Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Biomedical Engineering

Supervisor

Johnsrude, Ingrid

2nd Supervisor

Khan, Ali

Co-Supervisor

Abstract

Resting-state functional magnetic resonance imaging (fMRI) studies are criticized for their lack of control over cognitive states of individuals during observation, which may lead to increased variability in estimates of functional connectivity (FC). Engaging movies have been used in an attempt to synchronize the cognitive states of individuals during the scan, potentially reducing intersubject variability in connectivity estimates. The objective of this study was to investigate the differences in intersubject variability of FC between rest and movie conditions in a healthy cohort. The results demonstrate widespread reductions of intersubject variability of FC in the movie condition compared to the resting-state condition. These differences were pronounced in regions of the frontal, auditory, and visual cortex, suggesting effects on sensory areas as well as areas responsible for higher-order functioning. Because of its potential as a biomarker, less variable normative estimates of FC are beneficial for developing more sensitive tests for clinical use.

Summary for Lay Audience

Functional magnetic resonance imaging (fMRI) is a technique used to measure brain activity. Activity can be measured in response to a task or when the subject is in a resting state, that is, when there is no direct stimulus applied. Resting-state scanning is typically performed to investigate the interregional relationships between spatially disparate areas of the brain, that identify networks of regions which appear to be working together. The dysregulation of these networks has been implicated in certain disease states, such as Alzheimer’s, depression, and schizophrenia. This provides an opportunity for functional connectivity to potentially be used as a diagnostic or prognostic tool for these diseases. However, these tests have yet to be applied in the clinic due to a lack of sensitivity in detecting disease states. A possible explanation for its lack of clinical success may be the absence of behavioural constraints placed on subjects in resting-state scanning, allowing them to drift into a variety of different states of mind. These states are likely inconsistent across subjects during the scan and can therefore cause increases in variability of the measures. Increased variability may cause the networks in healthy people to look more different than they are, making it difficult to identify features separating them from individuals with disease. However, a recently popularized technique has attempted to use movies to synchronize the states of individuals during the scan. Using movies, researchers have shown that brain activity is synchronized across subjects based on the time locked events of the movie. In this study, we investigated the effects of movie watching on variability of the interregional relationships, known as functional connectivity, and compared it to what is observed in the resting state. We hypothesized that movie watching would result in less variable networks across individuals than the resting state because of the mental constraints placed upon individuals during movie-watching. The results of the study demonstrated that movie-watching led to less variable functional connectivity compared to resting-state scanning. Future work is needed to investigate whether the reductions in variability lead to more sensitive tests for clinical abnormalities.

Creative Commons License

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

Available for download on Saturday, October 31, 2020

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