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Suppose advancement in medicine and using cutting edge technology we could remove (halve) the amount of neurons in a healthy brain and allow the left over neurons to somehow grows extra dendrites that gradually forms up a dense networks within the brain.

I always have the impression that more dendrites are better than more neurons since their connections lead to intuition and creativity, am I mistaken because I read that people can still get through their lives with half a brain but just unable to control their temperament?

I believe each neuron can take over some essential functions due to plasticity and since there is more space now for cooling so I wonder who would such a brain fair in the modern society?

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    $\begingroup$ This doesn't seem to be about worldbuilding. It's more of a biology question. $\endgroup$ – TylerH May 21 '20 at 13:25
  • $\begingroup$ It is a worthwhile question about hypothetical creatures in a worldbuilding scenario, and their 'properties'. It would result in beings that are very wise about a limited number of topics. Quite useful in some scenarios. $\endgroup$ – Justin Thyme the Second May 21 '20 at 13:59
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    $\begingroup$ The function 'Intelligence = FUNC(neurons, dendrites, astrocytes, ...) is not even close to being understood. As such, you can't write anything that's scientifically valid here. You might as well go back to the standard SciFi trope of people with gigantic heads containing brains 5 times current size. $\endgroup$ – Carl Witthoft May 21 '20 at 14:24
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    $\begingroup$ @Carl Witthoft: Or at the other end, consider that some birds - parrots, crows, &c - seem to be quite intelligent despite having really small brains. The problem with answers to this question is that the only one yet supported by evidence is "Nobody really knows." $\endgroup$ – jamesqf May 21 '20 at 17:50
  • $\begingroup$ You will need to define an expected lifespan. Because, well, most or all of that great plasticity that our brain has is necessary as brain cells die. Stem cells can arguably replace some (though there's not nearly enough of them!), but all in all dead neurons are just that, dead neurons. Differentiated neurons are unable to do mitosis lacking spindula apparatus (and having a very odd shape with dendrites and all), so that's pretty much a one-way road. Worded very mundanely, if you have only half as many cells, then you had better not live longer than half as long, either. $\endgroup$ – Damon May 21 '20 at 18:17
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As you remembered, the human brain also has a lot of plasticity, your question remember me the case of a French man who has only 10% of the brain mass and, as far as I know, quite defies the understanding of how neurons work.

As for the dendrites, well ...

Dendrites of elephant neurons are similar to what you describe. Although these fantastic animals have traits of culture, knowledge transmission, the ability to use tools, complex languages and society, they still have not reached the same level as humans (Maybe with a little more time and more caloric fruits). And we are talking about an animal that already has a number of neurons in the cortex quite formidable.

There is also some research on how much information a neuron is capable of containing, or whether the information is a product of the network formed between them. These are similar searches 1 2, but I haven't found the paper that specifically talks about it.

A basic problem in this thesis is whether it would really be possible to force human neurons to assume a different architecture, with more dendrites.

A good example of how even with all the plasticity that the human brain has the thing does not work properly is the brain of those suffering from Alzheimer's, where neurons lose functions and even die without having functions reassigned to other neurons.

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    $\begingroup$ “I am the very model of a cortex quite formidable, in matters of the mind I have a form most inimitable, Though pachyderms and Frenchmen may think thoughts nonquantifiable my brain’s neurons and dendrites form connections most reliable“ - To the tune of ‘Modern Major General’ by Gilbert and Sullivan. $\endgroup$ – Joe Bloggs May 21 '20 at 6:06
  • $\begingroup$ How does the guy with 10% brain mass see, moves, hears or has any sense at all? $\endgroup$ – user75689 May 21 '20 at 9:41
  • $\begingroup$ @JoeBloggs That's probably the best thing I'll see today. Have a couple badges (voted up two deserving answers that already had a score of 9). $\endgroup$ – Joel Coehoorn May 21 '20 at 15:37
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    $\begingroup$ That article is a bit misleading. He's not missing 90% of his brain mass, the fluid build up has compressed his brain, but it's mostly still there. Discussion here: theness.com/neurologicablog/index.php/… $\endgroup$ – Harabeck May 21 '20 at 16:13
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I am afraid this cannot be answered in a black and white fashion. It strongly depends on where the discarded 50% of neurons was located, and when the cut happened.

The number of neurons alone doesn't account for an animal intellectual performance, else the sperm whale, having the largest brain in mass, would outsmart humans.

It is also true that some brain damages can be overcome with limited loss of functionality but only when they affect certain areas. That's what lobotomy did in the past: a damage to a specific area of the brain let the human survive with loss of certain functionalities. Even the example you give, it's not "half of the brain" which is damaged, but just a portion of the frontal lobe, if I remember correctly.

And plasticity depends on age: a young brain is surely more plastic than an old one.

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To paraphrase a great American President, "It's the synapses, stupid!".

Okay, so maybe he really, really wanted to get Americans to vote for him, and so he was being a bit dramatic, but the principle is the same. Sometimes, people just get hung up looking at the wrong thing, and need to be redirected.

First, a simplistic primer. A nerve (brain) cell has one neuron (output) but many dendrites (inputs). The cell 'fires' a signal down it's neuron, and where that neuron crosses a dendrite from another cell, a new connection, or synapse, is formed. This synapse transfers the signal from one cell to another, neuron to dendrite. The more interconnections between cells, the greater is the brain's 'understanding' of the world.These synapses can be excitatory (cause the cell to fire) or inhibitory (prevent the cell from firing).

Brain learning is primarily a result of new synapses forming from experience, and brain processing is a function of the number of synapses. For instance, there maybe a 'mother's face' cell, but it is just a cell until the cell dendrites connect with the visual neurons and get trained to recognize that particular face. The more synapses, the more this cell connects to other cells, and the greater the accuracy of recognition. It's like recognizing a face from a 100 pixel photo and from a 16 megapixel photo.The more the child sees its mother, the more synapses that form, and the greater the accuracy of recognition. One 'mother's face' cell, one 'mother's face' neuron, but thousands of synapses, results in greater resolution.

So the more dendrites that flow into a cell, the more interconnections (synapses) with other cells that can be made, the more accurate the perception. Instead of just connecting to the visual system, for example, the 'mother's face' cell can get inputs from the tactile, olfactory, hearing, and motion sensory systems. But the more neurons the brain has, then the more cells these sensory dendrites can connect with, and the more 'nodes of recognition'- that is, mother's face, father's face, brother's face, uncle's face.

The TL:DR, in very over-simplified terms, is that the fewer the neurons (cells) the less you can know, but the greater the dendrites, the better and more accurately you can know it. But without thousands of synapses forming from experience between all of the dendrites and neurons, you know nothing. Like a baby fresh from the womb.

But here is a fun fact. The more we learn, and the older we get, the more cells and neurons we lose, but the more synapses that are formed between what we have left. It seems that fewer neurons but a plethora of connections between them enhances our intelligence. Just like in a digital camera, more pixels per picture produces greater resolution but reduces the total number of pictures you can store on the memory card.

And perhaps that is the final answer - more dendrites, fewer neurons means greater resolution, but less 'breadth'. But in the balance, it is all about the number of synapses. In a paradoxical way, the less we can know but the more detail we can know about it.

See, for instance, https://human-memory.net/brain-neurons-synapses/ and https://en.wikipedia.org/wiki/Grandmother_cell

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