RESUMEN
Calculating prodigies are individuals who are exceptional at quickly and accurately solving complex mental calculations. With positron emission tomography (PET), we investigated the neural bases of the cognitive abilities of an expert calculator and a group of non-experts, contrasting complex mental calculation to memory retrieval of arithmetic facts. We demonstrated that calculation expertise was not due to increased activity of processes that exist in non-experts; rather, the expert and the non-experts used different brain areas for calculation. We found that the expert could switch between short-term effort-requiring storage strategies and highly efficient episodic memory encoding and retrieval, a process that was sustained by right prefrontal and medial temporal areas.
Asunto(s)
Aptitud/fisiología , Mapeo Encefálico , Cognición/fisiología , Corteza Prefrontal/fisiología , Lóbulo Temporal/fisiología , Adulto , Velocidad del Flujo Sanguíneo/fisiología , Circulación Cerebrovascular/fisiología , Lateralidad Funcional/fisiología , Giro del Cíngulo/irrigación sanguínea , Giro del Cíngulo/diagnóstico por imagen , Giro del Cíngulo/fisiología , Humanos , Inteligencia/fisiología , Masculino , Matemática , Memoria a Corto Plazo/fisiología , Recuerdo Mental/fisiología , Giro Parahipocampal/irrigación sanguínea , Giro Parahipocampal/diagnóstico por imagen , Giro Parahipocampal/fisiología , Corteza Prefrontal/irrigación sanguínea , Corteza Prefrontal/diagnóstico por imagen , Retención en Psicología/fisiología , Lóbulo Temporal/irrigación sanguínea , Lóbulo Temporal/diagnóstico por imagen , Tomografía Computarizada de EmisiónRESUMEN
PURPOSE: The objective of this study was to evaluate the ability of three adhesive systems to seal dentin by measuring the permeability of dentin before and after bonding procedures. MATERIALS AND METHODS: Thirty-six flat dentin surfaces were prepared from human extracted teeth and connected to a fluid-filled system for permeability measurements. The hydraulic conductance of the flat occlusal surface of dentin was measured by the filtration technique, before and after application of ScotchBond MP Plus, Prime & Bond 2.0, and All-Bond 2. Bonding procedures were followed by P-50 resin composite application. The specimens were then perfused with silver nitrate to permit morphologic localization of microleakage pathways using SEM. RESULTS: The results showed that the best dentin seal was produced by All-Bond 2, followed by Prime & Bond 2.0, and ScotchBond MP Plus. However, none of the three bonding systems tested was able to totally prevent the passage of fluid across the dentin in every specimen. When observed with SEM, each adhesive system exhibited different patterns of leakage. CONCLUSION: The inability of all three materials to create a perfect seal in vitro raises concerns about the ability of these adhesive systems to provide completely sealed restorations in vivo. However, because the current study applied pressure 3 to 6 times higher than physiologically normal, it is likely that the leakage represents a worst-case scenario.