" Professional musicians, in general, possess what most of us would regard as remarkable powers of musical imagery. Many composers, indeed, do not compose initially or entirely at an instrument but in their minds. There is no more extraordinary example of this than Beethoven, who continued to compose (and whose compositions rose to greater and greater heights) years after he had become totally deaf. It is possible that his musical imagery was even intensified by deafness, for with the removal of normal auditory input, the auditory cortex may become hypersensitive, with heightened powers of musical imagery (and sometimes even auditory hallucinations). "

― Oliver Sacks , Musicophilia: Tales of Music and the Brain