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.
It would be nice to attempt to make the puppy enjoy the grooming rather than having it be a constant unpleasant experience for both dog and owner. Have more than one person practice laying each puppy on its back, and teach the pup to be trusting of people to willingly lie on his/her back.