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Recent findings in AD models but also human patients suggest that amyloid can cause intermittent neuronal hyperactivity. The overall goal of this study was to use dynamic fMRI analysis combined with graph analysis to a) characterize the graph analytical signature of two types of intermittent hyperactivity (spike-like (spike) and hypersynchronus-like (synchron)) in simulated data and b) to attempt to identify one of these signatures in task-free fMRIs of cognitively intact subjects (CN) with or without increased brain amyloid. The toolbox simtb was used to generate 33 data sets with 2 short spike events, 33 with 2 synchron and 33 baseline data sets. A combination of sliding windows, hierarchical cluster analysis and graph analysis was used to characterize the spike and the synchron signature. Florbetapir-F18 PET and task-free 3 T fMRI was acquired in 49 CN (age = 70.7 ± 6.4). Processing the real data with the same approach as the simulated data identified phases whose graph analytical signature resembled that of the synchron signature in the simulated data. The duration of these phases was positively correlated with amyloid load (r = 0.42, p

Posttraumatic stress disorder (PTSD) is associated with abnormalities in functional connectivity of a specific cortico-limbic network; however, less is known about white matter abnormalities providing structural connections for this network. This study investigated whether the diagnosis and symptoms of PTSD are associated with alterations in fractional anisotropy (FA), an index reflecting white matter organization, across six, a priori-defined tracts. White matter FA was quantified by diffusion tensor imaging using 3 T-MRI among 57 male, combat-exposed veterans with no history of moderate to severe head injuries or current alcohol dependence: 31 met criteria for PTSD and 26 were demographically comparable, combat-exposed controls without PTSD. Clinician-administered and self-report questionnaires assessed PTSD severity, dissociation, and mood. PTSD + veterans had significantly higher FA than exposed controls in the superior fronto-occipital fasciculus (SFOF) and borderline higher FA in the anterior corona radiata (ACR) and cingulum (CGC), controlling for age and neurovascular comorbidities. When lifetime alcohol use disorders was included, only the association of PTSD with SFOF-FA remained significant. Among PTSD + veterans, higher SFOF-FA was associated with greater mood disturbance, dissociative symptoms, and re-experiencing, while lower FA of the uncinate fasciculus (UF) was associated with greater mood disturbance symptoms. Compared to combat-exposed controls without PTSD, veterans with PTSD exhibited higher white matter FA in the SFOF, and a similar tendency in the ACR and CGC, tracts involved in conflict-processing and spatial attention. Prior alcohol use might explain the associations of PTSD with ACR-FA and CGC-FA but not the association with SFOF-FA.