Frequency-dependent changes in local intrinsic oscillations in chronic primary insomnia: A study of the amplitude of low-frequency fluctuations in the resting state

New neuroimaging techniques have led to significant advancements in our understanding of cerebral mechanisms of primary insomnia. However, the neuronal low-frequency oscillation remains largely uncharacterized in chronic primary insomnia (CPI). In this study, the amplitude of low-frequency fluctuation (ALFF), a data-driven method based on resting-state functional MRI, was used to examine local intrinsic activity in 27 patients with CPI and 27 age-, sex-, and education-matched healthy controls. We examined neural activity in two frequency bands, slow-4 (between 0.027 and 0.073 Hz) and slow-5 (0.010-0.027 Hz), because blood-oxygen level dependent (BOLD) fluctuations in different low-frequency bands may present different neurophysiological manifestations that pertain to a spatiotemporal organization. The ALFF associated with the primary disease effect was widely distributed in the cerebellum posterior lobe (CPL), dorsal and ventral prefrontal cortex, anterior cingulate cortex, precuneus, somatosensory cortex, and several default-mode sub-regions. Several brain regions (i.e., the right cerebellum, anterior lobe, and left putamen) exhibited an interaction between the frequency band and patient group. In the slow-5 band, increased ALFF of the right postcentral gyrus/inferior parietal lobule (PoCG/IPL) was enhanced in association with the sleep quality (ρ = 0.414, P = 0.044) and anxiety index (ρ = 0.406, P = 0.049) of the CPI patients. These findings suggest that during chronic insomnia, the intrinsic functional plasticity primarily responds to the hyperarousal state, which is the loss of inhibition in sensory-informational processing. Our findings regarding an abnormal sensory input and intrinsic processing mechanism might provide novel insight into the pathophysiology of CPI. Furthermore, the frequency factor should be taken into consideration when exploring ALFF-related clinical manifestations.