Place your index finger and middle finger on your neck over the carotid artery and relax. Can you feel your pulse? Next time you have difficulty seeing something, because it's dark, because it's far away or for any other reason, take your pulse and concentrate on what you're looking at with every heart beat. Do you see the connection? Sight and heartbeats appear to be connected…

Since the brain receives signals from all the body's organs and in particular those signals from the heart, researchers at INSERM had the idea of testing the hypothesis that some signals may influence our sensory, cognitive or behavioral abilities. To be more precise, they measured the visual acuity of seventeen subjects, comparing it with fluctuations in heart rate.

Thanks to magnetoencephalography, a brain imaging technique that accurately measures neuronal activity using over 300 sensors placed on the head, scientists have been able to locate the areas of the brain where the activity is connected with heartbeats. Then, they showed volunteers a very low contrast image several times. The contrast is so low that the image is only visible half of the time. "We tested this phenomenon in normal conditions: the aim was not to artificially stimulate the heart rate; it was rather to find out whether variations in spontaneous and normal activity of the brain generated by the beats of the heart interfere with visual acuity," explains Catherine Tallon-Baudry, co-author of the study which was published in the prestigious journal, Nature.

And in quite an unexpected way, the results confirmed the initial hypothesis, demonstrating that the more the brain activity is associated with heart beats, the more the subjects were able to make out the images. "It's as if the signals coming from the body's organs enable the person to develop finer sensations, which ultimately distinguish us from a robot equipped with a camera processing visual information," says the researcher.

The perception of body signals by the brain does indeed have an influence on sensory abilities, and in this case, sight. Dr Tallon-Baudry goes further, suggesting that other senses, like hearing, may also be affected by cardiac activity.