PhD Proposal Examination – Annik Yalnizyan Carson (Richards lab)

PhD Proposal Exam

 

Tuesday May 16th, 10:10 am – Ramsay Wright Building, Rm. 432

 

Annik Yalnizyan Carson (Richards lab)

Episodic Control: The Role of Memory Systems in Decision Making”

Abstract

Reinforcement learning (RL) is an area of machine learning concerned with optimal behavioural control. RL provides a normative framework in which to understand how the brain can learn to make decisions for maximizing subjective reward in the absence of an explicit teaching signal. Currently, even agents using state-of-the-art control systems in RL tasks are data inefficient and challenged by nonstationary environmental conditions, including changes in statistics of reward probability and transitions between states, which biological agents handle with relative ease. It has been proposed that storing information about experienced episodes in a memory cache — modeled after the activity of the hippocampus in animals — can help bootstrap learning in RL systems to improve the speed of learning and ability to cope with nonstationary environments. My research proposes three different representations for episodic memories stored in such a system and aims to resolve which provides the greatest benefit to RL systems when used in conjunction with a standard controller. Furthermore I aim to resolve how these representations can account for features of animal behaviour, and which of these representations — if any — are likely to explain how episodic memory is represented in the hippocampus.

Ramsay Wright is a wheelchair accessible building.

 

PhD Proposal Examination – Abiramy Karunendiran (Stewart/Barzda labs)

PhD Proposal Exam

 

Tuesday May 2nd, 2:30 pm – Rm. CCT 3150, University of Toronto at Mississauga

 

Abiramy Karunendiran (Stewart/Barzda labs)

Investigating the Role of Sarcomere Structure and Bioenergetic Input on Muscle Contraction in Drosophila Using Nonlinear Optical Microscopy

Abstract

Nonlinear optical microscopy has been shown to be a superior imaging modality compared to fluorescence and electron microscopy. Imaging can be done without prior staining, providing a variety of valuable techniques that can be used to reveal structural and functional information in a biological system. Second harmonic generation is observed in non-centrosymmetric cylindrical molecules such as myosin and can be used to directly visualize muscle structure. It was found through polarization microscopy that the second harmonic signal is generated from the anisotropic bands. Hence, the objective of this research is to investigate dynamic properties of sarcomere structure as well as genetic and bioenergetic inputs in Drosophila Melanogaster muscles. This will be accomplished using three approaches. Recently, it was found that the second harmonic response was affected by the size of the sarcomere. To further characterize the second harmonic properties of muscle, changes in the SHG response as well as polarization dependency on myofibril organization will be investigated at various elongation lengths. These parameters will also be compared in somatic, cardiac and visceral muscles to investigate the changes in SHG response due to changes in myofibril organization. The technique will then be applied to examine changes in second harmonic properties of sarcomere due to presence/absence of various chaperones and co-chaperones responsible for thick filament maintenance. Lastly, THG intensity changes due to activity of mitochondria will be investigated along with its correlation to sarcomere contractions. This imaging technique offers new perspective on the dynamic properties of contraction, and how these properties may be altered in movement disorders.

PhD Proposal Examination – Christine Nguyen (Stewart lab)

PhD Proposal Examination

 

Friday April 21st, 1:10 pm – Room CCT 2150, University of Toronto at Mississauga

 

Christine Nguyen (Stewart lab)

The Characterization of the Electrophysiological Properties of Three-Dimensional Bioengineered Human Skeletal Muscle and Neuromuscular Junctions

 

Abstract

Two-dimensional (2D) in vitro models of human skeletal muscle lack the architecture and contractile properties of a native muscle fiber, limiting them from being used for in vitro neuromuscular junction (NMJ) experimentation. A new method for creating three-dimensional (3D) human skeletal muscle tissues from human primary myogenic progenitors has been reported. The bioengineered muscle tissues are contractile, mimic’s clinical responses to drugs, and possess the epilson acetylcholine receptor (AChR) unit expressed in mature NMJs. Central to the communication of neurons and cells is the synapse, where transmission occurs via electrical and chemical signals between the close apposition of the pre- and post-synaptic cell membrane. At the vertebrate NMJ, acetylcholine is released from the pre-synaptic nerve terminal where it binds to AChRs on the postsynaptic muscle fiber. The flow of cations into the postsynaptic muscle cell induces a change in the membrane voltage that activates the muscle. The characterization of electrical properties of the muscle cells at rest, and when excited is crucial to advancing our understanding of the bioengineered muscles functionality. This proposed thesis will characterize the electrical properties in vitro 3D skeletal muscle tissue, and use it as the foundation for studying synaptic transmission of skeletal muscle tissues co-cultured with human pluripotent stem cell (hPSC) derived motor neurons (MN). Duchenne’s muscular dystrophy (DMD) is a fatal muscle disorder involving the skeletal muscle system. Little is known regarding the functional properties of the NMJ in DMD patients due to difficulties of in vivo experiments, and the lack of in vitro models. A new in vitro system of the NMJ will allow for further analysis in studying the integrity of skeletal muscles with regards to neuromuscular activity. Electrophysiological analyses of the model NMJ will be studied in both normal muscle cells, as well as in mutant cells with DMD.