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Abstract:
We investigated lateralisation in response to the 'on-line'
perception of the lexical and sentential semantics of a narrative.
We studied 12 normal subjects using 15O2-labelled water PET. The
activation and baseline conditions were, respectively: children's
stories read aloud by several speakers (St); and the same stories
played backwards (RSt). Six subjects listened to the stimuli
without a task demand ('passive') and six were asked to determine
the number of speakers for each passage of St and RSt ('active').
The results were analysed using SPM99, P <0.05 corrected for
whole brain analyses. The stories activated bilateral anterior
temporal cortex. In contrast, the temporo-parietal junction and the
fusiform gyrus were only activated on the left: whether the stimuli
were listened to 'passively' or 'actively' made no difference to
the distribution of temporal activations. In the 'active' study,
voice discrimination was more difficult on the RSt (performance at
chance, compared to 80% correct on the St), and this was reflected
in a left anterior cingulate cortical activation. The only frontal
activation in the comparison of St with RSt was a small region in
the left inferolateral prefrontal cortex. We conclude that
'on-line' processing of a narrative's meaning involves left
anterior auditory association cortex and multimodal cortex in the
left fusiform gyrus and temporo-parietal junction, with no
involvement of 'classic' Broca's area
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