The brain of "P. lujiatunensis" is well known; a study on the anatomy and functionality of three specimens was published in 2007. Until the study, it was generally thought the brain of "Psittacosaurus" would have been similar to other ceratopsians with low Encephalisation Quotients. Russell and Zhao (1996) believed "the small brain size of psittacosaurs implies a very restrictive behavioural repertoire relative to that of modern mammals of similar body size". However, the 2007 study dispelled this theory when it found the brain to be more advanced. There is generally negative allometry for brain size with development in vertebrates, but this was shown not to be true in "Psittacosaurus". The EQ score for "P. lujiatunensis" is 0.31, significantly higher than genera such as "Triceratops". A higher EQ correlates with more complex behaviour, and various dinosaurs have high EQs, similar to birds, which range from 0.36 to 2.98. Thus, "Psittacosaurus" behaviour could have been as complex as that in "Tyrannosaurus", whose EQ ranges from 0.30 to 0.38. Behaviours influenced by high EQs include nest-building, parental care, and bird-like sleeping, some of which have been shown to be present in "Psittacosaurus".