Large mammalian brains are composed of cells that are highly susceptible to oxygen deprivation. Consequently, it has long been believed that, once blood flow (and oxygen delivery) has stopped for several minutes, an irreversible chain of events within the brain has been set in motion. These events ultimately lead to complete degradation of the tissue. However, the development of a new brain-fluid pumping system by researchers at the Yale School of Medicine challenges this idea. This experiment suggests that proper restoration of circulation even hours after death can restore several interesting cellular functions and preserve brain architecture, moving one step closer toward complete restoration of neurological function. Even without this complete restoration, preserving or restoring cellular function after death is useful in that it may allow biologists to study the functionality of cells in an environment similar to living organisms without some of the difficulties associated with live animal work. For example, isolated brains are far more accessible to study the effects of drugs once the influence of other organ systems is removed. Also, the ethical considerations associated with live animal work are substantially reduced so long as consciousness is not restored.
The scientists developed a pumping system which mimics normal blood flow patterns of the circulatory system and a pumping fluid that delivers oxygen and mimics the properties of blood but without any cells . This system was connected to the carotid arteries (which provide the brain’s main blood supply) in the brains of pigs. The experimental group of brains were connected to the system four hours after death and pumping was maintained for six hours. Three other groups of brains served as controls: one group was pumped with a control fluid, another was prepared in the same way as the perfused samples but not connected to the pumping system, and the last was not processed in any way, but measurements were still taken at the same 10-hour post-mortem time point. Aspects of tissue preservation and functionality, such as large-scale circulation and the architecture, shape, and functionality of major types of cells, were assessed. The pumping system could not restore global electrical activity, which is associated with consciousness, perception, and large-scale brain functionality. However, it did succeed in reducing the degradation of tissue architecture and the death of cells in important regions of the brain. This preserved the responsiveness of the blood vessels and cells to drugs, and even maintained the ability of neurons to respond to electrical input!
These results do not, by any means, suggest that fully reanimating a dead brain will be accomplished using this system or will be seen in the near future. It may be possible that by changing the chemistry of the pumping fluid, a state even closer to that of a functioning brain may be observed. But the lack of global electrical activity, a hallmark of any living brain state, highlights the pronounced difference between the current capabilities of this system and a functioning brain. Even so, these results do suggest that mammalian brains possess a previously unrealized potential for restoration of activity several hours after death and underscore the importance of considering what a potential restoration of global brain activity could mean for neuroscience, medicine, and life as a whole. Though it is still too early to claim that these results call into question the current distinction between life and death, one cannot help but wonder if similar interventions in the coming years could suggest that death may not be so final after all! In considering such a possibility, it will be essential for neuroscientists, engineers, doctors, and lawmakers to carefully evaluate the ethical implications well in advance.
Managing Correspondent: Andrew T. Sullivan
Press Articles: Scientists restore some functions in a pig’s brain hours after death, Science Daily
Brain Restoration System Explores Hazy Territory between Being Dead or Alive, Scientific American
Original Journal Article: “Restoration of brain circulation and cellular functions hours post-mortem,” Nature
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