Are there any ways to increase dopamine and serotonin levels when working or learning something complex? There is much information regarding learning styles and ways to leverage them, along with boosting focus, alertness and concentration.

However, I'm looking for accompanying information that would be useful in addition to those answers.

Witnessed countless times:
When one is either learning or working with a new concept that is - complex, untangle, counter-intuitive, tedious, multi-dimensional, boring and difficult, it appears mood is altered to a lower state, very similar to that of a depressive state, however is temporary, until another concepts comes along (still new) that is simple, clear and straight forward.

Are there any studies that show correlation to dopamine and serotonin in such a case - and more importantly, are there any studies or know methods that reverse this, causing instead increased dopamine and serotonin during such events?
I'm guessing you don't want to generally increase the level of those chemicals in the brain, just in the reward-motivation area.
In order to do so, you need to be rewarded and motivated, obviously. The learning need to be exciting,  with feedback and reinforcement. Socializing it will help, too.
There is a relatively new topic, called gameificatin, that try to do exactly that. It's the process of making the learning a game, so we can learn better,based on the reward-motivation effects.
In my opinion, there is no "hacking" the brain. Doing so is using drugs, and there is a price tag for that. If you want to use the normal brain pathways, there are no shortcuts.