A new study charts the IQ of people who went on to develop psychotic disorder.
Psychotic disorders are estimated to affect more than 3 percent of people in the United States across their lifetime.
Yet despite their relative prevalence, we still have much to learn about how and why they occur.
Individuals with psychotic disorders essentially lose contact with reality. Among other things, they may experience hallucinations and delusions.
Another core feature of psychotic disorders is a decline in cognitive ability. Some scientists focus on this aspect of the condition in an effort to gain insight.
Because the events that lead up to psychotic disorders are poorly understood, researchers hope that by learning more about cognitive decline — and perhaps being able to spot it early — there may be an opportunity to intervene and change the course of the condition.
Psychosis and IQ
The researchers behind a new study — who are all interested in the cognitive aspects of psychiatric disease — hail from King's College London's Institute of Psychiatry, Psychology, and Neuroscience in the United Kingdom and the Icahn School of Medicine at Mount Sinai in New York City, NY.
They recently published the details of their latest study in the journal JAMA Psychiatry.
The latest investigation, however, wanted to chart this drop in IQ further back in time to get a better understanding of when the decline first begins. This is important because, for years, scientists have wondered whether schizophrenia might be — at least in part — due to abnormalities in brain development.
Although adolescence is known to be a critical time for schizophrenia, few studies have looked further back into childhood.
The scientists behind the latest study also cast their net a little wider, comparing individuals with psychotic disorder with those with other mental disorders, including psychosis with depression, subclinical psychotic experiences, and depression.
Charting the cognitive deficit
In all, the study used data from 4,322 people from the U.K., all of whom were followed from the age of 18 months to 20 years.
After analysis, they found that individuals who went on to develop psychotic disorders in adulthood performed normally in IQ tests during infancy, but by the age of 4, there was evidence of a decline in cognitive ability.
When they reached adulthood, a 15-point gap had opened up between them and the control group. Deficits were found in working memory, attention, and processing speed.
When compared with the other conditions, only those with psychotic disorder had progressive IQ deficits.
Each aspect of the IQ test was dissected to explore whether different facets of cognitive function behaved differently. And, according to the authors, differences did emerge.
"Verbal IQ," they write, "declined in early childhood and remained stable thereafter, whereas decline in full-scale IQ and nonverbal IQ continued through adolescence and early adulthood."
A cautious approach and future directions
The findings are interesting and provide a new insight into the progression of psychotic disorders. However, when considering and interpreting the results, the researchers urge caution.
"It is important to bear in mind that many children will experience some difficulties with school work or other intellectual tasks at some point in their lives, and only a small minority will go on to develop a psychotic disorder."
Senior study author Dr. Abraham Reichenberg
The study authors are also clear that the results will need to be replicated. Although their sample size was large overall, only relatively small numbers of people with psychotic disorder were available to take some of the IQ tests.
As with any research into difficult-to-treat conditions, the authors hope that their findings will help to build more effective ways to manage psychotic conditions.
"There are early interventions offered to adolescents and young adults with psychosis," says Dr. Reichenberg. "Our results show the potential importance of interventions happening much earlier in life. Intervening in childhood or early adolescence may prevent cognitive abilities from worsening and this may even delay or prevent illness onset."
Following on from this, Dr. Reichenberg plans to study brain changes in individuals who eventually develop psychosis. He also wants to take a closer look at potential environmental and genetic risk factors that could predispose someone to poorer cognitive abilities.