Effort-related functions of nucleus accumbens dopamine and associated forebrain circuits

Background Over the last several years, it has become apparent that there are critical problems with the hypothesis that brain dopamine (DA) systems, particularly in the nucleus accumbens, directly mediate the rewarding or primary motivational characteristics of natural stimuli such as food. Hypotheses related to DA function are undergoing a substantial restructuring, such that the classic emphasis on hedonia and primary reward is giving way to diverse lines of research that focus on aspects of instrumental learning, reward prediction, incentive motivation, and behavioral activation. Objective The present review discusses dopaminergic involvement in behavioral activation and, in particular, emphasizes the effort-related functions of nucleus accumbens DA and associated forebrain circuitry. Results The effects of accumbens DA depletions on food-seeking behavior are critically dependent upon the work requirements of the task. Lever pressing schedules that have minimal work requirements are largely unaffected by accumbens DA depletions, whereas reinforcement schedules that have high work (e.g., ratio) requirements are substantially impaired by accumbens DA depletions. Moreover, interference with accumbens DA transmission exerts a powerful influence over effort-related decision making. Rats with accumbens DA depletions reallocate their instrumental behavior away from food-reinforced tasks that have high response requirements, and instead, these rats select a less-effortful type of food-seeking behavior. Conclusions Along with prefrontal cortex and the amygdala, nucleus accumbens is a component of the brain circuitry regulating effort-related functions. Studies of the brain systems regulating effort-based processes may have implications for understanding drug abuse, as well as energy-related disorders such as psychomotor slowing, fatigue, or anergia in depression

Memória de trabalho viso-espacial em crianças de 7 a 12 anos Visuo-spatial working memory in 7-12 year old children

O objetivo deste trabalho foi avaliar os mecanismos de processamento da informação viso-espacial em crianças. Setenta e oito crianças participaram do experimento em que foram manipulados os fatores idade, posição espacial, similaridade visual e cor dos estímulos memorizados. Os resultados mostraram que todos os fatores principais alcançaram significância estatística. As crianças mais velhas tiveram uma freqüência de acertos maior que as crianças mais novas. Os estímulos dos conjuntos com similaridade baixa foram mais bem recordados que os estímulos com similaridade alta. A taxa de recordação foi melhor nas provas em que as letras de um conjunto foram todas apresentadas com a mesma cor, assim como a porcentagem de respostas corretas variou de forma significativa em função da posição espacial dos estímulos. Os resultados foram interpretados de acordo com modelos que enfatizam aspectos do desenvolvimento de estratégias cognitivas ao longo do desenvolvimento humano, especialmente o modelo de memória de trabalho.<br>This study aimed to evaluate the mechanisms of visual-spatial memory in children. Seventy eight children took part in an experiment with four factors: children's age, stimuli spatial position, stimuli visual similarity, stimuli set color. The results have shown that all main factors are statistically meaningful. The oldest children presented a better performance than the youngest ones. Stimuli set formed by low similarity letters were better recollected than the stimuli set formed by high similarity letters. The recall of the spatial position of letters was better in trials where the letters of a set were presented in the same color. The percentage of correct recall changed meaningfully as a function of the spatial position in which the target had been presented. The results were interpreted according to models that emphasize aspects of development of cognitive strategies along with the human development, especially the working memory model