They have flip-flopped their way around this topic for over 100 years:
WHAT IS THE FUNCTION OF OUR PHYSICAL HEART?
JUST A PUMP - w1888 July p.6
The secret of how the mind operates upon disease undoubtedly lies in the fact that the brain is not only the seat of all thought, but of all feeling.
MORE THAN JUST A PUMP - w71 3/1 p. 134 par. 5 How Is Your Heart?
The brain, in which the mind resides, is one thing and the heart in our thorax, with its power of motivation, is another thing.
NOT JUST A PUMP - w71 3/1 p. 134 par. 6 - 7 How Is Your Heart?
we do not want to make the mistake of viewing the literal heart as merely a fleshly pump as does orthodox physiology today.
The heart is a marvelously designed muscular pump, but, more significantly, our emotional and motivating capacities are built within it. Love, hate, desire (good and bad), preference for one thing over another, ambition, fear—in effect, all that serves to motivate us in relationship to our affections and desires springs from the heart.
The sensations of the heart are recorded on the brain. It is here that the heart brings to bear on the mind its desires and its affections in arriving at conclusions having to do with motivations... The heart is a marvelously designed muscular pump, but, more significantly, our emotional and motivating capacities are built within it.
IT'S YOUR PERSONALITY - w71 3/1 p. 135 par. 10 How Is Your Heart?
One thing is sure, in losing their own hearts [by heart transplant], they have had taken away from them the capacities of "heart" built up in them over the years and which contributed to making them who they were as to personality.
IT HAS EMOTIONS - w75 8/1 p. 480 Questions From Readers
We should keep in mind that the human body is a harmonious whole, with all the members thereof being dependent on one another. Therefore, emotions, feelings, desires and the like cannot entirely be limited to any one specific organ such as the brain, heart or kidneys.
JUST A PUMP - w84 9/1 p. 12 par. 15 "Who Has Come to Know Jehovah's Mind?"
Regardless of whether a person is conscious or not, the heart keeps pumping the blood to the brain and all other parts of the body.
IT HAS THOUGHTS - w84 9/1 p. 19 The "Kidneys" and the "Heart" in the Scriptures
At Hebrews 4:12 it is stated that "the word of God . . . is able to discern thoughts and intentions of the heart." This signifies that "the heart" is the thing that induces and motivates the thoughts and intentions, which are discerned by "the word of God."
RIDICULE THOSE WHO SAID IT WAS MORE THAN JUST A PUMP - w86 6/1 p. 15 par. 2 Determined to Serve Jehovah With a Complete Heart
The ancient Egyptians believed that the physical heart was the seat of intelligence and the emotions. They also thought that it had a will of its own. The Babylonians said that the heart housed the intellect as well as love. The Greek philosopher Aristotle taught that it was the seat of the senses and the domain of the soul. But as time passed and knowledge increased, these views were discarded. Finally the heart became known for what it is, a pump to circulate the blood throughout the body.
IT DOES NOT MOTIVATE - w95 1/15 p. 16 par. 3 Serve Jehovah With Joy of Heart
Though the physical heart is mentioned in the Scriptures, it does not literally think or reason.