| |
Abstract:
It is a challenge to provide multimodal imaging
characterisation of word comprehension stages. Here we recorded
Event-Related Potentials (ERPs) and Event-Related Haemodynamic
Responses (EHRs) in subjects either performing semantic
categorisation (natural / manufactured) or grammatical
categorisation (feminine / masculine) of monosyllabic noun pairs.
Targets were couples of words both pertaining to a prespecified
category. Subjects could either make a decision after processing
the first word (RELEASE condition) or they needed to process the
second word (HOLD condition). Across condition early splits of ERPs
assessed by systematic MANOVAs occurred at 308 ms for semantics and
392 ms for gender showing that semantic processing started earlier.
However, delayed splits related to decision making processes
occurred in reverse order (754 ms for gender and 786 ms for
semantics) suggesting that semantic categorisation took longer than
grammatical processing. The very same language network was
activated in both task. However, whereas temporal regions EHRs were
synchroneous across conditions, Broca's area and homologuous right
regions EHRs were significantly delayed in the HOLD condition in
both the tasks. The latter result is consistent with significant
ERP differences focused above prefrontal regions during splitting
periods. Prefrontal regions appear to play a key-role in both
semantic and grammatical monitoring of words, and there seem to be
a temporal primacy of semantic processing upon gender
processing.
|
