The sensitive soul mediates the capacities of both animals and humans to sense the world and their bodies. It is the closest to what we moderns call “conscious experience.” Finally, the rational soul is the sole province of people, mediating reason, language, and speech. Of course, this is now increasingly mimicked by artificial intelligence algorithms.
The modern emphasis on machine learning, genomics, proteomics, and big data provides the illusion of understanding what the vegetative soul is. Yet it obscures the depth of our ignorance about what explains the breakdown of the vegetative soul.
A conceptual challenge remains to define what constitutes anyone’s living body—which is clearly more than the sum of its individual organs. How can one precisely delimit this body in space (are clothing, dental implants, and contact lenses part of the body?) and in time (its beginning and its end)?
Note the word “irreversible” in the contemporary definition of neurological death. In the absence of a precise conceptual formulation of when an organism is alive or dead, the concept of irreversibility depends on the technology du jour, which is constantly evolving.
What at the beginning of the 20th century was irreversible—cessation of breathing—became reversible by the end of the century. Is it too difficult to contemplate that the same may be true for brain death? A recent experiment suggests this idea is not just a wild imagining.
PARTIAL REVIVAL OF DEAD BRAINS
This year a large team of physicians and scientists at the Yale School of Medicine under Nenad Sestan took advantage of hundreds of pigs killed at a Department of Agriculture–approved slaughterhouse for a remarkable experiment, published in the journal Nature.
The researchers removed the brains from their skulls and connected the carotid arteries and veins to a perfusion device that mimics a beating heart. It circulates a kind of artificial blood, a synthetic mixture of compounds that carry oxygen and drugs that protect cells from damage.
The magic resides in the exact molecular constitution of the circulating solution. Think of closed-circuit dialysis machines that thousands of patients use daily to flush out toxins from their bodies because their own kidneys have stopped working.
These machines are needed because when blood stops flowing through the large, energy-demanding brain, oxygen stores are depleted within seconds, and consciousness is lost.
Depriving a brain of oxygen and blood flow for more than a few minutes begins to trigger irreversible damage. Cells start degenerating in all sorts of ways (tissue damage and decomposition, edema, and so on) that are readily visible under a microscope.
The Sestan team studied the brains’ viability four hours after the pigs were electrically stunned, bled out, and decapitated. (If this sounds gruesome, it is what happens to livestock in an abattoir, one reason I’m a vegetarian.)
The researchers compared a variety of biological indicators with those of postmortem control brains from pigs that did not undergo this perfusion procedure four hours after death, an eternity for the sensitive nervous system.
At first glance, the restored brains with the circulating solution appeared relatively normal. As the compound circulated, the fine net of arteries, capillaries, and veins that suffuse brain tissue responded appropriately; the tissue integrity was preserved with a reduction in swelling that leads to cell death; synapses, neurons, and their output wires (axons) looked normal.
Glial cells, the underappreciated entities supporting neurons proper, showed some functionality, and the brain consumed oxygen and glucose, the universal energy currency of the body, an indication of some metabolic functioning.
The title of the researchers’ paper announcing their technology boldly states “Restoration of Brain Circulation and Cellular Functions Hours Post-mortem.”
What was not present in these results were brain waves of the kind familiar from electroencephalographic (EEG) recordings. Electrodes placed onto the surface of the pig brains measured no spontaneous global electrical activity: none of the deep-slow waves that march in lockstep across the cerebral cortex during deep sleep, no abrupt paroxysm of electrical activity followed by silence—what is known as burst suppression.