Development and Investigation of Sparse Co-Adaptive Algorithms in ECoG based Closed-Loop Brain Computer Interface

Electrocorticography (ECoG) has gained a lot of momentum and has become a serious contender as a recording modality for the implementation of Brain-Computer Interface (BCI) systems in the last few years. ECoG signals provide the right balance between minimal invasiveness and robust spectral information to accomplish a BCI task. However, all the BCI studies until now have used signals recorded from a large number of implanted electrodes and a larger number of spectral features. The recording and processing of these signals uses a lot of electrical power and thus hinders its use outside the research setting. To translate this research to the clinic as a chronic recording modality for neural prosthesis, minimizing the number of features and thus, the power consumption to record and process them, is of prime importance. This thesis develops and investigates two different techniques to minimize the feature space required to obtain a robust BCI control in a virtual environment setting. ECoG electrodes embedded in thin-film polyimide or Silastic were implanted in the epidural space over pre-motor, primary motor and parietal cortical areas in non-human primates. Subjects tested this thesis had had their electrode arrays implanted at least 1-2 years before the beginning of these experiments. Monkeys were trained to perform a classic 2D center out task using the recorded signals and one of two new BCI decoding algorithms developed in this thesis. Both the algorithms used for BCI control updated the decoding model using data from the previous trials. The parameters of the decoding algorithms were varied every 1-2 weeks to gradually reduce the number of features being used for control. A robust BCI control was obtained using only 30-40% of the available feature set. Post hoc analysis of the reduced feature set revealed a significant presence of mid-gamma (75-115Hz) band followed by the beta band (15-30 Hz). A novel, 1D Up-Down BCI task was used to study the modulation frequency of these two bands and the differences between them. It was observed that though subjects gradually increased the frequency of modulation in both the bands over a few weeks, they were able to modulate the mid-gamma band at a faster rate. Finally, as a proof concept, two previously trained subjects were used to perform the 2D center-out task with features recorded from only 4 ECoG electrodes. The laboratory recording system and a low power recording system were used in different sessions of experiments, and a robust control was obtained in both the cases. The overall observations and results of these studies provide with a strong basis for ECoG as a low power recording modality that can be chronically used for neural prosthesis

Comparison of Point Cloud and Image-based Models for Calorimeter Fast Simulation

Score based generative models are a new class of generative models that have been shown to accurately generate high dimensional calorimeter datasets. Recent advances in generative models have used images with 3D voxels to represent and model complex calorimeter showers. Point clouds, however, are likely a more natural representation of calorimeter showers, particularly in calorimeters with high granularity. Point clouds preserve all of the information of the original simulation, more naturally deal with sparse datasets, and can be implemented with more compact models and data files. In this work, two state-of-the-art score based models are trained on the same set of calorimeter simulation and directly compared.Comment: 11 pages, 6 figures, 1 tabl

A carboxy terminal domain of the L protein of rinderpest virus possesses RNA triphosphatase activity - The first enzyme in the viral mRNA capping pathway

The large protein L of negative-sense RNA viruses is a multifunctional protein involved in transcription and replication of genomic RNA. It also possesses enzymatic activities involved in capping and methylation of viral mRNAs. The pathway for mRNA capping followed by the L protein of the viruses in the Morbillivirus genus has not been established, although it has been speculated that these viruses may follow the unconventional capping pathway as has been shown for some viruses of Rhabdoviridae family. We had earlier shown that the large protein L of Rinderpest virus expressed as recombinant L-P complex in insect cells as well as the ribonucleoprotein complex from purified virus possesses RNA triphosphatase (RTPase) and guanylyltransferase activities, in addition to RNA dependent RNA polymerase activity. In the present work, we demonstrate that RTPase as well as nucleoside triphosphatase (NTPase) activities are exhibited by a subdomain of the L protein in the C terminal region (a.a. 1640 1840). The RTPase activity depends absolutely on a divalent cation, either magnesium or manganese. Both the RTPase and NTPase activities of the protein show dual metal specificity. Two mutant proteins having alanine mutations in the glutamic acid residues in motif-A of the RTPase domain did not show RTPase activity, while exhibiting reduced NTPase activity suggesting overlapping active sites for the two enzymatic functions. The RTPase and NTPase activities of the L subdomain resemble those of the Vaccinia capping enzyme D1 and the baculovirus LEF4 proteins. (C) 2015 Elsevier Inc. All rights reserved