| Schizophrenia is a disabling mental illness that has been linked to dysfunction in neural circuitry that includes the frontal lobes. One model of schizophrenia describes a willed route to action, reliant upon motivation and self-initiation and a stimulus driven route to action, dependent upon environment cues and contingencies. In schizophrenia, the former is thought to be impaired, while the latter is considered intact. In relating this to brain structure, functional imaging and lesion studies in humans as well as physiological investigations in non-human primates have implicated the medial frontal cortex in intentional aspects of cognition. The aim of the present study was to map the hypothesis that schizophrenia patients have a deficit in the internal generation and monitoring of cognition on to neuroanatomical regions using whole brain functional MRI (fMRI). Two semantic word generation tasks that varied on the degree to which internal guidance was required were administered to a sample of 10 clinically stable, medicated male schizophrenia patients and 10 healthy control subjects matched on age, sex, parental SES and premorbid intellectual functioning. Monitoring of behavioral task performance revealed that despite pre-scanning training, schizophrenia patients produced an elevated number of incorrect responses during the word generation tasks. Analysis of the fMRI results demonstrated attenuated activity in the schizophrenia group relative to healthy controls in a number of brain regions including the left medial frontal cortex (BA 8), right dorsolateral prefrontal cortex (BA 46/9) and parahippocampal gyri bilaterally. The finding of attenuated medial frontal activity during the most internally guided task suggests that schizophrenia patients are unable to recruit critical medial frontal structures to the same extent as controls, reflecting a deficit in intentional aspects of cognition. The findings also suggest that attentional dysfunction, which increases in severity with greater semantic processing demands, characterized patients' performance during word generation. |
