Attentional Focus Modulated by Mesothalamic Dopamine: Consequences in Parkinson’s Disease and Attention Deficit Hyperactivity Disorder D. Q. M. Madureira • L. A. V. Carvalho • E. Cheniaux Published online: 24 November 2009 Ó Springer Science+Business Media, LLC 2009 Abstract In this work, we propose a mathematical model that describes how the mesothalamic dopamine pathway modulates the attentional focus via the thalamocortical loop, and how mesothalamic dopamine alterations can promote inattention symptoms in patients with Parkinson’s disease (PD) and attention deficit hyperactivity disorder (ADHD). We model the thalamocortical loop with a neu- ronal network where each thalamic neuron is described by a system of coupled differential equations reflecting neurophysiological properties. The computational simula- tions reflect neurochemical features of PD and ADHD. Our results suggest that the mesothalamic dopamine hypoac- tivity causes difficulties in attentional shifting. Conversely, the mesothalamic dopamine hyperactivity hinders the attentional focus consolidation. Furthermore, regardless of the amount of mesothalamic dopamine activity, the mes- ocortical dopamine hypoactivity leads to loss of attentional focus. Finally, we identify a unique neuronal mechanism underlying attention deficits in PD and ADHD and relate different inattention symptoms in ADHD to different dopaminergic levels in the brain circuit modeled. Keywords Attention  Dopamine  Parkinson  ADHD  Computational neuroscience Introduction It is hard for people with attention deficits to conduct a regular life. Irrelevant stimuli frequently interrupt tasks that are abandoned before completion. Conversely, atten- tion disorders may also be revealed by persistent behavior and difficulty in alternating the attentional focus. Not surprisingly, the variety of inattention symptoms observed in psychiatric or neurological disorders reflects the wealth of processes underlying the attention focusing. In fact, attention depends on both selection of appropriate stimuli and inhibition of distracting ones, and cognitive processes involving attention—such as reasoning—depend on the capacity of shifting as well as sustaining the atten- tional focus. Both PD and ADHD present inattention symptoms. In patients with PD, the presence of mental rigidity is com- mon, expressed by a stiff attentional focus, leading to a marked aversion to changes. In the case of ADHD, where inattention or distraction prevents concentration, two pos- sibilities are plausible to explain why the attentional focus becomes altered: incapacity to form attentional focus, and difficulty in shifting attention among different stimuli, as with patients with PD. D. Q. M. Madureira (&) Laborato ´rio Nacional de Computac ¸a ˜o Cientı ´fica, Coordenac ¸a ˜o de Matema ´tica Aplicada e Computacional, Av. Getu ´lio Vargas, 333, 25675-071 Petro ´polis, RJ, Brazil e-mail: daniele@lncc.br L. A. V. Carvalho Coordenac ¸a ˜o de Programas de Po ´s-Graduac ¸a ˜o em Engenharia, Programa de Engenharia de Sistemas e Computac ¸a ˜o, Universidade Federal do Rio de Janeiro, Caixa Postal 68511, 21941-972 Rio de Janeiro, Brazil E. Cheniaux Instituto de Psiquiatria, Universidade Federal do Rio de Janeiro, Av. Venceslau Bra ´s, 71 Fundos, 22290-140 Rio de Janeiro, Brazil E. Cheniaux Faculdade de Cie ˆncias Me ´dicas, Universidade do Estado do Rio de Janeiro, Pavilha ˜o Ame ´rico Piquet Carneiro-R. Prof. Manoel de Abreu, 444, 2° andar, 20550-170 Rio de Janeiro, Brazil 123 Cogn Comput (2010) 2:31–49 DOI 10.1007/s12559-009-9029-4