Masters Thesis Defense - The Integration of Continuous Wave Functional Near-infrared Spectroscopy with Event-related Potentials in a Visual Oddball Task
Date: August 7, 2003
Time: 1:00 PM
Location: Commonwealth Hall, Room: 610
George Charles McConnell
Advisors: Dr. Scott Bunce and Dr. Banu Onaral
The simultaneous acquisition of both hemodynamic and electrophysiological measures is vital for a better understanding of brain function, particularly the neurovascular coupling relating these parameters. Near infrared (NIR) spectroscopy (NIRS) has been widely used in functional brain studies for the non-invasive monitoring of local changes in blood oxygenation and blood volume. Furthermore, the feasibility of monitoring cognitive state via functional optical imaging using near-infrared light (fNIR) in an event-related task has recently been demonstrated. The possibility now exists to combine fNIR with the well established neuroelectrical detection modality, namely electroencephalography (EEG). The intent is to introduce a composite measure to provide a better tool to assess cognitive state by integrating two complementary modalities. Additional reasons for such integration are that both fNIR and EEG are safe, relatively affordable, non-invasive and non-intrusive. With the recently emerging miniaturization and wireless technologies, EEG-fNIR monitoring can be used in ambulatory applications under more natural, everyday living and working conditions.
In this thesis, the groundwork that will lead to the integration of fNIR with EEG is presented. fNIR and EEG data were collected simultaneously from human subjects in the study of selective attention using a standard event-related paradigm, the visual ‘oddball’ target categorization task. Functional magnetic resonance imaging (fMRI) and EEG findings were previously reported in the literature using this same paradigm. Event-related potentials (ERPs) and event-related fNIR (ER-fNIR) data were processed and inter-subject comparisons between target and context event-locked responses were conducted. ERP findings showed significantly larger peak amplitudes in response to target stimuli in comparison with context stimuli, as expected from the literature. In parallel, ER-fNIR indicated significant activation in the right dorsolateral prefrontal cortex in response to target stimuli compared with context stimuli, corroborating previous fMRI findings. To our knowledge, this study is the first to demonstrate the use of fNIR in conjunction with EEG to monitor prefrontal cortex activity in a cognitive, event-related task. The challenge remains to develop the data fusion methodologies necessary to design the optimal composite measure to assess cognitive state.
George Charles McConnell is a BS/MS student in the School of Biomedical Engineering, Science and Health Systems.
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