ORCID Identifier(s)

0000-0003-2050-0910

Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biomedical Engineering

Department

Bioengineering

First Advisor

Hanli Liu

Abstract

Functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG) are two non-invasive brain imaging or mapping modalities that allow us to measure cerebral hemodynamic and electrophysiological changes in the human brain, respectively. LABNIRS is a cutting-edge, whole-head, optical brain mapping system with 40 pairs of light sources (at 780 nm830 nm) and 40 detectors, forming up to 133 detection channels. In my study, whole-head LABNIRS and 64-channel EEG were utilized to investigate respective alterations in response to risk decision- making under business context and to non-invasive photobiomodulation. As the first part of my study, I utilized fNIRS (i.e., LABNIRS) as a tool to measure hemoglobin concentration changes across the frontal regions in response to the newsvendor problem (NP). NP is an essential concept in the research area of business operations. The scenario refers to the decision-making in an inventory management context in a highly uncertain environment where an individual must balance between potential loss and waste to achieve maximum expected profit. However, there are few studies to investigate this concept from the perspective of neuroimaging. Consequently, with 77-channel fNIRS measurements taken from 27 human subjects, I reported in Chap. 2 that significant activation induced by NP was shown in both the dorsolateral prefrontal cortex (DLPFC) and orbitofrontal cortex (OFC) across all subjects. Specifically, higher risk NP with low-profit margins (LM) activated left-DLPFC but deactivated right-DLPFC in 14 subjects while lower risk NP with high-profit margins (HM) stimulated both DLPFC and OFC in 13 subjects. Moreover, graph theory-based network analysis was performed and showed that global brain network properties altered when the human brain switched from rest to the NP-evoked phase. The clustering coefficient of the network was significantly enhanced under both LM and HM, while the small-worldness was boosted by higher-risk decision taking. Transcranial photobiomodulation (tPBM) is a light-based technique to stimulate the human brain non-invasively. It is proven to improve human cognition, such as memory and reaction time. tPBM is also shown that tPBM delivered to the healthy human forehead enhances not only hemodynamic and metabolic functions but also the EEG power in alpha and beta brain rhythms during eyes-open resting state. Nonetheless, the tPBM-induced effect under the eyes-closed resting state is unknown, and whether the measured changes in EEG powers could result directly from laser heating is also unclear. As the second part of my study, Chapter 3 explores the impact of tPBM on neuro-electrophysiological functions under the eyes-closed resting state and the effect of heat produced by the laser on the EEG power alterations. My results suggest that tPBM increased alpha, and beta EEG power during eyes-closed resting state relative to those under sham, consistent with our previous results reported under eyes-opened conditions. On the other hand, thermal stimulation reduced alpha and beta powers relative to sham, showing the opposite trends to those induced by tPBM and separating the confounding effects between tPBM and heat. While previous studies have reported tPBM-induced hemodynamic increases near the stimulation site, it is unclear if the impact is limited to only the stimulation site or across multiple cortical areas in the brain. To answer this question, as the third part of my study, whole-head fNIRS was used to detect/map tPBM-evoked hemodynamic activations and network alterations from 19 healthy human subjects. Chapter 4 reported that significant activation of hemodynamics near the right prefrontal cortex increased over the time span of the stimulation period relative to that during the sham condition. Some activation in the left primary somatosensory area was also seen, probably due to the heat sensation of the laser. Furthermore, dynamic functional connectivity analysis was performed and showed that the brain connectivity increased across the entire cortical areas during the later portion of tPBM, followed by slight decreases during the post-stimulation.

Keywords

fNIRS, EEG, Photobiomodulation, Decision making, Neuroimaging, Brain imaging

Disciplines

Biomedical Engineering and Bioengineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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