Bipolar sufferers may have enhanced mathematical abilities before diagnosis

Certain intellectual abilities may be impaired, while others are enhanced, in bipolar disorder sufferers before they are diagnosed with the condition, researchers have found.

Dr Jari Tiihonen, from the University of Kuopio in Finland , and colleagues explain that previous studies have "consistently shown that individuals who later go on to fulfil diagnostic criteria for schizophrenia in adulthood, as a group, achieve lower scores on intelligence tests in childhood and adolescence than their peers".

However, they add that little is known about the intellectual abilities of people with bipolar disorder or other forms of psychosis before their condition is diagnosed.

To investigate, the researchers studied data on 195,019 men aged an average of 19 years who had been conscripted into the Finnish army between 1982 and 1987. All the new recruits were required to complete a number of tests designed to measure general ability and logical thinking. These included a verbal reasoning test, an arithmetic reasoning test and a visuospatial reasoning task that required the participants to identify spatial relationships in patterns ranging from the very obvious to the very abstract.

The researchers then used hospital data to identify all those who had later developed bipolar disorder, schizophrenia or other psychoses after leaving the army.

Analysis of the findings revealed that a poor performance on the visuospatial reasoning test was associated with an increased risk of developing any of the disorders in later life.

In contrast, however, higher scores on the arithmetic reasoning test were associated with a greater risk of developing bipolar disorder in later life. Indeed, a high score on this test was associated with a 12-fold increased risk of bipolar disorder compared with a low score.

Performances on the verbal reasoning test were not associated with an increased risk of any of the disorders studied.