Amusia is a loss of the ability to appreciate music despite normal intelligence, memory, and language function. Subtypes have been described: receptive or sensory (loss of the ability to appreciate music) and expressive or motor (e.g., loss of ability to sing, whistle). Clearly a premorbid appreciation of music is a sine qua non for the diagnosis (particularly of the former), and most reported cases of amusia have occurred in trained musicians. Others have estimated that amusia affects up to 4% of the population (presumably expressive). Tests for the evaluation of amusia have been described.
Amusia may occur in the context of more widespread cognitive dysfunction, such as aphasia and agnosia. It has been found in association with pure word deafness, presumably as part of a global auditory agnosia. Isolated amusia has been reported in the context of focal cerebral atrophy affecting the nondominant temporal lobe. However, functional studies have failed to show strong hemispheric specificity for music perception, but suggest a cross-hemispheric distributed neural substrate. An impairment of pitch processing with preserved awareness of musical rhythm changes has been described in amusics.
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