key up vs stimulate

key up

verb
  • To raise the intensity, excitement, tension, etc., of. 

  • To produce nervous tension in. 

  • To raise the pitch of. 

  • To raise (the whole ring of an arch) off its centering, by driving in the keystone forcibly. 

stimulate

verb
  • To encourage into action. 

  • To arouse an organism to functional activity. 

How often have the words key up and stimulate occurred in a corpus of books? (source: Google Ngram Viewer )