The R-Complex

Table of Contents

The R-complex:  Basal Ganglia and Thalamus

When you have finished this Tour, you will have a simple understanding of the parts in this picture:

bgall (1)

These are the oldest parts of the brain: the ones that we share with reptiles and birds. They are thought to be the location of basic drives and instincts, basic needs and avoidances. This is “Brain One” in the “3 Brains in One” model discussed in a separate Tour. Mental health problems such as Obsessive Compulsive Disorder, Post-Traumatic Stress Disorder, and Panic Disorder are thought to have their roots in these structures.

Let’s learn about each part of the R complex by starting with its most basic structures and then adding pieces on, courtesy of Vesalius. com, which has graciously placed these images on line for educational uses.

Step 1: the Circulation System (“Ventricles”)

First, the most prominent structure in this group is one we can basically ignore: it’s just a circulation system! Imagine you are adding rooms to your little house. If you add enough, you’ll have to add some hallways too. As the brain became more complex through evolution, basic structures grew and others were added. Since all of the brain cells float around in “soup”, more “soup channels” were needed as the brain got bigger. Here are those channels:


Notice the “tips” that push out toward brain parts that are far from the center: these are the hallways. At the very center is the fluid supply for the original room. The “arch” – the big horseshoe — probably came along as the arc structures of the “limbic system” (Brain Two) evolved. You’ll notice that within this arch we find all of the older “R complex” structures.

Step 2: The Core

thalamus (1)

This yellow core is the original “room” around which everything else seems to have been arranged. It is called the thalamus. Researchers have not identified a clear role for it in mental health problems, although it seems to be involved as part of a “loop” of abnormal activity in several conditions. What does this look like in a real brain (as opposed to a drawing)? Here is an MRI scan in which I’ve outlined the general area of the thalamus (I’m not a radiologist, so understand this is only a rough localizing):


The thing to notice on this MRI is that the core of the brain does not have the same appearance as the cortex, the outer wrapping (that’s Brain 3). It’s built differently, we can see that much. What does the thalamus do? As medical students we learned that it is a “relay station” for information coming in from the senses. That is still true, but there is probably an awful lot more that the thalamus does that we
don’t really understand yet.

Step 3: The Arch

As we build up our model of the R complex (the basic, “reptilian brain”), the next structures out from the core are a pair that together are called the “basal ganglia”. A ganglion is a swelling, and these are our biggest brain swellings — at the center or base of the brain: thus, “basal ganglia”.


Here is the first of them, called the caudate. (The names don’t matter so much, because — lucky you — you’re not going to be tested on these names like a medical student would be. We’ll focus on where things are and what difference it might make to you.) Notice how the gold colored structure almost completely encircles the thalamus, just inside the circulation system. The caudate seems to be very directly involved in Obsessive Compulsive Disorder (OCD).

Step 4: The “Side Cover”

The other part of the “basal ganglia”, and the last part of the R complex, is added in the final picture below:

bgall (2)

So far, this purple structure, called the putamen, has not been shown to be involved in mental health problems. It is shown here just to complete your understanding of the “R complex” as the core set of structures in the brain.

If you wish to be very complete about the R complex, there is actually one more part (sorry) of the basal ganglia, the “globus pallidus”. It has not been shown to be involved in mental health problems. For now you could think of it as lying right “behind” the putamen in the picture above, toward the thalamus. In the picture below, you can see the putamen looking just as it does above; then within it, the “globus pallidus”. It is not inside but behind the putamen. Don’t worry if this is losing you now, the three dimension stuff is very, very difficult in this part of the brain (ask any 1st year medical student!).


Now you can say you have seen a picture of the basal ganglia, all three parts: caudate, putamen, and globus pallidus. We’ll see the caudate again in the “Fear” Tour.

If you’ve lost your track going through all these pictures, you can go back to Tour headquarters.

(updated 12/11/2014)

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