I think we're on the verge of some really big breakthroughs when it comes to understanding the brain though. The research group I work for (for only six more days.. sigh..) just released a pre-print of a paper mapping out all of the mouse brain's cell types[0][1].
> The mammalian nervous system executes complex behaviors controlled by specialised, precisely positioned and interacting cell types. Here, we used RNA sequencing of half a million single cells to create a detailed census of cell types in the mouse nervous system. We mapped cell types spatially and derived a hierarchical, data-driven taxonomy. (...) The resource presented here lays a solid foundation for understanding the molecular architecture of the mammalian nervous system, and enables genetic manipulation of specific cell types.
(you may wonder what mice have to do with human brains: on a "cellular" and "genetic" level, mice are already close enough to humans to be decent substitutes for researching quite a lot of fundamental stuff about how the brain works)
We already had an atlas of where every gene was activated in the mouse brain since 2006, but this was at the tissue level[2][3]. Only recently it has become possible to research at the cellular level which genes are activated. That has enabled the possibility of classifying cell types by gene activation. Not only that, by tracking gene activation over various stages of development, we can see how the genes interact and activate each other, and get a better insight in how the brain develops its various different cell types.
I am "merely" a programmer/interaction designer building tools for easier data exploration, and can't pretend to understand the fine details, but that sounds like it is Kind Of A Big Deal for anyone researching brains.
For example: until now, we could only see which genes are correlated with higher chances of a certain mental illness (by looking at the genetic makeup of people with and without these illnesses). But that is not the same as knowing what those genes do. Furthermore, many of mental illnesses are partially nature, partially nurture: you have to be unlucky enough to have a mix of genes that makes it possible or more likely to manifest an illness, but for the disease to truly manifest itself you also requires an environmental trigger.
When we can follow individual cell development at the genetic expression level, we can start to figure out what changes when certain genes and/or certain stimuli are present or absent.
There is an equivalent science project underway to map out all the cell types in the human body, not just the brain[4]. On top of that, the techniques that let scientists analyse the RNA expression in individual cells are getting cheaper and faster all the time[5]. My guess is that major breakthroughs in understanding how the body works, including the brain, will start coming in very quickly.
(and I'm not even talking about the implications for machine learning)
[0] https://twitter.com/slinnarsson/status/981919808726892545
[1] https://www.biorxiv.org/content/biorxiv/early/2018/04/05/294...
[2] http://mouse.brain-map.org/
[3] https://en.wikipedia.org/wiki/Allen_Brain_Atlas#Mouse_Brain
[4] https://www.humancellatlas.org/
[5] http://www.alleninstitute.org/what-we-do/brain-science/news-...