Many studies have demonstrated that individuals who develop psychotic disorders ( except bipolar disorder) in adulthood performed below the level of their peers in childhood.This premorbid cognitive deficit could be seen as a result of neuro developmental impairment. It is possible that poor cognitive performance and schizophrenia could be linked via social factors.Another view is that poor cognition is a prodrome of the illness.
We know that adolescence is a critical period for brain.ie brain is busy with synaptic pruning and a rapid reduction in gray matter volume occurs at this time. Incidence of psychosis show the peak at this time. Cannabis use emerges as a complicating problem during this stage. If we go by neuro developmental hypothesis,changes in cognitive performance over time, relative to the population, should predict the risk for psychosis more strongly than the overall level of performance.No one has prospectively measured changes in cognitive functioning during the adolescent and young adult period (age range, 13-18 years).
James H. MacCabe and team of investigators linked Swedish population registers to conduct a historical cohort study investigating the associations between cognitive change during adolescence and young adulthood and the risk for psychoses during adulthood.
All individuals ( since conscription data is used, only men are studied) in the sample underwent cognitive testing (verbal, spatial, and inductive ability) at age 13 years and 18 years.Those who screened positive for psychiatric disorders had undergone full diagnostic interview as part of enlistment process.
A relative decline in verbal ability scores clearly emerged as the strongest and statistically significant predictor of schizophrenia. This result is not confounded by urbanicity, parental educational level, or family history of psychosis.
Those who later developed bipolar disorder outperformed population norms on all tasks and at all time points, and a non significant trend was seen for the association of better verbal ability at age 18 years with increased risk for bipolar disorder.
In all diagnostic groups, verbal ability declined compared with the male general population between ages 13 and 18 years. Except in bipolar disorder, this decline was a significant predictor of later psychoses. Decline was a stronger predictor of later psychosis than poor verbal ability at age 18 year alone.
It is important to note that this decline is relative to general population,ie unlikely to represent an actual deterioration.In other words, relative decline could be due to lack of progress compared to others in the age group.
Limitations: Cognitive tests were brief. There were small differences in the tests administered at age 13 and 18.Diagnosis were made by clinicians. Register captured only hospital admissions.Data is restricted to men.
Conclusions: The findings support the idea that premorbid cognitive deficit observed in schizophrenia represents a disruption of neuro development during the teenage years.
Summary of the article:
Decline in cognitive performance between ages 13 and 18 years and the risk for psychosis in adulthood: a Swedish longitudinal cohort study in males. Maccabe JH, Wicks S, Löfving S, David AS, Berndtsson A, Gustafsson JE, Allebeck P, Dalman C.JAMA Psychiatry. 2013 Mar 1;70(3):261-70