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The neural correlates of inner speech have been investigated previously using functional imaging. However, methodological and other limitations have so far precluded a clear description of the neural anatomy of inner speech and its relation to overt speech. Specifically, studies that examine only inner speech often fail to control for subjects' behaviour in the scanner and therefore cannot determine the relation between inner and overt speech. Functional imaging studies comparing inner and overt speech have not produced replicable results and some have similar methodological caveats as studies looking only at inner speech. Lesion analysis can avoid the methodological pitfalls associated with using inner and overt speech in functional imaging studies, while at the same time providing important data about the neural correlates essential for the specific function. Despite its advantages, a study of the neural correlates of inner speech using lesion analysis has not been carried out before. In this study, 17 patients with chronic post-stroke aphasia performed inner speech tasks (rhyme and homophone judgements), and overt speech tasks (reading aloud). The relationship between brain structure and language ability was studied using voxel-based lesion-symptom mapping. This showed that inner speech abilities were affected by lesions to the left pars opercularis in the inferior frontal gyrus and to the white matter adjacent to the left supramarginal gyrus, over and above overt speech production and working memory. These results suggest that inner speech cannot be assumed to be simply overt speech without a motor component. It also suggests that the use of overt speech to understand inner speech and vice versa might result in misleading conclusions, both in imaging studies and clinical practice. [ABSTRACT FROM AUTHOR]

Both herpes simplex virus encephalitis (HSVE) and semantic dementia (SD) typically affect anterior temporal lobe structures. Using voxel-based morphometry (VBM), this study compared the structural damage in four HSVE patients having a semantic deficit particularly affecting knowledge of living things and six SD patients with semantic impairment across all categories tested. Each patient was assessed relative to a group of control subjects. In both patient groups, left anterior temporal damage extended into the amygdala. In patients with HSVE, extensive grey matter loss was observed predominantly in the medial parts of the anterior temporal cortices bilaterally in SD patients the abnormalities extended more laterally and posteriorly in either the left, right or both temporal lobes. Based on a lesion deficit rationale and converging results from several other sources of evidence, we suggest that (i) antero-medial temporal cortex may be important for processing and differentiating between concepts that are 'tightly packed' in semantic space, such as living things, whereas (ii) inferolateral temporal cortex may play a more general role within the semantic system. [ABSTRACT FROM AUTHOR]