Melodic and harmonic discrimination following unilateral cerebral excision

Seventy-seven subjects who had undergone unilateral temporal, frontal, or frontotemporal lobectomy for the relief of focal epilepsy as well as a group of 20 normal control subjects were tested in two discrimination tasks, requiring the detection of a single-note change in a pattern of three notes played either successively or simultaneously. Patients with right temporal and right frontotemporal excisions demonstrated a significant deficit in melodic discrimination in comparison to the normal control subjects. Further analysis showed that left-temporal lobectomy including excision of Heschl's gyri (the primary auditory receiving area) led to a significant impairment as well, whereas anterior left temporal-lobe damage did not result in a significant deficit. The results suggest that melodic discrimination depends largely but not exclusively on the right temporal lobe, and that the left Heschl's gyri also seem to be necessary to succeed in this task. In the harmonic task, the differences between the groups did not reach significance, although the two tasks were highly correlated.