Brain chemistry could change under the stress of migration, increasing a newcomer’s risk of developing schizophrenia and other psychoses, according to a new medical study.

The groundbreaking research, a joint effort by researchers at Toronto’s Centre for Addiction and Mental Health and King’s College in England, has identified a plausible biological mechanism that links the effects of migrant status to the risk of developing psychosis.

“We knew schizophrenia patients and those at risk of schizophrenia release more dopamine in their brains when exposed to a social challenge,” said Dr. Romina Mizrahi, a study co-author and director of CAMH’s youth psychosis prevention clinic and research program.

“Immigrants and their children have higher dopamine synthesis capacity versus non-immigrants. When they are under stress, they also release more dopamine. These brain changes might explain the higher risk to develop psychosis that has been observed in immigrants.”

The report consists of two parts: the Canadian study that examined the release of dopamine in its subjects when responding to arithmetic questions from a standard stress-inducing test known as the Montreal Imaging Stress Task; and the British study that looked at the dopamine production capacity among immigrants and non-immigrants.

It excluded any subject who was pregnant or had used illicit drugs other than cannabis in the six months before participating in the study.

“One of the most consistent findings in the epidemiology of schizophrenia is the high incidence of the disorder among immigrant groups. The risk is particularly increased in immigrant groups who migrate from a country where the population is predominantly black-skinned to a country where the population is predominantly white-skinned,” said the 20-page study published in January by the Oxford University Press.

“This increased risk of schizophrenia has been reported both in immigrants and in their children. These findings have been replicated in a number of high-income countries: the Netherlands, Denmark, Germany, the United Kingdom, and Canada, clearly establishing that the incidence of schizophrenia is higher among migrant groups as compared to host populations.”

Dopamine plays a major role in reward-motivated behaviour and our brain releases the compound when we are interested in something. However, those stress factors may tip the balance and alter the regulatory mechanism, said Mizrahi.

Although the pool of subjects in each study was small (56 in Canada and 76 in the U.K.), Mizrahi said the effect of immigration on stress-induced dopamine release among the subgroups of subjects — clinical high-risk subjects, patients with schizophrenia and healthy volunteers — was significant.

“Not everyone with high dopamine levels will develop schizophrenia. Not all immigrants develop psychoses. There are psychological and social interventions to minimize the risks. When experiencing stress, people have different coping mechanisms,” said Mizrahi, who recommended proper social and settlement support for newcomers.

Mizrahi said further studies should look at the impact of ethnicity and the generational aspect of immigration on dopamine function since the current project did not compare the results among immigration groups.

“While the reasons for the increased risk of schizophrenia and other psychoses in migrant groups are still unclear . . . there is increasing evidence that victimization, discrimination, social isolation, social defeat, and growing up in an urban environment may contribute,” the study concluded.