Attention shifts and anticipatory mechanisms in hyperactive children: an ERP study using the Posner paradigm.

BACKGROUND

The aim of this study was to assess attentional, decisional, and motor processing stages during the performance of an attention shifting paradigm, both in normal children and children with attention-deficit/hyperactivity disorder (ADHD).

METHODS

We recorded event-related potentials (ERPs) and performance measures during a variant of the Posner paradigm in 13 control subjects and 24 ADHD children. Subjects responded with a spatially concordant motor response to left or right visual targets, which could be either preceded by a spatial cue ("valid" = same side; "invalid" = opposite side) or presented uncued.

RESULTS

Patients made significantly more errors than control subjects, with predominance of the anticipatory type. As compared to control subjects, ADHD children had faster reaction times, as well as a shortened interval between the N2 and P3 ERPs and the motor response. Patients also showed a decreased attentional priming effect on early sensory responses (P1). Finally, the slow negativity (contingent negative variation/readiness potential) that preceded the target in the "no cue" condition was absent in ADHD patients.

CONCLUSIONS

The combined analysis of electrophysiological and behavioral data suggest a characteristic mode of response of ADHD in attention shifting tasks, characterized by "motor impulsivity" with release of motor responses before stimulus processing is adequately completed, as well as a lack of strategic planning/anticipatory mechanisms in the absence of warning stimulus. These deficits may be partly attributed to dysmaturation of executive frontal functions. In addition, a minor deficit in early attentional priming was also observed in ERPs, with no apparent behavioral counterparts.