Saccade eye movements as a quantitative measure of frontostriatal network in children with ADHD

Evidence of poor inhibition in attention deficit hyperactivity disorder (ADHD) comes primarily from neuropsychological tasks and neuroimaging studies, many of which have revealed structural/functional abnormalities of the frontostriatal network with opposing functions of disinhibition and inhibition. Studies of saccades have therefore contributed to the understanding of the pathophysiological basis of ADHD.

To investigate the development of reflexive/voluntary control of saccades in normal children, compare saccade parameters between ADHD and control groups, and clarify dysfunctional nervous systems in ADHD.

Subjects comprised 50 normal subjects (6-35 years), 19 ADHD patients (6-11 years) and four patients with frontal lesions (13-15 years). Saccade latency and accuracy were computed in all saccade tasks, while percentage of anticipatory errors (PAE) was determined in memory-guided saccade task, and percentage of direction errors (PDE) was determined in antisaccade task.

In normal controls, significant correlations were observed between saccade latency, saccade accuracy, error rates and age. Significant differences existed between ADHD and 6- to 8-year-old controls in saccade latency and accuracy. The ADHD group showed significantly higher PAE and PDE rates than controls. Patients with frontal lesions showed significantly higher PAE and PDE.

These results suggest that saccade eye movements do not fully mature until adolescence, and that ADHD patients show dysfunction in "response inhibition", which is modulated by the frontal lobe, particularly the prefrontal cortex, cingulate cortex and basal ganglia.