer reaction times to signal • Less inhibition of primary response • More variation in their inhibition of primary response

Evidence for Poor Inhibition of Prepotent Responses • Continuous Performance Test • Errors of Commission • During a direct observation study, children with ADHD interrupted more than control children (Malone & Swanson, 1993)

Response Inhibition • Inhibiting the initial prepotent response to an event • Interrupting an ongoing response, permitting a delay in the decision to respond or continue responding • Protecting this period of delay from disruption by competing events and responses (interference control) (Barkley, 1999)

Evidence for Difficulty Interrupting Ongoing Responses • Stop Signal Paradigm • Wisconsin Card Sorting Task (WCST) • Involves shifting to a more effective response pattern when feedback indicates that the ongoing response is incorrect • Children with ADHD often perseverate, even when feedback is given (Barkley, 1997) • Interestingly, first-degree relatives of individuals with ADHD are more prone to perseverations

Evidence for Difficulty Interrupting Ongoing Responses • On an information processing task, children with ADHD were less likely to change their response style (i.e. slow down) after corrective feedback • Card Playing Task • Children with ADHD bet on more trials than control subjects, despite increased liklihood of being incorrect

Response Inhibition • Inhibiting the initial prepotent response to an event • Interrupting an ongoing response, permitting a delay in the decision to respond or continue responding • Protecting this period of delay from disruption by competing events and responses (interference control) (Barkley, 1999)

Evidence for Poor Interference Control • Stroop Color-Word Test • Subjects with ADHD (and their siblings) perform poorly when responding to the color of words rather than reading the words (Barkley, 1997) • Differences are also found when comorbid conditions are controlled for • Neuroimaging studies have shown that the right prefrontal region is involved in the performance of this task

Working Memory • Holding information in mind, • manipulating or acting on the information • Hindsight (retrospection) • Foresight (prospection) • Empirical evidence in kids with ADHD: • Digit span (especially backwards) • Mental arithmetic

Self-Regulation of Affect-Motivation-Arousal • Emotional self-control • Social perspective taking • Ability to express emotions internally • Intrinsic motivation directed at long-term goals • Empirical evidence in kids with ADHD: • More negative and emotional peer interactions • Impairment in persistence of effort

Internalization of Speech • Self-directed speech (“private speech”) • Formulating rules and plans to solve problems • Internal reflection, description, questioning, instructing • Create internal rules for governing behavior • Empirical evidence in kids with ADHD: • Less compliant with verbal commands • Immature self-directed speech • Develop internal speech at a later age

Reconstitution • Ability to create complex and novel behavior sequences in order to attain future goals (generativity or fluency) • Involves analysis and synthesis • Empirical evidence in kids with ADHD: • Ideational fluency (Barkley, 1999) • Verbal fluency (esp. FAS) • Less info and organization in stories (Tannock, 1996) • Less creativity during free play (Funk, et al., 1993)

Motor Control/Fluency/Syntax • Deficits in response inhibition and the four executive functions lead to impairments in: • Control • Timing • Persistence • Flexibility • Goal-directed actions

Motor Control/Fluency/Syntax • Barkley asserts that these deficits manifest in ADHD children through: • Ability to adapt to new information • Ability to predict what will happen • Ability to generate responses to future info • ADHD = “nearsighted when it comes to time” or “time blindness” (Barkley, 1999)

Motor Control/Fluency/Syntax • Problems with sustained attention result from a limited intrinsic motivation for future goals • Effectiveness of stimulant medications: • Due to enhancement of inhibitory mechanismsimproved four areas of executive functioning

Barkley’s Theory: Limitations • Are difficulties in inhibition a result of ADHD or comorbid problems such as aggression, ODD, & learning disabilities • How much affect does response inhibition have on the 4 executive functions in the model? • How much does each executive function contribute to motor control? • Can the 4 executive functions be further reduced?

Barkley’s Theory: Limitations • Do stimulant medications differentially affect each of the 4 executive functions? • Is there some hierarchical organization to the executive functions? • Can this model be used to dissociate Inattentive- type ADHD from the other types? • Does socialization affect the development of these executive functioning? • What gender and ethnic differences exist in the development of these executive functions?

Barkley’s Theory: Treatment Implications • Basis of treatment Environmental modifications • No delay between response and outcomes • Breaking down tasks into smaller components • Key conceptPoint of performance

Barkley’s Theory: Treatment Implications • Place key information at the point of performance: • Provide external rewards/motivation • Minimize distractions • Put clock on student’s desk • Display rules at point of performance

Barkley’s Theory of ADHD