Cognitive problems are considered to be one of the main features of schizophrenia. However, it is unclear whether the problems are already there before people's first experience of psychosis or whether developing psychosis has a deleterious effect on people's cognition. A team of researchers from the Academic Medical Centre in Amsterdam studied 58 people, 41 of whom were deemed to be at ultra-high risk of developing psychosis while 17 were unaffected controls. Of the ultra-high risk group 17 developed psychosis during the course of the study. The participants' cognitive performance was assessed at the start of the study and again 18 months later. The people who developed psychosis did not perform any worse at the second test than before they became unwell and the ultra-high-risk group actually performed better on the second test. The control group of unaffected people scored significantly better on test of verbal learning, memory and verbal fluency. So this study at least suggests that problems with cognition come before the development of psychosis and not afterwards.
Becker, H.E. ... [et al] - Neurocognitive functioning before and after the first psychotic episode: does psychosis result in cognitive deterioration? Psychological Medicine, October 2010, 40(10), 1599-1606