Do Quantitative EEG Measures Differentiate Hyperactivity in Attention Deficit/Hyperactivity Disorder?

Attention Deficit/Hyperactivity Disorder (AD/HD) can occur with or without hyperactivity. However, much of the existing research collapses both AD/HD and AD/HD without hyperactivity participants into the AD/HD category, possibly confounding the samples with a heterogeneous population comprised of people with different disorders. The purpose of the present study was to examine the external validity of AD/HD without hyperactivity as a diagnostic category. Quantitative electroencephalogram (EEG) analysis was used to examine possible differences in brain wave activity of the two subtypes of AD/HD while completing the Test of Variables of Attention (TOVA), a computerized task that measures a variety of constructs associated with attention and impulsivity. Although behavioral ratings confirmed differential characteristics of both subtypes of AD/HD, EEG findings did not differentiate between AD/HD with and without hyperactivity. Implications to cognitive models of AD/HD are discussed.

Attention Deficit/Hyperactivity Disorder (AD/HD) is one of the most common childhood behavior disorders and is estimated to affect 3 to 5% of school-age children (DSM-IV; American Psychiatric Association, 1994). However, the disorder has a long and confusing history, having been referred to as the Hyperkinetic Reaction of Childhood Disorder (American Psychiatric Association, 1968), Hyperactivity (Zentall, 1975), Minimal Brain Dysfunction (Bloomingdale & Bloomingdale, 1980), and Childhood Hyperkinesis (Mattes, 1980).

The predominant symptoms of AD/HD are inattention, excessive impulsivity, and/or hyperactivity. Two subtypes of the disorder were included in the Diagnostic and Statistical Manual of Mental Disorders (DSM-III; American Psychiatric Association, 1980): Attention Deficit Disorder with Hyperactivity (ADD/H) and Attention Deficit Disorder without Hyperactivity (ADD/WO). With the publication of the DSM-III-R (American Psychiatric Association, 1987), the distinction between these two subtypes was effectively removed by adopting a unidimensional category referred to as ADHD. Instead, a new diagnosis called Undifferentiated Attention Deficit Disorder (UADD) was created that included some of the disturbances that were previously classified as ADD/WO.

After considerable debate, the publication of the DSM-IV (American Psychiatric Association, 1994) reinstated the diagnosis by establishing three subtypes of AD/HD: the Predominately Inattentive Type, the Combined Type, and the Predominately Hyperactive-Impulsive Type. Most of the evidence supporting the validity of attention deficit without hyperactivity as a subtype of AD/HD comes from observations of overt behavior, comorbid diagnoses, and familial patterns of psychiatric disturbances (see Stewart, 1994). In spite of the specificity in diagnostic criteria the DSM-IV provides, it is still unclear whether attention deficit without hyperactivity warrants recognition as a separate disorder.

From a theoretical and clinical standpoint it is important to establish the external validity of AD/HD without hyperactivity as a disorder that can be clinically differentiated from AD/HD. Presently, most research collapses both subtypes of AD/HD, possibly confounding the samples with a heterogeneous population comprised of people with different disorders (Castellanos, 1999; Hynd et al., 1991).

In recent years, electroencephalogram (EEG) analysis has been used in the diagnosis of AD/HD. Compared to normal controls, children who are described as hyperactive typically exhibit excessive slow wave activity (typically in the theta band) and/or concomitant decrease in fast wave (primarily alpha and beta) activity (Callaway, Halliday, & Naylor, 1983; Dykman, Holcomb, Oglesby, & Ackerman, 1982; Harper, Deering, Cavernos-Gonzales, McNeil, & Ulam, 1996; Mann, Lubar, Zimmerman, Miller, & Muenchen, 1992; Matsuura et al., 1993). Excessive slow wave activity in AD/HD is a neurophysiological response consistent with a hypoarousal hypothesis of hyperactivity (Klove, 1989; Zentall, 1975; Zentall & Zentall, 1983) and provides evidence that AD/HD is a neurophysiological disorder.

Researchers have begun to examine the differences in on-task EEG recordings between AD/HD without hyperactivity versus controls. Results suggest that children diagnosed with AD/HD without hyperactivity may exhibit EEG patterns that are similar to those exhibited by AD/HD with hyperactivity, that is excessive slow wave activity in the theta band and decreased activity in beta bands compared to matched controls (Janzen, Graap, Stephanson, Marshall, & Fitzsimmons, 1995; Mann, Lubar, Zimmerman, Miller, & Muenchen, 1992). However, there has been no comparison of AD/HD with or without hyperactivity. It is possible that these two groups exhibit different patterns of EEG characteristics while completing an attentional task and if so, EEG analysis may be an effective tool in differentiating children with and without the hyperactivity component of AD/HD.