Theses and Dissertations at Montana State University (MSU)
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Item Behavioral and physiological encoding of value and validity in the visual cortex of the macaque(Montana State University - Bozeman, College of Agriculture, 2021) Thuen, Adam James; Co-chairs, Graduate Committee: Jamie Mazer and Dominique ZossoSpatial attention and reward research in most humans and all animal models have inherent value and validity associated with task-relevant stimuli. To date, these variables have been investigation in isolation. Assumptions are made with the respect to the dissociability of value and validity effects on task performance and neural activity. Using a novel behavioral task, we varied value and validity within the same experiment in attempt to dissociate their effects on visual processing. Our results indicate that the assumption of dissociability between value and validity effects used to characterize attention and reward modulations is not a safe one to make. Researchers must consider complex interactions between these two variable quantities when investigating attention using incentives and while investigating incentive effects when attention is freely deployable.Item The Fronto-Parietal network and beyond : a study of the spatiotemporal patterns underlying visual working memory(Montana State University - Bozeman, College of Letters & Science, 2014) Dotson, Nicholas Monroe; Chairperson, Graduate Committee: Charles M. Gray; Rodrigo F. Salazar and Charles M. Gray were co-authors of the article, 'Spatiotemporal activity patterns reveal the interplay between integration and segregation during visual working memory' which is contained within this thesis.Working memory, an integral component of higher cognitive functions, involves the short-term retention and utilization of behaviorally relevant information when that information is no longer available in the environment. Tragically, individuals suffering from traumatic brain injuries, psychiatric disorders, and other neurological disorders often exhibit working memory deficits. The study of working memory may thus provide insight into the mechanisms underlying cognitive functions and the potential to alleviate major health problems. In order to understand cognitive processes, like working memory, several pieces of information must be considered: the cortical and sub-cortical areas involved, the manner in which these areas integrate, or share information, and the underlying dynamics of these integrative processes. These pieces form a hierarchical structure of investigation, from the individual areas to global principles of coordination. The objective of this study is to elucidate the relevant spatiotemporal patterns of oscillatory synchronization underlying visual working memory in the fronto-parietal network and across the brain. Relevant patterns for consideration are those that encode stimulus information, are modulated by the task, and those with distinct anatomical variations. The results of the studies presented in Chapters 2-4 provide extensive evidence that oscillatory synchronization is a mechanism for distributed integration. We show that the patterns of coherent activity 1) encode working memory items, 2) are indicative of the task period, 3) provide the potential for multiple functional networks, defined by the relative phase and, 4) are highly dynamic, with large fluctuations in magnitude and relative phase. Future studies will be necessary to further investigate the role of oscillatory synchronization. Efforts to perturb oscillatory activity in order to illustrate its utility, rather than simply correlating its activity with stimulus and task components, will be crucial. Finally, understanding the spatiotemporal activity patterns underlying working memory may ultimately allow for the identification of aberrant patterns, such as those brought on by disease, and allow for these patterns to be meaningfully interacted with - via neuroprosthetic devices.Item Exploration of cat striate cortex during natural scene stimulation(Montana State University - Bozeman, College of Letters & Science, 2013) Baker, Jonathan Lee; Chairperson, Graduate Committee: Charles M. GrayThe mammalian visual system evolved to process and represent objects within the complexities of the natural world to appropriately guide behavior in order to ensure survival and reproduction. Visual neuroscience has long sought to understand the neural basis of these processes, but the complexity of both the visual world and the brain has traditionally required a highly reductionist approach. The classical approach has led to the development of models of visual perception that are largely based on the analysis of how single cells within the visual system respond to simple and parametrically defined visual stimuli. However our ultimate goal is to understand how the visual system operates in the natural world. The experiments and results contained in this thesis were conducted, in part, to explore the cat's visual system during the presentation of time varying natural scenes, i.e. movies, and to attempt to validate our current working models of the visual system. Novel large-scale recording methods were employed to record from and characterize responses of large populations of cat primary visual cortex neurons during classical as well as movie stimulation. Contrary to the current models and our general understanding of how visual cortex represents information, groups of adjacent neurons responded heterogeneously to the movies presented and individual responses were very brief and highly sparse in time. The diversity and dynamics of the spiking activity was also significantly correlated with fluctuations of the ongoing local field potentials, specifically within the gamma frequency band, ranging from 25 to 90Hz. These gamma band oscillations also exhibited rich spatiotemporal dynamics throughout the movie presentations. In conclusion, time-varying natural scenes evoke response dynamics within the cat primary visual cortex not typically observed under more classical stimulus regimes. Future experimentation and the construction of biologically feasible models of visual cortex should take into account the diversity of responses observed under more natural stimulus conditions.