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