“The heart has its reasons that reason does not know ”said Blaise Pascal in his Thoughts. However, heart and brain are intimately linked, proves science to us. So, according to a new study published in the journal Proceedings of the National Academy of Sciences of the United States of America, our brain’s sensitivity to external sensory stimuli would change as our heart beats.
Scientists at the Max Planck Institute for Cognitive and Cerebral Human Sciences in Leipzig and the Berlin School of Mind and Brain, both in Germany, have been studying the relationship between brain and heart for a long time. For their new study, they recruited 37 volunteers and performed 960 trials. In 800 of them, they administered a slight electric shock to the index or middle finger of the left hand. The volunteers had to report in which finger they felt the stimuli. In the remaining 160 trials, they received no stimuli.
In parallel, the researchers used electroencephalography (EEG) to record the electrical activity of the brain and electrocardiography (ECG) to record the electrical activity of the heart. They discovered how the heartbeat phase could change the participants’ conscious experience.
A sharper awareness of external perceptions during the diastole
In the past, they had already shown that during systole, humans had more trouble detecting and locating a weak electric shock during systole (when the heart sends blood to the body) than during diastole (when the heart filled with blood). Here, they have successfully linked this change in sensitivity to a distinguishing characteristic of the brain’s electrical activity. Known as P300, the latter concerns consciousness.
They noticed that the P300 signal was stronger when the stimulus was unexpected and dropped during systole. This could be due to the fact that the high blood pressure pulse that sweeps across the body when the heart contracts is a predictable stimulus that does not deserve conscious attention.
Another mechanism highlighted during this study: that which connects the heart and sensory perception. Researchers noted that when subjects were more aware of their heartbeats, they tended to detect and locate electrical shocks less effectively.
Helping to care for patients after stroke or heart attack
“It seems to be the result of a focus of our attention between external environmental signals and internal bodily signals ”says Esra Al, who led the research. So if the brain can quickly switch conscious awareness to internal sensations, such as breathing or heartbeat, and external sensations, it would seem that we cannot focus on both simultaneously.
Since after a heart attack or stroke, the usual two-way communication between the heart and the brain may be impaired, these results “could help explain why patients with stroke often suffer from heart problems and why patients with heart disease often have impaired cognitive function ”, enthuses Arno Villringer, the study’s lead author.
What are the differences between a myocardial infarction or a stroke?
Heart attack or myocardial infarction (MI) is the death of a more or less large area of the heart muscle, called myocardium. The heart muscle cells in the affected area can no longer contract due to a lack of oxygen and die within hours. In France, according to Inserm, around 120,000 people have a heart attack every year. Among them, 10% die at this moment and 18,000 die in the following year.
Stroke, or “stroke”, is the blockage or rupture of a blood vessel in the brain. In France, there are more than 140,000 new cases every year, one every four minutes. In addition, stroke is the leading cause of acquired physical disability in adults, the second leading cause of dementia (after Alzheimer’s) and the second leading cause of death with 20% of patients dying within one year of the shock.
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