In the few seconds it will take you to read this sentence, your sense of time may expand and contract, and your perception of the world could change in ways you wouldn’t realize.
These subtle effects on the brain are imperceptible, ethereal tugs of the heart beating inside the chest, which, according to a new study, also stimulates motor function in short bursts.
Neuroscientist Esra Al of the Max Planck Institute for Human Cognitive and Brain Sciences in Germany has been studying the influence of the heart on the brain for several years, drawing on decades-old research and recent studies with more robust methods.
In 2020, Al and some of his colleagues discovered that our sensation of external stimuli decreases each time the heart squeezes in what is known as the systole period. These sensory acuities return when the heart relaxes in diastole. But with each contraction our sensory perception dulls.
So how do our bodies, our muscles, respond in those moments of silence when our senses are briefly affected? Are we prepared to act on the information we have just received or are we stuck in a pause?
Some research has suggested that reaction times are slow during systole and that it takes us longer to gather tactile information because our sensory perception is momentarily dampened. Other studies have found that rapid eye movements known as saccades occur more frequently as the heart contracts, and suggest that motor movements could be signaled to the cardiac cycle.
So far, scientists have failed to get a clear picture of these ebbs and flows. So Al and his fellow researchers set out to measure how the motor cortex, the part of the brain involved in controlling voluntary motor movements, responds throughout the cardiac cycle.
“Interestingly, this study uncovers a remarkable connection between the human heart and brain, revealing distinct time windows designed for action and perception,” the researchers said in a statement.
The researchers set up participants on a few different machines to take simultaneous recordings of brain, heart, and hand muscle activity while they were sitting in a chair and when they completed a motor task that involved pinching a meter.
Analyzing data from 36 people, the researchers found that nerve signals that control hand muscles increased during systole, which typically lasts three-tenths of a second. Hand muscle activity was also momentarily stronger when participants pinched the meter during systole, rather than diastole.
“Overall, we found that excitability in the sensorimotor cortex increases in systole and, consequently, this increase is reflected in the strength of the motor output,” the researchers write.
By squaring these results with their previous findings, the researchers suggest that the increase in muscle activity during systole complements the drop in sensory perception, so that there are different windows in the cardiac cycle where the brain prepares to process sensory information. and then act accordingly.
“It is possible that different time windows exist throughout the cardiac cycle, optimizing perception or action,” the researchers conclude.
The study has been published in More biology.