Q: But does this association (that the head is the place where thought processes happen) have any grounds in actual sensing?
A: Yes, the association (that the head is the place where thought processes happen) has the ground in evolutionary neurophysiology.
Thinking, analyzing, deciding, and other cognitive functions are the most important functions for a human or any other animal to survive in the environment that poses endless varieties of challenges. Thus, it is very crucial for a human/animal to be able to locate where these functions are in its body so that it can give the best protection at the correct place. For this, the organ where these cognitive functions occur – the brain – has evolved complex functional areas (mostly in the temporo-parietal junction and the fronto-parietal cortex) that can create the correct 3-D mental image of its body and environment with the correct relation to the brain itself, that is, with the brain correctly felt to be in the head, not in the hand, the leg, the abdomen, or anywhere else, including outside the body.
You don’t need anybody to tell you that the thoughts occur in your head. Just close your eyes and feel where your thought is. You’ll feel that you’re thinking in your head, again not in the hand, the heart, the body, or anywhere else, including outside your body. That’s the result of the functions of your brain areas that create the 3-D of your body image and your surroundings with the correct relation to the brain.
This is also true in animals. If animals do not evolve to the ability to know that it is in their heads that their thinking occurs, they will not give their heads the first and foremost priority in protection and caring. Their heads (which is the place where they think) will become susceptible to danger, and their species will become extinct from this, leaving only those animals that evolve this crucial ability to persist. Evidently, animals that persist nowadays always try to protect/care their heads above all other body parts. For example, in danger, if they decide to flee, they will turn with their heads furthest away from the danger and they will escape into the protection (cave, tunnel, shield, etc.) with their heads in first. When they hide from the sun or the rain to seek comfort, they always give the priority to their heads to be under the shelter even if other body parts have to stick out in the sun or the rain. So, what that is thinking in the animals knows where it is (i.e., knows that it is in the head) because it protects and takes care of itself correctly.
Moreover, humans and animals must have observed that when their heads are hit hard enough, they cannot think normally or even cannot think at all (i.e., lose consciousness, if the hit is severe). This doesn’t happen if the hand, the chest, the abdomen, or other part else is hit but the head is spared. They must also have witnessed these in other animals. So, in addition to the innate ability to know that the thinking is in their heads, they can learn from these experiences that it is definitely the head that the thinking occurs.
In conclusion, no human or animal needs to be taught that the head is the place where it thinks.
I think the above discussion answers the other questions already too.
Blanke O, Slater M, Serino A. Behavioral, Neural, and Computational Principles of Bodily Self-Consciousness. Neuron. 2015 Oct 7;88(1):145-66. The pdf file can be downloaded from here
Lenggenhager B, Smith ST, Blanke O. Functional and neural mechanisms of embodiment: importance of the vestibular system and the temporal parietal junction. Rev Neurosci. 2006;17(6):643-57. The pdf file can be downloaded from here or here.
Wikipedia. Body Schema