The idea that the heart contains the very 'essence' of a person might be more than just a spiritual concept. Ever since the first human heart transplants back in 1967, patients have reported, often reluctantly, some eerie and inexplicable changes to their personalities.
Following surgery, some say they feel less like themselves and more like their donor. For instance, one transplant recipient in the 1990s reported suddenly developing a love for music after receiving the heart of a young male musician.
"I could never play before, but after my transplant, I began to love music. I felt it in my heart," she told scientists in a paper published in 2000.
Other transplant recipients say they developed new tastes for food, art, sex, or careers following their surgeries. Some even claim to have new "memories" implanted.
Take the anonymous case of a 56-year-old college professor, who received the heart of a police officer killed by a gunshot to the face. A few weeks after the transplant, the recipient said they had dreams of "a flash of light right in my face… Just before that time, I would get a glimpse of Jesus."
"That's exactly how Carl died," the donor's wife told researchers. She said the main suspect looks "sort of like some of the pictures of Jesus."
Such controversial anecdotes verge on the unbelievable, but a new study from the University of Colorado (CU) suggests it's not just heart transplants that appear to trigger such fundamental changes to personhood.
If these symptoms can be directly linked to organ transplants, perhaps that means our 'sense of self' is contained in every cell of our bodies, not just one or two organs.
An online survey among 23 heart recipients and 24 other organ recipients found nearly 90 percent experienced personality changes after transplant surgery, no matter the organ they received.
Most patients in the study said they experienced four or more personality changes, and most of these changes had to do with temperament, emotions, food, identity, religious/spiritual beliefs, or memories.
While the study is too small to be statistically significant, medical researcher Brian Carter and his colleagues at CU conclude that "heart transplant recipients may not be unique in their experience of personality changes following transplantation."
Instead, they argue, "such changes may occur following the transplantation of any organ", and that demands further research.
The study from CU is one of the first to quantify the personality changes that occur after a wide variety of organ transplants. Previous studies have tended to focus on heart transplants, as these anecdotes are thought to be the most extreme and long-lasting.
In the case of liver or kidney transplants, patients in previous studies tend to report changing feelings of stress, anxiety, depression, or other mental health issues.
Some researchers have explained these differences by arguing there is a "little brain in the heart". These potential explanations, however, do not consider transplanted organs other than the heart.
In those cases, perhaps immunosuppressive drugs are to blame for personality changes. Or maybe a person's 'memories' are stored widely throughout the body, not just in a few crucial organs.
The "systemic memory hypothesis" predicts that all living cells possess "memory", and that a transplant recipient can sense a donor's history through their tissue.
Although a transplant organ's nerve connections are severed, nerves may still function within the organ. Some evidence suggests nerve connections may be partially restored a year after transplant surgery. Neurotransmitter interactions based on donor memories might then cause a physiological response to the recipient's nervous system that impacts their personality.
Scientists have found the cells of donors circulating in recipients as many as two years after a transplant. Where those cells go and what happens to their DNA is unclear. The DNA, once escaped from cells, does appear to trigger inflammation, and chronic, low-grade inflammation has been shown to alter personality traits.
If personality changes are really as common and widespread as the small study from CU suggests, then further research is desperately needed. In 2022, there were more than 150,000 organ transplants conducted worldwide.
The study was published in Transplantology.