PET studies of speech production – roles for auditory cortex in the control of timing and delayed auditory feedback

Sophie Scott, Hideki Takaso & Richard Wise

University College, London, UK

Previous PET studies have shown an important role for left posterior auditory fields and left anterior insula in speech production. Here we present a PET study of speaking under delayed auditory feedback: subjects read a story aloud during scanning, and received DAF at 0, 50, 125 or 200ms. Subjects were able to continue speaking under all DAF conditions, although they all rated their speech as harder as the DAF increased in duration. Neural activity (as indexed by regional cerebral blood flow) increased with amount of DAF in bilateral non-primary auditory fields, running lateral and posterior to primary auditory cortex. There was also activity in a right homologue of Broca’s area. This indicates that there is sensitivity not just to the existence of DAF in non-primary auditory fields, but also to the precise amount of DAF. We cannot however specify yet whether such activity relates to the processing of DAF discrepancy, or control of speech output timing, or both when the subjects speak under DAF. However it is striking that the same right Broca’s area has been shown to be suppressed during ‘propositional’ speech production and is activated in the same subjects during rhythmic counting (Blank et al, 2003). We suggest, therefore, that at least some of the activation seen is associated with aspects of timing control when speaking under DAF. These results also show a linking of speech input/output systems, which have basis in the known anatomy of the primate brain. We would also like to suggest that the dominance of the left hemisphere in speech production may be modulated by the timing constraints of the speech production task.