Cooperation & Competition Between Navigation Systems in the Rat Brain: The Role of the Hippocampus and Striatum During a Dissociative Maze Task

While many tend to think of memory systems in the brain as a single process, in reality several experiments have supported multiple dissociations of different forms of learning, such as spatial learning and response learning. In both humans and rats, the hippocampus has long been shown to be specialized in the storage of spatial and contextual memory whereas the striatum is associated with motor responses and habitual behaviors. Previous studies have examined how damage to hippocampus or striatum has affected the acquisition of either a spatial or response navigation task. However even in a very familiar environment organisms must continuously switch between place and response strategies depending upon circumstances. The current research investigates how these two brain systems interact under normal conditions to produce navigational behavior. Rats were tested using a task developed by Jacobson and colleagues (2006) in which the two types of navigation could be controlled and studied simultaneously. Rats were trained to solve a plus maze using both a spatial and a response strategy. A cue (flashing light) was employed to indicate the correct strategy on a given trial. When no light was present, the animals were rewarded for making a 90º right turn (motor response). When the light was on, the animals were rewarded for going to a specific goal location (place strategy). After learning the task, animals had a sham surgery or dorsal striatum or hippocampus damaged. In order to investigate the individual role of each brain system and evaluate whether these brain regions compete or cooperate for control over strategy, we utilized a within-animal comparisons. The configuration of the maze allowed for the comparison of behavior in individual animals before and after specific brain areas were damaged. Animals with hippocampal lesions showed selective deficits on place trials after surgery and learned the reversal of the motor response more rapidly than striatal lesioned or sham rats. Unlike previous findings regarding maze learning, animals with striatal lesions showed deficits in both place and response trials and had difficulty learning the reversal of motor response. Therefore, the effects of lesions on the ability to switch back and forth between strategies were more complex than previously suggested. This work may reveal important new insight on the integration of hippocampal and striatal learning systems, and facilitate a better understanding of the brain dynamics underlying similar navigational processes in humans.

STUDIES ON CHOLINERGIC FUNCTION AND MEMORY IN MICE (CHOLINOTOXINS, WORKING, REFERENCE MEMORY, RADIAL ARM MAZE)

Considerable evidence suggests that central cholinergic neurons participate in either acquisition, storage or retrieval of information. Experiments were designed to evaluate information processing in mice following either reversible or irreversible impairment in central cholinergic activity. The cholinergic receptor antagonists, atropine and methylatropine were used to reversibly inhibit cholinergic transmission. Irreversible impairment in central cholinergic function was achieved by central administration of the cholinergic-specific neurotoxins, N-ethyl-choline aziridinium (ECA) and N-ethyl-acetylcholine aziridinium (EACA).^ ECA and EACA appear to act by irreversible inhibition of high affinity choline uptake (proposed rate-limiting step in acetylcholine synthesis). Intraventricular administration of ECA or EACA produced persistent reduction in hippocampal choline acetyltransferase activity. Other neuronal systems and brain regions showed no evidence of toxicity.^ Mice treated with either ECA or EACA showed behavioral deficits associated with cholinergic dysfunction. Passive avoidance behavior was significantly impaired by cholinotoxin treatment. Radial arm maze performance was also significantly impaired in cholinotoxin-treated animals. Deficits in radial arm maze performance were transient, however, such that rapid and apparent complete behavioral recovery was seen during retention testing. The centrally active cholinergic receptor antagonist atropine also caused significant impairment in radial arm maze behavior, while equivalent doses of methylatropine were without effect.^ The relative effects of cholinotoxin and receptor antagonist treatment on short-term (working) memory and long-term (reference) memory in radial arm maze behavior were examined. Maze rotation studies indicated that there were at least two different response strategies which could result in accurate maze performance. One strategy involved the use of response algorithms and was considered to be a function of reference memory. Another strategy appeared to be primarily dependent on spatial working memory. However, all behavioral paradigms with multiple trails have reference memory requirements (i.e. information useful over all trials). Performance was similarly affected following either cholinotoxin or anticholinergic treatment, regardless of the response strategy utilized. In addition, rates of behavioral recovery following cholinotoxin treatment were similar between response groups. It was concluded that both cholinotoxin and anticholinergic treatment primarily resulted in impaired reference memory processes. ^

Heterogeneidade Linguística : Reflexões sobre questão de Língua Portuguesa na Prova Brasil 2009

A Prova Brasil é um instrumento de avaliaçao de larga escala, porém ao analisarmos uma questao de Língua Portuguesa do 5o ano do Ensino Fundamental aplicada em 2009, nos deparamos com o uso lingüístico da expressao ?DA HORA?, que nos remete a uma gíria, tipicamente relacionada a uma cultura específica. Todavia, entendemos que nao é adequada a utilizaçao deste tipo de conteúdo em uma avaliaçao de larga escala, pois acaba impondo que os alunos dominem uma determinada cultura, que passa ser a cultura dominante, ou seja, o modelo a ser apreendido. Com o intuito de analisar a questao supracitada, da Prova Brasil, construímos referencial teórico a partir de alguns conceitos/ideias como os de cultura (WILLIAMS, 1979 e 1992), cultura escolar (FORQUIN, 1993), diferença cultural (CARVALHO, 2009), currículo de acordo com a perspectiva da LDB no 9.394/96 (BRASIL, 2004). A metodologia adotada para esta pesquisa foi a Análise de Conteúdos de Bardin (2002). Concluímos, considerando que em avaliaçoes de larga escala deve-se verificar a apreensao, por parte dos alunos, sobre os conteúdos do currículo básico e nao da parte diversificada (BRASIL, 2004), visto que nao podemos generalizar a cultura já que esta é característica peculiar de um povo, regiao, grupo social, logo de caráter particular e nao de âmbito nacional

Heterogeneidade Linguística : Reflexões sobre questão de Língua Portuguesa na Prova Brasil 2009

A Prova Brasil é um instrumento de avaliaçao de larga escala, porém ao analisarmos uma questao de Língua Portuguesa do 5o ano do Ensino Fundamental aplicada em 2009, nos deparamos com o uso lingüístico da expressao ?DA HORA?, que nos remete a uma gíria, tipicamente relacionada a uma cultura específica. Todavia, entendemos que nao é adequada a utilizaçao deste tipo de conteúdo em uma avaliaçao de larga escala, pois acaba impondo que os alunos dominem uma determinada cultura, que passa ser a cultura dominante, ou seja, o modelo a ser apreendido. Com o intuito de analisar a questao supracitada, da Prova Brasil, construímos referencial teórico a partir de alguns conceitos/ideias como os de cultura (WILLIAMS, 1979 e 1992), cultura escolar (FORQUIN, 1993), diferença cultural (CARVALHO, 2009), currículo de acordo com a perspectiva da LDB no 9.394/96 (BRASIL, 2004). A metodologia adotada para esta pesquisa foi a Análise de Conteúdos de Bardin (2002). Concluímos, considerando que em avaliaçoes de larga escala deve-se verificar a apreensao, por parte dos alunos, sobre os conteúdos do currículo básico e nao da parte diversificada (BRASIL, 2004), visto que nao podemos generalizar a cultura já que esta é característica peculiar de um povo, regiao, grupo social, logo de caráter particular e nao de âmbito nacional

Heterogeneidade Linguística : Reflexões sobre questão de Língua Portuguesa na Prova Brasil 2009

A Prova Brasil é um instrumento de avaliaçao de larga escala, porém ao analisarmos uma questao de Língua Portuguesa do 5o ano do Ensino Fundamental aplicada em 2009, nos deparamos com o uso lingüístico da expressao ?DA HORA?, que nos remete a uma gíria, tipicamente relacionada a uma cultura específica. Todavia, entendemos que nao é adequada a utilizaçao deste tipo de conteúdo em uma avaliaçao de larga escala, pois acaba impondo que os alunos dominem uma determinada cultura, que passa ser a cultura dominante, ou seja, o modelo a ser apreendido. Com o intuito de analisar a questao supracitada, da Prova Brasil, construímos referencial teórico a partir de alguns conceitos/ideias como os de cultura (WILLIAMS, 1979 e 1992), cultura escolar (FORQUIN, 1993), diferença cultural (CARVALHO, 2009), currículo de acordo com a perspectiva da LDB no 9.394/96 (BRASIL, 2004). A metodologia adotada para esta pesquisa foi a Análise de Conteúdos de Bardin (2002). Concluímos, considerando que em avaliaçoes de larga escala deve-se verificar a apreensao, por parte dos alunos, sobre os conteúdos do currículo básico e nao da parte diversificada (BRASIL, 2004), visto que nao podemos generalizar a cultura já que esta é característica peculiar de um povo, regiao, grupo social, logo de caráter particular e nao de âmbito nacional