I have received some unusual phone calls in my nearly 40-year career as a psychiatrist, but Mary's* call was unique.
"Dr. Liester," she began, "I don't need to see you as a patient. I just want you to tell me if I'm crazy. You see, I'm having memories of things that have never happened to me."
That piqued my interest, so we agreed to meet for an appointment.
Mary was a pleasant, intelligent woman in her mid-40s who exhibited no signs of psychosis. In fact, she seemed quite rational and easy to engage in conversation. She began explaining why she had called: for the last year, Mary had been experiencing recurrent, intrusive memories of being hit by a car. In these "memories," she was a pedestrian and she not only saw herself being struck by the car, but she felt the impact as the car struck her torso, sending her airborne. The problem was, Mary had never been hit by a car. When asked about any trauma, Mary recounted she had undergone heart transplant surgery just prior to the onset of these new memories. Her transplant surgery had gone well, but she was left wondering, "Could my new heart have anything to do with these new memories?"
Mary then divulged that she had recently learned the identity of her donor's family. They lived in Seattle, and she was planning to visit them in the next week. We ended the appointment with me reassuring Mary that she was not crazy and asking her if she would meet once more after she returned from her trip. She agreed.
When Mary returned, she described what she had learned on her trip. Her donor was a pre-adolescent boy who was playing tag with friends when he ran between two houses, then into an alley where he did not see an approaching car. He was struck by the car in the torso in the same location where Mary had been experiencing the sensation of having been hit. The boy was declared brain dead, but his heart was not damaged, so his parents donated his heart. Mary's reaction to learning this information was a sense of relief and closure. She now knew she was not "crazy." But, I was left wondering, do organ transplants cause personality changes?
Relevant Research
One of the earliest patient accounts describing personality changes following organ transplantation is found in Claire Sylvia's book, A Change of Heart, published in 1997, and it wasn't until the 1990s that researchers began investigating this phenomenon.
In one in this area, neuropsychologist Paul Pearsall, PhD, investigated changes in the personality of 10 heart transplant recipients to see if they paralleled the personality of their donors. In each case he interviewed the heart transplant recipient, a member of their donor's family, and a member of the recipient's family. He found two to five similarities in each case between changes in the recipient's personality post-transplant and the donor's personality. These included changes in preference for food, music, art, sex, recreation, and career.
He also found specific instances in which the recipients were able to identify the names of their donors or had sensory experiences related to their donors. In , detailed in his 1998 book, The Heart's Code, Pearsall reported that recipients of kidney, liver, and other organs also described changes post-transplant including their sense of smell, food preferences, and emotions, but these changes were usually transitory and not as robust as the changes found in heart transplant recipients.
More recently, we on this topic at the University of Colorado School of Medicine, and found 89% of organ recipients (of any organ) reported changes in their personality following their transplant surgery.
These findings raise the question, what causes these personality changes? Numerous hypotheses have been proposed, including the effects of immunosuppressive drugs, the trauma of undergoing transplant surgery, and surreptitious acquisition of information about the donor from outside sources. Pearsall suggested another possibility: he hypothesized cellular memory might be responsible.
Where Are Memories Stored?
In 1894, Spanish neuroscientist Santiago Ramón y Cajal memories are stored in the brain. He believed this storage occurs by restructuring synapses, the connections between neurons. More than half a century later, by neurosurgeon Wilder Penfield, MD, found evidence to . The theory that memories are stored in the synapses of the brain persists to this day.
But memories stored in the brain would not likely account for the personality changes observed following organ transplants. Could a different type of memory explain these changes?
Several types of non-neurologic cellular memory exist. For example, the immune system remembers exposure to infectious pathogens and responds quicker if re-exposure occurs. This is known as immunological memory.
Another form of cellular memory involves DNA. The DNA in our cells is capable of storing . Almost all cells of the body are known to secrete DNA-containing packages known as exosomes that circulate throughout the body and deliver their contents to other cells where they are then incorporated into the recipient cell's DNA. Is it possible that donor organs secrete exosomes that deliver DNA to the organ recipient's cells, thus transferring DNA-encoded memory about the donor?
Epigenetic memory is another type of cellular memory. Epigenetics is the study of factors that turn genes on or off without altering the DNA sequence. Numerous types of epigenetic changes occur in human cells, and these changes create an epigenetic code that is stored and retrieved over time.
The totality of an individual's epigenetic changes at any point in time is referred to as the epigenome. The epigenome, which can be viewed as a record of the interactions between an individual and the environment, persists as a form of cellular memory known as epigenetic memory. Just as DNA memory can be transferred between cells via exosomes, epigenetic changes associated with DNA can also be exchanged between cells, suggesting a possible means of transferring information between organ donor and recipient cells.
RNA memory could also be at play. Researchers at UCLA used the sea slug Aplysia to demonstrate the between individuals. These animals were exposed to repeated electrical shocks to their tails, which established a memory of the shock. RNA was then removed from the trained animals and injected into naïve animals, who responded as if they had been trained to respond to the electrical shock. This demonstrated that memory can be transferred via RNA, raising the possibility that organ donors' memories might be transferred to recipients via RNA-containing exosomes.
Another potential method for transferring memory involves proteins. Over two decades ago, Sandra Peña de Ortiz and Yuri Arshavsky that novel proteins could encode long-term memories. Exosomes are known to transfer proteins between cells, suggesting memories stored in such proteins could be exchanged between a donated organ and a recipient.
Ramifications
For now, the jury is out on these theories, and much more research is needed. But if memories and personality traits can be exchanged via organ transplantation, this suggests multiple potential consequences of organ transplant surgery. Not only could the transfer of an organ affect the recipient's identity and personality, but relationships and surgical outcomes might be influenced as well. For example, my patient Mary wanted to stop taking her immunosuppressive medications because she believed she had "integrated" her new heart and therefore would not reject it if she stopped taking her medicines. Such a decision could have dire consequences, including rejection of the donated organ and death.
Future Directions
Further studies exploring personality changes following organ transplants may teach us not only about the types of personality changes that can occur, but also increase our understand of different aspects of personality and various processes involved in the storage and retrieval of memories. Although anecdotes do not prove personality changes occur as a result of organ transplantation, they do suggest the possibility of such changes, and provide a starting point for further explorations into this fascinating area of medical science.
*Patient name has been changed
Mitch Liester, MD, is an assistant clinical professor in the Department of Psychiatry at the University of Colorado School of Medicine.