FALSE ASSUMPTION 1
We equate brain death with death of the human being. Brain death is legally defined as the COMPLETE cessation of ALL functions of the ENTIRE brain. But that is not what clinicians are measuring. Brain death tests measure only a small subset of brain functions. For example, they does not test hormonal balance salt/fluid or temperature control. I too recently highlighted the "gap" between legal standards and medical standards in the Journal of Bioethical Inquiry.
FALSE ASSUMPTION 2
Before the 1990's, cardiopulmonary death quickly followed brain death, confirming the idea that that integrative functions cannot be sustained without the brain. But today, we can sustain brain dead bodies for prolonged periods of time. So, a human being still has integrative functions despite being determined brain dead.