Speech Movement Sequence versus Speech Movements in Sequence: fMRI Observations
V Gracco, P Tremblay, B Pike
The present study compared speech-related brain regional activation patterns using functional Magnetic Resonance Imaging (fMRI). A compressed block design was used to eliminate volume-related speech movement artifacts during scanning. Subjects were presented either three single words or a three word meaningful sentence and instructed to listen to or repeat the stimulus material. Bilateral activations were noted in primary motor and sensory areas (somatic and auditory) in both conditions. Activations were more distributed and of greater magnitude for the word condition compared to the sentence condition. Laterality differences were noted for the two speaking conditions. Left motor and premotor areas and right auditory/parietal areas were more active for the word condition with the opposite pattern for the sentence condition. The supplementary motor area (SMA), the cerebellum bilaterally, and the posterior insula were strongly activated for the word condition but not for the sentence condition. A strong activation was also noted in the basal ganglia when the two speaking tasks were subtracted. Overall, the results in the word condition are consistent with other brain imaging studies of sequential motor behavior implicating the cerebellum, basal ganglia and SMA as part of the neural network for serial speech timing.