There’s a time and a place for listening to your heart instead of your head, although in most situations you’re better off blocking out the sound of your ticker so that you can focus on the important stuff going on around you. Accordingly, our sensible brains have developed the perfect technique for filtering out the sound of our own heartbeats, and a team from Ecole Polytechnique Fédérale de Lausanne in Switzerland may now have figured out how it does it.

Even more amazingly, the researchers also discovered that it’s possible to essentially trick the brain into mistaking other stimuli for a heartbeat, causing it to filter them out in the same way so that we become unaware of them.

The reason for this phenomenon is that humans have spectacularly complex innards, with some pretty impressive plumbing and plenty of moving parts. However, if we allow ourselves to get distracted by all this internal commotion, then we run the risk of missing all the important activity going on around us – like cars driving towards where we happen to be walking, for instance – which could have disastrous consequences.

As lead researcher Roy Salomon explains, “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.” Fortunately, “the brain itself decides which information to bring to awareness,” automatically ignoring unimportant stimuli originating within the body – known as interoceptive signals – and prioritizing exteroceptive signals coming from the external environment.

Previous studies have shown that a brain region known as the insular cortex coordinates and integrates these two types of stimuli, so the researchers decided to test how this part of the brain responds to a person’s heartbeat.

Publishing their findings in the Journal of Neuroscience, the study authors describe how they used functional magnetic resonance imaging (fMRI) to monitor the activity of volunteers’ brains when viewing flashing images on a screen.

Amazingly, they found that when these images flashed exactly in sync with participants’ heartbeats, activity dropped dramatically in the insular cortex, as the brain attempted to filter out this visual stimulus. When this occurred, participants became less aware of the images on the screen, in some cases failing to see them at all.

The researchers conclude that the brain somehow mixed up this visual stimulus with the heartbeat, and therefore automatically suppressed its awareness of it by reducing the activity of the insular cortex when processing the image.

Summing up these remarkable findings, Salomon explained that it came as no shock to discover that the insular cortex plays a role in forcing our brains to ignore our heartbeats, but that “what's surprising is that our heart also affects what we see!”