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No, no zombies were created!

I don't get zombies. I mean I understand that they are undead and that they have a weird obsession with human flesh, but I don’t get the science behind their existence. Even to walk like a sleepwalker—that is the zombie walk—for example, you’d need a lot of coordination from your brain. And then there is their sense of sight and perhaps even smell that enables them to detect humans. That would also mean that a significant part of their brain is actually alive. How can they be dead then? And how come they crave human flesh? Do they feel satisfied once they have consumed enough human flesh? How could they tell whether or not someone is faking to be a zombie? Given all these problems I have with zombies, imagine my surprise when I saw a headline that claimed scientists have created zombie pigs because of a recent paper that was published in Nature magazine. The reality is far from the headline, and here, I want to go over that paper to explain why.
Courtesy: Gerd Altmann (Pixabay)
Before getting into the paper, let me briefly describe the chain of events that takes place when blood flow to our brain stops and the brain no longer receives oxygen. Studies have shown that oxygen stores, brain’s gross electrical activity, and consciousness go away within a few seconds. Within a few minutes, the brain’s energy reserve gets depleted. Things then fall apart rapidly: neurons fail to maintain their function and start accumulating and releasing high levels of some chemicals. The cellular environment becomes toxic. Unless something is done fast, these events lead to widespread cell death. Given all that, why did the scientists even attempted to study the possibility that some cells deaths may be prevented?

Vrselja and his colleagues—the team that wrote the paper—gave several reasons. One, under appropriate condition, it is possible to keep neurons alive even when the blood flow stops. It is, for example, possible to cut brain sections and record neurons’ electrical activity from these sections. It’s possible to record because neurons in those sections remain alive and functional (I will get come back to this later on). Second, mitochondria, the cells’ energy generator, remain functional up to 10 hours after death. Third, there have been some cases where people have survived long after having a cardiac arrest caused by hypothermia. Scientists thus reasoned that it might be possible to intervene in some rational way to mitigate the catastrophic events that usually occur when blood flow to the brain stops.

The researchers developed a pumping mechanism that would allow them to establish deep liquid circulation in the brains from pigs that had been dead for 4 hours. Instead of killing a bunch of pigs, they collected the brains from a food processing facility. They also conjured up a solution that they thought would give them the best chance to keep the brains healthy. They called this solution BrainEx or BEx. This hemoglobin-based (a blood protein that carries oxygen) fluid contained anti-coagulative, cell-protective chemicals.

Prudently, the researchers decided to limit the length of their experiments to 10 hours after death because they ran into circulation problems past that period. After ten hours, the blood vessels started to clog as brain structures started deteriorating. So all the results I go over here are all valid up to that period.

I have mentioned the pumping system before, but how do we know if the pumped fluid could reach the blood vessels? The researchers illustrate this in several ways. Ultrasound test and anatomical inspection revealed that BEx could flow through the blood vessels. They also detected the hemoglobin signal to show that their setup was working. Before going further, I want to explain how this was done to go over the experimental setup.

The scientists measured hemoglobin levels/signal intensity from various groups. They found that the hemoglobin intensity was similar between untouched pig brains and BEx-pumped pig brains. In other words, the leftover hemoglobin level in the blood vessels was similar to BEx-pumped brains. But couldn’t that signal come from residual hemoglobin in the BEx-pumped brains as well? To eliminate that possibility, they checked the hemoglobin levels in two other groups. In one group, they pumped control fluid—this mixture lacked hemoglobin among other things compared to BEx—into a group of pig brains and could detect only very weak hemoglobin signal. This showed that pumped fluid could flush out hemoglobin from the brain, and the strong hemoglobin signal detected in the BEx-pumped brain had to come from BEx. Similarly, when they flushed out the blood in another set of brains and looked at hemoglobin level after an hour (five hours since death), they saw weak hemoglobin signals.

To show that the gross morphology of the brain was okay, the scientists used MRI on the brains. The BEx-pumped brain structures looked intact under MRI. The structural integrity looked rather similar to five-hour post-death, flushed brains (the last group from the previous paragraph). The gross anatomical features, however, were abnormal in the untouched brains or the brains that had received the control fluid.

The scientists also cut sections from different parts of the brains and analyzed them carefully via various imaging techniques. The results were similar to what they saw before: the continuous flow of BEx kept neurons as well as non-neuronal cells in the brain alive and healthy. Moreover, connection sites between neurons—called synapses—appeared normal in BEx-pumped brains.

Since the integrity of the synapses is essential for neuronal communication, the researchers proceeded to see if the neurons still retained their electrical properties. To achieve this, they cut the thin slices from the brains and recorded neuronal electrical activity. The results they got were similar to what has been shown in neurons from similar slice preparations. As I mentioned earlier, it is possible to keep the neurons alive under appropriate conditions to record from them. Those slice preparations are done right after the death, but here, the researchers could get viable slices 10 hours after death.

But do any of these experiments suggest that the scientists actually revived the pig brains? No! They didn’t see any global brain electrical activity. They also didn’t detect spontaneous electric waves that appear in healthy, functioning brains. In other words, no zombie pigs. This is a quote from the paper:

“The observed restoration of molecular and cellular processes….should not be extrapolated to signify resurgence of normal brain function. Quite the opposite: at no point did we observe the kind of organized global electrical activity associated with awareness, perception, or other higher-order brain functions.”

In zombie movies, we often see protagonists killing off the zombies as if they are killing flies. This paper does present us with some moral difficulties if we find ourselves in a zombie apocalypse. Since a significant part of a zombie's brain has to work, can we say they are dead? If not, shouldn’t we be more empathetic towards them? Since my knowledge in zombiology is rather limited, I will let the experts argue over those questions, and focus on the paper instead.

It’s possible that a refined version of the technique described in the paper could be helpful in treating brain-damaged patients. But we also have to keep in mind the danger of such procedure: activating and maintaining awareness could cause excruciating pain in both animal subjects and humans. For now, though, we are far away from making the dead alive.

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