HEMISPHERIC PROCESSING AND METHYLPHENIDATE EFFECTS IN ATTENTION-DEFICIT HYPERACTIVITY DISORDER

To advance our understanding of attention-deficit hyperactivity disord er and medication effects we draw upon the evidence for (1) a neurotra nsmitter imbalance between norepinephrine and dopamine in attention-de ficit hyperactivity disorder and (2) an asymmetric neural control syst em that links the dopaminergic pathways to left hemispheric processing and links the noradrenergic pathways to right hemispheric processing. It appears that attention-deficit hyperactivity disorder may involve a bihemispheric dysfunction characterized by reduced dopaminergic and excessive noradrenergic functioning. In tum, favorable medication effe cts may be mediated by a restoration in neurotransmitter balance and b y increased control over the allocation of attentional resources betwe en hemispheres.