Defense Date

2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Neuroscience

First Advisor

M. Alex Meredith

Abstract

UNIQUE FEAUTRES OF ORGANIZATION AND NEURONAL PROPERTIES IN A MULTISENSORY CORTEX Multisensory processing is a ubiquitous sensory effect that underlies a wide variety of behaviors, such as detection and orientation, as well as perceptual phenomena from speech comprehension to binding. Such multisensory perceptual effects are presumed to be based in cortex, especially within areas known to contain multisensory neurons. However, unlike their lower-level/primary sensory cortical counterparts, little is known about the connectional, functional and laminar organization of higher-level multisensory cortex. Therefore, to examine the fundamental features of neuronal processing and organization in the multisensory cortical area of the posterior parietal cortex (PPr) of ferrets, the present experiments utilized a combination of immunohistological, neuroanatomical and multiple single-channel electrophysiological recording techniques. These experiments produced four main results. First, convergence of extrinsic inputs from unisensory cortical areas predominantly in layers 2-3 in PPr corresponded with the high proportion of multisensory neurons in those layers. This is consistent with multisensory responses in this higher-level multisensory region being driven by cortico-cortical, rather than thalamo-cortical connections. Second, the laminar organization of the PPr differed substantially from the pattern commonly observed in primary sensory cortices. The PPr has a reduced layer 4 compared to primary sensory cortices, which does not receive input from principal thalamic nuclei. Third, the distribution of unisensory and multisensory neurons and properties differs significantly by layer. Given the laminar-dependent input-output relationships, this suggests that unisensory and multisensory signals are processed in parallel as they pass through the circuitry of the PPr. Finally, specific functional properties of bimodal neurons differed significantly from those of their unisensory counterparts. Thus, despite their coextensive distribution within cortex, these results differentiate bimodal from unisensory neurons in ways that have never been examined before. Together these experiments represent the first combined anatomical-electrophysiological examination of the laminar organization of a multisensory cortex and the first systematic comparison of the functional properties of bimodal and unisensory neurons. These results are essential for understanding the neural bases of multisensory processing and carry significant implications for the accurate interpretation of macroscopic studies of multisensory brain regions (i.e. fMRI, EEG), because bimodal and unisensory neurons within a given neural region can no longer be assumed to respond similarly to a given external stimulus.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2012

Included in

Neurosciences Commons

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