Browsing by Subject "tinnitus"

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    Inducing Neural Plasticity and Modulation Using Multisensory Stimulation: Techniques for Sensory Disorder Treatment
    (2017-06) Gloeckner, Cory Dale
    In this dissertation, we characterized the modulatory and plasticity effects of paired multisensory stimulation on neural firing in sensory systems across the brain. In the auditory system, we discovered that electrical somatosensory stimulation can either suppress or facilitate neural firing in the inferior colliculus (IC) and primary auditory cortex (A1) depending stimulation location. We also tested plasticity effects in A1 in response to paired somatosensory and acoustic stimulation with different inter-stimulus delays in anesthetized guinea pigs, and found that plasticity induced by paired acoustic and right mastoid stimulation was consistently suppressive regardless of delay, but paired acoustic and pinna stimulation was timing-dependent, where one inter-stimulus delay was consistently suppressive while other delays induced random changes. These experiments were repeated in awake animals with paired acoustic and pinna stimulation, and two animal groups of different stress levels were used to assess stress effects on plasticity. We found that in low-stress animals, the same inter-stimulus delay was consistently suppressive and a neighboring delay was consistently facilitative across all animals, which matches previous invasive spike-timing dependent plasticity studies (anesthesia may have affected these trends). Meanwhile, high-stress animal results were not consistent with expected time dependence and exhibited no trends across inter-stimulus delays, indicating that stress can have adverse effects on neuromodulation plasticity outcomes. In all other primary sensory cortices, we found that differential effects can be induced with paired sensory stimulation such that the location, amount, type, and timing of plasticity can be controlled by strategically choosing sensory stimulation parameters for modulation of each sensory cortex. We also investigated the ability to target subpopulations of neurons within a brain region and found that by stimulating at levels near activation thresholds, specific subpopulations of IC neurons can be targeted by varying somatosensory stimulation location. Furthermore, acoustic stimulation can excite or modulate specific areas of somatosensory cortex, and we mapped the guinea pig homunculus to characterize this. Overall, these findings illustrate the immense interconnectivity between sensory systems, and multisensory stimulation may provide a noninvasive neuromodulation approach for inducing controlled plasticity to disrupt pathogenic neural activity in neural sensory disorders, such as tinnitus and pain.
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    Invasive and Noninvasive Brain Stimulation Strategies for the Treatment of Tinnitus
    (2014-06) Markovitz, Craig
    The central auditory system consists of a series of relay stations at which auditory information is processed in stages before reaching the auditory cortex for sound perception. However, descending projections and non-auditory inputs into the central auditory system also play a vital role in shaping neural coding along the auditory pathway. The work in this thesis seeks to investigate the organization and role of these modulatory pathways of the central auditory system, particularly to devise and improve upon existing neuromodulation strategies for treating neurological disorders related to the auditory system, including tinnitus and hyperacusis. Through animal studies, we have shown that the descending projections from primary auditory cortex to subcortical centers, particularly the central nucleus of the inferior colliculus, exhibit a precise spatial organization based on frequency coding, supporting the role of the corticofugal system for modulating specific and relevant coding features within the ascending auditory system. Further, by combining stimulation of auditory cortex with an irrelevant acoustic stimulus, we were able to suppress neural firing throughout the inferior colliculus, revealing at least one potential mechanism for gating relevant versus irrelevant sound inputs. Targeting this gating mechanism could provide a neuromodulation treatment for tinnitus and/or hyperacusis which are associated with hyperactivity across auditory centers. Finally, we introduce a new neuromodulation approach using simultaneous noninvasive stimulation of multimodal pathways, focusing initially on somatosensory and auditory inputs. We present our proof-of-concept studies showing the ability to modulate neural coding in the inferior colliculus up to auditory cortex in a systematic way depending on the stimulation parameters (e.g., interstimulus interval and body stimulation location). These invasive and noninvasive techniques for modulating the brain provide potential options for the treatment of hearing disorders as well as other neurological and neuropsychiatric conditions.