Editors' Note: Challenges to Brain Death in Revising the Uniform Determination of Death Act: The UDDA Revision Series.

Despite decades of striving to simplify the diagnosis of human death according to irreversible cessation of function of a single organ system-the brain-we are relentlessly plagued by disagreement between experts spanning disciplines from medicine to philosophy. Dr. Bernat summarizes the current state of this controversy in their narrative summary, recently published in Neurology . In this review, the first of a planned series on the Uniform Determination of Death Act (UDDA) and brain death determination in Neurology , Dr. Bernat appraises the current criteria for determining brain death and highlights the need for careful revision to the UDDA. Is death determined by irreversible loss of function of the brain-as-a-whole or loss of function of the whole brain? And how does one define irreversible brain dysfunction? With the upcoming revisions to this statute by the US Uniform Law Commission (ULC), we hope to find more answers than new questions, although both are likely to be a consequence of this update. In response to the article, Dr. Machado proposes death be defined by irreversible failure of the 2 elements of consciousness-arousal and awareness. Furthermore, Dr. Machado challenges the notion of biological death and emphasizes the value of specific testing depending on the region of brain injury, with ancillary (neurophysiologic) testing in patients with posterior fossa lesions. Dr. Bernat comments that the objective of the ULC is not to disentangle the controversy of defining death, which may be subjective -e.g., influenced by personal beliefs, religious background, and interpretation of diagnostic testing-but instead to provide objective criteria for determining death. The revised UDDA may provide clarity in medical decision-making; however, it may not reconcile our division over ontology.