grey matter vs thinker

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. 

thinker

noun
  • The brain; the mind. 

  • One who spends time thinking, contemplating or meditating. 

  • A poser; a conundrum that requires some thinking. 

  • An intellectual, such as a philosopher or theologian. 

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