The nub... Never heard of it? Not surprising. It's only found in one book, but the accounts are arresting!

Jedi Academy Trilogy Volume 1: Jedi Search by Kevin J. Anderson pp. 37-39. Paperback edition.

The first account begins with a practice session in which Luke is trying to train Leia, but with little success. After she fails to levitate a sculpture, Luke decides that as a politician, it's vital for her to have good mental shielding. In an exercise designed to test and strengthen her internal defenses, something unexpected occurs:

"Luke reached to the back of her mind, an area of deep primal memories but little conscious thought. He doubted he could get any defensive reaction there, but no attacker would be likely to strike at such places. Her thoughts were like a map laid out in front of him, and Luke touched inward to an isolated nub in her mind. He pushed-
"And suddenly felt as if a giant invisible palm had planted itself on his chest and shoved backward. Luke stumbled to keep his balance, taking two steps away from her. Leia's eyes went wide, and her mouth dropped open in surprise.
"Luke said, 'What did you do?' in the same moment Leia said, 'What did I do?'; then both answered, 'I don't know!' simultaneously.
"Luke tried to reconstruct what he had done. 'Let me try that again. Just relax.'
"She seemed anything but relaxed as he probed her mind, reaching to the back of her mind, finding the isolated nub among her instinctive centers. Touching it, he found himself knocked away again with physical force.
"'But I didn't do anything!' Leia insisted.
"Luke allowed himself to smile. 'Your reflexes did, Leia. When a medical droid taps your knee, your leg jerks whether you want it to or not. We may have just stumbled upon something a potential Jedi has that others don't. I want you to try it on me. Here, close your eyes and I'll give you and image of what I did to you.'"

~ conversation removed for sake of brevity ~

"Leia touched her brother's temples, and he took a deep breath, using Jedi relaxation techniques to drop his guard. He had erected so much mental armor in the past seven years that he hoped he could still let her inside. He felt the touch of her thoughts, delicate mental fingers tracing the contours of his brain. He directed her search toward the back, where primitive thought slept. 'Can you-'
"Before he could finish his question, Leia stumbled backward into the self-conforming seat. 'Wow! I found the nub, but when I touched it, you knocked me off my feet.'
"Luke felt wonder tingle through him. 'And it was completely unconscious on my part. I wasn't aware of doing anything.'
"Luke touched his lips as new thoughts raced through his mind. 'I need to try this on other people. If it's completely a reflex reaction, this could be a very useful test for finding people who have latent Jedi powers.'"

Needless to say, Luke does test other people. On pp 43-44, Luke tests Wedge, but without a positive reaction. On page 112, he touches the mind of Gantoris, on page 175 he tests Streen, and then lastly, he tests Kyp on page 351, all of course, with a positive result or reaction. (Note that the last three all went on to train as Jedi, but with various levels of success.)

Now, admittedly, that's not a whole lot of information to go on, but there was still less to consider on the part of the midichlorians. So, certainly there's quite a bit that can be drawn from the little information to be found.

Although most of us would think initially that the nub is simply a location in the human brain, it is unlikely that this refers only to the physical brain. Indeed, if the midichlorians are the connection between the physical and the non- or meta-physical, then how could the nub, which evidently controls a Force reflex, be purely physical? No, this must include the mind too.

What's the difference between the mind and the brain? Quite a bit. The mind is the compilation of all thoughts and mental processes. The brain is the location where these things occur. Interestingly, each one can be "damaged" with little effect on the other (rare but true.) An example is that depending on the location of a stroke, the victim may have little personality change at all. In contrast, there are some conditions that affect the mentality of a person-post traumatic stress disorder (PTSD)-so that while the person may be "shattered," the brain is fully functional. So, while the brain may provide the landmark of the nub, the nub itself is much, much more. It is a part of the mind. For me, that was one of the hardest things to get my mind around (no pun intended), so I hope that you, my readers, don't have too much trouble!

Besides which, the technical description of the location of the nub in the "mind" is inaccurate enough, that it doesn't seem to describe the brain very well at all. For instance, there is a reference to "the back of her mind, an area of deep primal memories but little conscious thought." While much of the cognitive mental function takes place in front of the brain (the area under the forehead), the physical "back" or rear of the brain is almost exclusively dedicated to the optical functions, which are highly developed in humans, and not "primitive" at all!

Also the passage states: "Her thoughts were like a map laid out in front of him." Although the cerebral cortex is the top layer of the brain, "thoughts" cannot be read physically in that manner. Areas that are active can be sensed with accuracy-that was how the motor cortex and various "areas" were mapped in the brain-but actual thoughts cannot be. Especially in consideration of how differently male and female brains work! Each is wondrous in its own way, but very, very different. Perhaps Jedi are different and can read the mind as if it was but a map, but from a scientific standpoint it becomes increasingly unlikely that the nub and the mind itself are purely physical. That assumption gains merit, especially in one very special case. But that's getting ahead of myself.

Next, how do the midichlorians and the nub come together to affect Force potential and sensitivity?