Dr. Sergiu Pașcă

in the somatosensory cortex, so like the part of the brain that senses, it receives information from whiskers.

And we've done that in the first few days after birth.

And it turns out that that was key because if you do it later, the cells don't really integrate that well.

They integrate, but they don't fully integrate.

And if you transplant that organoid into the somatosensory cortex of the rat, and then you wait for a few months, that graft starts to grow

The cells become vascularized by the rat.

They will even receive microglia.

The immune cells of the nervous system of the rat start to populate.

And then when you look on an MRI, you now can see that about a third of one hemisphere of the rat is now made up of human cells.

So you can see really from an MRI from the ventricle to the PR.

Now, you may think that that's like an inert piece of tissue that sits there, but it turns out that it is quite well connected to the host.

And that happens because the brain is still eager to connect at that early stage of development, but later on is not.

And so, for instance, you can do experiments where you can actually record the activity of human neurons and at the same time move the whiskers of the rat.

So if you move the whiskers of the rat onto the opposite side, obviously because the pathway is crossed, then human neurons now start to respond to that.

And then I think probably the most important consequence of that is that they receive now input.

They're now in an environment that is much more physiological.

So when we now looked at the cells, it turned out that they're like six to eight-fold larger than when we were making the dish.

They're not yet identical replica.

but they're very, very close.

And that for us has actually been key and started to actually understand the biology of some of these conditions.