The Turkey-Sleep Controversy
We’ve all experienced that overwhelming desire to take a nap after our Thanksgiving meal. Holiday lore has it that the culprit is the turkey. This theory is based on the fact that turkey meat contains high quantities oftryptophan, an amino acid that we use to produce the neurotransmitter serotonin. It has long been speculated that serotonin plays a role in promoting sleepiness. Even more incriminating is the fact that serotonin is a precursor for the production of melatonin, which is known to have an effect on sleep as well.
The connection between serotonin and sleep has long been a point of debate among scientists, however. Multiple studies on this subject have yielded conflicting results. In fact, some research suggests that serotonin may even play the opposite role, promoting wakefulness. This is based on the observation that serotonin-producing neurons are most active during the day.
Enter: A Science Experiment
To settle this controversy, a team of researchers at Caltech conducteda series of experiments on zebrafish and mice. Both these animal models have been used to better understand the physiology of sleep in humans. The results were published in the journalNeuron.
The team focused on a region of the brain called theraphe nuclei, where serotonin-producing neurons are concentrated. The experiment consisted of genetically mutating zebrafish so that this part of their brain would not produce any serotonin. What they found was that these mutated fish slept half as much as normal ones. The team also tried removing the raphe altogether and observed that the treated fish slept a lot less.
The researchers then went one step further, genetically modifying the raphe so that it would be stimulated by light. The result was that shining a light on these fish put them to sleep. Conversely, when they stimulated the raphe in other species of fish that do produce serotonin, it had no effect on their sleep.
The same experiments were then repeated in mice, yielding the same results. The mice that had their serotonin-producing neurons genetically removed slept a lot less than usual. Similarly, stimulating the genetically modified neurons with light also put the mice to sleep.
The Seratonin Paradox
This research sheds light on the apparent paradox of serotonin: stimulating the neurons indeed causes animals to sleep, and yet the neurons are normally at their most active during the day.
The research team points out that there are two factors that control sleep: one is the circadian clock and the other is called homeostatic sleep pressure. The latter refers to the normal process by which we grow increasingly tired as we go through our day. As we run down our energy, the pressure to sleep starts increasing.
The plausible explanation is that the firing of serotonin during the day is a necessary precursor for the brain to generate the necessary sleep pressure we need to fall asleep when night falls.
Back to the Turkey
In short, the science says: with the bird’s meat containing high amounts of tryptophan, used to produce serotonin and in turn creating sleep pressure and melatonin production, the turkey may indeed be the culprit for our post-meal torpor.
Then again, it just might be the result of eating way too much.