Background:
Abnormalities in semantic processing are commonly proposed to be central to cognitive abnormalities and thought disturbances in schizophrenia. Deficits have been reported on a range of tasks including a categorization task. The current study investigated the underlying neural substrates involved during categorization.
Method:
A revised version of Chen et al.'s (1994) categorization task was used. The task consisted of 18 categories with five different exemplar words (ie high frequency, low frequency, borderline, related but outside category and unrelated) selected for each category. Subjects were asked to say whether exemplars were or were not part of the category. Data for each exemplar type were examined; this included behavioural accuracy and an event-related analysis of the functional magnetic resonance imaging data using SPM2.
Results:
Behaviourally, patients with schizophrenia had difficulty categorizing related words, while the controls had most difficulty with borderline examples. Performance in the controls was related to activity in the left inferior frontal, left inferior occipital/posterior temporal, bilateral precunues and the cerebellum; areas typically reported during semantic processing. Even when behavioural performance on some of the category types was no different to control performance, the patients with schizophrenia did not show any activation of this network.
Conclusions:
The imaging data showed impairments in the distributed frontal temporal network that is engaged in the representation and processing of meaning of words, text and discourse. It is these abnormalities that may underlie schizophrenic thought disturbance.
