Musical functioning, speech lateralization and the amusias.
Amusia is a condition in which musical capacity is impaired by organic brain disease. Music is in a sense a language and closely resembles speech, both executively and receptively. For musical functioning, rhythmic sense and sense of sounds are essential. Musical ability resides largely in the right (non-dominant) hemisphere. Tests have been devised for the assessment of musical capabilities by Dorgeuille, Grison and Wertheim. Classification of amusia includes vocal amusia, instrumental amnesia, musical agraphia, musical amnesia, disorders of rhythm, and receptive amusia. Amusia like aphasia has clinical significance, and the two show remarkable similarities and often co-exist. Usually executive amusia occurs with executive aphasia and receptive amusia with receptive aphasia, but amusias can exist without aphasia. Severely executive aphasics can sometimes sing with text (words), and this ability is used in the treatment of aphasia. As with aphasia, there is correlation between type of amusia and site of lesion. Thus in executive amusia, the lesion generally occurs in the frontal lobe. In receptive amusia, the lesion is mainly in the temporal lobe. If aphasia is also present the lesion will be in the left (dominant) hemisphere.