Holiday getting you down? Pass the Turkey.

Nov 26 2008 Published by under Behavioral Neuro

Thanksgiving is my favorite holiday, hands down. Well, ok, I also celebrate a series of personal holidays on the day after Valentine's, the day after Easter, the day after Halloween, and the day after Christmas. Why hinge your emotions on the uncertainty of a holiday when you have the certainty of all the chocolate going on sale the day after? Day after holidays are beautiful things and I encourage you all to celebrate with me (though I warn you, stay AWAY from the Russel Stover "european" chocolates. Nasty).
But of the real holidays, Thanksgiving is my favorite. It's the one holiday where my family actually gathers (we are spread up and down the East Coast and now on the West Coast as well), and my family is a lot of fun. A lot of geeky fun. Don't knock it 'til you've tried it.
And of course there's the food. I've got a cousin that makes cranberry relish (amazing!) and my mother has this double-decker pumpkin pie (my brother and I are always asking her to make two, because we each need one). The same cousin also makes this fantastic pumpkin cheesecake. And there are casseroles, and ham, and my father makes this amazing breakfast spread for everyone (with Polyface meats this year!). An aunt makes another amazing breakfast (I really hope she does the homemade scones again). It's a family with two professional chefs, a professional cook (I don't know, does he count as a chef? The other two had culinary school), and a bunch of extremely talented amateurs. With the exception of Sci, whose culinary abilities are limited to a damn good cup of coffee.
You may have noticed one rather large omission here. There's no turkey. We had one last year, and all the years before that, but this year, we're giving up our free-range, organic, happy turkey (which presumably died a free-range, organic, happy death before we ate it). We never ate the whole thing, and turkeys always get so DRY, even though you try and try...

Our first Thanksgiving without turkey. How will it go?! Will everyone be...depressed? And is it just the lack of a large bird sitting in the middle of the table getting us down, or is it...something else? Roiser et al "The effect of acute tryptophan depletion on the neural correlates of emotional processing in healthy volunteers", Neuropsychopharmacology, 2008.

Everyone wonders why you're so sleepy after Thanksgiving dinner, and for many years people have been saying that it's the turkey. Turkey is a good source of the amino acid tryptophan, which is a precursor to the neurotransmitter serotonin (on which I will write a post some day, honest). And serotonin is hypothesized to be one of the culprits in major depressive disorder. The hypothesis is that depression is characterized (and possibly caused by) chronic low levels of serotonin, and came about because the most common anti-depressants (Prozac, Celexa, Zoloft, etc) are all selective serotonin reuptake inhibitors, meaning they stop serotonin from getting recycled and increased the concentrations floating around in the synapses and extracellular fluid of your brain.
(Note: the serotonin theory of depression is hotly debated, and may be only part of the real story, if it turns out it plays any role at all. I've got a couple of posts on depression at my old place, but unfortunately I never got to the serotonin vs. BDNF theories in their entirety. It's on my to-do list. Really it is, I think this stuff is endlessly fascinating.)
Anyway, what we're going with here is the serotonin theory of depression, because that is the one on which this paper is based. There are various studies out there that show the effects of depleted serotonin levels in both depressed and non-depressed individuals. How do they deplete the serotonin? Do they suck it all out with a very specific syringe? No, indeed. It is far easier than that. Because tryptophan is the precursor for making serotonin in your body, all you need to do to deplete serotonin levels in the body is to delete tryptophan from your diet! And this is not a diet you need to follow for ages either. All they have to do is give you a drink containing lost of amino acids, but NOT tryptophan. The amino acids will kick your body into high gear, processing them all, but there is no tryptophan, and so while other products will go up, your serotonin levels will not.
The practical upshot of this is that you get decreased serotonin levels in the body. The downside of this is that the amino acid drink they make you drink is very, very nasty. VERY nasty. So nasty that some studies had limitations in that people threw it up! I think part of the problem was that they tried to cover up the taste with chocolate mint. Not cool. Luckily, this study circumvented this problem, instead having the subjects swallow vast amounts (70!) of amino acid containing pills. 5 hours later (I really hope they got paid), the researchers checked that they subjects had low levels of serotonin (they did). Then the subjects were tossed in an MRI scanner and checked for responses to emotional words, as well as being given a battery of other tests.
Why emotional words? Well, it turns out that serotonin depletion can actually cause a recurrance of a depressive episode in someone who already has major depression, but in a healthy person, it doesn't. So we have to use more sensitive tests. Serotonin depletion in healthy people has been shown to impair decision making, impair recognition of emotional expression (whether someone is smiling or frowning at you), and impair responses to verbal emotional stimuli, which are all effects that are found in depressed individuals without the serotonin depletion.
So they took people, depleted their serotonin, and put them in a scanner. What did they see? Well, it turns out that when healthy, non-depressed people are given emotional verbal stimuli, they pay significantly more attention to positive words, and less attention to neutral or negative words. Not only that, healthy patients when given something called a "go-no-go" task will making far more errors associated with positive stimuli than negative stimuli, implying that a normal human brain actually is trained to ignore negative stimuli. Depressed people, on the other hand, pay more attention to negative stimuli, and make more errors toward negative stimuli in the go-no-go task.
In this study, when healthy subjects were tryptophan depleted, they paid less attention to positive stimuli, too! They even paid more attention to negative stimuli, just like depressed patients. And this difference showed up in different activation of areas of the brain including the superior temporal gyrus and the posterior cingulate cortex (both associated with more response to negative words). Also, areas like the caudate, which is associated with the salience of stimuli, or how much a stimulus stands out, was activated more in response to negative stimuli following tryptophan depression. The patients also scored higher for things like anxiety, even though they never noticed any change in their subjective mood state (they rated themselves just as happy as before).
What all this means is that tryptophan depletion, which results in lower levels of serotonin in the brain, can causes changes in healty people that are similar to those seen in untreated depressed individuals, and this means that serotonin may play a role, not only in mood, but in the way our brains process emotional stimuli that are positive and negative.
Now now, no need to go buying an extra turkey. Our normal diets supply all the tryptophan we need for our daily serotonin supply. And despite the lack of turkey in my family this year, I hope that the Sci fam will not be in any way adversely affected. But you never know, that turkey might help your reaction to the negative stimuli of your football team losing the next day...
Jonathan P Roiser, Jamey Levy, Stephen J Fromm, Hongye Wang, Gregor Hasler, Barbara J Sahakian, Wayne C Drevets (2007). The Effect of Acute Tryptophan Depletion on the Neural Correlates of Emotional Processing in Healthy Volunteers Neuropsychopharmacology, 33 (8), 1992-2006 DOI: 10.1038/sj.npp.1301581

12 responses so far

  • HolfordWatch says:

    Scurious - where these 'never-depressed' volunteers accepted on the basis of no documented history of depression or where they screened for the experiment and on the basis of their response to positive or negative stimuli? (I don't have access to the full paper.)
    Whenever I've looked at resilience research, it sometimes looks as if there are substantial differences in the way that people respond to positive or negative stimuli: it doesn't necessarily follow that the people who are reactive to the negative stimuli are clinically depressed.
    As a shorthand for this - I know many british people can't bear the 'feedback sandwich' because they are waiting for the 'but' and the negative remark and that is pretty much all they hear, no matter what positive remarks are made.
    So - before giving feedback to british people, should there be some turkey sandwiches or chicken soup administered beforehand? Over-simplifications aside, there are lots of nutritionists who advocate tryptophan supplementation and complain that the pills are banned in many countries. Why might people think that they needed supplementation rather than relying upon dietary sources?

  • Scicurious says:

    HolfordWatch: ack! I crafted a beautiful reply and then my browser shut down! Ok, here's what I remember.
    I'm not at all sure what you mean by "feedback sandwhich", but the participants were actually screened and studied in America, in the Washington DC area. They were all screened for depression and other psychistric disorders prior to the study, and the authors also made sure that participants had no first degree relatives with psychiatric disorders of any kind.
    You are very right, tryptophan depletion does NOT cause depression, and certainly people shouldn't start taking supplements! The tryptophan depletion here was artifically induced (you'd have to be taking in a lot of amino acids and no tryptophan at all to get these effects otherwise). They have found that depressed individuals repond more strongly to negative stimuli (there are lots of studies out there on this), but it's true, it doesn't mean that people who respond to negative stimuli are depressed, it's just one of the cognitive results.
    I should also emphasize that tryptophan depletion did NOT cause depression in the subjects, they reported no changes in mood. The reason I like this study is actually because of the interesting results they got in the area of the caudate, where tryptophan depletion gave negative words enhanced salience. But we have PLENTY of tryptophan in our daily diet, and no one needs to go worrying about it.
    Thanks so much for asking such probing questions! I'm glad you gave me a chance to clarify some of this. I guess this is what I get for writing a post at 3am...

  • ScottKnick says:

    Reading a post on serotonin would give me such a serotonin boost!

  • Neuroskeptic says:

    I've got a post discussing serotonin here and one touching on "serotonin vs. neurogenesis" here
    This study is decent, although I'm always a little doubtful of the value of researching these kind of things in healthy volunteers because we know all the interesting stuff only happens in recovered depressed people.

  • Dr. John says:

    Regarding dry turkey, simple fix: brine it 1-2 days beforehand, rub under teh skin with olive oil before it goes in the oven, and cook it upside down. Seriously. Gravity pulls the juices into the breast meat - and who doesn't love juicy breasts?
    In all seriousness, the H-Bomb has used this technique to perfection the last 3 years.

  • Coturnix says:

    I think people focus too much on serotonin. Every time I repost this (and I do it every Thanksgiving) I get a lot of protestations in the comments. But nobody could really show why the idea is wrong, only why alternatives may also work, i.e., we have several alternative hypotheses, each equally untested.

  • Ben_Wraith says:

    I wish this post had been more clear about the real role of tryptophan in turkey and Thanksgiving sleepiness, the amount consumed from turkey probably wouldn't be enough have an effect and turkey isn't a particularly good source of it.

  • Scicurious says:

    Ben_Wraith: I actually tried to find an article on turkey and tryptophan and sleepiness, and I couldn't find anything! I'll gladly cover it if someone can find me an original article. There are tons of press releases but nothin I could find on Medline. And yes, turkey is not a particularly good source, at least, no more than any other kind of white meat, it's just that everyone thinks of turkey and tryptophan together.

  • Coturnix says:

    Speaking of Polyface, I have read "Holy Cows & Hog Heaven" and it is a very interesting read - it is incredible how a person who instinctively groks evolution and ecology can also be a Creationist libertarian.

  • HP says:

    Dr. John; an even simpler fix for dry turkey:
    1) Cook turkey the way you normally do.
    2) Build a time machine.
    3) Go back in time two (2) hours.
    4) Remove bird from oven ~ 1.5 hours earlier than you normally would. You may need to forcibly evict agents of the FDA or NIH, if present.
    5) Loosely cover the bird with foil and don't you dare touch it. Post armed guards if necessary.
    6) Go forward in time 1.5 to 2 hours.
    7) Carve your delicious, juicy, moist, fully cooked turkey.
    If you don't have a time machine, remember that the bird continues to cook after you remove it from the oven. Take the damn thing out of the oven well before the plastic timer pops, and let it sit, covered and unmolested, until you're ready to eat.
    I have never cooked a turkey for as long as they say, and I always let it rest before anyone can eat it. The tantalization is maddening.
    Let me know if you get food poisoning, and I will send you some saltines and 7UP.

  • Scicurious, you are such an adorable thing, I could just pinch you. Nice use of graphics.