Researchers from the Departments of Neurology at Harvard Medical School and at Beth Israel Deaconess Medical Center have published a study of how persons with large left-hemisphere lesions and chronic non-fluent aphasia respond – behaviorally and neuroplastically – to intensive Melodic Intonation Therapy (MIT). The goals of this proof-of-concept study are to characterize – following MIT intervention – [i] improvements in spontaneous speech production, and [ii] new loci of neural activity following therapy in the right – that is, undamaged – cerebral hemisphere, during speech production.
The researchers recruited fourteen subjects (13 m, 1 f) with non-fluent aphasia and large left-hemisphere lesions. Mean age of participants was 54.5 y/o (SD 14.3), and mean time post-onset was 2.97 years (SD 2.6). Their mean left-hemisphere lesion volume was 168.6 cc (SD 73.9), which represents a bit over one quarter of an average cerebral hemispheric volume. The MIT intervention comprised 75 90-minute sessions (total = 112.5 hrs). Spontaneous speech performance of the subjects was assessed before, during, and after intervention, plus four weeks later, by counting Correct Information Units per minute during conversational interviews and picture description tasks, and by completing the Boston Naming Test. Functional magnetic resonance imaging was done before and after intervention, with subjects vocally repeating a designated set of bisyllabic words.
After the therapy, speech production showed significant improvements compared to intake assessments. In spontaneous speech samples, the subjects increased the number of Correct Information Units/minute from 1.9 to 5.1. In confrontation naming, mean scores on the Boston Naming Test improved from 5.0 to 7.7. Both these improvements were statistically significant. Comparison of brain images pre- and post-intervention showed new areas in the right cerebral hemisphere were actively engaged during verbal repetition of bisyllabic words. These newly engaged areas were in the posterior superior temporal gyrus, the inferior frontal gyrus, the inferior pre- and post-central gyrus, the pre-supplementary motor area, and the supramarginal gyrus. The brain scans also show, that in these subjects, the corresponding areas of the left hemisphere remained inactive during the speech production. MIT thus appears to promote recruitment and neuroplastic repurposing of parts of the right-hemisphere to support improved language production processing – areas that, in neurotypical adults, are recruited instead in mirror-image locations of the left hemisphere.
For further reading: S. Marchina, A. Norton, G. Schlaug, 2023, Effects of melodic intonation therapy in patients with chronic nonfluent aphasia. Annals of the New York Academy of Sciences, 1519(1): 173-183, https://doi.org/10.1111/nyas.14927