<p>This study aimed to investigate the impaired cognitive flexibility and its underlying neural mechanisms in insomnia. By combining resting-state fMRI and the Cognitive Flexibility Inventory (CFI), we examined the associations between insomnia severity, spontaneous brain activity (the fractional amplitude of low-frequency fluctuations, fALFF) and functional connectivity (FC) with total cognitive flexibility scores. Behavioral results showed that insomnia severity significantly affected the control sub-dimension of cognitive flexibility. The fALFF analyses indicated that the right insula (Ins) was a key brain region significantly associated with cognitive flexibility. Further analysis based on the Ins revealed that FC between Ins and the bilateral superior temporal gyrus (STG), as well as Ins and the right precuneus, were significantly positively correlated with the total cognitive flexibility scores, with the right supplementary motor area (SMA) in the alternative sub-dimension, with the left lingual gyrus, right STG, right precuneus, and left paracentral lobule (PCL) in the control sub-dimension. The results suggest that the different sub-dimensions represent different neural pathways for cognitive flexibility, of which the PCL may be a brain region specific to insomnia patients. These findings reveal the impact of insomnia on the neural basis of cognitive flexibility and provides potential brain targets for future intervention and treatment.</p>