grey matter vs imagination

grey matter

noun
  • Brains; a person's ability to think. 

  • A collection of cell bodies and (usually) dendritic connections, in contrast to white matter. 

  • Literal brains as a general substance. 

imagination

noun
  • A mental image formed by the action of the imagination as a faculty; something imagined. 

  • Particularly, construction of false images; fantasizing. 

  • Creativity; resourcefulness. 

  • The image-making power of the mind; the act of mentally creating or reproducing an object not previously perceived; the ability to create such images. 

How often have the words grey matter and imagination occurred in a corpus of books? (source: Google Ngram Viewer )