Retrieving Meaning after Temporal Lobe Infarction: The Role of the Basal Language Area David J. Sharp, MRCP, Sophie K. Scott, PhD, and Richard J. S. Wise, FRCP During speech comprehension the auditory association cortex in the superior temporal cortex is involved in perceptual analysis of the speech signal, whereas the basal language area in the inferior temporal cortex mediates access to word meaning. Disruption of the interaction between the superior and inferior temporal cortices is one factor that may determine recovery from aphasic stroke. We used positron emission tomography to investigate semantic processing within inferior temporal cortex in control subjects and after infarction involving the superior temporal cortex. In the control group, semantic decision making on clear speech activated both anterior fusiform gyri. Chronic aphasic patients were impaired at the task and demonstrated reduced activation within the left anterior fusiform gyrus. A similar pattern of impaired performance and reduced left anterior fusiform gyrus activation was observed when control subjects heard perceptually degraded speech. Performance in both groups predicted activity in the right anterior fusiform gyrus and the temporal poles, where accuracy linearly correlated with activity. These results demonstrate that the function of the basal language area is sensitive to changes in the quality of perceptual input. In addition, different profiles of response observed in each hemisphere suggest distinct contributions of both left and right inferior temporal cortices to the semantic processing of speech. Ann Neurol 2004;56:836 – 846 Studies during epilepsy surgery were the first to asso- ciate language with a basal language area within the inferior temporal cortex (IT). 1 Surface electrical stimu- lation, variously applied to the left parahippocampal gyrus, fusiform gyrus, and inferior temporal gyrus, was shown to produce a range of aphasic disturbances. 1,2 Subsequently, human intracerebral recordings from both left and right anterior fusiform gyri, close to perirhinal (limbic) cortex, have demonstrated responses evoked by word meaning, 3,4 and aphasia has been de- scribed in patients with spontaneous seizures originat- ing in IT. 5 In the literature on aphasic stroke, the left IT is one region that has been associated with transcortical sen- sory aphasia, 6–8 although deficits after lesions within IT are usually transient. 6 Transcortical sensory aphasia is characterized by impaired speech comprehension but intact repetition, 9 demonstrating that the perception of speech and the route to articulation are preserved, whereas the route to comprehension is impaired. Pa- tients with the progressive variant of transcortical sen- sory aphasia, known as semantic dementia, develop at- rophy of structures within the IT and the temporal poles. 10,11 The outcome is profound anomia followed by a progressive loss of comprehension, affecting knowledge about the meaning of language and objects. The involvement of IT in language processing also has been demonstrated by functional imaging. 12–14 At the cortical level, the perceptual analysis of heard speech begins in primary auditory cortex, with further processing in the superior temporal gyrus and superior temporal sulcus 15–18 (for review, see Scott and Johnsrude 19 ). After initial acoustic processing, familiar words are recognized and their meaning accessed. 20 IT appears to be one part of a network of regions involved in this access to word meaning, mediating the mapping of language onto long-term stores of semantic mem- ory. 14 In keeping with this proposal, functional imag- ing studies have demonstrated that IT, and in particu- lar the fusiform gyrus, is activated when the meanings of both visual and auditory stimuli are processed. 21–27 This study used functional neuroimaging to investi- gate the response within IT during the semantic pro- cessing of heard words. We studied two groups of sub- From the MRC-Cyclotron Unit, Clinical Sciences Centre, Imperial College London, London, UK. Received Apr 23, 2004, and in revised form Aug 20. Accepted for publication Aug 24, 2004. Published online Oct 27, 2004, in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ana.20294 Address correspondence to Dr Sharp, MRC-Cyclotron Unit, Clini- cal Sciences Centre, Imperial College London, London, UK, W12 0NN. E-mail: david.sharp@ic.ac.uk 836 © 2004 American Neurological Association Published by Wiley-Liss, Inc., through Wiley Subscription Services