Half a brain is enough

[Nogbad]

http://uk.news.yahoo.com/21/20090720/tsc-half-brain-girl-sees-all-in-one-eye-4b158bc.html

Often when we look at human evolution we tend to focus on the increased cranial capacity as man has developed. Do we perhaps over-emphasise the importance of the brain size. It would seem that we could have remarkably similar capabilities with less.

[Pixel42]

Half a brain girl recovers vision (http://news.bbc.co.uk/1/hi/health/8159631.stm)

Scientists say they have solved the mystery of how a girl with half a brain has near perfect vision in one eye.

The experts were baffled by the 10-year-old girl who was born missing the right side of her brain, whose job it is to map the left field of vision.

Scans revealed the German girl's brain rewired itself during development when she was still in her mother's womb.

The University of Glasgow researchers report the findings in Proceedings of the National Academy of Sciences.

The girl's underdeveloped brain was discovered when, aged three, she underwent an MRI scan after suffering seizures of brief involuntary twitching on her left side.

Apart from the seizures, which were successfully treated, and slight weakness on her left side, the girl has had a normal medical history, attending school and taking part in regular activities. [...]

Dr Lars Muckli, of the university's Centre for Cognitive Neuroimaging, working with German colleagues from Frankfurt, said: "The brain has amazing plasticity but we were quite astonished to see just how well the single hemisphere of the brain in this girl has adapted to compensate for the missing half.

"Despite lacking one hemisphere, the girl has normal psychological function and is perfectly capable of living a normal and fulfilling life. She is witty, charming and intelligent."

He said understanding the powerful algorithms the brain uses to rewire itself could help advance artificial intelligence work.
Good grief. Makes you wonder why we have two hemispheres at all.

[Soapy Sam]

Reminiscent of Lorber's findings at Sheffield.
http://www.flatrock.org.nz/topics/science/is_the_brain_really_necessary.htm

[Ladewig]

A fascinating topic. The MRI image is awe inspiring.

[Rolfe]

A fascinating topic. The MRI image is awe inspiring.


I'll bet that gave someone a turn when they first saw it!

Rolfe.

[Myriad]

Articles like this often focus on the surprising positive, without mentioning deficits. There are probably some drawbacks to having half a brain. (I'm tempted to... nah, never mind.)

It's also possible that thriving today with only half a brain is quite possible (I'm tempted to... nah, never mind), but it wouldn't have been possible to evolve that way. Monocular vision or monaural hearing would be a severe competitive disadvantage for, for instance, some of our arboreal ancestors.

Respectfully,
Myriad

[HansMustermann]

Well, there was at least one guy with even less brain tissue left, who had a normal life as a civil servant (I know, I know;)) and an IQ of 75.

http://www.newscientist.com/article/dn12301-man-with-tiny-brain-shocks-doctors.html

ETA: Look at the pictures on the right side.

[laca]

Half a brain girl recovers vision (http://news.bbc.co.uk/1/hi/health/8159631.stm)


Good grief. Makes you wonder why we have two hemispheres at all.

Just in case...

[soylent]

I'm with laca.

The brain is a very sensitive organ. It's soft enough that blows to the head can leave minor deformation from the brain hitting the inside of the skull or twisting. It can be attacked by bacteria, parasites(e.g. neurocysticercosis. Incidentally, an MRI of a brain riddled with tapeworm larvae is a very effective way to convince children to wash their hands, not drink out of puddles or generally put gross stuff in their mouts) the ravages of aging, blood clots/stroke, plaques etc.

[soylent]

Rats. Hans beat me to the french government worker with a 75 IQ and most of his brain missing. It's amazing that he is alive at all, even more so that he is not a vegetable.

[technoextreme]

Isn't there a guy who had a part of his brain removed and lost his short term memory?

[shadron]

It has always been known that quality (that is, organization) is at least as significant as quantity, with respect to the cerebrum, but this is going to make for some exciting, rather large re-examinations of arguments in brain size. You are always hearing that H. ergaster only had half the brain capacity we do, and that neanderthal had very close to the same brain capacity as sapiens, but this sort of puts the lie to that sort of yardstick. I hope she likes being looked at, because that's going to be a big part of her life from now on, unless she or her parent's put a foot down, just as Genie (feral child)'s mother did.

Or perhaps this is already known The thrust of the article is about her vision, not about the brain itself.

Yes, Rolfe, before I saw your post I was thinking, "I wonder what the doctor thought whe the scan started to show that. "Aha, I think we found the problem..." Not to speak of what her parents must have thought.

EDT: fixed link. Thanks, AezME.

[SezMe]

shadron, that link does not lead to a useful page.

[Roboramma]

You are always hearing that H. ergaster only had half the brain capacity we do, and that neanderthal had very close to the same brain capacity as sapiens, but this sort of puts the lie to that sort of yardstick.

Just to point out, for clarity's sake: "very close to the same", regarding Neanderthal brain size, here is "slightly larger", not "slightly smaller", than modern humans.

Neanderthal brain size: "1,200–1,900 cm³ (73–116 cu in) skull capacity"
Modern homo sapiens sapiens:"The balance of findings, which have been largely on participants of European ancestry, indicate an average adult brain volume of 1130 cubic centimetres (cc) for women and 1260 cc for men"

Quotes taken from wikipedia. The one below also:

it is notorious that Neanderthals, which went extinct about 40,000 years ago, had larger brains than modern homo sapiens.
That last from here: http://en.wikipedia.org/wiki/Brain_size

[bpesta22]

I think the key issue here is the power of development-- before stuff is hard wired. I think an adult losing a hemisphere would have a very different outcome. So, I'm not so sure this case would necessitate changing the idea that big brains are smarter.

[rjh01]

I wonder what is in the place where the brain should be but is not? Has it been taken over by the other half?

If part of the brain is not needed then I would have expected evolution to have eliminated that bit as the brain uses a lot of blood.

[Z]

I wonder what is in the place where the brain should be but is not? Has it been taken over by the other half?

If part of the brain is not needed then I would have expected evolution to have eliminated that bit as the brain uses a lot of blood.

That assumes there's intent and thought involved, though.

It's more likely that the brain grew to the size it did because it could - partially because of no longer needing huge jaw muscles any more, for example. Once the genetic damage (mutation, whatever) removed the chromosomes for powerful jaws, the skull had more room to expand and allow for more brain growth. There wasn't any particular selection pressure telling the brain to stop growing.

And with brain growth (and increase in complexity) came abstract thinking - which itself confers a tremendous evolutionary advantage, and hence brought about the rise of mankind.

But when it comes to mutations of the brain, most are fatal. Those that aren't, for whatever reason, generally result in a less-than-desirable mate - lower intelligence, etc. Had, at some point, a human been born with a more compact brain design that didn't result in mental deficiencies - or, in fact, conferred greater abilities due to more blood in the body or something - we'd have probably seen the rise of a superior species of humanoid... but either the mutation hasn't occured, or the results are typically inferior, or the mutation occured alongside another trait which weakened the species' survival ability significantly.

Of course, this is assuming we know more about a brain than we actually do. For all we know, these people with half-brains and compressed brains may actually have any number of brain issues that aren't reported. It could be that when we're in fight-or-flight mode, more of the brain becomes active. It could be that information is being routed incorrectly and causing other problems. One case I recall - though I admit to faulty memory - about a man who lost a portion of his brain from an injury, mentioned that though he now functioned normally, he was prone to periodic seizures - generally from certain types of lighting and music. So the brain apparently had to cross-wire a few things in order to get the rest to work...

Just remember, there are a ton of traits that are less-than-efficient, and 'evolution' doesn't weed them out or seek to remove them. It's a blind process that sometimes does good and sometimes does terrible.

[rjh01]

There is massive selection pressure for the brain to stop growing. I understand that 25% of the oxygenated blood leaving the heart goes to the brain. If the brain could be smaller then selection would have favored those with smaller brains who could function with less food. The fact that the brain is as big as it is means that ALL of it is needed.

[Pixel42]

Interesting article in Scientific American which may shed some light on this:

http://www.scientificamerican.com/article.cfm?id=evolutionary-origins-of-your-right-and-left-brain

Here we present evidence for a radically different hypothesis that is gaining support, particularly among biologists. The specialization of each hemisphere in the human brain, we argue, was already present in its basic form when vertebrates emerged about 500 million years ago. We suggest that the more recent specializations of the brain hemispheres, including those of humans, evolved from the original ones by the Darwinian process of descent with modification. (In that process, capabilities relevant to ancient traits are changed or co-opted in the service of other developing traits.) Our hypothesis holds that the left hemisphere of the vertebrate brain was originally specialized for the control of well-established patterns of behavior under ordinary and familiar circumstances. In contrast, the right hemisphere, the primary seat of emotional arousal, was at first specialized for detecting and responding to unexpected stimuli in the environment.

In early vertebrates such a division of labor probably got its start when one or the other hemisphere developed a tendency to take control in particular circumstances. From that simple beginning, we propose, the right hemisphere took primary control in potentially dangerous circumstances that called for a rapid reaction from the animal—detecting a predator nearby, for instance. Otherwise, control passed to the left hemisphere. In other words, the left hemisphere became the seat of self-motivated behavior, sometimes called top-down control. (We stress that self-motivated behavior need not be innate; in fact, it is often learned.) The right hemisphere became the seat of environmentally motivated behavior, or bottom-up control. The processing that directs more specialized behaviors—language, toolmaking, spatial interrelations, facial recognition, and the like—evolved from those two basic controls.

[HansMustermann]

It's more likely that the brain grew to the size it did because it could - partially because of no longer needing huge jaw muscles any more, for example. Once the genetic damage (mutation, whatever) removed the chromosomes for powerful jaws, the skull had more room to expand and allow for more brain growth. There wasn't any particular selection pressure telling the brain to stop growing.

Actually, no, that brain is a significant evolutionary disadvantage by itself. If it didn't also have a bigger advantage, the evolutionary pressure would have been against it by itself.

Quoth Wikipedia: "Although the brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization. The demands of the brain limit its size in some species, such as bats."

A species with a smaller brain would need a lot less food, for a start, and that's a major advantage in the survival game.

Also, that big brain is what makes infants defenseless for a such a long time. The brain is still growing a long time after birth. A kitten can at least move to avoid a danger on its own within weeks and is an adult cat in a year, while a primate baby will be still defenseless in a year and can only start reproducing in more than a decade.

So, yes, my take is that there must have been some advantage in it too.

And maybe that 75 IQ civil servant just proves that IQ isn't everything.

Primates also have the most state-of-the-art image recognition, for example. E.g., stripes on a zebra are a nightmare for lions, but just make them stand out to you. E.g., you can triangulate a counter-shaded bunny's position just fine, but against most animals counter-shading is actually effective. E.g., primates are supposedly better at seeing snakes than most other species.

A lot of the larger brain's power really went into such advanced signal processing. So it would be interesting to know how much of that his brain had to give up, to keep the higher level functions running.