Introduction

Tyrosine is an amino acid. It is also the precursor of two important neurotransmitters, namely norepinephrine and dopamine. Taking in more tyrosine stimulates the release of norepinephrine and dopamine. Previous research has focused primarily on the role of tyrosine as a counteract of conditions that cause a depletion of norepinephrine and dopamine. One of these conditions is stress. The results indicate that tyrosine may perhaps replete cognitive resources, but only under certain demanding conditions.

Executive control and dopamine

Executive control emerges from both cognitive stability and cognitive flexibility. These two functions are related to the prefrontal cortex, which is modulated by dopamine. Research indicates that high levels of dopamine are good for the stability of representations, but they may also reduce the ability to flexibly change cognitive representations. On the other hand, low levels of dopamine may be good for flexibly changing the cognitive representations, but it may lessen the ability to maintain representations.

This research

This research focuses on the acute effect of tyrosine supplementation on the updating and monitoring of working memory representations. Working memory updating was measured by the N-back task. In this task the participants are required to decide whether each stimulus in a sequence matches the one that appeared n items earlier. When n is two or higher, this requires online monitoring and updating of the working memory content. This will be called the N-2 condition. The N-1 condition is the control condition, because the participant can rely on immediate perceptual priming and is not demanding for the working memory.

The hypothesis is that the depletion of cognitive resources affects performance in the N-2 condition more than performance in the N-1 condition. If the repleting effect of tyrosine really is restricted to cognitive challenging conditions, the positive effect of tyrosine should be stronger in the N-2 condition than in the N-1 condition.

Conclusion

Tyrosine supplementation promotes working memory updating. The N-2 condition was more sensitive to the effect of tyrosine. This reinforces the idea that only tasks with high cognitive demands profit from tyrosine. This may be because more demanding cognitive operations are more likely to use all the available cognitive resources, which can then be repleted by tyrosine.

(Practical) implications

On a short term level, consuming tyrosine-rich food is a safe and healthy way to improve cognitive processes. It can be an alternative to cognitive-enhancing drugs, that come with a lot of side-effects, such as Ritalin.