What does talking to oneself actually do? Who knows? There may be some science out there on this subject but I have not encountered it. If any readers have info, please let me know.
However, even without firm ground we can still speculate. Talking to ourselves seems to me to be one part of the brain or one neural process sending information to other parts of the brain or neural processes via consciousness as a link in the form of language. Why not just communicate without the conscious link? Presumably that is how most communication in the brain is done, but for some reason it is not always possible. And why does the communication involve language? Again, presumably it usually doesn’t, all the sense information that is made globally accessible through consciousness does not have to pass through a language description. Instead we experience the perceptual model of ourselves in the world.
I notice that a large proportion of the internal talk has to do with action: setting goals, planning action, doing actions, resisting action, preparing not to do a reflex act. It may be that this self talking is a way for the motor system to communicate within itself and with other systems.
One of the simplest instances of internal talk to understand is the stopping of a reflex. If we pick up something very hot, we immediately drop it. This is a spinal reflex that does not use the brain at all. It would seem that I have no choice, but I know that if I decide ahead of time (and it must be ahead of time) that it is more important to not drop the object than it is to avoid a burn, then I can tell myself to be prepared for the heat and steel myself against the reflex to drop a hot object. I say to myself, “OK now, keep your concentration, whatever happens, don’t let it drop!”. So the process that decided priorities for goals/actions and can see the reflex coming has communicated through conscious language with the process that can reach down into the spinal cord and interfere with a spinal reflex. These two processes may have other ways to communicate (or not), but the conscious language route may be the fastest or the easiest. I suspect they can communicate by other means because it is possible to form a habit in these situations (I can drop red objects but not white ones, or the like) and this habit does not need the verbal command to myself each time it is used.
It is thought that although we do not speak aloud and do not actually hear the words, that internal language uses all the normal language processes including the motor and sensory ones. We actually form the action plan to say a word and we actually mimic the auditory input from hearing the word. And the word although not said, affects memory recall and formation, emotional states and cognitive thinking just like a real word would. So an internal command (or question or other type of statement) has the same effect on our brain as an external command. Whether we follow the command/answer the question depends on who/what/why etc. We do not always follow commands like a robot. But the process is probably the same in responding to language whether it is internal or external in origin. If someone shouted at me just before I reached for a hot object, “Don’t drop it!”, I probably would react in the same way as when I tell myself the same message. We are harnessing a very powerful phenomenon in language – as a communication tool IT WORKS. When someone says something to us it forces us to find the meaning and that amounts to finding what those meanings are associated with in our brains. It is like that person has reached into our brains and created a thought out of what they found there matching their thought. We can barely stop the process no matter how hard we try. But we can accept or reject the usefulness of the new thought. When people communicate with us they do not necessarily convince us and the same goes for internal language – it can broadcast the thought but not force any part of the brain to use the thought if it is not actually useful.
It is said that you can’t play games with your mind. I presume that is true in the same way that other’s cannot play games with your mind. If I find that someone is untrustworthy or gaming me for a fool – I simply ignore them. If I try and lie to myself – I simply ignore the message. I get the message but I do not use it. If something happens unexpectedly that is bad and someone says, “don’t let that happen again”. My reaction would be, “and how am I supposed to stop it, smarty-pants?”. And so I would be wise not to give the command to myself but instead ask the question, “how am I going to see this coming next time and stop it?” That is something the brain will work on.
There are very many people who imagine they are divided in two, and they have pictured one (me-part) as the commander and the other (my brain part) as the slave. The commander only needs will and if he holds his mouth right and he can force the brain to do things the way he wants. But the slave brain is not to be trusted and will sabotage the commander. The commander can summon more will and the brain can become more stubborn. They have created an image of a state of battle, a power struggle, like Freud described. If we are used to thinking this way, we have to remind ourselves that we are one person and we are simply using language internally to be more effective – it is not half of us talking to the other half. We have to talk to ourselves in a realistic, honest, effective way if we want to get things done and solve problems using internal speech.
So there is my speculation without very much scientific evidence. I find it useful and I hope you can too.