As we ran other close-proximity experiments and collected more examples of synchronisation we began to wonder if anyone else had seen the same effect. It didn’t take us long to find several academic studies that showed similar heart rate variability correlations in bonded pairs.
A research team from Gothenburg University 3 in Sweden had monitored the hearts of a choir and found that their heart rate variability moved into synchrony when they were singing together. They also showed that the degree of synchronisation was related to distinctive styles of song. Slow, rhythmic chanting created more synchrony than free singing or humming. This study concluded that the heart rate synchronisation was caused by the common breathing and rhythmic patterns that were induced by the music and the shared experience.
Whilst the rhythm and breathing might have added to the entrainment effect, given our own results, we suspected that the singers were communicating energetically, perhaps directly through their hearts and their associated nervous systems. We then came across another piece of published research that had been conducted by the University of California 4. Their project had more in common with our own research. They had measured the heart rate variability of loving couples who were sitting close to each other and found similar synchrony to that which we had seen in our experiments. In addition, they found that the breathing pattern of the partners synchronised at the same time as their heart rate variability. Significantly, they also found that the hearts and breathing patterns did not entrain when they repeated the experiment with people who did not know each other. Clearly bonding was a crucial factor in the heart synchronisation. The University of California research suggested some possible sensory mechanisms for the synchronisation but did not suggest any direct energetic communication between experimenters.
One of the most striking pieces of research that we came across was conducted at a fire-walking ritual in Spain. A research group from Aarhus University 5 in Denmark compared the heart rate variability of a mother, who was in the audience watching, and her son, as he walked across the hot embers. They simultaneously measured the heart rates of the mother and son, and as a control, also measured the heart rates of audience members who did not know the mother or son. The results were fascinating. The heart rate variability of the fire walker and his mother synchronised markedly, but that of strangers in the audience did not. This suggests once again that the level of bonding in a relationship is a key factor in the heart rate variability synchronisation. In this experiment the mechanism for entrainment was thought to be the empathy and shared emotions between the mother and son, leading to similarity in heart rate variability. Once again, there was no suggestion of a direct, heart-to heart communication.
The HeartMath Institute have been researching local physiological entrainment for many years, looking primarily at brainwave, heart rate and breathing patterns in pairs of people who are separated by a few metres and who are in a loving, bonded relationship. They have observed similar heart rate variability correlation to those that we have seen in our experiments. The HeartMath Institute believe that the mechanism for the close-proximity HRV synchronisation is electromagnetic in nature. It is a fact that the muscles of the human heart generate the most powerful electromagnetic field within the body, and this can be measured out to a few metres from the heart with sensitive instruments. HeartMath postulate that our hearts can sense the electromagnetic field of another person’s heart, like a radio transmitter and receiver, and respond accordingly. Although this is a possible mechanism for the local synchronisation, further research is needed to confirm this hypothesis.
An unexpected result
We carried on running close-proximity experiments for about a year, trying different controls on the amount of sensory information that was available to the experimenters. For instance, in some experiments we closed our eyes, to see if the heart rate entrainment was being caused by visual cues. We discovered that the correlation effects were still present in these situations. As we accumulated more and more data, we became confident that the hearts of the experimenters were becoming entrained, but we had assumed, like the other researchers, that it was a purely local effect. Our next experiment was to fundamentally challenge this assumption.
Around this time, I was working away in Scotland. Out of curiosity, and as a bit of fun, I set up an experiment with my wife who remained in Essex, southern England. I was in a hotel room in Edinburgh and my wife was in the bedroom of our home 318 miles (512km) away.
We used the same experimental procedure as we had in the room together at home, but this time started the heart rate monitors simultaneously by one of us saying ready-steady-go during a mobile phone conversation. Once we had checked that both of us were successfully recording data, we said goodbye and switched our phones off. No telephone, internet or other communication devices were in use in this experiment, and we did not look at the computer screens. We simply relaxed for twenty minutes, brought each other to mind and felt our love for each other. The software switched off automatically at the twenty-minute mark, and the heart rate data was recorded into a file on each of our laptops.
I combined and plotted the two datasets from Edinburgh and Essex when I returned home a few days later. Figure 4 shows our heart rate variability for this experiment. As usual I have shifted my wife’s heart rate data vertically so that the two waveforms overlie each other to aid the identification of correlation.
Figure 4. The first long distance synchronisation experiment (318 m./512 km. apart) Overlain heart rate variability of a married couple (Husband, person 1 – black line, Wife, person 2 – solid fill) when separated by a large distance and without telephone or other communication devices in operation. Experimenters felt love for each other for the duration of the experiment. (Best viewed using QR code)
When we first saw this result, we could not believe our eyes. Our heart rates showed significant synchronisation for much of the twenty-minute experiment. Furthermore, when we zoomed in on the first 300 seconds of the experiment, we noticed that even the fluctuations in heart rate caused by our breathing patterns were synchronising (Figure 5).
Figure 5. Detail of results from Fig. 5. First 300 seconds. Overlain heart rate variability (Husband – black line, Wife – solid fill). Notice synchronisation of HRV breathing patterns.
This surprising result was the beginning of a major research effort where we reproduced and ran controlled experiments to confirm if what we had seen was a chance occurrence or a real effect. We have now conducted experiments at various distances of separation and have observed visual and statistically significant correlation in the results of many of them.
Given the radical nature of our discoveries we were aware that they were likely to meet considerable resistance from the scientific community. For this reason, we kept our research procedures simple and cheap to run, so anybody could reproduce our experiments and have a go at replicating our results. As you will see, the correlations that occur in our data are visually obvious which meant we did not need sophisticated statistical analysis to extract them from what can be noisy datasets. In fact, the effect size in our results is high compared to equivalent effects from physiological synchronisation research that focuses on the EEG signal of two brains. The relatively low cost of the heart rate monitoring equipment that we used in our research and the simplicity of analysis and display makes this sort of research easily accessible to citizen scientists.
Extracting emotional information from heart rate variability
In the case of some heart rate variability datasets, a comparison of the recorded heart rates is sufficient to identify correlation, but we were also able to further process the waveforms to extract additional information. This involved a frequency analysis of the changing heart rate patterns which allowed us to identify the periods when we were experiencing the strongest feelings of love and positive emotion.
In figure 6 you can see a graph of my heart rate recorded against time for a period of nearly six minutes. Notice how my heart rate changes throughout this period, falling to around sixty beats per minute and rising at other times to nearly eighty beats per minute. The regular rise and fall of heart rate that you can see clearly on the right-hand side of the graph is a response to my breathing. When we breathe in, our heart rate rises and when we breathe out, it falls. When a doctor measures our heart rate, they average these changes over say, one minute, but as you can see this ignores the breathing changes as well as those caused by our varying emotions. Heart rate tends to rise when we are frightened or excited but also when we experience love.
Figure 6. Heart rate variability for one person feeling two contrasting emotions.
I was aware of my emotions as I recorded this data and jotted them down on a notepad. For the first three minutes I was feeling anxious because I was thinking about my work and worrying about my financial situation. Then I deliberately put those negative feelings aside and felt love, appreciation, and gratitude for my wife. You can see that there is an immediate change in the character of the waveform. On the left-side it is jagged, with small beat-to-beat changes in heart rate, but when I was feeling love and the other positive emotions, the waveform becomes smooth, and the heart rate rises and falls in a regular and higher amplitude pattern – called a sine wave. This is related to a change in breathing to a slightly deeper and longer breath when we experience love and positive emotions. The sine wave shape, known as the respiratory sinus arrythmia (RSA) is also associated with the baroreflex where low frequency blood pressure waves appear in the pulse.
The example shown in figure 6 is very important in our understanding of what is happening in the synchronisation research. It shows that we can monitor our feelings and experience of love by measuring our heart rate and watching how it changes with time. In everyday life these heart rate character changes are largely controlled by what is happening to us in our relationships, although we are mostly unaware of these physiological changes. With advances in technology, it is now easy to scientifically monitor these changes in real-time and relate them to our feelings and the degree of bonding we are experiencing in our relationships.
This is Part III of a chapter of the book of Peter Granger: Connected Hearts. Finding love, happiness and spiritual meaning through the wisdom of your heart.
Peter received a First-Class Honours degree in Geophysics from Southampton University in 1981. He then worked for a seismic contractor in Libya and South Africa before joining BP where he was involved in oil and gas exploration. Having enjoyed working as a seismologist, Peter felt a calling to better understand psychology. In 1992 he set up and ran a successful training company that delivered business creativity and innovation courses to a variety of industries. During his training, Peter had noticed distinct physiological changes when he connected deeply with another person.
Peter’s latest book Love Connects, which will be published soon, tells the fascinating story of the heart synchronisation research and describes the incredible power of the heart to heal us and bring us together with the people and things we love.