Attention-Deficit Disorder
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Development and Psychopathology 17 ~2005!, 807–825 Copyright © 2005 Cambridge University Press Printed in the United States of America DOI: 10.10170S0954579405050388 Attention-deficit disorder ~attention-deficit0 hyperactivity disorder without hyperactivity!: A neurobiologically and behaviorally distinct disorder from attention-deficit0hyperactivity disorder ~with hyperactivity! ADELE DIAMOND University of British Columbia, Vancouver, and BC Children’s Hospital, Vancouver Abstract Most studies of attention-deficit0hyperactivity 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 ~under- arousal! 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 pat- terns of comorbidities, different responses to medication, and different underlying neurobiologies. I join the growing chorus of those who argue 2001; Cantwell, 1983; Carlson, 1986; Carl- that attention-deficit0hyperactivity disorder son & Mann, 2000; Goodyear & Hynd, 1992; ~ADHD! of the “truly” inattentive subtype Hynd, Lorys, Semrud–Clikeman, Nieves, ~what I will call “attention-deficit disorder” Huettner, & Lahey, 1991; in particular see @ADD#! is a different disorder from ADHD the outstanding paper by Milich, Balentine, where hyperactivity is present ~e.g., Barkley, & Lynam, 2001!. Not only is “ADHD with- out hyperactivity” ~ADHD of the predomi- nantly inattentive type! an awkward locution, Preparation of this manuscript was supported by grants but it also tries to squeeze ADD into a box in from NIDA ~R01 DA19685-16A2! and the McDonnell which it does not belong. The term ADHD Foundation ~JSMF Grant 21002016!. The author grate- fully thanks Russ Barkley, Dante Cicchetti, Michael Pos- should be reserved for when hyperactivity is ner, and Margaret Weiss for comments on an earlier draft present ~as the term implies!, regardless of of the manuscript. Of course, only the author bears re- whether inattention is also present. sponsibility for any errors in this paper. The points I make in this paper include the Address correspondence and reprint requests to: Adele following: many individuals currently diag- Diamond, Department of Psychiatry, University of Brit- ish Columbia, 2255 Wesbrook Mall, Vancouver, British nosed with the inattentive subtype of ADHD Columbia V6T 2A1, Canada; E-mail: adele.diamond@ appear to be misdiagnosed. ADD appears to ubc.ca. be an instance of childhood-onset “dysexecu- 807 808 A. Diamond tive syndrome.” ADD and ADHD are charac- mind, which can make arithmetic calculation, terized by dissociable cognitive and behavioral reading, or abstract problem solving difficult. profiles, different patterns of comorbidities, Individuals with ADHD of the inattentive different responses to medication, and differ- type also tend to have a hard time sustaining ent underlying neurobiological problems. The focused attention on a task or activity. They core cognitive deficit of ADD is in working are quite poor at following through on some- memory. Contrary to what many have claimed thing to completion. They tend to get bored ~that laboratory tests cannot capture the core with a task fairly quickly and often abandon a cognitive deficits in ADD!, I argue that task unfinished, bouncing from one partially complex-span and dual-task dichotic listening begun project to another. They may have a tasks can indeed capture them. The working hard time keeping their mind on any one thing memory deficit in many children with ADD is at a time. When doing homework or reading, accompanied by markedly slowed reaction they often find their minds wandering. Be- times, a characteristic that covaries with poorer cause focusing deliberate, conscious attention working memory in general. Individuals with on completing a task is so arduous or aversive ADD are not so much distractible as easily for individuals with the inattentive subtype of bored and underaroused. I hypothesize that ADHD, they tend to try to avoid beginning a the DAT1 gene will be found to be more closely task, procrastinate, may forget to write an as- linked to ADHD than to ADD, whereas the signment down, forget to bring home the ma- DRD4 gene will be found to be more closely terials needed to complete an assignment, or linked to ADD than to ADHD, and that the lose materials needed for an assignment. primary neural circuit affected in ADHD is In 1986 Baddeley coined the term dysex- frontal–striatal, whereas the primary neural cir- ecutive syndrome to refer to adults who seem cuit affected in ADD is frontal–parietal. to have a deficient “central executive” and The current DSM-IV ~American Psychiatric who thus appear to be disorganized, easily Association @APA#, 1994! diagnostic guide- pulled off course, forgetful, and inattentive. lines list three subtypes of ADHD: ~a! primar- As far as I know, dysexecutive syndrome has ily inattentive, ~b! primarily hyperactive and always been used with reference to adults. I impulsive, or ~c! both combined. ADHD con- would like to suggest that children with ADHD ceived in this manner is by far the most com- of the inattentive subtype provide an instance monly diagnosed psychological0behavioral of the dysexecutive syndrome in children. Dys- disorder of childhood ~e.g., Barkley, DuPaul, executive syndrome patients may go off on & McMurray, 1990; Szatmari, 1992; Weiss & tangents or lose their train of thought. Individ- Hechtman, 1979!. ual skills, such as encoding an item into mem- Individuals with ADHD of the inattentive ory or retrieving an item from memory, are subtype tend to be disorganized, easily pulled intact. However, dysexecutive patients “have off course, forgetful, and inattentive ~DSM-IV; problems in initiating @a chore#, monitoring APA,1994!. They tend to be disorganized men- their performance, and . using such informa- tally and physically. They tend to make care- tion to adjust their behavior. As most tests less mistakes, and are not good at paying close concentrate on the building blocks or compo- attention to detail. They have difficulty orga- nent skills and are less concerned with the nizing their work, setting priorities, planning integration of these skills into real-life tasks, out a strategy, and remembering to do all re- many @dysexecutive# patients . perform ad- quired tasks. They have difficulty organizing equately on frontal lobe tasks . In contrast, their things and tend to be sloppy. They have many everyday activities involving executive trouble keeping track of their belongings and abilities require patients to organize, or plan forget where they have put them, in part be- their behavior over longer time periods or to cause they rarely put things away. If multiple set priorities in the face of two or more com- items are needed for an assignment or task, they peting tasks” ~Wilson, Evans, Emslie, Alder- will typically forget one or more. They have man, & Burgess, 1998, p. 214!. It is on such trouble keeping track of multiple things held in everyday activities that the dysexecutive def- ADD as distinct disorder from ADHD 809 icit is most evident. Dysexecutive patients of- blurt out an answer before hearing the whole ten start out performing a task well, but quickly question, and may interrupt others. They may become sidetracked. It is hard for them to stay intrude on others’ conversation or game, with- focused on the task at hand, and they com- out considering beforehand that it might be monly must be reminded of what it was they inappropriate. Because they tend to act impul- were supposed to be doing. sively, they may run into the street without The DSM-IV cutoffs for the inattentive, hy- looking or grab a toy from another child. peractive, and combined subtypes of ADHD were derived largely from research with young ADD and ADHD That Includes males, who are more prone to hyperactivity Hyperactivity Are Dissociable Disorders and impulsivity than are girls or older males or females. Hence, some individuals get mis- Whereas children with ADHD are frenetic and categorized as inattentive-type ADHD, de- hyperactive, a significant proportion of chil- spite being hyperactive for their gender or age, dren with ADD are exactly the opposite. A because they are not significantly more hyper- significant subset of children with ADD are active or impulsive than young boys ~e.g., Carl- hypoactive, sluggish, and very slow to respond son & Mann, 2002; deHaas & Young, 1984; ~see Table 1!. Children with ADHD are often Milich et al., 2001; Weiss, Worling, & Was- insufficiently self-conscious; children withADD dell, 2003!. Such individuals should be con- tend to be overly self-conscious. Both groups sidered the combined type. In this article, I tend to have social problems, but for different focus on individuals with ADD ~those who reasons.