The processing of spoken language has been attributed to areas in the superior temporal lobe, where speech stimuli elicit the greatest activation. However, neurobiological and psycholinguistic models have long postulated that knowledge about the articulatory features of individual phonemes has an important role in their perception and in speech comprehension. To probe the possible involvement of specific motor circuits in the speech-perception process, we used event-related functional MRI and presented experimental subjects with spoken syllables, including [p] and [t] sounds, which are produced by movements of the lips or tongue, respectively. Physically similar nonlinguistic signal-correlated noise patterns were used as control stimuli. In localizer experiments, subjects had to silently articulate the same syllables and, in a second task, move their lips or tongue. Speech perception most strongly activated superior temporal cortex. Crucially, however, distinct motor regions in the precentral gyrus sparked by articulatory movements of the lips and tongue were also differentially activated in a somatotopic manner when subjects listened to the lip-or tongue-related phonemes. This sound-related somatotopic activation in precentral gyrus shows that, during speech perception, specific motor circuits are recruited that reflect phonetic distinctive features of the speech sounds encountered, thus providing direct neuroimaging support for specific links between the phonological mechanisms for speech perception and production.cell assembly ͉ functional MRI ͉ perception-action cycle ͉ mirror neurons ͉ phonetic distinctive featue N eurological theories of language have a long-standing tradition of distinguishing specialized modular centers for speech perception and speech production in left superior temporal and inferior frontal lobes, respectively (1-3). Such separate speech-production and -perception modules are consistent with a number of neuroimaging studies, especially the observations that frontal circuits become most strongly active during speech production and that speech input primarily activates the left superior temporal gyrus and sulcus (4-6). Superior temporal speech-perception mechanisms in humans may be situated in areas homologous to the auditory belt and parabelt areas in monkeys (5,7,8). In macaca, this region includes neurons specialized for species-specific calls (9, 10). Therefore, it appeared to be reasonable to postulate a speech-perception module confined to temporal cortex specifically processing acoustic information that is immanent to speech.In contrast to this view, neurobiological models have long claimed that speech perception is connected to production mechanisms (11-16). Similar views have been proposed in psycholinguistics. For example, the direct realist theory of speech perception (17, 18) postulates a link between motor and perceptual representations of speech. According to the motor theory of Liberman et al. (19,20), speech perception requires access to phoneme representations that are c...

The brain basis of action words may be neuron ensembles binding language- and action-related information that are dispersed over both language- and action-related cortical areas. This predicts fast spreading of neuronal activity from language areas to specific sensorimotor areas when action words semantically related to different parts of the body are being perceived. To test this, fast neurophysiological imaging was applied to reveal spatiotemporal activity patterns elicited by words with different action-related meaning. Spoken words referring to actions involving the face or leg were presented while subjects engaged in a distraction task and their brain activity was recorded using high-density magnetoencephalography. Shortly after the words could be recognized as unique lexical items, objective source localization using minimum norm current estimates revealed activation in superior temporal (130 msec) and inferior frontocentral areas (142-146 msec). Face-word stimuli activated inferior frontocentral areas more strongly than leg words, whereas the reverse was found at superior central sites (170 msec), thus reflecting the cortical somatotopy of motor actions signified by the words. Significant correlations were found between local source strengths in the frontocentral cortex calculated for all participants and their semantic ratings of the stimulus words, thus further establishing a close relationship between word meaning access and neurophysiology. These results show that meaning access in action word recognition is an early automatic process ref lected by spatiotemporal signatures of word-evoked activity. Word-related distributed neuronal assemblies with specific cortical topographies can explain the observed spatiotemporal dynamics reflecting word meaning access.

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