I have never actually clearly understood how we can 'talk in our head' (I don't know how else to put it)?
Do I have an article for you

(
http://www.ncbi.nlm.nih.gov/pubmed/21498087). I'll draw your attention to the last line of the abstract:
Subjective event times should therefore be interpreted as the result of complex interactions between introspection and experience networks, rather than as direct reproduction of the individual's conscious state or as a mere post hoc interpretation.
Essentially, 'talking in our own head' is just regular thought patterns, but introspective ones rather than outwards-looking thought. I'll try to give a bit of an example:
Think about what your mind is doing when you are solving a maths problem: You have a problem (let's say that this maths problem is on the 'outside', i.e. it is not in our head, or of our own creation and therefore we do not have the predetermined answer) and you use conscious thought - albeit varying levels of conscious thought, because some of the thought processes are rote if you're proficient at the task at hand - to attack, quantify/qualify and resolve this problem.
Now take this same pattern of thoughts, and think about what happens when we turn them inwards and use these critical procedures to evaluate both our own experiences and our projections for coming events. This results in a form of critical analysis of these past, present and future events, manifesting itself as a form of internal mono/dialogue.
Hope this kinda makes sense lol