LAUSANNE, Switzerland, May 4 (UPI) -- The brain suppresses the sound and physical sensation of the heartbeat in order to tell the difference between internal sensations of the bodily and stimuli from the outside world, researchers in Switzerland found in a recent study.
The brain's actions to minimize noticing one's own heartbeat may also give a clue to the origin of some anxiety disorders, researchers at the Federal Institute of Technology in Lausanne report in The Journal of Neuroscience.
During gestation, the heart forms and starts beating before the brain forms, so the researchers were not shocked it can filter out noise that predates its existence in order to get its job done.
The surprise, they said, was on the discovery that external stimuli in rhythm with the heart instigates less activity in the brain, resulting in less awareness of of the stimulation.
"We are not objective, and we don't see everything that hits our retina like a video camera does," Roy Salomon, a researcher at the institute's Laboratory of Cognitive Neuroscience, said in a press release. "The brain itself decides which information to bring to awareness. But what's surprising is that our heart also affects what we see!"
For the study, the researchers recruited 150 people for a series of experiments to find what was happening in the brain in response to stimuli. They flashed an octogonal shape on a screen at varying speeds, finding it could not be perceived when flashing in rhythm with the volunteers' hearts.
MRI scans of the volunteers during the experiments showed the insular cortex region of the brain was responsible for their perception of the flashing shape. When the experiments were run again, the researchers noted that as the flashing light got closer to a person's heart rate, they were less aware, or unaware, the shape was on the screen.
Although awareness of one's heartbeat is linked to psychological problems and anxiety disorders, the researchers say more work is needed to understand how the brain's filter between internal and external stimuli may affect them.
"You don't want your internal sensations to interfere with your external ones. It's in your interest to be aware of what's outside you," Roy said. "So it's not surprising that the brain acts to suppress it and make it less apparent."