Intellectual decline in schizophrenia has been an area of active investigation for well over two decades. In a twin paradigm, we reported evidence for intellectual decline in the schizophrenia proband, using both reading level and current IQ (Goldberg et al., 1990). In a later study we determined that intellectual decline is present in about 50 percent of patients and appears to be the modal presentation (Weickert et al., 2000).

In the current paper, MacCabe and colleagues attempt to pinpoint the timing of cognitive decline in a Swedish population-based study. They found strong evidence for decline in verbal ability in the 13-18 years of age period. Nevertheless, there are several unexpected features to the report.

First, though it is “population based,” the schizophrenia/schizoaffective N = 50 and bipolar N = 18 are rather small compared to many other studies in the area.

Second, the schizophrenia group has a relatively late onset (28 years at first hospitalization). This has important implications for the authors’ claim that the decline was not related to a prodrome and invites some skepticism.

Third, the authors comment that decline does not reflect frank deterioration, but rather a slowing of developmental gains. I agree with this, but this could have been directly addressed by examining raw scores, not standardized scores. See work which suggests slowed maturation by taking this former approach (Bedwell et al., 1999).

Conceptually, it is unclear what is behind the decline. One possibility not commented upon is that compromises in episodic memory prevent the acquisition of new information, including vocabulary. Hence, the language decline would be secondary to a failure in memory. A study by Elvevåg et al. (Elvevåg et al., 2003) is in keeping with this view.

References:

Bedwell JS, Keller B, Smith AK, Hamburger S, Kumra S, Rapoport JL Why does postpsychotic IQ decline in childhood-onset schizophrenia? Am J Psychiatry 156:1996-7,1999. Abstract

Elvevåg B, Kerbs KM, Malley JD, Seely E and Goldberg TE. Autobiographical memory in schizophrenia. An examination of the distribution of memories. Neuropsychology 17: 402-409, 2003. Abstract

Goldberg TE, Ragland DR, Gold J, Bigelow LB, Torrey EF and Weinberger DR: Neuropsychological assessment of monozygotic twins discordant for schizophrenia. Archives of General Psychiatry 47: 1066-1072, 1990. Abstract

Weickert T, Egan MF, Weinberger DR and Goldberg TE: Cognitive impairments in patients with schizophrenia displaying preserved and compromised intellect. Archives of General Psychiatry 57: 907-913, 2000. Abstract

View all comments by Terry Goldberg

Adolescence is a period of dramatic brain maturation and reorganization, and may also be a time of particular risk for pathophysiological processes underpinning neurodevelopmental models for psychiatric disorders such as schizophrenia. It, therefore, represents a particularly good period to examine for cognitive changes, as indices of that neurobiological risk, as they occur during that time of development. MacCabe’s excellent work complements numerous other streams of research that point in a similar direction, i.e., that a failure of normal verbal maturation during adolescence indicates later psychosis risk. However, without wanting to take anything away from the value of the study, we are left wondering whether we have been distracted by large samples, and association studies, for too long, perhaps confusing bigger with better? Epidemiological studies cannot tell us about the underlying neurobiology of the changes that occur during this period of development, and isn’t that where we should focus?

View all comments by Timothea Toulopoulou