More and more resting-state functional MRI (fMRI) studies have been carried out in recent years. Most of these studies investigated the synchrony of low frequency fluctuations (LFFs) of blood-oxygen level dependent (BOLD) signals, that is, they analyzed the functional connectivities between brain regions from a functional integration perspective. Based on resting-state fMRI, we carried out studies not only on the applications of functional connectivity analyses, but proposed a novel method to detect resting-state brain activities, and applied the method to psychiatric disease analyses. The contents as well as the innovations of these studies are as follows: 1. We proposed a resting-state activity index (RSAI), which utilizes both the spatial and temporal information of BOLD signals, to test the resting-state brain activities. We evaluated the resting-state brain activities of the attention deficit / hyperactivity disorder (ADHD) patients and their matched controls by using RSAI, and compared the brain activity pattern differences between the two groups. We found that the ADHD patients exhibited more significant resting-state activities in sensory and sensory related cortices. We suggest that these more significant resting-state activities in the ADHD patients may be related to the inattention symptoms in them. 2. For the first time, we analyzed the dorsal anterior cingulate (dACC) functional connectivity pattern differences between the ADHD adolescents and their matched controls by using resting-state fMRI. We found that the bilateral brainstem, pons, bilateral insula, bilateral thalamus, bilateral cerebellum and bilateral posterior cingulate cortex exhibited more significant functional connectivities with the dACC in the ADHD adolescents. We suggest that the more significant dACC functional connectivities in the ADHD patients might be result from the autonomic control abnormalities in these patients. 3. For the first time, we analyzed the stabilities of the negative correlations of resting-state BOLD signals. We found that the negative correlations associated with the motor and visual cortices were unstable. The significance of this study lies in that it highlighted the importance of paying attention to the influence of the stabilities of negative correlations of BOLD signals in related studies and establishes the need for further studies on negative correlations of BOLD signals.
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