Control of Purposive Saccadic Eye Movements and Visual Fixation in Children with Attention-Deficit Hyperactivity Disorder

Abstract

Attention-deficit hyperactivity disorder (ADHD) is a common disabling disease affecting approximately 5% of children (Barkley 1990; Silver 1992). ADHD is characterized by the symptoms of impulsivity, hyperactivity, and inattention and these core symptoms persist into adulthood. The diagnosis of ADHD remains difficult because it usually involves the subjective evaluation of a child’s behavior by parents, teachers, and physicians. At present, the etiology of ADHD remains unknown. A frontostriatal deficit as been hypothesized for the following reasons. First, ADHD subjects lack inhibitory control and often act impulsively (Chelune et al. 1986; Grodzinsky and Diamond 1992), which is similar to other frontal lobe disorders. Second, regional blood flow and glucose metabolic studies have revealed frontal and/or striatal abnormalities in ADHD subjects (Lou et al. 1984, 1989; Zametkin et al. 1990). Third, neuroimaging studies have shown altered architecture in the frontal lobes, caudate nucleus and rostrum of the corpus callosum (Giedd et al. 1994; Castellanos et al. 1996a). A dopamine disorder has also been proposed (Levy 1991) for the following reasons. First, the action of methylphenidate, the main pharmacotherapy for ADHD, is to block dopamine reuptake. Second, there is evidence for abnormal levels of catecholamine metabolites in the CSF of ADHD subjects (Castellanos et al. 1996b).