(S (S (NP (BASENP (DT A) (NN 1991) (NN study)) (PP (IN of) (NP (BASENP (JJ human) (NN brains)) (PP (IN of) (BASENP (NN AIDS) (NNS victims)))))) (VP (VP (VBD showed) (BASENP (DT a) (JJ similar) (NN hypothalamus) (NN size) (NN difference))) (PP (IN between) (BASENP (ADJP (JJ gay) (CC and) (JJ heterosexual)) (NNS men))))) (PERIOD .))