A functional study of auditory verbal imagery

Background. We used functional MRI to examine the functional anatomy of inner speech and different forms of auditory verbal imagery (imagining speech) in normal volunteers, We hypothesized that generating inner speech and auditory verbal imagery would be associated with left inferior frontal activation, and that generating auditory verbal imagery would involve additional activation in the lateral temporal cortices. Methods. Subjects were scanned, while performing inner speech and auditory verbal imagery tasks, using a 1.5 Tesla magnet. Results. The generation of inner speech was associated with activation in the left inferior frontal/insula region, the left temporo-parietal cortex, right cerebellum and the supplementary motor area. Auditory verbal imagery in general, as indexed by the three imagery tasks combined, was associated with activation in the areas engaged during the inner speech task, plus the left precentral and superior temporal gyri (STG), and the right homologues of all these areas. Conclusions. These results are consistent with the use of the "articulatory loop" during both inner speech and auditory verbal imagery, and the greater engagement of verbal self-monitoring during auditory verbal imagery.