Adults who were born prematurely, and also suffered small brain injuries around the time of birth, have lower brain levels of dopamine, new King’s College London research reports.
This chemical change has been linked to lack of motivation and enjoyment in normal life, and changes to attention and concentration, which could all be early signs of more serious mental health issues such as substance dependence and depression.
The study, a collaboration between researchers from King’s, Imperial College London and the Icahn School of Medicine at Mount Sinai in New York, also shows that most people born prematurely have completely normal dopamine levels.
Thirteen million infants are born too early every year. Improved care allows many to survive, but these “preterm infants” still face an increased risk of death and many other complications.
Infants born very early, before 32 weeks, are at risk of brain injury because the brain is normally still developing in the later stages of pregnancy. They also have an increased risk of developing mental health problems later in life.
However in 15-20 per cent of babies born before 32 weeks of pregnancy, bleeding happens in the first week of life in fluid-filled spaces called ventricles, which are contained in the brain. If bleeding is significant, it can cause long-term problems.
Whole striatal dopamine synthesis capacity by group. Credit: Sean Froudist-Walsh et al. CC-BY
Although the biological link between birth complications and greater risk of mental health issues is unclear, one theory is that the stress of a complicated birth could lead to increased levels of dopamine.
The researchers used a combination of positron emission tomography (PET) scans and magnetic resonance imaging (MRI) scans of the brain with a range of psychological tests in order to identify the precise changes to chemistry and structure of the brain following early brain damage. They compared three groups of people: adults who were born very preterm who sustained early brain damage, adults who were born very preterm who did not sustain brain damage and controls born at term.
“People have hypothesised for over 100 years that certain mental illnesses could be related to problems in early brain development. Studies using animal models have shown us how early brain damage and mental illness could be linked, but these theories had not been tested in experiments with humans.
We found that dopamine, a chemical that’s important for learning and enjoyment, is affected in people who had early brain injury, but not in the way a lot of people would have thought – dopamine levels were actually lower in these individuals. This could be important to how we think about treating people who suffered early brain damage and develop mental illness. I hope this will motivate scientists, doctors and policymakers to pay more attention to problems around birth, and how they can affect the brain in the long-term.”
Further studies may help scientists understand how early brain injuries may cause brain chemical differences later in life, and how these brain changes affect individual’s mental health. They may also help scientists develop treatments to prevent or treat mental illness in people who experienced a brain injury after a very early birth.