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.
The dog that drops his tail slightly and wags in low is usually the sign of a happy and slightly submissive dog. This is the wag you usually see when returning home to your dog. He is happy to see you and submits to your authority. This is also my one of my favorite wags to see when my dog greets another person.