It's common knowledge that the human brain is probably the most complex system that evolution has produced to date. For (as far as we can tell) the first time in evolutionary history, life is able to turn its curiosity right back at itself and ask the most ridiculous questions ever asked on this planet: "How did I get here?", "How can I make green pigs?", and most importantly, "Why am I even asking questions?". The very endeavour seems almost paradoxical; we are trying to use brains to figure out how brains work.
Absurdity aside, the weirdness goes far beyond just boring philosophy, and well into the realm of useful things (i.e. science). Neuroscientists have been peering into the brains of unsuspecting mice, monkeys, and even humans, and as with pretty much any hard scientific problem, all they have come up with is just more and harder questions. Here are some of the weird things going on inside your brain:
- There are an estimated 10,000 different types (or sub-types) of neuron. We, of course, have no clue how the diversity arises, but our best guess is that the mechanism is something analogous to the V(D)J mechanism in antigen receptor diversity of the immune system. Also, there appears to be some sort of selection mechanism, once again much like in the immune system, whose function we have very little clue about.
- Your brain is a mosaic of euploid and aneuploid neurons (aneuploid cells have more or less chromosomes than the "normal" 23 pairs). Depending on the region of the brain, aneuploidy varies from 10% up to 50%. Aneuploidy has generally been associated with diseases such as Down's syndrome and cri-du-chat syndrome, but since studies on mice brains in 2001 by Rehen et al., all evidence has shown that there are aneuploid neurons in healthy mammalian brains. Only vague speculation is provided as to why this is the case, and it is generally that differential levels of gene expression between cells increases the complexity of the brain, contributing to behavioural variability.
- LINE-1 retrotransposons seem to play a significant role in neuronal differentiation. L1 activity is kept at bay in neural stem cells by Sox2, but its downregulation seems to trigger several events that bring about differentiation. Subsequently, L1 insertion sites seem to be most commonly found near or in genes related to neuronal function, even though insertions are generally uncommon. This suggests that L1 insertion may be regulated and that neuronal development may lean heavily on insertion events.
These are just a few of the extremely unusual properties of brain cells. You can read about the above in more detail and discover even more neuronal weirdness in Muotri & Gage (2006). We still, of course, have no clue whatsoever where that bloody engram is.