Specific executive functions (EFs) and attention deficit patterns in ADHD subtypes were studied in 50 boys (ages 8-14 years, mean 10.42) with ADHD and 44 controls, at the University of Rome, Italy. The executive functions test battery included the Wisconsin Card Sorting Test (measure of cognitive flexibility), Stroop Test (interference control), Tower of London (planning ability), Digit Span Backwards (verbal working memory), FAS Test (verbal fluency), Trail Making Test (visual search and divided attention), Continuous Performance Test II (sustained attention and inhibition), and visual-spatial, visual-object, and phonological working memory tests. ADHD patients, both inattentive and combined subtypes, differed from controls on tests of response inhibition, divided attention, phonological, and visual object working memory, and reaction times. Executive functioning profiles were similar for ADHD subtypes. Response inhibition predicts performance on working memory tests but not on divided attention/set shifting and on sustained attention. Boys with ADHD have a selective impairment of executive functions and attention tasks. Neural circuits that control response inhibition (right prefrontal cortex) and divided attention (left dorsolateral prefrontal cortex) in ADHD subtypes are involved independently in the pathogenesis of neuropsychological deficits. Impairments in phonological and visual-object working memory are additional characteristics of ADHD males with inattentive or combined subtypes. [1]

COMMENT. Executive functions may be defined as mental control cognitive processes that facilitate goal directed behavior. They include response inhibition, planning, cognitive flexibility/set shifting, working memory, and verbal fluency. Attention is defined as a set of processes that enhance cognitive, motor, and sensory processing. Sustained attention is the ability to maintain performance without distraction during continuous activities. Divided attention is the ability to simultaneously respond to multiple stimuli. The present study investigated all five executive functioning domains and attention in ADHD subtypes. The ADHD subtypes (inattentive and combined) are homogeneous in neuropsychological profiles except for the role of interference inhibition on working memory. Inhibition of interference predicts performance on working memory only in the inattentive subtype. The findings support the involvement of partially independent neuronal circuits that control inhibition and divided attention in ADHD. Right prefrontal cortex controls response inhibition, while left dorsolateral prefrontal cortex modulates divided attention.

Role of neuropsychological tests in diagnosis of ADHD. In a study performed in Columbia and at the University of Georgia, neuropsychological measures, including the continuous performance tests (CPT), had strong sensitivity but weak specificity when used in diagnosis of ADHD [2]. CPT is not recommended as a measure for clinical diagnosis of ADHD. CPT is sensitive to attention problems caused by medication, depression, ADHD and other causes, and is not specific for ADHD. Neuropsychological measures are important in planning interventions for the ADHD child with concomitant learning problems or academic underachievement.