The least accessible area of my tongues in terms of awareness is the back of the left tongue.
back of tongue
sagittal view of tongue
It has been the feeling in most of my life that my tongue is that little piece that I move around on top. My perception now is that is just the tip of the proverbial iceberg. I think somewhere back in my past I developed patterns of use that favored the right tongue especially in the mechanics of speech. That huge mass of muscle that is the left tongue only developed a certain amount of control in the mechanics of swallowing and breathing. When I try to have the back of my left tongue come forward and the back of my right tongue go backward it is difficult. There is a tremendous asymmetry in the use of my tongues favoring the right. That asymmetry feels to extend to how I use the whole left and right side of my head.