nerve center vs nerve centre

nerve center

noun
  • A point at which nerves come together for the processing of signals. 

  • A physical location in a business, organization, or agency where information procured from different sources is brought together to be considered and acted upon by decision-makers. 

nerve centre

noun
  • Standard spelling of nerve center. 

How often have the words nerve center and nerve centre occurred in a corpus of books? (source: Google Ngram Viewer )