Well if you really think about it, what is passion? How does that passion comes to be a passion.
One of the main topics you might want to touch here is conditioning and thus motivation.
Think about the following:
I have a passion for programming
Why do I have a passion for programming?
Because when I wrote my first program I was positively reinforced by the fact that I completed a program, I was negatively reinforced because I removed my frustration of not completing the program
How come that I have gone through that programming frustration and
stick to it even if I was frustrated?
Because I wanted to learn programming
Why did I wanted to learn programming?
Because I wanted a light on an arduino to turn on (projected reinforcer)
Why did I wanted to turn the arduino light on?
So I could learn programming and because I though it was cool (classical conditioning association that will later be reinforced, projected reinforcement happened right after the classical conditioning association between turn on a led happened)
This can be done through a neural network, where each association is reinforced through a probability of outcome
For example, I did learn arduino, on purpose because it seemed the easiest way to start coding, so the probability of positive outcome was high
This about an opposite situation
Let's say I do not know calculus, and I barely know elementary algebra, if someone started to teach me about integrals saying that this is the only way to start learning more math, I will not be motivate to do so because since I cannot even conceptualize what an integral can be, it will be really hard for me to understand it thus I will not learn calc
Thus we can also discern that motivation is reinforced in small behaviors
Another more practical and realistic example you might use is
If you trow a rat in a cage, and make him lever-press do you think he is going to? No. Although if you reinforce the behavior of going next to the lever slowly and at the end he will lever press and you then reinforce that behavior he will.
Thus, passion is compartmentalized, and that's what you have to do in your NT and make it mathematically
Small hint, it's a progressive function