Death is a process: Rouleau excerpt #3

Rouleau writes: To appreciate the significance and implications of brain death, I will now provide a brief overview of the living brain’s structure and function. The human brain is approximately 1350 cubic centimeters of water, fat, and protein with lesser concentrations of metals and other molecules (Figure 1A). Its outer structure, the cerebrum, resembles a raveled knot of hills and valleys – gyri and sulci – which are connected like a wrinkled but continuous sheet. 

The one-to-four millimeter outer shell of the cerebrum, which is appropriately called the “cortex” or the Latin word for tree bark, is generally considered to be the most important structural correlate of consciousness within the brain. It receives information from sensory organs that define vision, hearing, taste, smell, touch, and other perceptual modalities. The cortex also governs language, voluntary movement, decision-making, reasoning, moral judgements, emotional regulation, and countless other brain functions. Most neural correlates of consciousness (NCCs) are fundamentally cortical including high-frequency (gamma) synchronous activity. 

Further, distinct activations of the cerebral cortices are apparent in near-death experiences (NDEs), out-of-body experiences (OOBEs), and God experiences (GEs), which are frequently cited in survival research. Finally, the clinical criteria for brain death hinge on specific diminishments of cortical activity as inferred by brain imaging. Therefore, the cerebral cortices are undoubtedly areas that we must focus on if we are going to address the survival of consciousness after death.

The cerebral cortices (Figure 1B,C) are composed of 10 to 100 billion cells which includes both neurons – the definitive brain cell – and the supportive glial cells. Originally described as “the butterflies of the soul” by the great neuroscientist Santiago Ramón y Cajal, neurons maintain an electric charge across their membranes like other cells. However, unlike most cells, they are specialized to be highly polar and rapid communicators. The brain is considered an electrochemical organ and neurons reflect this duality by signaling to each other by both electrical and chemical means. 

The quintessential signal of the neuron is the action potential: an all-or-nothing, 1 millisecond discharge of electromagnetic energy that results in the release of chemicals called neurotransmitters that trigger downstream action potentials in turn. Every time a neuron discharges its membrane potential, it briefly reverses its charge from internally negative to positive, crossing an important electrical threshold of 0 millivolts, which indicates the cell and its environment are electrically indistinguishable. Under normal circumstances, neurons readily re-polarize themselves and continue signaling; however, for a very brief but real moment they are electrically neutral: this is a property of dead and dying cells. 

As far as modern neuroscience is concerned, an uncharged neuron is incapable of generating cognition. In other words, every time a neuron is activated, it crosses the electrical equivalent of the life-death boundary and then comes back again. Of course, this state is transient, but it is important to realize that neurons operate on the edge of life and death. Indeed, over 85,000 neurons die and are never replaced as a normal part of brain aging every single day. Unlike most other organs, brains are in a constant state of incremental degeneration, though what connections remain become increasingly efficient and define the individual’s personality and memory. But what happens when brains become irreversibly non-functional?

As was previously discussed, a still heart is no longer the gold standard definition of death in medicine. In recent years, the consensus has moved toward brain death and detailed criteria have been put forward to guide clinical assessment. One technical definition, for example, specifies the amplitude of electroencephalography (EEG) voltage should be below 2 microvolts for over 30 minutes. However, beyond black-and-white definitions of life and death is a more accurate view of what actually occurs when consciousness appears to stop.

Death is usually understood to be a fixed time that can be reported on a medical chart; however, this is clearly not the case. Living and dying are processes, not events, and processes take time. Furthermore, the boundaries of processes are always blurry or undefined. We now know that when the heart stops pumping oxygen-and nutrient-rich blood to the head, the brain remains functionally active for 3 or 4 hours post-mortem. Because the means by which we detect brain activity such as EEG depend on the synchronous activity of thousands of cells working together, there is likely asynchronous neural activity that persists undetected well- beyond that – the random beating wings of a billion dying butterflies.

Organotypic slice cultures, which are pieces of brain tissue from mice and other laboratory animals that are maintained artificially in a dish, can functionally persist for weeks given the right environmental conditions. Death is by no means a moment. Rather, dying, as evidenced by the brain’s normative state of persistent degeneration, is a lifelong process that becomes suddenly accelerated after heart death. 

Indeed, brain death is likely only a meaningful concept when the brain has become physically dissociated following cellular breakdown and is actively decomposing. It should also be noted that the longer a person’s brain is deprived of oxygen, the less likely they are to ever regain consciousness. For example, following cardiopulmonary resuscitation, the likelihood of recovering consciousness after 24 hours, 72 hours, and 5 days is 34%, 25%, and 20% respectively. Brain death is clearly a process, and we can expect its interaction with consciousness, including survival, to track those changes over time.

Nicolas Rouleau, PhD, a neuroscientist and bioengineer, is an assistant professor at Algoma University in Canada. He received an award from the Bigelow Institute for Consciousness Studies "An Immortal Stream of Consciousness" in response to its search for "scientific evidence for the survival of consciousness after permanent bodily death." Footnotes and bibliography are omitted from these excerpts from his essay, but the full essay is available online at https://www.bigelowinstitute.org/index.php/contest-runners-up/.