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Thesis Format



Master of Science




Butler, Blake E


The cerebral cortex contains myriad cortical areas that differ in structure, function, and connectivity. Current methods of delineating cortical structures and their subregions are insufficient for in vivo applications, either being highly invasive or requiring a detailed knowledge of a region’s tuning properties. To address this, we seek to establish a structural biomarker capable of delineating the cortex that possesses a non-invasive correlate. We explore myelin as a potential candidate by evaluating its efficacy in parcellating the feline auditory cortex through the generation of depthwise myelin density profiles for each of the 13 auditory cortical subregions. Our analyses revealed significant differences between several auditory cortical subregions, as well as significant correlations between both processing complexity and cortical depth with myelin content. By establishing myelin as a useful biomarker for cortical parcellation, we hope to better describe the brain regions and networks that underlie complex human behaviours and reorganized function.

Summary for Lay Audience

The brain comprises a number of distinct regions, each of which makes unique contributions to one or more complex behaviours. For example, the region of the brain responsible for perceiving sounds (i.e., the auditory cortex), has traditionally been thought of as distinct from the region that makes sense of what we see (i.e., the visual cortex). Moreover, within a region like the auditory cortex, there exist subregions that are sensitive to the many different features of sound. For example, core auditory areas are typically involved in identifying that a sound is present in the environment, while higher-order areas are sensitive to features including direction of motion, or a speaker’s identity. The ability to identify the location of these distinct regions in the brain is essential to understanding their function, and is especially useful in identifying the source atypical brain activity, and in designing therapies to help affected individuals. Localizing specific areas of the brain often relies on the ability to visualize characteristic patterns of brain activity; however this limits our ability to accurately locate areas of interest in people who have atypical function (e.g. blindness, deafness, etc.), or to discern between parts of the brain that are activated by the similar stimuli or processes. Thus, the work described here uses a structural property of the brain – patterns of myelin content – to discern between regions of the feline auditory cortex. Myelin is present throughout the brain, and previous research has suggested that small but distinct regions of the brain can be distinguished from one-another based on their total myelin content. We demonstrate that many subregions of the auditory cortex differ with respect to their total myelin content, with core areas contained the most myelin, and higher-order areas containing significantly less. These results suggest there are predictable changes in the myelin content of the auditory cortex between regions, suggesting that myelin may be a useful structural marker for parcellating the auditory brain.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.