Encoding mechanisms based on fast oscillations in the retina of the cat and their dependencies on anesthesia

Processing in the visual system starts in the retina. Its complex network of cells with different properties enables for parallel encoding and transmission of visual information to the lateral geniculate nucleus (LGN) and to the cortex. In the retina, it has been shown that responses are often accompanied by fast synchronous oscillations (30 - 90 Hz) in a stimulus-dependent manner. Studies in the frog, rabbit, cat and monkey, have shown strong oscillatory responses to large stimuli which probably encode global stimulus properties, such as size and continuity (Neuenschwander and Singer, 1996; Ishikane et al., 2005). Moreover, simultaneous recordings from different levels in the visual system have demonstrated that the oscillatory patterning of retinal ganglion cell responses are transmitted to the cortex via the LGN (Castelo-Branco et al., 1998). Overall these results suggest that feedforward synchronous oscillations contribute to visual encoding. In the present study on the LGN of the anesthetized cat, we further investigate the role of retinal oscillations in visual processing by applying complex stimuli, such as natural visual scenes, light spots of varying size and contrast, and flickering checkerboards. This is a necessary step for understanding encoding mechanisms in more naturalistic conditions, as currently most data on retinal oscillations have been limited to simple, flashed and stationary stimuli. Correlation analysis of spiking responses confirmed previous results showing that oscillatory responses in the retina (observed here from the LGN responses) largely depend on the size and stationarity of the stimulus. For natural scenes (gray-level and binary movies) oscillations appeared only for brief moments probably when receptive fields were dominated by large continuous, flat-contrast surfaces. Moreover, oscillatory responses to a circle stimulus could be broken with an annular mask indicating that synchronization arises from relatively local interactions among populations of activated cells in the retina. A surprising finding in this study was that retinal oscillations are highly dependent on halothane anesthesia levels. In the absence of halothane, oscillatory activity vanished independent of the characteristics of the stimuli. The same results were obtained for isoflurane, which has similar pharmacological properties. These new and unexpected findings question whether feedfoward oscillations in the early visual system are simply due to an imbalance between excitation and inhibition in the retinal networks generated by the halogenated anesthetics. Further studies in awake behaving animals are necessary to extend these conclusions

A legitimidade da jurisdição de primeiro grau na concretização dos direitos fundamentais: proposta de um novo modelo jurídico-administrativo para o segundo grau de jurisdição

The current study is about the legitimacy of lower court jurisdiction as a way of exercising basic legal rights, proposing, therefore, a new legal-administrative model for appellate court. In order to achieve that, a demonstration of the importance of basic legal rights in the Brazilian legal system and an open interpretation in light of the Constitution, as a way to affirm said rights, among which are accessibility to the justice system and proper legal protection, is required. As a result, the legitimacy to access the legal system resides in the Constitution, where the interpreter should seek its basic principles to achieve basic legal rights. It is observed that the lack of credibility regarding lower court decisions comes from the dogmatic view of truth born from power, and therefore, that the truth resides in decisions from appellate court and not from lower court judges. A lower court judge holds a privileged position in providing basic legal rights for citizens, considering his close contact to the parties, the facts, and the evidences brought forth. Class action suit is presented as an important instrument able to lead the lower court judge to provide basic legal rights. Small Claims Courts may be used as paradigm to the creation of Appellate State Courts formed by lower court judges, reserving to higher jurisdiction courts and Federal Circuit Courts, the decisions of original competency and the management and institutional representation of the judiciary system. Instilling an internal democratization of the judiciary is also required, which means the participation of lower court judges in electing their peers to chief positions in the court system, as well as establishing a limited mandate to higher court judges.