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.

Competition and the Legal Environment: Intellectual Property Rights in the Early American Film Industry

No abstract available.

Roldán, C. T. Ausín y R. Mate, Guerra y Paz. En nombre de la política. Madrid, El rapto de Europa, 2004, pp. 349

Fil: Ercoli, César Adrián. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Roldán, C. T. Ausín y R. Mate, Guerra y Paz. En nombre de la política. Madrid, El rapto de Europa, 2004, pp. 349

Fil: Ercoli, César Adrián. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Roldán, C. T. Ausín y R. Mate, Guerra y Paz. En nombre de la política. Madrid, El rapto de Europa, 2004, pp. 349

Fil: Ercoli, César Adrián. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Experiment: Competition between calcifying and noncalcifying temperate marine macroalgae under elevated CO2 levels

Since pre-industrial times, uptake of anthropogenic CO2 by surface ocean waters has caused a documented change of 0.1 pH units. Calcifying organisms are sensitive to elevated CO2 concentrations due to their calcium carbonate skeletons. In temperate rocky intertidal environments, calcifying and noncalcifying macroalgae make up diverse benthic photoautotrophic communities. These communities may change as calcifiers and noncalcifiers respond differently to rising CO2 concentrations. In order to test this hypothesis, we conducted an 86?d mesocosm experiment to investigate the physiological and competitive responses of calcifying and noncalcifying temperate marine macroalgae to 385, 665, and 1486 µatm CO2. We focused on comparing 2 abundant red algae in the Northeast Atlantic: Corallina officinalis (calcifying) and Chondrus crispus (noncalcifying). We found an interactive effect of CO2 concentration and exposure time on growth rates of C. officinalis, and total protein and carbohydrate concentrations in both species. Photosynthetic rates did not show a strong response. Calcification in C. officinalis showed a parabolic response, while skeletal inorganic carbon decreased with increasing CO2. Community structure changed, as Chondrus crispus cover increased in all treatments, while C. officinalis cover decreased in both elevated-CO2 treatments. Photochemical parameters of other species are also presented. Our results suggest that CO2 will alter the competitive strengths of calcifying and noncalcifying temperate benthic macroalgae, resulting in different community structures, unless these species are able to adapt at a rate similar to or faster than the current rate of increasing sea-surface CO2 concentrations.

The Degree of Competition in the Thai Banking Industry before and after the East Asian Crisis

This paper analyzes the influence of the East Asian crisis and the subsequent reforms on the oligopolistic nature of the Thai banking industry. Since the crisis, there have been substantial changes in competitive environment, including a decline in the family ownership of banks as well as the arrival of new entrants. How did these changes affect a banking industry in which the six largest local banks accounted for over 70 percent of market share? The estimated Lerner index from Bresnahan's [1989] conjectural variation model indicates the possibility of a decline in the degree of competition.

Imperfect Competition and Costly Screening in the Credit Market under Conditions of Asymmetric Information

This article provides an analysis of how banks determine levels of information production when they are in imperfect competition and there is a condition of information asymmetry between borrowers and banks. Specifically, the study concentrates on information production activities of banks in duopoly where they simultaneously determine intensity of pre-loan screening as well as interest rates. The preliminary model of this paper illustrates that due to strategic complementarities between banks, banking competition can result in inferior equilibrium out of multiple equilibria and insufficient information production. Policymakers must take into account the possible adverse effects of competition-enhancing policies on information production activities.