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Thesis Format

Monograph

Degree

Master of Science

Program

Neuroscience

Supervisor

Johnsrude, Ingrid

Abstract

In movie-activation fMRI, intersubject correlation (ISC) indicates a functional correspondence across viewers. Brains differ in shape; spatial normalization and smoothing enhance inter-subject functional overlap. We compare 3 normalization methods (SPM12, DARTEL and ANTS) and 6 smoothing levels to discover which method yields the best functional overlap, indexed by ISC. This is key to optimizing data analysis in clinical studies using movie-activation fMRI in future. In a 3T scanner, 44 healthy subjects watched an 8-min movie. Both normalization and smoothing affected the strength and extent of the ISC. ISC values were more robust for ANTs and DARTEL than for SPM12 and were (asymptotically) the strongest at 12mm smoothing. When image data are preprocessed with high-dimensional volumetric spatial registration methods, such as ANTs, and 12mm smoothing, the sensitivity of the movie-fMRI paradigm will be optimal for detecting abnormalities in presurgical evaluation of neurological patients, providing less variable and more reliable ISC measures.

Summary for Lay Audience

1.7 in every 1000 of the world population has a neurologic disorder that requires brain surgery. Effective surgical treatment requires that the lesion be localized precisely, and resection does not result in unexpected cognitive decline. It is usually accomplished through preoperative assessment of patients using implanted electrodes or functional MRI (fMRI).

Current methods are not very sensitive to abnormalities in cognitive function. We propose to use fMRI to rapidly and noninvasively identify and map brain function. When neurologically healthy individuals watch an engaging film while undergoing fMRI (movie-driven fMRI), reliable and distinctive time-locked fluctuations in fMRI signals are observed throughout the brain. These fluctuations are different in different brain regions, reflecting the perceptual and cognitive demands of the film, but are very similar across people without neurological disorders (controls). The degree to which a patient’s data matches predictions derived from control data can be tested statistically, region by region, to reveal functionally important cortex and local abnormalities of brain function. Because different brains differ in shape and size they should be registered to a standard template for comparison. The way the patient’s data is registered to the template affects the sensitivity of the method to abnormalities.

We asked people without any neurological disorder to watch a short, suspenseful movie while they underwent a functional brain scan. We -for the first time- evaluated three different ways to register the movie- driven fMRI data. We found that the registration method that uses more points in data to match it with the template was more sensitive to fluctuations of the fMRI signal and as a result more sensitive to abnormalities. We also compiled this data set as a normative pattern of activity in a neurologically healthy population.

Movie-driven fMRI and this method of registration may be a valuable adjunct assessment method in the presurgical evaluation of neurologic patients. Future studies can compare the fMRI data from any individual patient with a neurologic disorder, such as focal epilepsy, with this normative pattern of brain signal fluctuation.

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

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