Verbal memory in first-episode schizophrenia: heterogeneity in performance?

It is unclear if the commonly observed "subcortical" verbal memory profile in schizophrenic patients is present at the onset of the disease. Therefore, the performance of 43 first-episode patients with schizophrenia or schizophreniform disorder on the Dutch version of the California Verbal Learning Test (VLGT) was compared to that of 43 normal comparison participants. We hypothesized that the first-episode patients would exhibit a "subcortical" memory profile, that is, they would show a primary retrieval deficit. This hypothesis was not confirmed: the patients displayed a profile suggestive of a prominent storage deficit, that is, a "cortical" memory profile. Subsequently, patients' VLGT performance was cluster analyzed to determine whether subgroups could be identified exhibiting a cortical, subcortical, and normal profile, respectively. Two subgroups (N=22; N=13) exhibited memory impairments, while one subgroup (N=8) was unimpaired. The memory profiles of the two impaired subgroups differed both qualitatively and quantitatively, but did not conform neatly to a cortical and a subcortical profile. Demographic and verbal fluency data provided limited validation of the subgroup classification. Our results may suggest that combining the verbal memory performance of first-episode patients obscures meaningful heterogeneity. Alternatively, the cluster solution could merely reflect a continuum of severity.