Validation of Animal Models of ADHD

Attention-deficit/hyperactivity disorder (ADHD) is a neurobehavioral disorder of childhood onset that is characterized by inattentiveness, hyperactivity, and impulsiveness. All clinical criteria are behavioural. Inattentiveness, overactivity, and impulsiveness are presently regarded as the main clinical symptoms. The dynamic developmental behavioural theory (DDT) is based on the hypothesis that altered dopaminergic function plays a pivotal role by failing to modulate nondopaminergic (primarily glutamate and GABA) signal transmission appropriately (Johansen, Sagvolden, Aase, & Russell, 2005; Sagvolden, Johansen, Aase, & Russell, 2005a). A hypofunctioning mesolimbic dopamine branch produces altered reinforcement of behaviour and deficient extinction of previously reinforced behaviour (Figure 1). This gives rise to delay aversion, development of hyperactivity in novel situations, impulsiveness, deficient sustained attention, increased behavioural variability, and failure to “inhibit” responses (“disinhibition”). A hypofunctioning mesocortical dopamine branch will cause attention response deficiencies (deficient orienting responses, impaired saccadic eye movements, and poorer attention responses toward a target) and poor behavioural planning (poor executive functions).