This little section here, this little lateral geniculate,
is actually part of the thalamus.
If you were to take that thalamus and take a slice of it,
which is what they're showing here.
And then you stained for cell bodies and, and the neuroanatomists, they
really have all sorts of clever ways of applying different kinds of chemicals
that light up in different colors or intensities the different types of
cellular structures that are there, so you can actually see what's going on.
If you took this slice,
you would see that the lateral geniculate has got these layers, right?
You can see this layer 1 right here, right layer 2,
and it's really remarkable that they have these, fixed layers, right?
because remember, these things just grow,
it's not like somebody got there with a soldering iron and built them.
These things grow to have these computational structures, right?
So, if you take, you know, the double EEs or
computer scientists among you, you're used to seeing schematic charts
of high end chips that have all these layered structures in them.
You know, you've got your trans, your, your transistor arrays here and
different memory things there.
These things just grow like this, pretty cool.
And the layers are different.
In fact, you can actually tell a little bit that layers 1 and
2 seem to be a little bit different from layers 3, 4, 5, and 6.
And in fact they are.
Layers 1 or 2 are called the magnacellular layers and
these are referred to as the parvocellular layers.
And the, most important difference for you is that 1 and
2 tend to be the where cells.
And these are referred to as the what cells, and
that has to do with where they project going forward.
And we'll talk about that in a minute.
The other thing to know is that both eyes project to the left side for
whatever's looking at the right half side of the visual field.
And both eyes, project to the right side from what's looking at
the left hand side of the visual field.
Well, you can see that explicitly in the lateral geniculate.
Layers 1, 4, and 6 come from the same side eye,
and layers 2, 3, and 5, I get that right yet, yep.
Come from the other side of the eye.
So we haven't combined the two eyes yet.
Right? We still have two separate channels.
Why do we have to combine the two eyes?
Well, how about things like stereo?
Well, that's going to go on up in the cortex, right?
You have to be able to get both of the images together.
But at the, at the LGN level, lateral geniculate, they are still separate.
The what, goes, the where goes up to the superior colliculus,
which you can see on this kind of creepy picture here.
so here it is, kind of creepy right you got your eyeball.
Anyway what you're seeing here is this, coming in at the chiasm,
through the lateral geniculate,
and then projecting up to the superior colliculus.
And the thing that matters as i said, i think earlier,
the superior colliculus is involved in eye movements.
So one of the things that has to happen very quickly, is if something moves over
here, I have to be able to get my eyes over there very, very fast.
All right? So
you have very good sensitivity to motion in your retina, in the periphery.
And then you've got a circuitry that's involved in rapidly going, you know,
it doesn't go very, it doesn't make many neural stops along the way, right.
We go from your retina which is doing some chemical stuff right away.
One electrical stop into the lateral geniculate and
directly to the superior colliculus.
Now, as I said earlier, this is an overly simplified story.
I encourage you to take a course on sensation,
perception and neuroanatomy if you are interested in this.
But it, the story is pretty close.
So anyway, so those layers 1 and 2 go directly to the superior colliculus.
But where is the really cool stuff happening?
Well the really cool stuff happening is when you leave the lateral geniculate
and you get up to the cortex.
So here is a another picture of your brain just to remind you of where
pieces are.
Again, your nose is over here.
Here's your cerebellum back here, involved in like balance and
motor controls.
And here are a bunch of the different corti, cortex, cortical regions.
All right? There's the sulcus,
which is this sort of gap here, right behind it, this is somatosensory,
this is where you feel, your touch senses are.
Right in front of it, by the way, not drawn in here,
is a bunch of stuff having to do with motor control, controlling your muscles.
Auditory cortex in here.
And then this massive piece of stuff and the, it doesn't looks quite so
massive in here, but it actually folds inside your brain.
We're going to have to unfold your brain in a minute.
That's all visual cortex and that's all the processing of visual information