follow up vs perseverate

follow up

verb
  • To take further actions remaining after an event; to continue, revisit, or persist; especially, to maintain communication or verify. 

perseverate

verb
  • To persist in doing something; to continue to repeat an action after the original stimulus has ended. 

  • To cause the perseveration of (a given reflex or response). 

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