Most physiological processes are either voluntary (finger movement, leg movement, etc.) or autonomic (heartbeat, digestion, blood circulation, etc.)
Only two are quasi-autonomic: breathing and thinking. We can control these processes but only to a point - they will become autonomic when we take our attention away from them.
The unique similarity between these two processes is the reason disciplines around Yoga and Meditation place such emphasis on breathing - because consciousness around breathing can lead to consciousness around thinking. The two are related.
The 'chatter' in your head is not YOU - it is the voice of ego.
You are the 'focus' that can direct the chatter and you are the spaces between the thoughts. It is in the moments when we still the chatter that we are most ourselves.
-"Be still and know that I am God."(Psalm 46:10)