Different levels of lexical processing – evidence from an fMRI study with normal subjects and aphasic patients

Samenvatting

Psycholinguistic models assume different levels of lexical processing: the conceptual, the lemma- and the lexeme level. The aim of the present study was to disentangle the neural substrates of these different levels in normal subjects and to investigate mechanisms of functional reorganisation of lexical processing in two aphasic patients. 14 young, right-handed, native speakers of German participated in the fMRIstudy consisting of three different decision tasks each focussing particularly on one level of lexical processing. Additionally we examined two aphasic patients (RK and WR) with left hemisphere lesions. In the normal subjects we found activation for the concept condition in the anterior part of Broca’s area (BA 45) and the frontal operculum (BA 47), for the lemma condition activation was observed in the posterior part of Broca’s area (BA 44) and the lexeme condition revealed an increase in BOLD response in both the anterior and the posterior part of Broca’ area (BA 45 and 44). Behavioural data show that the lemma task was by far the most difficult for both patients. They showed no left inferior frontal activation during this task. Instead activation was observed in left perilesional (RK) and right frontal and parietal areas (WR) respectively.