What we eat affects our neurotransmitters in our brain, and our neurotransmitters affect our mood and coping skills. One day when all the chemicals are in happy equilibrium and the cashier is rude to you, it is easy to smile and decide that person might be having a bad day. Serotonin a little low, hey, then you might have the urge to reach over the counter and throttle the rude cashier. We’ve all experienced these more short-tempered days, but scientists didn’t know too much about what was going on (it is, after all, very difficult to study a brain while it is in use), and only recently have we been able to gain some insight with advanced imaging technology.
Not too long ago this paper appeared in Biological Psychiatry: Effects of Acute Tryptophan Depletion on Prefrontal-Amygdala Connectivity While Viewing Facial Signals of Aggression
It's a cool little study. Involves humans, which is always a plus. It is one of those "view angry faces whilst in a functional MRI machine" which has some limitations, but it is pretty much the only way to see what's going on in real time in the old noggin, seeing as how it's rather awkward to test gene expression and neurotransmitter levels other ways without decapitation (not likely to pass the institutional review board any time soon, unless you were unfortunate enough to be born as a research rodent).
As we know, depletions in serotonin, especially in a particular communication circuit between the frontal lobes (the policeman) and the amygdala (the emotional/rage center of the brain) leads to anger and aggressive behaviors. Now, there are some people who are just aggressive altogether—I'm thinking Drew Barrymore's boyfriend in one of the Charlie's Angels movies. We're not talking about that. We're talking about impulsive aggression. All the sudden, you just want to jump out of your car and punch the other driver who cut you off (please don't do this). Impulsive aggression can be unexpected and very scary, and can certainly ruin lives.
So what if it happens just because you forgot to eat your banana this morning??? Oh, don't worry, we are likely more resilient than all that… but in an experimental setting, one can pretty much abolish serotonin via a weird laboratory tryptophan-depleting drink. Tryptophan is the dietary precursor to serotonin, so if you don’t eat tryptophan (present in protein), then you can’t make serotonin. After taking swings of the anger drink, you get into an MRI machine. Then you look at pictures of angry faces. If you read A Clockwork Orange you might have some uneasy feelings about this experiment. The tryptophan-depleting drink significantly reduced both plasma tryptophan levels and the ratio of tryptophan to other long-chain neutral amino acids (remember, tryptophan competes with these other amino acids for entrance into the brain).
In the end, the difference in reactions of the tryptophan-depleted individuals to the angry faces vs. controls was statistically significant. Tryptophan-depleted folks had a higher response to the angry faces within the amygdala (the rage/anger part of the brain) compared to controls, and compared to the response to neutral faces. These findings would suggest that, as suspected, serotonin helps you chill out and assess the situation when faced with an angry horde.
Between the mind reading and the availability of a rapid acting tryptophan-depleting anger drink that will affect our aggressive reactions, I'm a little worried about the future of our free will. But I'll try to eat some protein, micronutrients, a banana, and hope to be plenty mellow enough for nearly any situation.
Copyright Emily Deans, MD