Neural & Behavioral Correlates of Speech and Melody Repetition in Aphasia

Speech and music are traditionally thought to be primarily supported by different hemispheres. A growing body of evidence suggests that speech and music often rely on shared resources in bilateral brain networks, though the right and left hemispheres exhibit some domain-specific specialization. While there is ample research investigating speech deficits in individuals with right hemisphere lesions and amusia, fewer investigate amusia in individuals with left hemisphere lesions and aphasia. Many of the fronto-temporal-parietal regions in the left hemisphere commonly associated with speech processing and production are also implicated in bilateral music processing networks. The current study investigates the relationship between damage to specific regions of interest within these networks, and an individual’s ability to successfully match the pitch and rhythm of a presented melody. Twenty-seven participants with chronic-stroke lesions were given a melody repetition task to hum short novel piano melodies. Participants underwent structural MRI acquisition and were administered an extensive speech and cognitive battery. Pitch and rhythm scores were calculated by correlating participant responses and target piano notes. Production errors were calculated by counting trials with responses that don’t match the target melody’s note count. Overall, performance varied widely, and rhythm scores were significantly correlated. Working memory scores were significantly correlated with rhythm scores and production errors, but not pitch scores. Broca’s area lesions were not associated with significant differences in any of the melody repetition measures, while left Heschl’s gyrus lesions were associated with worse performance on pitch, rhythm, and production errors. Lower rhythm scores were associated with lesions including both the left anterior and posterior superior temporal gyrus, and in participants with damage to the left planum temporale. The other regions of interest were not consistently associated with poorer pitch scores or production errors. Although the present study does have limitations, the current study suggests lesions to left hemisphere regions thought to only affect speech also affect musical pitch and rhythm processing. Therefore, amusia should not be characterized solely as a right hemisphere disorder. Instead, musical abilities of individuals with left hemisphere stroke and aphasia should be characterized to better understand their deficits and mechanisms of impairment.