Sleep spindles have been implicated in sleep protection, depression and anxiety. However, spindle-related brain imaging mechanism underpinning the de cient sleep protection and emotional regulation in insomnia disorder (ID) remains elusive. The aim of the current study is to investigate the relationship between spindle-related brain activations and sleep quality, symptoms of depression and anxiety in patients with ID. Participants (n = 46, 29 females, 18-60 years) were recruited through advertisements including 16 with ID, according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, and 30 matched controls. Group differences in spindle-related brain activations were analyzed using multimodality data acquired with simultaneous electroencephalography and functional magnetic resonance imaging during sleep. Compared with controls, patients with ID showed signi cantly decreased bilateral spindle-related brain activations in the cingulate gyrus (familywise error corrected p 0.05, cluster size 3834 mm 3 ). Activations in the cingulate gyrus were negatively correlated with Self-Rating Depression Scale scores (r = -0.454, p = 0.002), Self-Rating Anxiety Scale scores (r = -0.362, p = 0.014) and subjective sleep onset latency (r = -0.374, p = 0.010), while positively correlated with subjective total sleep time (r = 0.343, p = 0.020), in the pooled sample. Besides, activations in the cingulate gyrus were negatively correlated with scores on the Self-Rating Depression Scale (r = -0.650, p = 0.006), in the ID group. These ndings underscore the key role of spindle-related brain activations in the cingulate gyrus in subjective sleep quality and emotional regulation in ID.