The overlap of cognitive impairment in depression and schizophrenia: a comparative study

Schizophrenia (SCH) is primarily a cognitive dysfunction. Its specific cognitive impairment profile was identified and suggestions have been made to include it in present diagnostic instruments as a special differential diagnostic criterion. However, studies indicate a substantial overlap of cognitive deficits between SCH patients and those with depression (DEP). In order to elucidate the structure of cognitive functioning in both entities, principal cognitive domains of SCH and DEP patients were assessed in the acute phase of disease.

44 SCH and 30 DEP patients, matched according to age, gender, education, IQ score, and duration of hospitalization were included. Neurocognitive assessments were performed in the first week of hospitalization using Digit Span test (working memory, attention), Trail Making Test (psychomotor speed, sustained attention, shifting), Rey's Complex Figure Test and Verbal Learning Test (perceptual organization, visual and verbal learning and memory). Results were evaluated according to demographically matched test norms. For statistics Student's t tests were used.

In both study groups deficits in maintenance and shifting of attention during psychomotor tasks were found, while automatic processes (working memory, sustained attention) were preserved. In both groups memory and learning processes were impaired, in DEP however, deficits in attention shifting during cognitive tasks and delayed recall of visual material were more intense.

In the acute phase of schizophrenia and depression similar cognitive impairment profiles can be found. Further studies are needed to assess longitudinal dynamics and possible later development of specific patterns of cognitive functioning in these patients.