Is 90% of his brain actually missing or is the volume reduced by 90%? I.E. are the mass and connections still mostly there but just squished by extra fluid?

From what I can tell googling about this, it seems it is mostly just squished, so volume is down 90% but mass or neuron count is not missing 90%

Gwern was skeptical, & noted that an IQ of 75 [1] in this case study is very low. He additionally raises a few points, including that volume loss is not the same as neuron loss. He also predicts several deficits the case studies didn't report that he'd expect to see, including many small deficits in simple tasks adding up to large deficits in complex tasks.

[1] https://gwern.net/hydrocephalus#sn3

But how many wrinkles?

It's not any miracle, it's just that "normal life" can run on a fraction of compute power humans have on their shoulders.

Phew. I checked, it wasn't me.

> He was living a normal life. He has a family. He works. His IQ was tested at the time of his complaint. This came out to be 84, which is slightly below the normal range … So, this person is not bright — but perfectly, socially apt

Was he born this way or did he lose 90% as an adult? If the latter, it would be interesting to compare his current IQ to his childhood IQ ( if he took one in school ). Maybe there is a correlation because brain matter and IQ.

> there is not one region of the brain responsible for consciousness

I think we have known that for a long time.