Theses and Dissertations at Montana State University (MSU)
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Item Small scale stimuli and the cricket cercal system(Montana State University - Bozeman, College of Agriculture, 2022) Mulder-Rosi, Jonas L.; Co-chairs, Graduate Committee: Charles M. Gray and R. Steven Stowers; This is a manuscript style paper that includes co-authored chapters.The cricket cercal system has been a model system in neuroscience for over 30 years. Anatomy, physiology, and theory have all come together to produce a picture of a system with a clear purpose: encoding air direction around the animal. However, certain features of the system have suggested that these cells may be sensitive to additional stimulus dimensions. To address this limited stimulus space I designed new experiments to test these neurons' responses to previously untested stimuli. I used a novel extracellular recording mechanism able to record and sort several neurons' responses at the same time. I built and tested several stimulators to provide small-scale puffs to specific parts of the sensory array at specific times. With these, I was able to test this model neural system against a complex stimulus space. I show here that these neurons respond to several additional stimulus dimensions. They are tuned to the timing of stimuli across the array. They show differential responses to even more complex stimuli with varying stimulus directions in different locations across the array. This implies that the previous understanding of the system was likely limited by how it was tested. While these cells accurately encode the direction of large-scale airflow, they also encode other aspects of stimuli, such stimulus timing and small-scale variations in stimulus direction. Thus the "function" of these neurons may be far more complex than previously understood.Item Large-scale spatiotemporal cortical dynamics in visual short-term memory: from spiking activity to oscillations(Montana State University - Bozeman, College of Agriculture, 2020) Hoffman, Steven Joseph; Chairperson, Graduate Committee: Charles M. Gray and Jamie Mazer (co-chair); Nicholas M. Dotson was an author and Baldwin Goodell and Charles M. Gray were co-authors of the article, 'A large-scale semi-chronic microdrive recording system for non-human primates' in the journal 'Neuron' which is contained within this dissertation.; Nicholas M. Dotson and Charles M. Gray were co-authors of the article, 'The cortical local field potential exhibits distinct spatial gradients that vary with frequency and time during visual short-term memory' which is contained within this dissertation.; Dissertation contains a article of which Steven Joseph Hoffman is not the main author.Cognitive processes occur through coordinated activity via disparate cortical and subcortical brain structures. Although these structures may be widely separated, evolutionary pressures dictate that cognition must occur rapidly and efficiently. In order to capture these brain-wide activity patterns the tools for measuring them need to be similarly capable of measurements of both high spatial coverage, and high temporal resolution. Additionally, the measurements would ideally be of the activity of the fundamental units involved in cognition, that is the neurons, rather than an extrapolation of their activity via a different signal source. However, outside of the work presented here, current technologies are rare that allow both the requisite coverage and spatiotemporal resolution to achieve these measurements. The results of the studies presented in Chapters 2-4 provide both the tools for making such measurements, and the initial analyses of the neuronal dynamics during short-term memory. In Chapter 2 we present the technological and methodological process for recording neural activity (both action potentials and local field potentials) from across roughly a hemisphere of cortex in the macaque monkey performing a visual short-term memory task. In visual short-term memory a visual percept must be maintained then recalled when it is no longer present. This cognitive process is one we use nearly incessantly in every-day life. In Chapter 3 we found task dependent spiking activity during short-term memory is wide-spread, and that most areas display a balanced state of both increases and decreases in firing rate. Within these areas we found a hierarchically organized subset of cortical areas that also showed stimulus specific activity during the memory period of the task. In Chapter 4 we used spectral analysis to investigate the oscillatory make-up of neural activity across the recorded areas. We found within specific frequency bands there are different gradients of amplitude of spectral power across cortex. Additionally, we found that we could use a small number of spectrally derived variables in order to decode the brain area origin of the signal. This shows that areas have a characteristic spectral composition, that varies systematically across the cortical mantle.Item Design and implementation of a real-time system to characterize functional connectivity between cortical areas(Montana State University - Bozeman, College of Engineering, 2017) Parsa Gharamaleki, Mohammadbagher; Chairperson, Graduate Committee: Brendan MumeyDespite a thorough mapping of the anatomical connectivity between brain regions and decades of neurophysiological studies of neuronal activity within the various areas, our understanding of the nature of the neural signals sent from one area to another remains rudimentary. Orthodromic and antidromic activation of neurons via electrical stimulation ('collision testing') has been used in the peripheral nervous system and in subcortical structures to identify signals propagating along specific neural pathways. However, low yield makes this method prohibitively slow for characterizing cortico-cortical connections. We employed recent advances in electrophysiological methods to improve the efficiency of the collision technique between cortical areas. There are three key challenges: 1) maintaining neuronal isolations following stimulation, 2) increasing the number of neurons being screened, and 3) ensuring low-latency triggering of stimulation after spontaneous action potentials. We have developed a software-hardware solution for online isolations and stimulation triggering, which operates in conjunction with two hardware options, Hardware Processing Platform (HPP) or a Software Processing Platform (SPP). The HPP is a 'system on a chip' solution enabling real-time processing in a re-programmable hardware platform, whereas the SPP is a small Intel Atom processor that allows soft real-time computing on a CPU. Employing these solutions for template matching both accelerates spike sorting and provides the low-latency triggering of stimulation required to produce collision trials. Recording with a linear tetrode array electrode allows simultaneous screening of multiple neurons, while the software package coordinates efficient collision testing of multiple user-selected units across channels. This real-time connectivity screening system enables researchers working with a variety of animal models and brain regions to identify the functional properties of specific projections between cortical areas in behaving animals.Item The intercellular spread of alphaherpesviruses(Montana State University - Bozeman, College of Letters & Science, 2018) Herr, Alix Elise; Chairperson, Graduate Committee: Matt Taylor; Kyles S. Hain and Matthew P. Taylor were co-authors of the article, 'Limitations on the multiplicity of cellular infection during human alphaherpesviral disease' in the journal 'Current clinical microbiology reports' which is contained within this thesis.; Theresa Thornburg, Max DePartee, Ryan Waters and Matthew P. Taylor were co-authors of the article, 'The route of transmission from neurons impacts pseudorabies virus coinfection in vivo' submitted to the journal 'Journal of virology' which is contained within this thesis.There are three prominent alphaherpesviruses that infect humans: Herpes Simplex virus-1, Herpes Simplex virus-2, and Varicella Zoster virus. Each virus is harbored within 15-98% of the population. Prototypical infections involve only a handful of intercellular spread events within a host. Most spread events involve neurons. Only one virion is thought to be successfully transmitted from a neuron to another cell -- but this has yet to be verified during infectious spread within a host. In this dissertation, we used Pseudorabies virus to trace the number of virions spreading infection from infected neurons to uninfected cells. Pseudorabies virus is a prominent model alphaherpesvirus that infects mice. To quantify the number of virions transmitted between cells, we intravitreally injected different, genetically engineered Pseudorabies virus strains and quantified spread to the murine central nervous system. We calculated the average number of expressed viral genomes per infected neuron by utilizing the Poisson distributions of neurons expressing one, two, or three different viral strains. We found that when a neuronal axon transmitted infection to cells, a cell became infected with one virion on average. In contrast, when neuronal soma or dendrites transmitted the viral strains to surrounding cells, each cell expressed three viral genomes on average. Most importantly, we discovered that the absence of a specific alphaherpesviral protein, US9, diminished the capacity of the virus to infect a cell with a plurality of viral particles. This dissertation advanced the field of herpesviral research in two ways: by quantifying the number of alphaherpesviral particles transmitted between infected neurons in a host and identifying a viral protein instrumental in determining the number virions transmitted from neurons to other cells. The average number of viral particles infecting cells within a host determines the viral genetic dosage and impacts viral gene expression, viral replicative rates, and viral diversification.Item The growth-promoting action of the insulin-like growth factor family in the magnocellular neurosecretory system during axonal sprouting(Montana State University - Bozeman, College of Letters & Science, 1998) Zhou, XinrongItem Using FPGAs to accelerate the training process of a Gaussian mixture model based spike sorting system(Montana State University - Bozeman, College of Engineering, 2003) Zhu, Yongming; Chairperson, Graduate Committee: Ross K. Snider