The number of sleep spindles remains relatively stable within individuals from night to night. However, there is little explanation for the large interindividual differences in spindles. The authors investigated the relationship between spindles and intelligence quotient (IQ) in 3 separate studies. The number of spindles and sigma power were positively correlated with performance IQ (PIQ), but not verbal IQ (VIQ). The perceptual/analytical skills measured by the PIQ Picture Completion subscale accounted for most of the interindividual differences in spindles. Furthermore, there was a relationship between the rapid eye movements (REMs) of REM sleep and VIQ in individuals with higher IQ scores. A similar pattern was observed between spindles and PIQ. It was hypothesized that high-IQ individuals have more spindles that can support more complex cortical networks underlying perceptual/analytical abilities.
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