Fluctuations in Heart Rate Influence Brain Activity
Post by Meagan Marks
The takeaway
Heart Rate Variability (HRV), a component of cardiac rhythm, directly affects brain activity important for neural communication.
What's the science?
In neuroscience, it is typically understood that the brain controls the body. But emerging evidence suggests that involuntary functions like heartbeat can influence the brain. Recent research has found that heart rate variability (HRV), the fluctuation in time intervals between adjacent heartbeats, is connected to neural activity. Those with higher HRV – or a heart more adaptable to the environment – are shown to have improved emotional regulation, cognitive function, and well-being. This relationship is especially prominent with high-frequency HRV (HF-HRV, which reflects the variation in heart rate associated with breathing). However, how neural activity and HF-HRV directly affect each other remains unknown. This week in Psychological Science, Sargent and colleagues explored the causal relationship between HF-HRV and neural activity by comparing oscillations from the heart and brain.
How did they do it?
The authors recruited 37 healthy adult participants and asked them to stare at a white cross on a black screen for 5 minutes. During the task, cardiac rhythm was recorded via electrocardiogram (EKG) and brain rhythm via electroencephalogram (EEG). The HF-HRV oscillations were then extracted from EKG recordings and temporally aligned to match EEG data (brain waves), which had been filtered into oscillations occurring at each frequency band (alpha, beta, gamma, delta, theta). The authors then analyzed the oscillations to look for evidence of phase-amplitude coupling, where it was predicted that the phase series (cycles) of HF-HRV oscillations would be coupled with, or associated with, the magnitude of change in brain waves (amplitude). Once phase-amplitude coupling was established, the authors calculated to what extent HF-HRV oscillations successfully predicted brain oscillations and vice versa to establish the direction of the causal relationship (heart-to-brain or brain-to-heart influence).
What did they find?
Upon analysis, the authors found a strong relationship between HF-HRV and neural activity via phase-amplitude coupling, where the phase series of HF-HRV oscillations modulated the amplitude of the brain waves. It was found that a majority of participants also showed a significant heart-to-brain effect, where HF-HRV oscillations significantly predicted and regulated brain waves. This suggests that cardiac rhythm can influence neural activity. In addition, for all brain wave frequency bands except gamma, the heart-to-brain effect was significantly stronger than the brain-to-heart effect. This was true for EEG signals coming from all areas of the brain, suggesting that the heart was influencing neural communication and activity between multiple regions and multiple brain wave rhythms.
What's the impact?
This study is the first to show that fluctuations in heart rate can modulate neural activity. The findings suggest that improvements in cardiac rhythm may enhance connectivity and communication between neurons in the brain, in turn boosting cognitive functions like emotional regulation, executive functioning, and stress management. Cardiac variables such as HRV could also be a potential therapeutic target for mental health disorders, where methods like HRV biofeedback could help improve well-being.
