The WTS used secular sources of the time that said that person who received a heart transplant, literally took on the characteristics of the heart donor. This was during the time when the WTS said organ transplants were not for jws. (This changed in 1980 though) When the medical community backed off from the idea of "personality transplants," so did the WTS but tried to disavow their initial position.
The WTS likes to re-invent their position on their pre-1980 viewpoint, in the following Question From Readers. But note this statement at the end. Why would the elders have to be told that in 1980 they should not disfellowship a jw who has an organ transplant, unless it had been a disfellowshipping offense prior to that?
https://wol.jw.org/en/wol/d/r1/lp-e/1980212#h=1:0-5:779
The congregation judicial committee would not take disciplinary action if someone accepted an organ transplant.
Here is the secular source of the WTS viewpoint that those having an organ transplant, heart, took on the personality of the donor.
https://wol.jw.org/en/wol/d/r1/lp-e/1975642?q=transplant+personality&p=par
Transplant Problems
● It has long been known that heart-transplant patients have a higher-than-average amount of postoperative psychiatric problems. But it seems that the same is true with regard to some other vital organ transplants, such as kidney transplants. U.C.L.A. psychiatry professor Dr. Pietro Castelnuovo-Tedesco is quoted as saying: “An outstanding finding following transplantation is the not infrequent occurrence of serious emotional disturbance.” One study of 292 kidney-transplant patients showed that nearly 20 percent experienced severe depression after the operation, a few even attempting suicide. By contrast, only about one out of every 1,500 general-surgery patients develops a severe emotional disturbance.
A peculiar factor sometimes noted is a so-called ‘personality transplant.’ That is, the recipient in some cases has seemed to adopt certain personality factors of the person from whom the organ came. One young promiscuous woman who received a kidney from her older, conservative, well-behaved sister, at first seemed very upset. Then she began imitating her sister in much of her conduct. Another patient claimed to receive a changed outlook on life after his kidney transplant. Following a transplant, one mild-tempered man became aggressive like the donor. The problem may be largely or wholly mental. But it is of interest, at least, that the Bible links the kidneys closely with human emotions.—Compare Jeremiah 17:10 and Revelation 2:23.
In the WTS Index under Beliefs Clarified , they point to this change:
https://wol.jw.org/en/wol/d/r1/lp-e/1200001948#h=5:0-11:176
All such functions, capabilities, emotions, and qualities are ascribed, not to the literal heart organ, but to the figurative heart as representing the total inner personality.
Also, here is another turn around:
https://wol.jw.org/en/wol/d/r1/lp-e/1984641#h=1:0-19:498
What an amazing number of different functions and capabilities are ascribed to the heart! Do all of these reside in the literal heart? That could hardly be so. This is indicated by those languages that make a clear distinction between a fleshly heart and a figurative heart....(but then they try to explain why they were not really wrong in the first place) Thus a clear distinction is made between the physical organ and the person’s motivations and emotional qualities, though a relationship between the two is maintained.
(When the WTS came out with the literal heart idea, my jw family thought is was totally wrong, but did not advertise it to other jws. When the "clarification" came out, they felt vindicated. In hindsight, we should have seen it as a good reason to leave.)