( ( ( ( ( ( ( ( Migraine or ) ( Vascular Headaches ) ) ( ( These headaches ) ( are ( caused ( by ( an ( initial narrowing ) ) ) ) ) ) ) , ) ( then dilation ) ) , ) ( of ( ( the ( blood vessels ) ) ( in ( the head ) ) ) ) ) . )
(ROOT (NP (NP (NP (NNP Migraine)) (CC or) (NP (NNP Vascular) (NNP Headaches))) (S (NP (DT These) (NNS headaches)) (VP (VBP are) (VP (VBN caused) (PP (IN by) (NP (DT an) (JJ initial) (NN narrowing)))))) (, ,) (VP (ADVP (RB then)) (VBN dilation)) (, ,) (PP (IN of) (NP (NP (DT the) (NN blood) (NNS vessels)) (PP (IN in) (NP (DT the) (NN head))))) (. .)))
Migraine or Vascular Headaches These headaches are caused by an initial narrowing, then dilation, of the blood vessels in the head.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NN blood) (NNS vessels)) (PP (IN in) (NP (DT the) (NN head)))) (VP (VBP dilate)))) (, ,) (NP (NP (DT a) (NN migraine)) (, ,) (NP (DT a) (JJ severe) (NN headache)) (, ,)) (VP (MD can) (VP (VB occur))) (. .)))