Just curious. How tiny can an adult human brain and still provide a median or normal level of intellectual ability?
This isn’t necessarily “small” but it’s worth mentioning:
Not sure it’s quite what it’s made out to be. Wiki is at least a little more doubtful.
What I’m confused about is why don’t they just go scan the guy’s head again. Unless he died in an unfortunate accident, he should be in his fifties.
I once had the opportunity to (briefly) discuss this case with a couple of the neuroscientists at Caltech. They knew about the case, and did not seem to disbelieve the basic claims, but their attitude was to shrug it off as unimportant. As I understood from what they told me, that it is not that the guy did not have a cerebral cortex at all, just that it had been compressed to a very thin layer lining the inside of his skull, with the fluid filled ventricles (that everybody has at the center of their brains) much larger than normal.
It is as well to realize that even normal human brains can differ quite widely in their gross anatomy from one person to another without these variations seeming to bear much relation to any differences in the people’s mental functioning. For instance, the size of V1, the primary visual cortex can vary by a factor of about 2.5 between normal individuals, and as far as we know this this variation has no significant (certainly no very obvious) impact on their visual capacities. People with a small V1 seem to be able to see just as well as people with one that is two and a half times as big.
Another thing the Caltech neuroscientists told me was that some people manage to get by alright without a cerebellum, despite the fact that the cerebellum is a fairly large chunk of neural tissue at the back of a normal human brain.
Looking back, though, I find I am not sure whether they meant (as I thought at the time) that some people are simply born without a cerebellum, and never miss it, or perhaps that if someone loses it to injury or disease, the ill effects are not necessarily all that serious.
Yet another thing to note is that some severe epilepsy patients have had an entire cerebral hemisphere of their brain removed, and are still able to function. Although they do have impairments, they remain aware and may still be reasonably intelligent. Apparently the effects of removing a whole cerebral hemisphere can, in some circumstances, be less severe than those of removing certain smaller areas within the hemisphere, even though the latter might be sufficient to cure the epilepsy.
Brains are weird. Sometimes quite small lesions can lead to very noticeable (and sometimes very strange) impairments, but then you can also apparently sometimes lose almost half of it (or perhaps more, in the case of Lorber’s patient) and still be able to function.
This is not quite an answer to your question, but maybe you’ll find it interesting… Homo floresiensis, a prehistoric, miniaturized human species (closely related and probably descended from Homo erectus) that lived in Flores island (Indonesia) thousands of years ago had a brain capacity of about 426 cubic centimeters, versus I believe 1.300-1.400 cubic cms for modern day humans (please correct me if I’m wrong, I’m in no way a brain expert).
Apparently, even with such a small brain, Homo floresiensis was smart enough to make tools and control fire, if finds in the caves where it sought shelter are any indication…
Of course, it WAS a very small species, and different from us, but I guess it still shows that you can be pretty smart without having a humongous brain…
Surely these observations are of profound importance to neuroscience?
Seems to me that it undermines everything we have been taught about the brain. It raises the question of whether or not we need a brain at all.
If we don’t need a brain, then where or what is consciousness?
I don’ t know about the neuro-scientists, but if something this profound came up in my field of science I would be doing cartwheels to find out the whys and howfors.
“It is not how well the dog sings, it is the fact that he sings at all”.
Maybe they’re much more comfortable forgetting about it…
It wouldn´t be the first time they relegate a major discovery to the shadows because it turns all current knowledge on its head- I remember reading that an anthropologist once found a fossil that didn´t quite fit the tree of human evolution as then accepted, and he actually considering burying it again and forgetting about it…
The human brain IS weird. I’ve got the white matter of a baby. I should be at the intelelctucal level of a baby…but I’m a college grad.
The Nobel Literature Laureate Anatole France had a brain only 2/3 the size as that of an average human, whereas Lord Byron and Jonathan Swift had one getting towards twice that size.
IANA brain doctor, but isn’t it the neurons that do the work, couldn’t you have as many (or more) neurons and networks in a smaller area? Maybe our heads are ideal for our body sizes and the demands on our vision and hearing, not for the size our brains need to be.
Take a look at hemispherectomys - the removal or replacement of one side of the brain. If carried out on a child, outcomes can be within the range of function considered normal. It is not always the case, though, and the surgery is a last-resort option for intractable and/or life-threatening conditions such as severe epilepsy.
All these examples show that neuroplasticity (the ability of the brain to adapt) is more capable than previously thought, and that a developing brain has more neuroplastic potential than that of the adult brain. However, some adults do exhibit remarkable recoveries, but these are exceptional cases. Medical researchers are looking into into approaches that encourage neuroplasticity in adults to compensate for brain injury, as well as trying to prevent scarring which inhibits neuronal regrowth. Recent research on using stemcell injections for stroke patients has shown some promise in this regard.
All this demonstrates that it is not the case that we should question whether we need a brain (it is obvious we do), or whether we could use more of our brain (brain size or utilization is no indicator of intelligence/creativity), but how best we can assist those who have lost function through brain injury recover as much functionality as possible, because we know can (sometimes) be done. I like the story of a man (22) who suffered a stroke and was locked-in (near total paralysis) shortly after his daughter was born. In what I consider a brilliant move, he was encouraged (and allowed) to spend considerable time on the ground with his developing daughter as she learned to speak and walk, and by watching and imitating and trying to keep up, he recovered the ability to both walk and talk. He was young, and some patients do recover function spontaneously, but I wonder if by lowering his own expectations (can I do what my baby daughter can do, as opposed to why can’t I do what I think I should be able to do as an adult) and being allowed and encouraged to do it (babble, roll, crawl, toddle as opposed to restraint/sedation/coping) he was able to put himself into a re-development mode that encouraged recovery. Of course, he had the best of whatever other therapies were available, but his recovery was considered remarkable by his neurologist.
As noted above, structure is far more important than size when it comes to brains. Women have smaller brains than men, and those with dwarfism have smaller brains than the general population, but both groups seem to get along and function normally just fine. And homo floresiensis had a brain comparable in size to that of a chimp, but with structure and abilities sufficient that we call them human.
But I doubt anyone would ask if a brain is required. At the very least its lower functions keep our lungs breathing and out heart pumping, and when you lose significant chunks sometimes that’s pretty much all you’re left with. I mean if you think you’re fine without it it’s not particularly hard to remove…
Based off patients who have had radical hemispherectomies and odd cases like Daniel Lyons, I’d say an upper limit to the question posed in the OP is half a brain, or ~600cc, given how many people are able to function normally in society with such conditions. Remarkable, given that it’s barely more than the upper bound for a chimp, and around the estimated size of the brain homo habilis possessed.