insist vs perseverate

insist

verb
  • To demand continually that something happen or be done; to reiterate a demand despite requests to abandon it. 

  • To hold up a claim emphatically. 

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 insist and perseverate occurred in a corpus of books? (source: Google Ngram Viewer )