Question

What are the limitations of Miller's rat study? The information that we were given is lacking and only says the following about the study and the way it worked.

Neal Miller, for one, found that rats could modify their heartbeat if given pleasurable brain stimulation when their heartbeat increased or decreased. Later research revealed that some paralyzed humans could also learn to control their blood pressure. After a decade of study, however, researchers decided the initial claims for biofeedback were overblown and oversold.