Intact short-term memory and impaired executive functions in obsessive compulsive disorder

Previous neuropsychological studies produced inconsistent results with tasks tapping short-term verbal and visual-spatial memory and executive functions in obsessive compulsive disorder (OCD). The aim of this study was to investigate the presence of deficits in these cognitive domains. A further goal was to describe the distribution of patients in different impairment ranges for all functions, and clarify the relationship between symptom severity and cognitive impairments.

Thirty patients with OCD (DSM-IV) and 30 healthy volunteers were compared using well-known neuropsychological tasks. We assessed short-term verbal memory with the Digit Span Forward and Digit Span Backward Tasks, short-term visual-spatial memory with the Corsi Block Tapping Task, while we measured the level of executive functions with the StroopTask and the Wisconsin Card Sorting Test (WCST).

Compared with a matched healthy control group, the performance of OCD patients was in the impaired range only in the two executive tasks. We find a significant positive correlations between the Y-BOCS (Yale-Brown Obsessive Compulsive Scale) total scores and the number of perseverative responses (r(28) = 0.409, p < 0.05) and perseverative errors (r(28) = 0.385, p < 0.05) in the WCST.

Our results gave evidence that executive functions are impaired while short-term memory is intact in OCD. This is in line with neuropsychological model of OCD that the deficit of cognitive and behavioral inhibition are responsible for the main cognitive findings of this disorder, most prevalently the deficit in set shifting and prepotent response inhibition.