compulsion vs on the brain

compulsion

noun
  • The use of authority, influence, or other power to force (compel) a person or persons to act. 

  • An irrational need or irresistible urge to perform some action, often despite negative consequences. 

  • The lawful use of violence (i.e. by the administration). 

on the brain

prep
  • Obsessively in mind. 

How often have the words compulsion and on the brain occurred in a corpus of books? (source: Google Ngram Viewer )