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Mood

Mood is probably influenced by several parts of the brain, but we know a few areas that appear to be at the center of mood experiences.    This Tour will show you pictures of mood changes occuring in those areas and explain just where they are located in the brain.  

Limbic System

This is the part of the brain that appears to be most directly involved in human emotion-regulation problems.  There are several main parts of this system, and recently the role of several of these parts has become a little clearer (we still have a long way to go).   At least we can point to some parts of your brain that are clearly participating in your emotional experience of the world.  The rest of this section will talk about one such part, the "limbic cortex".  After that you can understand better how other limbic structures such as the memory center ("hippocampus") and fear center ("amygdala") fit in.  Finally we'll look at the "master gland", the hypothalamus.  

The following pictures show a main portion of the limbic system "in action" -- while your friend Cindy is feeling a mood shift.  You'll see a particular part of the system called the cingulate. 

The Cingulate

To see this part of the brain, we're going to imagine that Cindy's fairy Godmother split her in two, very gently, with her magic wand, and took Cindy's left half off to lunch.  Off she goes, there on your left.  Meanwhile, there you were, looking at Cindy's left ear, and all of a sudden you're looking at the right half of her brain (on your right, below).  She's still looking to the left, watching where her other half is going for lunch:  

 

Just to make sure you're clear on what you're seeing, notice that Cindy's occipital lobe is still easy to recognize at the back (red line).  Below that is her cerebellum, looking like a fat Christmas tree on it's side (yellow line).  We haven't talked about the cerebellum because its role in emotion is unclear.  Until recently the cerebellum was not thought to be involved in anything but balance and planning motions; this story is now looking more complicated.  The green line marks the brainstem -- the swelling where the golf club shaft joins the clubhead, in our visual-model-to-remember.   And the blue outlines a "ventricle", which we'll see again soon.

I'm going to lead you to Cindy's limbic system, her cingulate in particular, but if you want to see the evolutionarily older structures highlighted, so that you can see how the limbic "lobe" encircles them,  click here.   (You don't believe in evolution? Here's some brief help with that). 

     

In the photo above I have circled Cindy's cingulate (sometimes called the "limbic lobe") in red.  Before you get tired of all this, let me show you why you should care where Cindy's cingulate is.  Imagine Cindy all of a sudden felt very sad. Here's her brain feeling sad, in a picture taken from the same point of view: 

Sorry Cindy, not your greatest picture.  But let's see what we can figure out here.  First of all, you need to know that the left hand picture is a "PET" scan, a fancy way of seeing what parts of the brain become more active when Cindy does something.  It's a bit like Penfield poking around, but no surgery (what a wonderful gift, this research).  In this case, Cindy became sad, and we see that there's this very active region up there marked Cg25.  That's the "anterior cingulate", which you should remember, because next time you get sad, there's a very good chance Cg25 is active in your head too. 

To help you get oriented to Cindy's PET scan, we'll use the "ventricle" we saw before (outlined in blue on the right).  Brains have a cave system inside filled with fluid (cerebrospinal fluid, or CSF; it even goes all the way down the spinal cord, bathing the cells there; that's why a doctor can take a fluid sample from your brain by poking a needle in your back). The caves are called the ventricular system, and one ventricle is is outlined in blue.  You can see the same shape in the PET scan, although Cindy tilted her head down a little there.  

So what's the point of all this?  Well, for one thing, isn't it amazing that we can "see" emotion in the brain like this? -- just amazing.  Secondly, now you know about one part of your brain that is perhaps involved when you feel sad.  And there's one more really important thing.

If Cindy had epilepsy, and her right arm started jerking all over the place, you could see the increased activity on a PET scan just as you saw it here when she got sad.  In that case, we'd say she had epilepsy, and we'd know why, and we'd know where (it would be in the parietal cortex, the white one in our side views here).  We could show anyone who doubted with a simple painless test called an EEG (electroencephalograph). We could explain to her employer "sorry, Cindy has epilepsy; she can't work on that forklift anymore, and while she's getting another job she'll be entitled to disability, and you can't fire her for having epilepsy because that's against the Americans With Disabilities Act."  We could explain to Cindy, or her family, or spouse, or teachers -- or anybody that Cindy wanted to know -- that even though it's scary when her right arm starts flailing around, Cindy is okay.  We'd tell them they're not in danger and everybody can relax because it's a medical problem and we know what it is, and we'll take responsibility for helping Cindy get it taken care of

This story goes differently when people have a mood illness.  But maybe it shouldn't be so different: that's the other point of these pictures.  Did you notice how the cingulate has the same squiggly pattern, even though it is deep in the brain, as the outside part of the brain? (Scroll up and have a look.)  What does that mean?  That means that limbic cortex is cortex, just like "motor cortex" (the outermost part of the brain that controls muscles).  So let's say Cindy has epilepsy in her cingulate, instead of her motor cortex.  Think for a minute: what would that look like?  We have no reason to think that cingulate cortex is any less likely than motor cortex to end up having an epileptic area.  But did you ever hear anybody explain that they had "emotional epilepsy"?  Suddenly, for no reason, they get really sad, or anxious, or agitated and angry? We just don't have a model for this.  

Hold on a minute, though.  I'm offering this only as a way of thinking.  So far no one has identified a person with "emotional epilepsy" as such ("temporal lobe epilepsy" comes pretty close...).  Yet the way seizure disorders are identified on lab tests is using an electroencephalogram (EEG ) -- and EEG's don't record all the way down to cingulate cortex.  So cingulate epilepsy, if it exists, would be basically invisible to routine EEG's.  Think a bit further: many of the medications used as mood stabilizers are anti-seizure medications -- there must be something to that.  Finally, what if there was a way to have sustained overactivity in a brain region -- not as intense as a seizure, but abnormally active?  That would be more like the sustained abnormal moods of bipolar disorder. New research on how lithium and antidepressants work suggests that a sustained decrease in brain activity due to decreased synaptic connections may be the basis of at least some depressions. 

But try explaining this fuzzy, "maybe", "well, we can't see it but we think it might be there" thinking to an employer or skeptical spouse (not to mention Cindy herself).  Psychiatry desperately needs some way of showing people that mood symptoms can come from abnormal brain activity over which the person has no control, just as they have no control over epileptic seizures.  Some such test looks very possible within the next 5 or 10 years. 

Before we leave the cingulate, you may have wondered about that other spot lighting up on Cindy's scan, the Cg31 spot.  To see how that fits in,  let's look at John, who's just come out of a severe depression.  If you read the article this work came from, you'll see he might have taken Prozac, or he might have taken a placebo.  The brain changes were the same in either case.  If it was placebo, what you are seeing here are the brain changes we ourselves can generate if given the right suggestion!  Here's John -- or rather, an unusual snapshot of him.  His "ventricle" is shaped like a teardrop pointing forward, you'll notice: 

            

The anterior cingulate (area 25), on which we focused in Cindy's brain, is in John showing a decrease in activity (green).  Compared to when John was depressed, now that he is feeling better his area 25 is less active.  That makes sense, because when Cindy became sad, this area became more active. 

So what's this pCg31?  Well, that's the back part of the cingulate, as you can see looking at the red-circled cingulate on the right.  In John we see a large increase in activity back there, compared to when he was depressed.  This was brought about by Prozac, or maybe even by placebo, but in either case he was measurably much less depressed.  You'll remember this back part of the cingulate actually showed a decrease in activity when Cindy got sad (have a look).   It's as though the cingulate is a seesaw: when the front goes up, the back goes down, and vice versa. 

Now what if we watched these areas while Cindy's friend Joan, who has bipolar disorder, became "manic"? (see the chapter here about bipolar II to learn about how many different ways "manic" can show up)   Would we see the back part of the cingulate "light up" red?  That would be logical, given what we have seen here so far.  But that study has not been done yet, and these brain stories almost always turn out to be more complicated than we would have thought, so wait for more PET scans to be reported before you conclude anything.  

To summarize,  what we have learned so far is that the "cingulate", which is "cortex" like the outside stuff but buried one layer deeper, is one place where emotion occurs in the brain.  There's more to the story, but for now this was complicated enough, don't you think?  

Put yourself on the "email updates" list and you'll be informed when the next Tour comes out.  I hope that'll be soon.   We'll be looking at the hypothalamus (you spotted it up there, did you, that little green thing marked "hth"?), which plays a crucial role in hormone regulation as well as mood;  and the inside of the temporal lobe, called the hippocampus, which is involved in the memory process.  For more on the how lithium may affect the hippocampus, see the update on what causes bipolar disorder from 8/2000.    

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Image credits

PET scans: American Journal of Psychiatry 156 (5): 675-682, 1999.  Copyright 1999, the American Psychiatric Association.  Reprinted by permission.  

Brain sections: Slice of Life image series, reprinted by permission. 

 

 

 

 

 

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