derived from a rat model, the theory of sagvolden et al. offers an all-explanatory model of attention-deficit/hyperactivity disorder (adhd) anatomy, behaviour, and cognition as being caused predominantly by a hypo-dopaminergic mesolimbic (affecting the mesocortical and nigrostriatal) system, leading to abnormal reward and extinction processes. this model suffers from oversimplification and reductionism, reflecting the limitations of the use of animal models to explain higher mental disorders.