Refueling your mental engine, cheap and easy!
Ever feel like your brain is running out of fuel? Our study shows that eating the right food can give you back that edge needed to keep up your great performance. In fact, food is found to be an efficient and easy way to enhance your cognition!
About fifteen years ago, Roy Baumeister and colleagues proposed a concept called ‘ego-depletion’, something we are all likely to experience at several moments in our lives. Put simply, the authors argued that processes like switching quickly between different tasks and actively holding and manipulating information in memory all expend a shared ‘mental resource’ in the brain. In other words, your brain is an engine that runs on limited fuel.
Simply refuelling your brain?
When your car runs out of gas, what do you do? Fill up the tank of course. Could things be that simple with our brains as well? Together with several other researchers at Leiden University, we have proven it can be that simple!
To start with, what exactly is this all-important fuel we are running on? One essential neurotransmitter in our brains is dopamine, a substance driving a wide array of cognitive functions. Amongst many other processes, dopamine levels are closely associated with working memory functioning, or as I like to call it ‘working with memory’.
Working memory can be described as an online storage space of sorts where you can temporarily hold and manipulate information, such as your grocery list for the day or the phone number you are about to dial. While these tasks seem trivial and simple, the continuous engagement of working memory leads to dopamine depletion, which coincides with decreased performance. However, no one likes declining results. So how do we remedy this inconvenient depletion?
Enter L-Tyrosine, a simple amino-acid and biochemical precursor to dopamine. You may have never heard of it, but tyrosine is present in plenty of common foods such as banana’s, fish, soy and milk. Ingesting tyrosine has been found to raise dopamine levels in the brain as quickly as within one hour. Now things are getting interesting: if our brains are running out of dopamine because of all this working with memory, can tyrosine counteract that depletion and help maintain proper cognitive performance?
First test of L-Tyrosine effect on cognitive-control operations
We are the first to investigate this intriguing possibility, by supplementing individuals with 2.0 grams of either a placebo or tyrosine, a low dose comparable to a decent serving of 200 grams of spinach at dinner. After one hour the participants were subjected to a visual n-back task, in which a sequence of letters is presented - for example A D M M K J K C. For each single letter the participants were asked to indicate whether it was identical to either the previously shown letter (1-back condition) or the letter shown two steps back in the sequence (2-back condition). Whereas the 1-back condition is relatively easy, the 2-back condition is quite a challenge of working memory and dopamine depletion is expected to occur.
So, does tyrosine supplementation improve working memory performance in this cognitively demanding 2-back condition? Yes it does! Accuracy in this condition was significantly higher after people had ingested tyrosine than after they had taken a placebo.
In conclusion, this study has shown that while our brains run out of mental resources when faced with cognitively demanding tasks, we can keep performing smoothly by eating the right nutrients. Forget expensive cognition enhancing drugs, just go for the cheap and easy method known as food!
Want to know more? Read our paper:
Colzato L., Jongkees B., Sellaro R., and Hommel B. (2013), Working memory reloaded: Tyrosine repletes updating in the N-Back task, Frontiers in Behavioral Neuroscience. 7:200. doi: 10.3389/fnbeh.2013.00200
3 Comments
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@Hamid First of all, thank you for your constructive challenge of my story.
While glucose is certainly a fundamental resource for our functioning, it is not a ‘mental’ one per se. DA on the other hand is closely associated with executive functions and widespread modulatory influences and its depletion has detrimental effects on aforementioned functions. As such I believe DA better suits the role of mental resource. However as Baumeister’s concept is rather broad, alternative versions of his story need not exclude each other.
Efficient signal-to-noise processing because of DA could certainly play a role here. However if it were only that, then one would expect that performance is enhanced regardless of cognitive load and subsequent DA depletion. Instead, we find a beneficial effect of TYR only in the demanding 2-back condition. Should this signal-to-noise processing be susceptible to DA depletion, then the repletion story makes a lot of sense.
Monetary rewards are strong motivators that might make people ‘go that extra mile’. If I were to enthusiastically encourage one participant to try her very, very hardest, she’d likely perform better. Did I just verbally replete her DA? Probably not, but it may have urged her to use the resources she has left more efficiently, something she may otherwise not be motivated to do. As such, monetary rewards and TYR supplementation may both, in their own way, enhance performance.
It is unlikely that performance was improved through mood as we found no effect of TYR on our measure of mood, the Affect Grid (Russel, Weis, & Mendelsohn, 1989), a 9x9 pleasantness vs. arousal grid. We took this measure at baseline, 1 hour after supplementation and after the task was finished. As for a mood manipulation, it could also be that good mood induces a carefree attitude that is more prone to mistakes, which leads to decreased performance. So it is tricky to say whether it would have the same effect.
Thank you for taking the time to leave this thoughtful response.
Cool stuff, but there remain a few issues. Baumeister's ego-depletion resource is often considered to be glucose, which is still a very controversial idea (if only for the fact that it doesn't seem to make a lot of physiological sense). Where would tyrosine come in, in the glucose-is-the-resource story?
What if it has nothing to do with repleting some illusive and undefined resource at all? What if it is just increased efficiency of signal-to-noise processing because of DA/tyrosine? The same effects would be seen, but we would not need to conjure up a story about resources, depletion, and repletion. But even if there is some mental resource, how do we know it is a matter of repletion and not increased efficiency with the same amount of the resource?
Furthermore, ego-depletion studies show repletion effects even when secondary rewards are involved. People do a difficult task, but when offered monetary rewards (rather than nutritional) on a subsequent task, still show repletion. Why would money replete the mental resources? It refutes the original ego-depletion story. If we add a third experimental group to those in this article wherein we offer monetary reward as the manipulation, what would happen? Would there be a difference between the tyrosine-group and money-group?
Finally, depletion is also counteracted by good mood. In a similar vein, accuracy on many tasks is increased by being in a good mood. Amino acids like Tyr could be creating a bump in mood and increasing motivational control (rather than resource expenditure via cognitive control). Would a mood manipulation do the same trick?
Thanks for the good read.