The Melbourne first-episode medium term follow-up study: Decline in attentional set-shifting, but not spatial working memory after the onset of psychosis

Available evidence of neuropsychological functioning (including working memory) in first-episode psychosis has generally found stable deficits from illness onset. However, cross-sectional studies would suggest a decline in attentional set-shifting ability after illness onset. However, there are no reported longitudinal studies investigating this ability in first-episode psychosis. In this study we examined change over time in visuospatial memory and executive functioning in a first-episode psychosis sample. The measures used were the Spatial Working Memory, Pattern Recognition Memory, and the Intra-/Extra-Dimensional Set-Shifting tests from the CANTAB. The study cohort was first tested from 1996 to 2001, and re-assessment began in 2002. Our preliminary data from 32 patients and 20 controls (mean time between assessments = 86.4 months, range = 63.5 – 120.9 months) showed no significant decline in the patient group on any of Spatial Working Memory Total Between search Errors (repeated-measures (RM) ANCOVA; Time x Group interaction F[1,48]=0.27, p=0.61), Spatial Working Memory Strategy (RM ANCOVA; Time x Group interaction F[1,48]=1.21, p=0.28), Pattern Recognition Total Correct (RM ANCOVA; Time x Group interaction F[1,38]=0.89, p=0.35), and Set Shifting Total Errors (RM ANCOVA; Time x Group interaction F[1,48]=0.33, p=0.57). Further analysis of the Set-Shifting data revealed no differences between patients and controls in the percentage passing each stage at Time 1. At Time 2 the patients were significantly more likely than controls to fail the final extra dimensional shift reversal stage (Chisquare( 1)=4.62, p=0.03), with the finding restricted to the non-remitted group. These data support previous studies of stable working memory in schizophrenia that are present from illness onset. In contrast, attentional set-shifting ability, which is not impaired at the onset of illness, deteriorates with progression of illness. These findings may be understood in relation to the progressive brain structural changes affecting prefrontal cortex in the first few years following onset of psychosis