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
