A new study published in PLOS Biology suggests that our heartbeat plays a crucial role in determining our brain’s ability to perceive and react to the world around us. Researchers have discovered that during the 0.8 seconds of a heartbeat, there are optimal windows for action and perception, potentially impacting treatments for conditions like depression and stroke.
Previous research has shown that various bodily systems, including respiratory, digestive, and cardiac systems, influence our brain’s perception and action capabilities. Specifically, cardiac activity has been found to affect visual and auditory perception. However, the understanding of how cardiac activity, particularly the phases of the cardiac cycle, influences cortical and corticospinal excitability — the brain’s responsiveness — was limited. This study aimed to fill this knowledge gap.
The new study, conducted by Esra Al and colleagues at the Max Planck Institute for Human Cognitive and Brain Sciences in Germany, involved 37 healthy human volunteers aged 18 to 40. These individuals, free from neurological, cognitive, or cardiac health issues, underwent a series of non-invasive transcranial magnetic stimulation (TMS) pulses. These pulses were administered to the right side of the brain to stimulate nerve cells. The team measured the participants’ motor and cortical responses, as well as heartbeats, during the stimulation.
The researchers found that the timing of our heartbeat affects the brain’s responsiveness. They discovered that both the brain’s direct responses and muscle activities were more pronounced during the heart’s contracting phase.
Specifically, the study found that motor evoked potentials (MEPs), which are indicators of corticospinal excitability, varied significantly with the cardiac cycle. Specifically, MEP amplitudes were higher during the systole phase (when the heart muscle contracts) compared to the diastole phase (when the heart muscle relaxes). This suggests that our brain’s responsiveness to stimuli is not constant but fluctuates with our heartbeat. It indicates that the heart’s pumping action might influence how effectively the brain can signal to the rest of the body.
TMS-evoked potentials (TEPs), which measure cortical excitability, were observed to be stronger during systole. This indicates that the brain’s cortical areas are more excitable during certain phases of the heart cycle and provides insight into how internal bodily processes like heartbeats can modulate brain activity at a cortical level.
The researchers observed that muscle activity and sensorimotor oscillations (brain waves related to movement) were stronger when participants initiated a pinch movement during systole. This suggests that the timing of a heartbeat could influence motor functions and coordination. It points to a potential synchronization between cardiac activity and muscle responses, which could be crucial for tasks requiring precise timing and coordination.
Heart rate was found to change depending on when the TMS was administered in the cardiac cycle, with notable deceleration during systole, suggesting a direct influence of brain stimulation on heart rate, depending on the cardiac phase.
Finally, higher heartbeat-evoked potential (HEP) amplitudes were associated with stronger motor excitability levels. This suggests a correlation between the brain’s response to heartbeats and its readiness for motor action.
Together, the findings contribute to a deeper understanding of how the brain and body interact, emphasizing that physiological processes like heartbeats are not isolated from brain functions. The study also has potential implications for treatments involving brain stimulation, like those for depression and stroke recovery. Understanding the optimal timing in the cardiac cycle for such interventions could enhance their effectiveness.
“Using simultaneous recordings of brain activity, heart activity, and muscle activity, this study discovered that the timing of heartbeats and their neural processing were linked to changes in the excitability of the motor system,” the researchers wrote. “Our study sheds light on the existence of distinct time windows across the cardiac cycle that potentially optimize perception and action.”
The study, “Cardiac activity impacts cortical motor excitability“, was authored by Esra Al, Tilman Stephani, Melina Engelhardt, Saskia Haegens, Arno Villringer, and Vadim V. Nikulin.
