The brain responsiveness to the scenes very much depended on the personality of these individuals

Dr John Gabrieli

However, a study carried out at Stanford University in the US claims to be able to differentiate the happy-go-lucky types from those with a more cynical slant on life.

The researchers looked at a group of women aged between 19 and 42.

These had been split into two types by a questionnaire - optimists or extroverts, and those who were more anxious or neurotic.

Both of these types were then shown pictures of "happy" scenes, such as birthday parties, and those with a grimmer connotation, such as hospital wards.

Grim picture

While this was going on, brain scans were taken to measure the activity in various parts of the brain.

The team found that the "optimists" responded far more strongly to the "happy" pictures than the "anxious" group.

The reverse was also true: there was far more brain activity in the anxious types when they were viewing the "unhappy" pictures.

Dr John Gabrieli, who led the study, said: "The brain responsiveness to the scenes very much depended on the personality of these individuals."

Of course, the study did not reveal whether the lack of brain activity was the root cause of the pessimism, or whether it was simply a symptom of some other physical change.

But Dr Gabrieli suggested that the extra knowledge of the "brain's architecture" could prove useful in treating conditions such as depression.

He said: "We don't know to what extent this involves genetics or pre-disposition, or a learned response."