Most studies of attention-deficit/hyperactivity disorder (ADHD)
have focused on the combined type and emphasized a core problem in
response inhibition. It is proposed here that the core problem in the
truly inattentive type of ADHD (not simply the subthreshold combined type)
is in working memory. It is further proposed that laboratory measures,
such as complex-span and dual-task dichotic listening tasks, can detect
this. Children with the truly inattentive type of ADHD, rather than being
distractible, may instead be easily bored, their problem being more in
motivation (underarousal) than in inhibitory control. Much converging
evidence points to a primary disturbance in the striatum (a
frontal–striatal loop) in the combined type of ADHD. It is proposed
here that the primary disturbance in truly inattentive-type ADHD (ADD) is
in the cortex (a frontal–parietal loop). Finally, it is posited that
these are not two different types of ADHD, but two different disorders
with different cognitive and behavioral profiles, different patterns of
comorbidities, different responses to medication, and different underlying
neurobiologies.Preparation of this
manuscript was supported by grants from NIDA (R01 DA19685-16A2) and the
McDonnell Foundation (JSMF Grant 21002016). The author gratefully thanks
Russ Barkley, Dante Cicchetti, Michael Posner, and Margaret Weiss for
comments on an earlier draft of the manuscript. Of course, only the author
bears responsibility for any errors in this paper.