[ooooo00000]

There is a phenomenon where individuals with hydrocephalus, a condition where the brain cavity is filled with fluid, can still exhibit normal intelligence. I suppose the two broad explanations are that brain matter is either denser in these individuals, or that a brain can still compute well with less brain matter at least in some cases (possibly by sacrificing on some other not-easily-measured mental faculties)

"There's a young student at this university," says Lorber, "who has an IQ of 126, has gained a first-class honors degree in mathematics, and is socially completely normal. And yet the boy has virtually no brain."

http://www.psych.ufl.edu/~steh/PSB6099/brainnecessary.pdf

[Natanael_L]

One guess is that our brains are "lazily" allocating neurons to tasks, since we have so much space available compared to most animals. The signals are simply allowed to branch out / propagate much further (and redundancy is probably involved too). The paths are simply built where the signals goes.

But when it is constrained, and there's still enough of all the important brain structures, the density (interference?) of different signals probably causes them to propagate much less such that the processing of each signal will get processed by fewer neurons, and the same functions are still achieved.

Kind of like a space optimized FPGA design vs a lazy one that uses all the logical elements because there's no need to be compact.