When does cognitive decline occur in the period prior to the first episode of schizophrenia?

Cognitive impairment is common in people with schizophrenia. These impairments are detectable prior to any signs of illness in people who are destined to develop the disease and they are as severe at the time of the first psychotic episode as they are after many years of illness. It was formerly believed that the major decline from the minor impairments seen in childhood to those seen at the time of the first episode occurred during the prodrome. Recent data suggests that there is little cognitive decline during the prodrome and that at the detection of the prodrome, decline has already occurred. Thus, the period of cognitive decline must be very early in the prodrome to psychosis.