Neural correlates of memory organization deficits in schizophrenia. A single photon emission computed tomography study with 99mTc-ethyl-cysteinate dimer during a verbal learning task.

Regional cerebral blood flow (rCBF) during a verbal learning task was measured using 99mTc-ethyl-cysteinate dimer and single photon emission computed tomography in 10 patients with schizophrenia and nine normal controls. Verbal repetition was used as a control task. The schizophrenic patients showed failure to spontaneously utilize implicit category information to learn the word lists. In the normal controls, rCBF in the left inferior frontal and left anterior cingulate regions was significantly increased during the verbal learning task, compared with the verbal repetition task. In contrast, there was no significant frontal lobe activation by the verbal learning in the schizophrenic patients. The patients had lower rCBF during the verbal learning task than the controls in the bilateral inferior frontal, left anterior cingulate, right superior frontal, and bilateral middle frontal regions. Activation in the left inferior frontal region was significantly positively correlated with categorical clustering in the task in the controls, but no such correlation was found in the patients. These results indicate that memory organization deficits in schizophrenia may be related to dysfunction in the prefrontal areas, especially in the left inferior frontal region.