Saturday, August 29, 2009

Cerebellum and Foreign Accent Syndrome

Cohen DA, Kurowski K, Steven MS, Blumstein SE, Pascual-Leone A. Paradoxical facilitation . The resolution of foreign accent syndrome after cerebellar stroke. Neurology 2009; 73:566-67.

Background: Lesions are usually left parietal. 2 previous cases were described with cerebellar hypoperfusion that resolved with FAS .

Case: 58 yo woman had left frontoparietal infarct with aphemia and right upper limb paresis. It resolved to right arm ataxia and English with an accent. 2 years later, after a right cerebellar hemorrhagic infarct, the FAS resolved. Her speech was analysed after each stroke. Abnormalities which were detected that comprised the FAS included pathologic prosody, vowel formant freqency, vowel durations, and increased variabilities on these vowel measures, and normal voicing and placement of stop consonants and preservation of the distinction between tense and lax vowels.

Alterations in timing and rhythm of speech, as seen in FAS, are characteristic of cerebellar lesions (see Ivry R., Cerebellar timing systems, Int Rev Neurobiol, 1997; 41: 555-573). The author speculates that the prosodic problems in FAS may " reflect deficits in timing resulting in impairments of speech melody, in maintaining the correct vocal posture for the production of vowels, in maintaining the correct durational patterns of speech, and in producing syllabic stress and quantity."

Re mechanism, the authors propose that the lesioned right cerebellum then gives way to the now dominant left cerebellar hemisphere, which is disinhibited and now functional.