At the Boundary of Sleep and Awakening: an FMRI Study

• Main Authors: Pei-Jung Tsai, 蔡佩容
• Other Authors: Tsuo-Hung Lan
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/22359526714445134468

碩士 === 國立陽明大學 === 腦科學研究所 === 100 === Sleep is an indispensable procedure to plays an important role in regulating the mental and physical situations. Previous studies indicated that sleep facilitates brain plasticity and allows change of brain physiology after self-regulation in sleep. How sleep modulates the brain function? Preceding research used neuroimaging techniques to examine brain activities upon awakening, which passes through sleep regulation and re-establishes condition of awakening for wondering the sleep’s modulation effect. However, the spatial details and the connectivity information were insufficient to specific answer how sleep modulated the brain functions. Therefore, we applied fMRI-based functional connectivity (FC) and amplitude of low frequency fluctuation (ALFF) to investigating the brain oscillation after sleep. In this study, we recruited twenty-two healthy participants (all male, mean age: 23.8±4.2 y/o, non-sleep-deprivation). With combined EEG and fMRI recordings, we applied to six minutes resting state fMRI scan before and after two hours of sleep maximum, respectively. Two indices were used to demonstrate changes of brain signal, including functional connectivity (seed-based correlation) and fluctuation amplitude. We focused on three networks (responder for sleep related functions: 1) Default mode network: is related to consciousness and memory. 2) Hippocampal network: is associated with memory consolidation and working memory. 3) Sensory-motor network: is linked to refreshing effect on body sensory and motor system. For each session, correlation and spectrum analyses were used to detect default mode network (DMN), hippocampal network (HPC) and sensory-motor network (SMN) to assess functional connectivity and their corresponding ALFF. Indices between pre-sleep and post-awakening were compared by paired t-test. In the result of functional connectivity, we found that the changes of DMN connectivity were not significant after awakening, whereas sensorimotor connectivity reduced significantly after sleep. However, in hippocampus network, the correlation between bilateral hippocampi did not show differences, but its connection to MPFC and PCC increased significantly upon awakening. Interestingly, thalamo-cortical connections were enhanced dramatically within every observed network. From the view of fluctuation amplitude, in contrast to pre-sleep, the global mean ALFF reduced after sleep. However, the low-oscillation activity enhanced in anterior but reduced in posterior after awakening. The thalamic-motor networks had significantly reduced ALFF while other observed networks have sustained ALFF after sleep. Breakdown of cortico-cortical connection and reduced activity may be the cause of poor performance in sleep inertia. Enhanced thalamo-cortical connection and activity may lead to consciousness recovery. At last, increased connectivity from limbic system to frontal lobe may be associated with onset of self-awareness.