People with schizophrenia often have cognitive impairment as well and this is evident before, during and after their illness. At the same time people with a mild learning disability - an IQ of between 50 and 70 - are between three and five times as likely to develop schizophrenia as the rest of the population. This could be because learning disabilities could make people more likely to develop schizophrenia as they become overwhelmed by, and fail to make sense of, the world around them or because the factors that make people vulnerable to schizophrenia also cause cognitive problems. Researchers from Edinburgh University compared 28 people with learning difficulties thought to be at risk of schizophrenia, 39 people with learning difficulties not thought to be at risk and 29 people who were neither at risk nor who had learning disabilities. They used brain scans to measure the size of the participants' amygdalas and looked at the relationship between amygdala size and schizophrenia symptoms. They found that those people with learning disabilities at high risk of developing schizophrenia had significantly larger right amygdalas. In the high-risk group the smaller the left side of their amygdalas was the more negative symptoms - depression and lethargy - of schizophrenia they had.
Welch, K.A. ... [et al] - Amygdala volume in a population with special educational needs at high risk of schizophrenia Psychological Medicine June 2010, 40(6), 945-954