In late 1980s, there were further researches about the subtypes of ADD that the differences between the subtypes were believed to be significant. Due to the development of neuroimaging techniques, there were evidences in supporting an argument of structural abnormalities found in the brain of children with ADHD, i.e. in the 1990s, the prefrontal-striatal network was found smaller in children with ADHD. Besides, ADHD was believed to be a disorder not only limited to children, but adult as well. ADHD was believed to be a chronic, and persistent disorder affecting an individual from childhood to adulthood. Lahey et al. (1994) conducted a large field trial and identified three different subtypes of ADHD, including a predominantly inattentive type, a predominantly hyperactive-impulsive type, and a combined type with symptoms of both dimensions. DSM-IV criteria of ADHD was believed to be highly empirically based that ADHD with three subtypes and ADHD in adulthood were included.
Lahey, B. B., Applegate, B., McBurnett, K., Biederman, J., Greenhill, L., Hynd, G. W., et al. (1994). DSM-IV
field trials for attention deficit hyperactivity disorder in children and adolescents. Am J Psychiatry
Lange, K. W., Reichl, S., Lange, K. M., Tucha, L., and Tucha, O. (2010). The history of attention deficit
hyperactivity disorder. Atten Defic Hyperact Disord. 2(4), 241-255.