Date of Award
Master of Science in Biomedical Engineering - (M.S.)
Richard A. Foulds
Mirror visual feedback (MVF), a technique by which movement of one limb is perceived as movement of the contralateral limb, has the capacity to relieve phantom limb pain or promote motor recovery of the upper limbs after stroke (Ramachandran et al., 1995). Functional MRI studies have demonstrated activation of the motor areas in the hemisphere ipsilateral to the moving hand in response to MVF. However, the neural mechanisms of MVF are still unclear. This Electroencephalography (EEG) study was designed to investigate the timing of neural responses to MVF presented in virtual reality. 16 right-handed, neurologically healthy subjects participated in a series of four experimental sessions. Two factors (visual feedback: no-mirror (M-) and mirror (M+) and movement target: no-goal (G-) and goal (G+)) were systematically manipulated to form four testing conditions (M-G-, M+G-, M-G+ and M+G+). The time course of cortical oscillations was captured using a 64-channel EEG system (ANT Neuro). Index finger kinematics and surface Electromyogram (EMG) of the right First Dorsal Interosseous (FDI) muscle were synchronized with the EEG signals to explore the timing of MVF effects on cortical activity. In all four conditions, pronounced decrease in power of beta-band activity relative to reference was observed during movement planning and execution in C3 and C4 electrodes (bilateral primary motor cortex). Moreover, MVF reduced inter-hemispheric differences in beta-band power during movement preparation and execution. Significantly stronger reduction in inter-hemispheric power difference during the execution phase of the movement was observed in the M+G+ compared to M+G-. In all four conditions, prominent decrease in alpha range power was observed in the P3 and P4 electrodes (bilateral parietal cortex) during the preparation phase. The effect of MVF decreased the asymmetry in hemispheric activation in alpha-range power during the preparation phase of goal-directed movements, M+G+ and M-G+, when compared to M+G- and M-G- conditions. In addition to spatial- and frequency-specific power analysis, the effects of MVF were also explored using topographic maps which reflect scalp potential distribution. Global field power during movement preparation phase in the M+G+ condition was more lateralized to the hemisphere ipsilateral to the moving hand when compared to M-G+ condition. In conclusion, MVF applied during unilateral hand movement significantly attenuates hemispheric activation asymmetry.
Mu, Chuang, "Investigating neural mechanisms of hand movements in virtual reality" (2015). Theses. 260.