Hemispheric Lateralization Effects of Rhythm Implementation During Syllable Repetitions: a fMRI Study

Rhythm in terms of the modulation of syllable durations represents an information-bearing feature of verbal utterances contributing both to the meaning of a sentence (linguistic prosody) as well as a speaker’s emotional expression (affective prosody). In order to delineate the neural structures subserving rhythmic shaping of speech production, functional magnetic resonance imaging (fMRI) was performed during (a) monotonous syllable repetitions and (b) production of syllable triplets with lengthening either of the initial or final unit. The latter pattern of syllable durations can be considered the prototypical rhythmic structure contributing both to linguistic and affective prosody. A cognitive subtraction approach (rhythmic versus monotonous iterations) revealed activation of right-sided perisylvian areas (superior temporal gyrus, Broca analogon and adjacent premotor cortex) as well as contralateral subcortical structures (putamen and thalamus). Presumably, these responses reflect a righthemisphere rehearsal mechanism of rhythmic patterns and lefthemisphere monitoring of verbal output.