Working Memory in Patients with Schizophrenia and Bipolar Affective Disorder: Quantitative or Qualitative...

Some authors suggest that working memory may underlie most of cognitive deficits found in schizophrenia and contribute to the most salient features of the disorder. Many authors further believe that, despite the differences in magnitude, profile of cognitive impairment is quite similar across schizophrenia and affective psychosis. To test the hypothesis of profile similarity between SCZ and BPD compared to healthy individuals, we carried out a comparative study applying several working memory tasks.

A total of 64 subjects participated in the study, 20 diagnosed with schizophrenia, 18 with bipolar affective disorder and 26 healthy controls. Groups were matched according to age, sex and education, and two clinical groups were also matched according to the number of hospitalizations. To measure working memory we applied se Wisconsin Card Sorting Test (WCST), STROOP task, Trail making test (TMT), Digit span forward and backward tasks. To test the size and profile similarities of the groups, we used ANOVA and Kruskal-Wallis tests on individual measures and on factor scores.

Most indicators of the WCST did not differentiate between the groups, but all of the remaining indicators indicated weaker working memory of the two clinical groups compared to the healthy controls. All applied measures could be reduced to two latent constructs provisionally named WM Attention and WM Capacity. Both clinical groups scored lower on the capacity component than controls, whereas the three groups could not be distinguished according to the attention component. Results provided no evidence of difference in either size or profile of working memory impairment in patients with SCZ and BDP.

The current study determined impairment of WM in patients diagnosed with SCZ and BPD compared to healthy controls. However, no difference was found regarding either the size or the profile of impairment between SCZ and BPD patients.