Use of a sequencing task designed to stress the supervisory system in schizophrenic subjects

We investigated whether schizophrenic subjects are impaired in non-routine behaviour because of the dysfunction of a general executive component labelled, in neuropsychological terms, the supervisory system.

A specific verbal sequencing test was designed for this purpose. Subjects had to perform sequential reasoning with verbal material. Each test sequence consisted of a series of words presented in jumbled order. The construction of some sequences had to be done using familiar routine associations (valid conditions). In contrast, some other sequences required the overriding selection of familiar routine associations, which were inappropriate within the general context of the task (invalid conditions). Twenty verbal sequences (10 valid-10 invalid) were administered. Thirty-seven DMS-IV schizophrenic patients and 21 normal volunteers matched for age and educational level were recruited.

Compared to the control group the schizophrenic group was impaired in both valid and invalid conditions. The number of 'capture errors' specific to supervisory system failure was significantly higher in the schizophrenic group and only the schizophrenic patients had significantly fewer correct sequences in invalid conditions than in valid conditions. Poor performance in invalid conditions alone was observed only among the schizophrenic subjects without a general cognitive defect.

These findings suggest that sequencing procedures requiring an executive input are impaired in schizophrenia.