(S (S (NP (BASENP (JJ Previous) (NNS studies)) (PP (IN by) (NP (BASENP (NNP Wurtman)) (CC and) (BASENP (NNS colleagues))))) (VP (VBD showed) (SBAR (IN that) (S (NP (NP (BASENP (JJ small) (NNS doses)) (PP (IN of) (BASENP (NN melatonin)))) (PRN (COMMA ,) (BASENP (QP (RB about) (NN 0.3)) (NNS milligrams)) (COMMA ,))) (VP (VBP are) (ADJP (JJ necessary) (PP (IN for) (BASENP (JJ restful) (NNS effects))))))))) (PERIOD .))