I work with neural networks for complex scene processing and object detection on the roads. Best of part of my job is watching a network "learn/train itself" to classify various object categories.

Are there any good theories on what happens during the training process of the brain (for example, while learning a new skill or something very basic/simple) and how individual neurons get affected by this "learning" process? So, I understand from a psychological perspective, we see the brain as this beautiful system but I am asking from physiological perspective. What kind of changes can we observe in neurons when we learn something new?

P.S: Thanks a lot for your replies. Means a lot. :)