Decreased encoding efficiency in schizophrenia.

BACKGROUND: Working memory deficits are a cardinal feature of schizophrenia that contribute to social and occupational dysfunction.
METHODS: We used functional magnetic resonance imaging to compare the response to varying task demands during the performance of an item recognition task. Study design and analysis procedures were optimized for the detection of load dependent activity during the encoding phase of working memory.
RESULTS: At the lowest load conditions the schizophrenia group performed as well as controls, however to achieve this equivalent performance the schizophrenia group had a significantly higher magnitude of activation compared to the controls. At the higher load conditions, the magnitude of activation between groups became more similar and we began to see performance deficits in the schizophrenic group.
CONCLUSIONS: These results suggest that patients with schizophrenia have decreased efficiency in the cognitive processes that underlie the early encoding phase of this task. For lower demand tasks, patients with schizophrenia can compensate for decreased efficiency by working harder to achieve equivalent performance. Encoding utilizes attentional and perceptual cognitive operations that are likely common to many other cognitive tasks; therefore, inefficiency may underlie the deficits observed in a wide range of cognitive tasks in schizophrenia compared to healthy controls.