Conduction aphasia is characterized by relatively frequent phonemic speech errors with self-correction attempts and difficulty repeating speech verbatim; comprehension is relatively well-preserved. The classical account holds that conduction aphasia is caused by damage to the arcuate fasciculus. However, we have been arguing for some time that conduction aphasia is caused by damage to area Spt -- a functionally defined region in the vicinity of the left planum temporale that exhibits auditory-motor response properties, and which we claim computes a mapping between auditory and motor speech representations, critical for aspects of speech production.
Our hypothesized link between conduction aphasia and area Spt just got stronger. In a forthcoming paper in Brain and Language Buchsbaum et al. show that the region of maximal overlap in lesion distribution of a group of 14 conduction aphasics includes area Spt (based on fMRI data from over 100 participants).
We argue that the auditory-motor transformation function carried out by Spt is necessary for verbatim repetition but also plays a critical role in internal monitoring during speech production, thus explaining the increased speech error rate when the system is damaged. This explanation does a better job of explaining the co-occurrence of phonemic paraphasias and repetition deficits than does the current dominant model of the deficit in conduction aphasia, namely, that it is a working memory deficit.
Buchsbaum BR, Baldo J, Okada K, Berman KF, Dronkers N, D'Esposito M, & Hickok G (2011). Conduction aphasia, sensory-motor integration, and phonological short-term memory - An aggregate analysis of lesion and fMRI data. Brain and language PMID: 21256582
Baldo, J.V., Klostermann, E.C., and Dronkers, N.F. (2008). It's either a cook or a baker: patients with conduction aphasia get the gist but lose the trace. Brain Lang 105, 134-140.
Hickok, G., Buchsbaum, B., Humphries, C., and Muftuler, T. (2003). Auditory-motor interaction revealed by fMRI: Speech, music, and working memory in area Spt. Journal of Cognitive Neuroscience 15, 673-682.
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Hickok, G., Okada, K., and Serences, J.T. (2009). Area Spt in the human planum temporale supports sensory-motor integration for speech processing. J Neurophysiol 101, 2725-2732.