REGIONAL CEREBRAL BLOOD FLOW (RCBF RCBF): Regional cerebral blood flow monitoring may help boost the validity of the regional localization theory, in which specific parts of the brain control specific functions.. measure of the blood flow in a specific area of the brain, using positron emission tomography (PET scans) and/or single photon emission computed tomography.
If a dog goes on his back to you he is accepting you as his master. This is part of the answer but here's a little more in-depth version as reported by USA Today. In general, dogs lie on their back for three reasons.
Similarly to cats, a dog's tail can express a lot of different emotions, from anxiety to relaxation. Doggie tails are rather sophisticated communicators. If your dog's tail is dangling down in a loose manner, it actually may be in its default position, as long as its not hidden between the back legs. When a dog is feeling calm, cool, relaxed and content, he may keep his tail down next to his hind legs and lower thigh area.