ego vs grey matter

ego

noun
  • The most central part of the mind, which mediates with one's surroundings. 

  • The self, especially with a sense of self-importance. 

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. 

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