Gordon Johnson: We’ve talked about the neuron and we’ve talked about some of the larger lobes in the cerebral cortex. You had some other issue you felt we should talk about now.
Dr. Erin Bigler: Yes, I want to show you a very, very important pathway that’s often effected and a system that’s often effected in brain injury – this is the memory network, the memory system. So what I’m going to do is, I’m going to peel away the hemispheres, again noting the beautiful symmetry of the brain. And notice when we get down at this level here, again you have the beautiful symmetry of the brain. This is the corpus callosum that I’m taking off. This is the structure –
Gordon Johnson: Ooh, that hurts.
Dr. Erin Bigler: Yes. That’s the structure that connects the two brains, so it’s an information highway between the two, uh, hemispheres here.
This is what’s called the orbital frontal region of the brain. If I just turn this over here, you can see that there’s a little groove right here, and this is the inner hemispheric fissure. And in the skull, right here, you can, let me just sort of hold this up so you can see that this goes in right there. But you can see that there’s a little groove right here. We call this the olfactory groove, and this right here is the olfactory bulb.
So this is the neural part of what we smell with and this right here is very commonly injured, in moderate-to-severe brain injury in particular because of grating action and movement of the base of the frontal lobe against that part of the brain. And since this sits just above the eyes, the eye socket sits on either side here, this is called the orbital, meaning orbit or eye, frontal, so orbital frontal cortex. So I’m going take off the orbital frontal cortex.
Gordon Johnson: You just did a lobotomy like they used to do in the ’50s, right?
Dr. Erin Bigler: Yep. I just did a frontal lobotomy there. Except they didn’t remove, in a frontal lobotomy they did not remove this. If you look carefully here, you can see sort of striating, pathways that come out. A frontal lobotomy would just transect that pathway right there, and that would isolate them the frontal cortex. So here is again, this beautiful symmetry, that we see. This is the lateral ventricle. The lateral ventricle has a front, or frontal horn or anterior horn.
Gordon Johnson: Okay, before we go there, what’s a ventricle?
Dr. Erin Bigler: A ventricle is the cavity in the brain. It’s a space, and it’s very important because if the brain is soft, you have to have an internal pressure gradient. And that internal pressure gradient is pushing out but the brain volume is holding it in check. So as it pushes out, brain volume keeps it in a constant position.
Gordon Johnson: Is essentially what we have is a water balloon inside holding the brain where it’s supposed to be?
Dr. Erin Bigler: That is correct.
Gordon Johnson: And the ventricle is the water balloon?
Dr. Erin Bigler: The ventricle is the water balloon. And we pay a lot of attention to the size of the ventricle because it can tell us whether the brain is swelling, whether the brain is shifting across midline or whether the brain is degenerating because the ventricle changes in shape depending on what is happening in the brain tissue.