| |
Abstract:
The present study makes use of fMRI to specifiy the
mechanisms subserving speech comprehension. In particular, the
cerebral network underlying syntactic processing is not yet fully
identified. Neuropsychological models and brain imaging experiments
describe Broca's area in the left inferior frontal cortex to
support syntax. In contrast, recent lesion studies report severe
grammatical impairments during comprehension after damage of the
left temporal lobe. In an event-related design 18 participants were
presented with auditive stimuli, sentences as well as word lists,
systematically varying the absence/presence of syntactic and
semantic information. Eight Gradient echo EPI images were obtained
in eight horizontal slices for each of the 144 trials using a
Bruker 3 Tesla scanner. The primary auditory cortex and the
posterior parts of the superior temporal gyrus bilaterally were
found activated in all conditions, but were more strongly involved
when considering only the sentence conditions. In contrast to word
lists the processing of syntactic information evoked additional
activation in the thalamus, in the temporal operculum and most
specifically in the left frontal operculum. Interestingly in all
conditions but the normal prose clear hemodynamic responses in the
superior-dorsal part of Broca's area could be detected. This
finding indicates the involvement of additional resources in the
frontolateral cortex whenever the input deviates considerably from
normal speech. Thus, the functional contribution of Broca's area to
syntactic processing has to be reexamined.
|
