RESUMO
It has been suggested that internally generated visual perception involves the primary visual cortex V1. To test this hypothesis, a functional MRI study was conducted with a female subject with orthographic color-word synesthesia. This subject was selected as she reported clear involuntary visualization of auditorily presented verbal material. Hearing a word resulted in seeing the word in a particular color. fMRI scans were acquired while the subject performed two verbal tasks (passive listening to words and verbal fluency). Significant activity was detected in primary visual cortex, in the absence of external visual stimulation. This finding provides evidence for a role of modulatory feedback connections between associative and primary visual areas in visual experience without direct visual stimulation.
Assuntos
Percepção Auditiva/fisiologia , Retroalimentação/fisiologia , Alucinações/fisiopatologia , Comportamento Verbal/fisiologia , Córtex Visual/metabolismo , Vias Visuais/fisiologia , Percepção Visual/fisiologia , Estimulação Acústica , Adulto , Mapeamento Encefálico , Circulação Cerebrovascular/fisiologia , Percepção de Cores/fisiologia , Feminino , Lateralidade Funcional/fisiologia , Alucinações/patologia , Humanos , Imageamento por Ressonância Magnética , Rede Nervosa/anatomia & histologia , Rede Nervosa/metabolismo , Testes Neuropsicológicos , Estimulação Luminosa , Córtex Visual/anatomia & histologiaRESUMO
OBJECTIVES: The aim of this study was to prove a nondestructive method to evaluate the strength of dental ceramic materials with respect to its potentiality and limitations. METHODS: The Young's moduli of 13 dental ceramic materials were determined by the resonance frequency method. Additionally, the flexural strengths of eight of these materials were evaluated by the four-point bending test. Strength values for the other five ceramic materials were taken from the literature. The Young's moduli were correlated with the strength values by Hook's law, respectively. RESULTS: Young's modulus for ceramics can be determined using a resonance frequency method. Fracture strain values of the ceramic materials tested (with the exception of Empress 2) have fracture strain values between 0.08 and 0.15%. A mean strain can be calculated (0.11%) and used with the value of Young's modulus to estimate fracture strength of ceramics. For the materials evaluated, predicted strength was within 39% of the measured values. SIGNIFICANCE: A non-destructive method to estimate strength of dental ceramic materials is possible, even though the accuracy of the predicted values is not very high. Nevertheless, the method permits new materials proposed for dental ceramic restorations to be screened for probable clinical success. Expensive and time-consuming testing would only need to be done on those materials which pass this initial criterion.
