Anxiety is described as a feeling of fear, worry or unease, and its cause is often difficult to determine. Whatever the cause, it makes the heart beat faster – and a new study conducted on mice by researchers at Stanford University in California found that the reverse was also possible.
The results, published in the journal “Nature”, show that a faster heart rate generates anxiety in the body.
This study addresses a question that has puzzled the medical profession for over a century: do physical sensations follow emotion or vice-versa? To find out, the team turned to optogenetics, a method that uses light to control cellular activity.
The scientists created a tiny vest that incorporated a red light directed at the chest of the mice. When a mouse’s vest emitted a pulse of light, the animal’s heart muscles fired, making the heart beat.
The team trained the animals to expect to receive a shock when they pressed a lever for a water reward. Using optogenetics, the scientists artificially accelerated the mice’s heart rate from 660 beats per minute to 900.
At this point, the rodents no longer have the reflex to press the lever or find other alternatives, which results in them exhibiting signs of anxious behaviour.
On the other hand, when the mice did not perceive any danger in the context, the increased heart rate had no influence on them. The researchers thus theorised that the brain and heart actually work together to produce anxiety.
By measuring the brain activity of the mice, they found that the insula, a part of the brain associated with emotions and body signals, becomes more active when heart rate increases, particularly in a state of anxiety.
This allowed them to deduce that the insula becomes an intermediary between the heart and the brain in such moments of stress. It puts together signals from the heart reacting with environmental threats before transmitting the information to the areas involved in higher cognition.
“The insular cortex is known to be involved in interoception – the ability to perceive the body’s internal states, including heart rate, hunger, temperature and pain,” the authors explained.
“It receives all kinds of information from all across the body, so the insular cortex could be playing a general role across a broad range of emotional states,” added senior author Dr Karl Deisseroth. This discovery could contribute to a rethinking of treatment methods for chronic anxiety disorders.
The team now intends to retest the system to analyse links between the human brain and other organs, such as the intestines and facial muscles.