Music and language in degenerative disease of the brain.

Music and language functions were studied in two musicians with degenerative disease. Both patients were tested on a standardized language battery and a series of music tasks. In the first case with left cortical atrophy and primary progressive aphasia, expressive music functions were spared with impaired reception of rhythm. The second case with posterior cortical atrophy, greater on the right, was nonaphasic, had spatial agraphia, a visuopractic deficit, and severe expressive music deficits, but intact rhythm repetition. The aphasic patient showed dissociations between music and language in fluency and content; continuous, organized, although reiterative music production was contrasted with nonfluent language. The nonaphasic patient showed the opposite pattern of deficits; unmusical production with impaired melody and rhythm organization that was contrasted with fluent, intelligible language. The double dissociation between language and music functions supports the existence of independent cognitive systems, one consistent with conventional left lateralization models of language, temporal sequence, and analytic music processing and another with a right lateralization model of implicit music cognition.