Biology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2749

Browse

Filters

2016 - 20202

Settings

Subject: search.filters.subject.Cortex

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Development of the translaminar circuits in the mouse cortex
    (2020) Deng, Rongkang; Kanold, Patrick O; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The elaborated connections among cortical neurons form the cortical circuits, which are essential mechanisms underlying various cortical functions such as sensory perception, motor control, and other cognitive functions. The cortical circuits are composed of excitatory neurons and GABAergic interneurons. Excitatory neurons send excitatory connections to cortical neurons, while inhibitory neurons send inhibitory connections. Building the neural circuits is no easy task involving complex genetic programs and the influence of the environment through sensation. Malformation of the cortical circuits during development is implicated in causing neurological disorders, but our knowledge about the developmental process is scarce. The work in this dissertation uses in vitro electrophysiology in brain slices from transgenic mice to investigate how the excitatory connections onto GABAergic interneurons in the primary auditory cortex develop during the first two postnatal weeks. Furthermore, this dissertation explores the mechanisms that could regulate the early development of the cortical circuits by testing the requirement of sensory epithelium and N-methyl-D-aspartate receptors (NMDARs) in the early postnatal development of the neural circuits in the primary sensory cortex and temporal association cortex (TeA), respectively. Results from these studies fill crucial gaps in our understanding of how GABAergic interneurons are integrated into the cortical circuits and highlight the importance of sensory epithelium in the normal development of excitatory connections onto cortical GABAergic interneurons. My results also showed impaired development of GABAergic connections onto excitatory neurons lacking functional NMDARs in the TeA, suggesting an essential role of NMDARs for the early development of inhibitory circuits in the cortex.
  • Thumbnail Image
    Item
    EFFECTS OF AGING ON MIDBRAIN AND CORTICAL SPEECH-IN-NOISE PROCESSING
    (2016) Presacco, Alessandro; Andreson, Samira; Simon, Jonathan Z.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Older adults frequently report that they can hear what they have been told but cannot understand the meaning. This is particularly true in noisy conditions, where the additional challenge of suppressing irrelevant noise (i.e. a competing talker) adds another layer of difficulty to their speech understanding. Hearing aids improve speech perception in quiet, but their success in noisy environments has been modest, suggesting that peripheral hearing loss may not be the only factor in the older adult’s perceptual difficulties. Recent animal studies have shown that auditory synapses and cells undergo significant age-related changes that could impact the integrity of temporal processing in the central auditory system. Psychoacoustic studies carried out in humans have also shown that hearing loss can explain the decline in older adults’ performance in quiet compared to younger adults, but these psychoacoustic measurements are not accurate in describing auditory deficits in noisy conditions. These results would suggest that temporal auditory processing deficits could play an important role in explaining the reduced ability of older adults to process speech in noisy environments. The goals of this dissertation were to understand how age affects neural auditory mechanisms and at which level in the auditory system these changes are particularly relevant for explaining speech-in-noise problems. Specifically, we used non-invasive neuroimaging techniques to tap into the midbrain and the cortex in order to analyze how auditory stimuli are processed in younger (our standard) and older adults. We will also attempt to investigate a possible interaction between processing carried out in the midbrain and cortex.