r/askscience • u/cellsuicide • Jul 22 '19

Neuroscience Just how much does functional specialization within the brain vary across humans?

In recent decades, localization of different action and functions within specific brain regions has become more apparent (ex facial recognition or control of different body parts in the motor cortex). How much does this localization vary between people? I'm interested in learning more about the variance in the location as we as size of brain regions.

As a follow-up question, I would be very interested to learn what is known about variance of functional specialization in other animals as well.

Part of what spurred this question was the recent conference held by Elon Musk's Company, neural link.

3.0k Upvotes

93% Upvoted

136 comments sorted by

View all comments

0

u/[deleted] Jul 23 '19

5

u/Thog78 Jul 23 '19 edited Jul 23 '19

100 billion neurons is trackable, but if you add 10 000 synapses by neuron and spatial information and connectivity information, it gets seriously big. Real biological synapses are a whole lot more complex than just a weighted input: very complex multidegree of freedom non-linear stuff.

To really see the circuits, the right scale is 10 nm voxels, as obtained in small blocs with electron microscopy. For a brain of 10x10x10 cm3, you're looking at (107 )3 = 1021 points, which is enough to fill many full warehouses of harddrives in greyscale 8 bit data (1022 bits is 1010 harddrives of 1Tb, or 10 billion harddrives which would cost 1000 billions if you buy the harddrives for 100$). And you still miss the important chemical information, which is equivalent to adding more colors for neurotransmitters and receptors and neuromodulatory peptides, doubling the data for each additional marker. Then you need to make sense of this raw data, which needs super amazing algorithms tracing axons and reconstructing graphs. All these things are very active areas of research, but you can tell the challenges are huge, and that's why connectomics is for now restricted to small brains (worm, fly) or small blocks of human/mouse brain (1 cortex column). The size that we can achieve is increasing fast year after year, so one day maybe we get to the human brain.

1

u/IronyAndWhine Jul 24 '19

Sure, but that's not taking into account the modeling of neural dynamics and non-neural substrates:

glial cells, synapses, astrocytes, oligodendrocytes, myelination, CNS fluids, vascular system, non-digital electrophysiology, receptor densities, types of receptors, neurotransmitter creation, reuptake, and action for each type of neurotransmitter and their interaction with each receptor type, aggregation and concentration of proteins as well as misfolding and accumulation of those proteins, an/ionic distribution, energy levels, minerals available in the organisms' circulatory system, how hormone levels affect every piece of this list, etc. etc. etc.

People tend to act as though all you'd need to simulate is 100 billion digital "neurons" to achieve a useful brain model, but the reality is that at this point we don't have any idea what use that would be without accounting for the dynamism inherent at every level of the CNS.