Author's School

School of Engineering & Applied Science

Author's Department/Program

Biomedical Engineering

Language

English (en)

Date of Award

1-1-2009

Degree Type

Thesis

Degree Name

Master of Arts (MA)

Chair and Committee

Dennis Barbour

Abstract

Functional imaging can reveal detailed organizational structure in cerebral cortical areas, but neuronal response features and local neural interconnectivity can influence the resulting images, possibly limiting the inferences that can be drawn about neural function. Historically, discerning the fundamental principles of organizational structure in the auditory cortex of multiple species has been somewhat challenging with functional imaging as the studies have failed to reproduce results seen in electrophysiology. One difference might result from the way most functional imaging studies record the summed activity of multiple neurons. To test this effect, virtual mapping experiments were run in order to gauge the ability of functional imaging to accurately estimate underlying maps. The experiments suggest that spatial averaging improves the ability to estimate maps with low spatial frequencies or with large amounts of cortical variability, at the cost of decreasing the spatial resolution of the images. Despite the decrease in resolution, the results suggest that current functional imaging studies may be able to depict maps with high spatial frequencies better than electrophysiology can; therefore, the difficulties in recapitulating electrophysiology experiments with imaging may stem from underlying neural circuitry. One possible reason may be the relative distribution of response selectivity throughout the population of auditory cortex neurons. A small percent of neurons have a response type that exhibits a receptive field size that increases with higher stimulus intensities, but they are likely to contribute disproportionately to the activity detected in functional images, especially if intense sounds are used for stimulation. To evaluate the potential influence of neuronal subpopulations upon functional images of the primary auditory cortex, a model array representing cortical neurons was probed with virtual imaging experiments under various assumptions about the local circuit organization. As expected, different neuronal subpopulations were activated preferentially under different stimulus conditions. In fact, stimulus protocols that can preferentially excite one subpopulation of neurons over the others have the potential to improve the effective resolution of functional auditory cortical images. These experimental results also make predictions about auditory cortex organization that can be tested with refined functional imaging experiments.

Comments

Permanent URL: http://dx.doi.org/10.7936/K7PG1PQB

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