British scientists say they have found that a part of the brain responsible for functions such as learning and memory can also destabilise the heart during times of stress.
It seems that when a person becomes stressed the normal response includes increasing heart activity to pump more blood around the body; however this response can have an adverse affect on those with heart disease and increase their risk of heart failure.
The scientists from University College London and the Brighton and Sussex Medical School studied 10 patients with specific heart conditions.
The researchers measured the electrical changes at the surface of the skull to examine how the brain operated while the patients performed a mildly stressful task, i.e. counting backwards in sevens.
Their results showed that the brain's cortex made the body's stress response worse by creating a feedback loop that could eventually destabilise the heart muscle.
Study author Marcus Gray of the Brighton & Sussex Medical School, says they found a close association between the actual performance of the heart and the activity in the cortex, which suggests that these brain regions listen closely to the beat-to-beat activity.
Gray says this suggests that the cerebral cortex may play a significant role in these events by becoming involved in a vicious circle.
He says it is already known that stress can increase the risk of sudden death through cardiac arrest and that the brain areas responsible for regulating heart function can be unbalanced by stress.
For the study electrical changes at the surface of the skull were measured while the patients performed the task.
The results showed that activity in the 'higher level' regions of the brain, such as the cortex closely reflected the response measured in the heart.
This has the potential to destabilised the heart muscle, raising the possibility of abnormal and potentially dangerous rhythms, which can cause sudden death in vulnerable patients.
The study is published in the Proceedings of the National Academy of Sciences.