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Neurophys
Talks
Neurophotonics: exploiting non-invasive optical techniques to study brain functions
Anderson Gomes, Physics Department, Laboratory of Photonics and Biophotonics, UFPE.
Neurophotonics is a recently founded multidisciplinary research area combining photonics and neuroscience. It includes invasive and non-invasive techniques for animal and human studies. In this talk, I will focus only on non-invasive methods that uses near infrared light to probe functional activity in the brain. I will review recently reported works on fast optical signal, diffuse correlation spectroscopy, functional near-infrared spectroscopy and optical coherence tomography (OCT). In particular, I shall exploit more deeply the OCT method, due to its availibility in our laboratory and recent tests using adult mouses and an OCT system at 930nm.
Spintronics – might somehow be of interest to neuroscience?
Antonio Azevedo, Physics Department, UFPE
We know from very basic courses that the electron is a particle with two degrees of freedom: a charge and a spin. Most of the electrical phenomena are due to the electron charge, including the huge advances in conventional electronics that gave birth to the “information age”. For many decades, the electron spin was used to explain the magnetism phenomena with no application in electronics. The things started to change in the 80´s with seminal discoveries that gave birth to the emerging area of “spintronics”. In this short presentation, I will try to give you an overview of what we are doing at UFPE, pushing to the direction of the state of art where spintronics meets neuromorphic.
NanoBio Convergence: Use of Polymeric Membranes and Nanocomposites in Molecular Biology
Celso Melo, Physics Department, UFPE
Over the last few years, the special properties of conducting polymers, such as a simple charge transfer, good electrical conductivity, electrochromism and fluorescence, have been explored for the development of devices that could be easily adapted for use in different technologies, such as electronic noses, photovoltaic systems and printed electronics. In this seminar, we will discuss the application of polymeric nanocomposites and membranes to problems of interest at the interface between Physics and Biology. By a suitable adjustment of its physico-chemical characteristics, it is possible to optimize the interaction of these materials with biomolecules, to allow their use for both the capture and purification of nucleic acid and protein chains, and for the development of rapid diagnostic tests. As a first example, we will examine the use of polymeric substrates in diagnostic assays of a molecular nature, which do not require amplification of the target nucleic acid and that can be performed in a matter of minutes. Preliminary results indicate that the sensitivity and specificity of these new platforms are comparable to (or greater than) those of the currently available serological tests. In addition, we will show results of the use of hybrid composites (metal oxides)/(conductive polymer) for extraction of DNA/RNA and capture of proteins. Protocols based on the use of these nanocomposites have several competitive advantages over those nowadays adopted, such as simplicity and non-use of toxic solvents, leading to a higher yield and an increase in the purity of the desired nucleic acid. Finally, we will discuss the use of polymeric membranes and hybrid organic/inorganic nanocomposites for the purification of water through the removal of biological contaminants and metallic ions, dyes and pesticides.
Anticipated synchronization and criticality in the brain
Mauro Copelli, Physics Department, UFPE
In this presentation, I will discuss two topics of potential collaboration between the Brain Institute (UFRN) and our group in the Physics Department (UFPE). The first topic is anticipated synchronization (AS), which is a counterintuitive regime that can occur in a sender-receiver configuration, where the latter can predict the future dynamics of the former for certain parameter values.
AS has been found both experimentally and numerically in different fields, such as optics and electronic circuits. Later, the phenomenon was extended to neuroscience. On the one hand, AS was shown to occur for biologically plausible models of neuronal activity. On the other hand, models exhibiting AS were able to explain the apparent discrepancy between information flow and time lag observed experimentally in the cortical activity of monkeys. We will review the current state of the field and outline the possibilities and challenges ahead.
The second topic is brain criticality. Since the first measurements of neuronal avalanches, the critical brain hypothesis has gained traction. However, if the brain is critical, what is the phase transition? For several decades, it has been known that the cerebral cortex operates in a diversity of regimes, ranging from highly synchronous states (with higher spiking variability) to desynchronized states (with lower spiking variability). Using both new and publicly available data, we tested independent signatures of criticality and showed that a phase transition occurs in an intermediate value of spiking variability, in both anesthetized and freely moving animals.The critical exponents point to a universality class different from mean-field directed percolation. Importantly, as the cortex hovers around this critical point, the avalanche exponents follow a linear relation that encompasses previous experimental results from different setups and is reproduced by a model.
Mind the map! How cortical layout may account for gamma oscillations
Sergio Neuenschwander, Vislab, Brain Institute, UFRN
Gamma rhythms have been implicated in visual binding and attention. So far, most of the evidence in support of this hypothesis was based on simplified stimuli such as gratings and bars. Here we use a paradigm in capuchin monkeys that allows for direct comparisons between fixation vs. free-view conditions and gratings vs. natural stimuli. In V1, gamma is characteristically strong for optimally oriented stimuli regardless of the viewing condition. Gamma is surprisingly absent, however, during free viewing of natural images and movies. In a recent study, in collaboration with Martin Vinck (ESI, Frankfurt), we found a distinct class of bursting excitatory cells in monkey V1 for which gamma is highly predictive of its orientation preferences. Notably, these cells are not present in the mouse. Primates, carnivores, and rodents exhibit profound differences in their cortical arrangement. Monkeys and cats show a well-organized layout; similar orientation domains are preferentially connected. Rodents, on the other hand, have a dispersed arrangement (salt-and-pepper). It is possible that the particular robust gamma synchronization commonly observed in cats and monkeys arises from the distinct cortical organization they have. Complex stimuli, such natural scenes, induce fundamentally different patterns of interactions in the cortex, as compared to moving bars or gratings. Thus, gamma oscillations may reflect different activation dynamics without any particular significance for visual processing.
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