| Author: | Zhang, Bingbing |
| Title: | Testing the neuromodulatory effects of theta burst stimulation |
| Advisors: | Kranz, S. Georg (RS) Fong, Kenneth (RS) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Department: | Department of Rehabilitation Sciences |
| Pages: | xxviii, 199 pages : color illustrations |
| Language: | English |
| Abstract: | Intermittent theta-burst stimulation (iTBS) is a non-invasive brain stimulation technique that enhances cortical excitability beyond the stimulation period. It has become increasingly favored as a therapeutic intervention for various neuropsychiatric disorders, such as depression, by targeting the left dorsolateral prefrontal cortex (DLPFC). However, several challenges need to be addressed, including variability in individual responses, uncertainty about the optimal stimulation intensity, and unclear effects of timing in priming protocols. Additionally, differences in head anatomy, such as scalp-to-cortex distance, may influence treatment outcomes. To tackle these issues, several experimental studies have been conducted to investigate the mechanisms of iTBS and the parameters that affect its efficacy, aiming to optimize iTBS protocols for future clinical use. Functional near-infrared spectroscopy (fNIRS) has been employed as a non-invasive neuroimaging tool to measure the effects of iTBS on brain function and aid in this investigation. Study I: Pilot Study I (published) Chapter 2 explores how stimulating different brain areas with iTBS affects associative learning. The results demonstrated that stimulating the DLPFC and lateral parietal cortex (LPC) produced distinct effects on brain activity patterns and associative learning, highlighting the specific roles these regions play in memory. Study II: Pilot Study II (published) Chapter 3 investigated the impact of varying iTBS intensity on the left DLPFC in healthy adults. Each of the twenty participants underwent iTBS sessions at 50%, 70%, and 100% of their individual resting motor threshold (RMT). The results indicated that 70% RMT is the most effective stimulation intensity and was therefore used in the main study. Study III: Main study (under preparation) Chapter 4 presents the main study of this thesis. This study examined how timing influences the neuromodulatory effects of priming theta burst stimulation (TBS) in individuals with depressive symptoms. The results indicated that a 10-minute interval between continuous TBS (cTBS) and iTBS optimally leveraged metaplasticity to alter hemodynamic responses. However, these neurophysiological changes did not translate into significant behavioral improvements. These findings highlight the potential of priming TBS protocols to enhance the efficacy of iTBS by optimizing stimulation timing and utilizing metaplasticity mechanisms. Study IV: Computational study I (under preparation) Chapter 5 explored the neurobiological sources of variability, specifically the scalp-to-cortex distance, that may influence transcranial magnetic stimulation (TMS) efficacy. The results indicated significant ethnic differences in scalp-to-cortex distance and associated electrical field (EF) strengths. The findings highlight the need to account for individual anatomical variability when designing stimulation protocols. Study V: Computational study II (Published) In Chapter 6, the relationship between TMS-induced EF characteristics and antidepressant effects was investigated in patients with treatment-resistant depression (TRD). The results showed that the normal component of the EF was significantly associated with symptom relief, providing insights into the neurobiological mechanisms underlying TMS efficacy in depression. Overall, the studies presented in this thesis contribute to the optimization of iTBS protocols by addressing factors such as stimulation intensity, time interval, and individual anatomical morphology, with the goal of enhancing the therapeutic effects of TMS for future use. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/14579