Sentence:  Irregular bedtimes may disrupt healthy brain development in young children, according to a study of <WSD>intelligence</WSD> and sleeping habits.  &para; Going to bed at a different time each night affected girls more than boys, but both fared worse on mental tasks than children who had a set bedtime, researchers found. 
Meaning of the word marked with <WSD> tags:  Capacity of mind, especially to understand principles, truths, facts or meanings, acquire knowledge, and apply it to practice; the ability to comprehend and learn.