Hemispheric lateralization at different levels of human auditory word processing: a functional magnetic resonance imaging study

We used functional magnetic resonance imaging to disentangle the functional anatomy of brain systems involved in the processing of auditory word form and meaning. Three monitoring tasks on auditory stimuli, aimed at phonetic, lexical and semantic processing, were used. We found no lateralization of temporal lobe activations, when word processing was contrasted versus the complex phonetic task. Bilateral middle temporal activations (Brodmann Area [BA] 21) were attributed to processing of word-form. Areas specific to semantic processing were restricted to the left hemisphere: the posterior middle frontal (BA 9) and posterior parietal (BA 7/40) cortex, as well as an inferior temporal area (BA 20/21). Our data suggest, that left hemispheric dominance for auditory word comprehension occurred at the level of semantic processing.