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ADHD Assessment: A Neuropsychological Perspective

ADHD Assessment: A Neuropsychological Perspective. Shelley Heaton, Ph.D. ADHD Seminar; October 13,2003. Neuropsychological Perspective. Neuropsychology is the “applied science concerned with the behavioral expression of brain dysfunction” (Lezak, 1995) What brain regions

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ADHD Assessment: A Neuropsychological Perspective

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  1. ADHD Assessment: A Neuropsychological Perspective Shelley Heaton, Ph.D. ADHD Seminar; October 13,2003

  2. Neuropsychological Perspective • Neuropsychology is the “applied science concerned with the behavioral expression of brain dysfunction” (Lezak, 1995) • What brain regions may be responsible for the behavioral symptomotology seen in ADHD? • How do we measure the functioning of those brain regions – i.e., how do we measure inattention?

  3. Brain Bases of ADHD • Anatomical and functional neuroimaging studies implicate several brain regions • Frontal Cortex • Corpus Callosum • Cerebellum • Basal Ganglia • Caudate • Putamen • Globus Pallidus “Striatum”

  4. Neuroanatomy suggests a pathway involving these brain regions known as the “Frontal-Striatal Loop” prefrontal cortex  striatum  thalimus  prefrontal cortex “Striatum” – caudate & putamen (all part of the basal ganglia)

  5. Prefrontal Cortex • Region of the brain responsible for monitoring, planning, integrating • Structural MRI studies of ADHD have reported smaller volumes of right-hemispheric anterior-superior white matter • poorer performances on measurements of sustained attention in ADHD (Semrud-Clikeman et al., 2000)

  6. Caudate • Has been primary site of investigation • Reversal of normal brain asymmetry (normal L>R) • Smaller left head of the caudate (Semrud-Clikeman et al.)

  7. Caudate Conclusions • Reversal of caudate asymmetry is related to deficits in response execution tasks in ADHD • Caudate dysfunction and hypo-activity of frontal lobes is the primary site of dysfunction

  8. Putamen Previously not the focus of anatomical studies, but… • Symptom specific? • Changes in structure is likely relate to symptoms of hyperactivity and impulsivity • Subtype specific? • combined type which show more motor problems • Disorder specific? • Children with TBI or stroke damage to putamen show secondary ADHD symptoms (Max et al., 2002)

  9. fMRI Evidence • Functional differences in regions with structural dysfunctions • reduced activity in the frontal-striatal region • Correlated with impaired performance on a response inhibition task • Methylphenidate • increased frontal-striatal activity • increased performance on response inhibition tasks • (Vaidya et al., 2001) • Decreased in blood flow to the caudate in ADHD (Castellanos, 1997; Peterson, 1995).

  10. Implicated Neurotransmitters • Norepinephrine (NE) • Dopamine (DA)

  11. Dopamine & ADHD • Dopamine Hypothesis of ADHD: Dopamine is disrupted in fronto-striatal circuit • Dopamine is lower in ADHD • Treat with dopaminergic drugs • Methylphenidate increased levels of DA in synapse • Ritalin inhibits DA reuptake transporters

  12. Brain-Behavior Relationship • Fronto-striatal circuitry is disrupted, both functionally and structurally. • frontal cortex is responsible for inhibition of attention and behavioral responses to salient but off task events • basal ganglia is responsible for the motor response to these interfering events • Disruption of dopamine regulation in fronto-striatal circuit leads to decreased dopamine release & blunted response of receptors, resulting in behavioral presentation seen in ADHD

  13. Measuring the ADHD Behavior -Neuropsychology • Implicate deficits in frontal lobe functions • Attention • Disinhibition of behavioral responses • Working memory • Planning • Verbal fluency • Perseveration • Motor frequency • “Executive Dysfunction” and “Inattention”

  14. A Look at the Tests • Disinhibition of behavioral responses • Stroop, CPT, Go No-Go • Working memory • Arithmetic, Digit Span, Trails • Verbal fluency • FAS • Perseveration • WCST, Trails (B) • Motor frequency • CPT

  15. Neuropsychology – The Tests • How do we measure “ATTENTION”? • Multidimensional Construct • Multiple tests • CPT • Trails • TEA-Ch

  16. Domains of Attention Focused/Selective Selectively focusing on target stimuli while ignoring non-target stimuli Sustained Maintaining attentional focus over time (extended) Controlled/Switching Shifting or controlling attentional processes, either by inhibiting a pre-potent response or changing response according to environ. cues

  17. ADHD and Attentional Domains • What would we expect? • Selective attention? • Sustained attention? • Controlled/switching attention (i.e., executive function)?

  18. Measuring Attention as a Multidimensional Contruct Test of Everyday Attention for Children (TEA-Ch) Sky Search Map Mission

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