When a teacher writes grades in a report card, a single grade tells you little about how a student is doing overall. You need the whole report card, with everything gathered in one place. For drugs that act on the brain, there was no such report card for a long time. Each test on a tiny copy of the brain, grown in a dish, gave its own result, and comparing the drugs with one another simply didn't work.
On it, the scientists tested five drugs and collected data in different ways. Then they came up with a simple scale: every change in the cells was assigned in advance a sign, "good" or "bad." These signs were averaged within four categories: development, inflammation, degeneration, and cell resilience. The result was an overall score for each drug, like a grade point average on a report card.
It turned out that one drug scored 1.06 points and landed in the "green" zone, while another, a popular antidepressant, got only 0.44. With a scale like this, pharmaceutical companies can quickly weed out harmful or useless drugs even before animal testing.
The organoid grew for 200 days, roughly 6.5 months, which is comparable to the second trimester of a human pregnancy. In that time it formed 26 cell types, including cells of the vascular network.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.