Are here any nonspecific theories in relation to brain chemistry?
There are many theories going on for brain chemistry. I would start by learning just about the different types of neurotransmitters (GABA, Serotonin, Norepinephrine, dopamine, etc). By learning their functions on a molecular stratum, it forms a foundation for learning the physiology.
You might relish reading Eric Kandell's biography, In Search of Memory. Kandell won the Nobel Prize in Medicine for his work on memory. His bio is also a simple review course surrounded by neuro anatomy, neuro chemistry and neuro physiology.
Sure. There are many books written on the subject. If you are not a college chemistry graduate, do not look for them. You will not be capable of read even one page !