What would a zombie's brain look like?

Question

In this universe, a type of bacteria has been created by evil people who want to kill everyone else has been infecting people and turning them into zombies. Here's how it works:

An unfortunate person gets infected, then the unfortunate person dies. After the unfortunate person dies the corpse is preserved (The bacteria brutally murders other pathogens that are near/in the body that cause decomposition) and the brain neurons are brought back. When someone dies it takes a while for the neurons to die as well so I think it's possible. :) The brain cells also get mutated so they would be xenotolerant and anaerobic. The infected unfortunate person rises a minute after death to eat other guys. Yay.

In this case what would a zombie's brain look like if (By this I mean: Which parts of the brain will get destroyed/affected, and how would the brain be shaped like in the end if the destroyed parts are broken down as food for the bacteria?):

1. The zombies have absolutely no emotion at all. (For example no more morality, empathy, or remorse. Also no more anger, happiness, excitment, sadness, or fear.) They also don't have a memory function.
2. They don't feel/don't react to pain.
3. They have an insatisable desire to eat the flesh of non-zombie humans. They are also attracted by sound/light sources.
4. They constantly move at a speed of 1.5mph, maybe slower if they are crawling because their legs are bashed in. They try to knock down things that stand in their way but they are too dumb to find a way around. Zombies have enough muscle memory to let them climb staircases.
5. They are dumb and can't communicate or reason.

Anything I did wrong or did not make clear, tell me and I will fix it.

EDIT: I specified that zombies walk because I can't think of why zombies choose to shamble their way to their victims instead of sprinting. Explain this if you could too please

Answer 1

Frame challenge. You don't want to disable emotions.

For the zombies to be effective they need to be able to distinguish friend from foe, which requires emotions. Desire and hunger need emotions to function.

You'll want degraded emotions which make them find the taste of zombies disgusting and constantly hunger for humans, even when full. For that you need lesions. Basically, if you scan the brain there will be lots of black spots that partially disable unwanted brain aspects or alter them.

The amygdala will be damaged

This manages emotions, but it has some important functions to keep them moving.

The insular cortex will be damaged

It manages hunger so you need that, but you don't need empathy or pain. You want hunger to constantly be high so that they keep eating. If you want them to be able to navigate an environment and chase humans and attack them they need enough brain function remaining to want that, and to not want to attack other zombies.

The cerebellum needs to be damaged, but not destroyed.

Presumably there's enough damage to the motor core of the brain that they can't do fine movements, as needed for sprinting. They can do basic movements to seek out prey, but complicated muscle memories fail.

The rest of the brain will have general damage over a lot of it.

Presumably the custom bacteria is eating things to build new things. There's gonna be lots of holes as it eats non critical parts, but no big holes. Many functions are distributed over the brain, so you want to leave a lot of it intact.

Answer 2

I suspect the zombie brain would look like a normal brain.

Even the simple capabilities you describe like walking on two legs, feeding oneself, navigating towards objectives, climbing staircases, etc are all functions that, at least in humans, require higher brain function. Consider that infants aren't able to do these things for several years after being born, and while these zombies don't need the "higher" processes of the brain, any zombiefication that wants to keep those simple abilities intact, would also need to keep the brain intact or replace it's function entirely.

This is also generally why I find "slow/dumb zombies" rather unrealistic as a concept. The human body is an extremely fine-tuned machine that relies on a coordinated symphony of trillions of cells, microorganisms, etc. The idea that corpses, even well-preserved ones, can continue on as "flesh-mechs" for some zombie-infection seems to ignore a lot of the realities that are required in "operating" a living being.

There is, of course, the "magic space zombie" option, where the zombies and their undead status are blatantly (or subtly) simply magic, and there is the "smart zombie" option where the zombies are basically healthy humans that have had specific and targeted neurological damage/partial lobotomies that allow them to still operate as intelligent organisms but lacking in empathy/emotion and having a desire for human flesh.

Answer 3

It does not necessarily need any brain changes. Substances such as MDPV and PCP are known to induce behavior changes that have characteristics of your zombies, so if the bacteria secrete something similar, it might possibly be enough to make the victims act like such zombies.

See eg.

https://www.npr.org/sections/thetwo-way/2012/05/30/153989768/bath-salts-drug-suspected-in-miami-face-eating-attack

Answer 4

Why attribute a zombie disease to bacteria? There is a fungus -- Ophiocordyceps unilateralis -- that has this effect on ants. An infected ant looses all control of its body, is forced out of the hive to climb up the stem of a plant then clamps with its mandibles to a leaf vein with abnormal force to secure itself before dying from the infection.

Posit a related fungus that infects humans, takes control of its body, & forces the victim to attack other humans with the goal of infecting them either thru biting or tearing the skin, either of which would provide an entry point for the fungus' spores to infect the other human. Meanwhile the zombie host is exhaling spores, so it is possible for someone to become infected without having physical contact with the infected human.

The victim would have some low-level brain function left, to support basic functions like breathing, eating, & expelling waste -- as well as locomotion. But these would be on a very low level, which means an infected human would try to eat anything that appeared to be edible, much as a 2-year-old would.

One could then also posit that if an infected human is unable to find other humans after so long -- say 30 to 60 days -- the fungus then proceeds to kill the host & produce a reproductive structure that expels spores in massive volumes.

But to answer the original question, unless one were to examine the host brain under a microscope there would be no difference except for late stages when the fungus decided to kill its host in order to fruit.

PS -- AFAIK, we still do not understand how Ophiocordyceps unilateralis controls its victims in such a sophisticated manner, so my solution is simply replacing one mystery -- the mechanism of a zombie -- with another. But at least this is a known & documented mystery.